A Practical Mechanic’s Guide to TKM Karting 1. Introduction ........................................................................... 9 1.1 Essential reading .................................................................................... 9 1.2 References ............................................................................................... 9 1.3 What’s in this guide? .............................................................................. 9 1.4 About the Author................................................................................... 10
2. Before & After Each Race .................................................. 10 2.1 Your First Race ...................................................................................... 11 2.2 Preparing a new Kart ............................................................................ 11 2.2.1 Seat................................................................................................. 11 2.2.2 Weights ........................................................................................... 11 2.2.3 Race Numbers ................................................................................ 11 2.3 Keeping a Record ................................................................................. 12 2.4 Pre-Race Checks ................................................................................... 13 2.5 On the Grid ............................................................................................. 13 2.6 Starting the Kart .................................................................................... 14 2.6.1 Starting clutch karts ........................................................................ 14 2.6.2 Starting non-clutch karts ................................................................. 14 2.6.3 If your Kart won’t start ..................................................................... 14 2.7 After Each Race ..................................................................................... 15 2.7.1 In the track run-off area .................................................................. 15 2.7.2 Back in the pits ............................................................................... 16 2.8 After a Crash .......................................................................................... 16
3. Looking After Your Kart ..................................................... 16 3.1 Cleaning ................................................................................................. 17 3.1.1 After a Wet Race ............................................................................ 17 3.2 Chassis check ....................................................................................... 17 3.3. Petrol/Oil mix ........................................................................................ 17 3.3.1 Petrol............................................................................................... 17 3.3.2 '2-Stroke' Oil ................................................................................... 17 3.3.3 Mixture ............................................................................................ 18 3.3.4 Storage ........................................................................................... 18 3.4 Engine re-builds .................................................................................... 18
4. Set-up ................................................................................... 18 4.1 Tools required ....................................................................................... 19 4.2 Carburettor set-up................................................................................. 20 4.2.1 Setting the Jets ............................................................................... 20 4.2.2 Initial settings .................................................................................. 20 4.2.3 Jet Adjustment ................................................................................ 21 4.2.4 Checking the mixture ...................................................................... 21 4.2.5 Setting Tick-over on Clutch Karts ................................................... 21 4.2.6 Throttle Cable ................................................................................. 22 4.3 Timing Set-up ........................................................................................ 22
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A Practical Mechanic’s Guide to TKM Karting 4.4 Exhaust length Set-up .......................................................................... 22 4.5 Spark Plug .............................................................................................. 23 4.6 Fuel ......................................................................................................... 23 4.6.1 Bleeding air out from the Fuel Line ................................................ 23 4.6.2 If Bleeding Doesn't Work ................................................................ 24 4.7 Keeping the Inside of the Engine Clean. ............................................ 24 4.8 Other engine adjustments ................................................................... 24 4.9 Tyres ....................................................................................................... 25 4.9.1 Slicks ............................................................................................... 25 4.9.2 Wets ................................................................................................ 25 4.10 Track width .......................................................................................... 26 4.10.1 Over-steer, Under-steer and Balance. ......................................... 26 4.10.2 Effects of Track Adjustment ......................................................... 28 4.10.3 A (Crude) Method of Setting the Track Width. ............................. 29 4.10.4 Asymmetric Track Settings. .......................................................... 29 4.11 Front wheel Toe-in/Toe-Out. .............................................................. 29 4.12 Engine to Axle Gearing ...................................................................... 29 4.12.1 Gearing in the Wet ....................................................................... 30 4.13 Chain Tension ..................................................................................... 30 4.14 Kart set-up for Wet Racing ................................................................ 31 4.14.1 Chassis ......................................................................................... 31 4.14.2 Wheels .......................................................................................... 31 4.15 Set-up at Various Tracks .................................................................... 33
5. Engine Maintenance ........................................................... 33 5.1 Tools Required ...................................................................................... 33 5.1.1 Torque Wrench ............................................................................... 34 5.1.2 Sockets ........................................................................................... 34 5.1.3 Special Tools .................................................................................. 34 5.1.4 Measuring Tools ............................................................................. 34 5.2 Basics ..................................................................................................... 34 5.2.1 Basic Checks .................................................................................. 34 5.2.2 After a Wet Race ............................................................................ 35 5.2.3 Engine Record ................................................................................ 35 5.3 How the BT82 works ............................................................................. 36 5.4 Running in .............................................................................................. 38 5.4.1 Running a New Piston In ................................................................ 39 5.5 Removing and replacing the Engine .................................................. 39 5.5.1 Removing the Engine ..................................................................... 39 5.5.2 Replacing the Engine ..................................................................... 39 5.5.3 Engine Mounts................................................................................ 40 5.5.4 Removing the Engine Mounts ........................................................ 40 5.5.5 Checking the Engine Mounts ......................................................... 40 5.5.6 Replacing the Engine Mounts ........................................................ 41 5.6 Cylinder Head ........................................................................................ 41 5.6.1 Removing the cylinder Head .......................................................... 41 5.6.2 Replacing the cylinder Head .......................................................... 42
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A Practical Mechanic’s Guide to TKM Karting 5.6.3 Cleaning the cylinder head............................................................. 42 5.6.4 Checking the cylinder head. ........................................................... 42 5.7 Cylinder Barrel....................................................................................... 42 5.7.1 Removing the barrel ....................................................................... 43 5.7.2 Replacing the barrel ....................................................................... 43 5.7.3 Cleaning the barrel ......................................................................... 43 5.7.4 Checking the barrel ........................................................................ 44 5.7.5 The Squish Band Clearance .......................................................... 44 5.7.6 Measuring the Squish Band Clearance ......................................... 45 5.8 Piston Assembly ................................................................................... 46 5.8.1 Removing the Piston assembly ...................................................... 46 5.8.2 Replacing the Piston Assembly...................................................... 49 5.8.3 Small-End Bearing Surface ............................................................ 53 5.9 Piston...................................................................................................... 53 5.9.1 Cleaning the Piston ........................................................................ 54 5.9.2 Checking the Piston........................................................................ 54 5.9.3 Removing the Piston Rings ............................................................ 55 5.9.4 Replacing the Piston Rings ............................................................ 55 5.9.5 Cleaning the Piston Rings .............................................................. 56 5.9.6 Checking the Piston Rings ............................................................. 56 5.9.7 Measuring the piston ring gap ........................................................ 56 5.10 The Bottom End .................................................................................. 57 5.10.1 Crank Alignment ........................................................................... 57 5.10.2 Big End Bearings.......................................................................... 60 5.10.3 Oil Seals ....................................................................................... 60 5.11 Ignition.................................................................................................. 60 5.11.1 How the Ignition works ................................................................. 60 5.11.2 Looking After the Ignition ............................................................. 60 5.11.3 Setting the Ignition Timing ............................................................ 61 5.11.4 Checking that the Ignition works .................................................. 62 5.11.5 Wiring the Ignition Switch ............................................................. 63 5.12 Spark Plugs ......................................................................................... 63 5.12.1 Checking and Cleaning Spark Plugs ........................................... 63 5.13 Engine Sprocket .................................................................................. 63 5.14 Exhaust ................................................................................................ 64 5.14.1 How the Exhaust works ................................................................ 64 5.14.2 Cleaning the exhaust.................................................................... 65 5.14.3 Assembling the exhaust ............................................................... 66 5.14.4 Fitting the exhaust correctly ......................................................... 66 5.14.5 Setting the Exhaust Length .......................................................... 66
6. Clutch ................................................................................... 67 6.1 How the Clutch Works .......................................................................... 68 6.2 After each Event .................................................................................... 69 6.3 Removing the Clutch ............................................................................ 70 6.4 Dismantling the Drive Hub Assembly ................................................ 71 6.5 Servicing the Clutch ............................................................................. 72
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A Practical Mechanic’s Guide to TKM Karting 6.5.1 Checking the Friction Plate ............................................................ 72 6.6 Reassembling the Drive Hub ............................................................... 73 6.7 Refiting the Clutch ................................................................................ 74 6.8 Thrust Washers ..................................................................................... 76 6.9 Sprocket Drum Clearance .................................................................... 77 6.10 Clutch: Major Overhaul ...................................................................... 77
7. The Carburettor ................................................................... 78 7.1 How the Fuel Pump Works .................................................................. 79 7.1.1 Physical Layout of the Fuel Pump ................................................. 80 7.2 Carburation ............................................................................................ 80 7.2.1 Metering the fuel ............................................................................. 81 7.2.2 The Jets .......................................................................................... 81 7.2.3 Positions of the Jets ....................................................................... 82 7.2.4 The Shutter ..................................................................................... 83 7.3 Tools ....................................................................................................... 84 7.3.1 Work area; ...................................................................................... 84 7.4 Removing & Servicing the Carburettor .............................................. 84 7.4.1 Frequency of Servicing ................................................................... 84 7.4.2 Removing the Carburettor .............................................................. 84 7.4.3 Sequence........................................................................................ 85 7.5 Servicing the Pump .............................................................................. 86 7.5.1 Dismantling the Fuel Pump ............................................................ 86 7.5.2 Cleaning the Fuel Pump ................................................................. 86 7.5.3 Checking the Fuel Pump ................................................................ 87 7.5.4 Assembling the Fuel Pump ............................................................ 87 7.6 Servicing the Metering Mechanism .................................................... 87 7.6.1 Dismantling the Metering Mechanism ............................................ 87 7.6.2 Cleaning the Metering Mechanism ................................................ 90 7.6.3 Checking the Metering Mechanism................................................ 90 7.6.4 Reassembling the Metering Mechanism ........................................ 90 7.7 Checking the Pop-Off ........................................................................... 91 7.7.1 Checking for Leaks ......................................................................... 91 7.7.2 Measuring the Pop-Off ................................................................... 91 7.7.3 Adjusting the Paddle Lever Arm .................................................... 92 7.7.4 Adjusting the Pop-Off ..................................................................... 93 7.8 Re-fitting the Carburettor ..................................................................... 94 7.9 Carburettor Return Springs ................................................................. 95 7.10 Fuel line and petrol tank .................................................................... 95 7.11 Preventing water from entering the carburettor ............................. 96 7.12 Carburettor service kits...................................................................... 96 7.12.1 D10-WB 618 ................................................................................. 96 7.12.2 K10-WB 618 ................................................................................. 96
8. Kart Maintenance ................................................................ 97 8.1 Special Tools Required ........................................................................ 97 8.2 Basics ..................................................................................................... 97
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A Practical Mechanic’s Guide to TKM Karting 8.2.1 After a wet race;.............................................................................. 98 8.3 Sprocket Alignment & Wear ................................................................ 98 8.3.1 Engine Sprocket Alignment ............................................................ 98 8.3.2 Rear Sprocket Alignment ............................................................... 99 8.3.3 Effects of Sprocket Misalignment ................................................. 100 8.3.4 Sprocket Damage & Wear ........................................................... 100 8.4 Chain..................................................................................................... 100 8.4.1 Selecting Chain Length ................................................................ 100 8.4.2 Chain Tension .............................................................................. 101 8.4.3 Adjusting Chain Tension .............................................................. 101 8.4.4 Cleaning Chains ........................................................................... 102 8.4.5 Checking Chains for Wear ........................................................... 102 8.4.6 Checking Chains for Damage ...................................................... 103 8.5 Back Axle Assembly ........................................................................... 104 8.5.1 Removing the axle assembly ....................................................... 104 8.5.2 Positioning the Axle in the Bearings ............................................ 105 8.5.3 Bent Axle ...................................................................................... 105 8.5.4 Checking for a bent axle;.............................................................. 107 8.5.5 Replacing an Axle......................................................................... 108 8.5.6 Checking Sprocket & Brake disc alignment ................................. 108 8.6 Chassis ................................................................................................. 109 8.6.1 Back end parallel to front.............................................................. 110 8.6.2 Rear axle Bearing Supports ......................................................... 110 8.6.3 Chassis Twisted? ......................................................................... 110 8.6.4 Front Stub axle lugs...................................................................... 111 8.7 Body-work ............................................................................................ 111 8.7.1 Removing the Side-Pods ............................................................. 111 8.8 Brakes................................................................................................... 112 8.8.1 How the Brake System Works...................................................... 112 8.8.2 Removing the Complete Brake System ....................................... 113 8.8.3 Cleaning the Brake System .......................................................... 113 8.8.4 Checking the Brake System ......................................................... 114 8.8.5 Replacing the Brake Pads ............................................................ 114 8.8.6 Draining Old Brake Fluid .............................................................. 115 8.8.7 Refilling & Bleeding the Brake System ........................................ 115 8.8.8 Adjusting the Brake System ......................................................... 116 8.8.9 New Brake System? ..................................................................... 117 8.9 Wheels .................................................................................................. 117 8.9.1 Checking Wheels.......................................................................... 117 8.9.2 Wheel Sizes .................................................................................. 117 8.9.3 Front Wheel Spacers .................................................................... 118 8.9.4 Checking and changing front wheel bearings.............................. 119 8.9.5 Rear Hub Carriers ........................................................................ 119 8.9.6 Rear Wheel Hubs ......................................................................... 119 8.10 Tyres ................................................................................................... 120 8.10.1 Looking after Tyres ..................................................................... 120 8.10.2 Tyre wear .................................................................................... 120 8.10.3 Removing tyres ........................................................................... 121
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A Practical Mechanic’s Guide to TKM Karting 8.10.4 Replacing Valves ........................................................................ 122 8.10.5 Replacing Tyres.......................................................................... 122 8.11 Seat height adjustment .................................................................... 124
9. Steering.............................................................................. 125 9.1 How the Steering Mechanism Works ............................................... 125 9.1.1 What is Castor angle? .................................................................. 126 9.1.2 What is Camber angle? ................................................................ 127 9.1.3 How the Stub Axle and Lug geometry work ................................ 127 9.2 Tools required ..................................................................................... 129 9.3 Centring the steering with the front wheels parallel ...................... 129 9.3.1 To Set the Steering Straight and Central ..................................... 130 9.3.2 Centring Bar.................................................................................. 130 9.4 Checking the King Pin Bolts & Bearings ......................................... 130 9.5 Checking the Stub Axle ...................................................................... 131 9.5.1 Stub Axle Bent Vertically .............................................................. 131 9.5.2 Stub Axle Bent Horizontally .......................................................... 132 9.6 Checking the Stub-Axle Lugs............................................................ 134 9.6.1 Checking the camber angle of the lugs. ...................................... 134 9.6.2 Checking the castor angle ............................................................ 134 9.7 Checking the Track rods .................................................................... 135 9.7.1 Track rod ends .............................................................................. 135 9.7.2 Checking that track rods are straight ........................................... 136 9.8 Checking the Steering column .......................................................... 137
10. Buying a Kart................................................................... 137 10.1 Chassis ............................................................................................... 137 10.2 Transmission ..................................................................................... 138 10.3 Brakes ................................................................................................ 139 10.4 Wheels & Tyres ................................................................................. 139 10.5 Engine ................................................................................................ 139
11. Tools ................................................................................ 139 11.1 Special Tools ..................................................................................... 140 11.1.1 Folding Plug Spanner................................................................. 140 11.1.2 Dial Gauge & Adapter ................................................................ 140 11.1.3 Dummy Gudgeon Pin ................................................................. 140 11.1.4 Clutch Holding Spanner ............................................................. 140 11.1.5 Clutch Puller Tool ....................................................................... 140 11.1.6 Sprocket Extractor ...................................................................... 140 11.1.7 Tyre Pressure Gauge ................................................................. 140 11.1.8 Tyre Press .................................................................................. 141 11.1.9 Valve Extractor ........................................................................... 141 11.1.10 Carburettor Tester .................................................................... 141 11.2 Home-made Tools ............................................................................. 141 11.2.1 Stub Axle Lug alignment bars. ................................................... 141
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A Practical Mechanic’s Guide to TKM Karting 11.2.2 Centring Bar ............................................................................... 141 11.2.3 Straight edge .............................................................................. 141 11.2.4 Toe-Out alignment tool ............................................................... 142 11.2.5 Tyre Replacement Tools ............................................................ 142 11.2.6 Gudgeon Pin Extractor. .............................................................. 143 11.2.7 Gudgeon Pin Alignment Spring ................................................. 144 11.2.8 Chain Measure ........................................................................... 144
12. Jargon Buster.................................................................. 144 12.1 Engine, Carburettor & Exhaust ....................................................... 144 12.1.1 Air Intake Box ............................................................................. 144 12.1.2 Axle Sprocket.............................................................................. 145 12.1.3 End Can ...................................................................................... 145 12.1.4 Engine Sprocket ......................................................................... 145 12.1.5 Exhaust Silencer......................................................................... 145 12.1.6 Flexible pipe ............................................................................... 146 12.1.7 Manifold Bend............................................................................. 146 12.1.8 Pop-Off ....................................................................................... 146 12.2 Chassis & Bodywork ........................................................................ 146 12.2.1 Bearing Supports ........................................................................ 146 12.2.2 Bearing Retention Plates ........................................................... 146 12.2.3 Bodywork .................................................................................... 146 12.2.4 Brake Disc Carrier ...................................................................... 147 12.2.5 Chain Guard ............................................................................... 147 12.2.6 Chassis ....................................................................................... 147 12.2.7 Front Bumper.............................................................................. 147 12.2.8 Front Panel ................................................................................. 147 12.2.9 Rear Bumper .............................................................................. 147 12.2.10 Seat Stay .................................................................................. 147 12.2.11 Side Pods ................................................................................. 148 12.2.12 Sprocket Carrier ....................................................................... 148 12.2.13 Track ......................................................................................... 148 12.2.14 Wheel hubs............................................................................... 148 12.2.15 Wheel Rims .............................................................................. 148 12.2.16 Wheel Studs ............................................................................. 148 12.2.17 Wheelbase ................................................................................ 149 12.3 Steering and Wheels......................................................................... 149 12.3.1 King-Pin ...................................................................................... 149 12.3.2 Stub Axle .................................................................................... 149 12.3.3 Castor Angle ............................................................................... 149 12.3.4 Camber Angle............................................................................. 149
13. Spares & Products .......................................................... 149 13.1 Wheels [8.9] & Tyres [5.3] ................................................................ 149 13.2 Chains [8.4] & Sprockets [5.13] & [8.3]........................................... 150 13.3 Spark Plugs [5.12] ............................................................................. 150 13.4 Nuts, Bolts and springs ................................................................... 150
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A Practical Mechanic’s Guide to TKM Karting 13.5 Track rods [9.7] ................................................................................. 150 13.6 Carburettor [7.] .................................................................................. 150 13.7 Exhaust & Flexs [5.14] ...................................................................... 151 13.8 Cable ties ........................................................................................... 151 13.9 Steering column [9.8] ....................................................................... 151 13.10 Bearings - all types ......................................................................... 151 13.11 Body-work and number plates [8.7] ............................................. 151 13.12 Back axle[8.5] .................................................................................. 152 13.13 Engine .............................................................................................. 152 13.14 Useful Products .............................................................................. 152
14. Publications..................................................................... 152 14.1 ‘Karting’ Magazine ............................................................................ 153 14.2 The ABkC Racing Reg’s ................................................................... 153 14.3 Formula TKM Regulations & Technical Guide .............................. 153 14.4 MSA Kart Race Yearbook................................................................. 153 14.5 MSA Competitors' Yearbook ........................................................... 153 14.6 The Complete Guide to Formula TKM Karting .............................. 153 14.7 Maintaining 100cc Kart Engines ..................................................... 153 14.8 Two-Stroke Performance Tuning .................................................... 154 14. 9 Videos ................................................................................................ 154
15. Forms & Records ............................................................ 154 15.1 Track Record ..................................................................................... 154 15.2 Best Settings Summary ................................................................... 155 15.3 Engine Record ................................................................................... 156
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A Practical Mechanic’s Guide to TKM Karting
1. Introduction This guide is designed to provide a novice karter with the engineering information required to prepare a Formula TKM kart for racing. If you are new to karting, you need to contact one of the Karting schools offering introductory karting courses. Karting schools often advertise in 'KARTING' magazine. You will not be permitted to race until you have completed an appropriate course. If you are intending to buy a formula TKM kart, wait until you have completed the introductory course. If you have no one to give you advice then ask other club members. It is my experience that you will always get help, but keep an open mind about any advice that is offered. Start racing as soon as possible because that's what it's all about. 1.1 Essential reading •
'How to Start Kart Racing' & ' Kart Racing Regulations’ from the Association of British Kart Clubs (ABkC).
•
‘Formula TKM Regulations & Technical Guide’.
•
Any local rules or restrictions specified by your club.
The Official TKM Video and 'The Complete Guide to Formula TKM Karting' are both well worth the cost. These are all listed in section 14 of this guide. 1.2 References Where a reference is made to another paragraph within this guide it is shown in square brackets, thus: [3.4.5]. This indicates that associated information, or a more detailed description is available in paragraph 3.4.5. 1.3 What’s in this guide? This ‘Practical Mechanics Guide to TKM Karting’ is a combination of the author’s personal aide-mémoire and a set of detailed engineering notes. It
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A Practical Mechanic’s Guide to TKM Karting is not authoritative and doesn’t claim to be 100% accurate. It does however contain many good ideas and is intended to form the basis of the readers own engineering notes. The content was assembled over a two-year period during which the author worked as an amateur mechanic on Gillard-204/TKM karts, but most of the information is relevant to all TKM karts. It contains a great deal of detail that many karters will not require, but no apology is offered for including it. The author would have been very grateful for such detailed information when he was first confronted with a kart. This is, in part, a step-by-step guide and is best read whilst working on the kart. This guide does not cover complete engine rebuilds, racing techniques or strategy. 1.4 About the Author I have a varied background in many aspects of mechanical engineering, but I’m currently working as a Computer Systems Engineering Consultant, which has nothing whatsoever to do with Karting. I gained a lot of experience rebuilding two and four stroke motor bikes starting with small BSAs in the mid 60s graduating up to 250cc Hondas in the 70s. I am relatively new to karting, but I regarded that as an advantage when I was writing this guide. I am still able to clearly understand the problems encountered by new karters. I will attempt to answer any questions and would greatly appreciate any additions or corrections to this guide via my e-mail address: ‘chris@compark.co.uk'.
2. Before & After Each Race This section contains a few notes on preparing your kart for practice and racing.
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A Practical Mechanic’s Guide to TKM Karting 2.1 Your First Race Before your first race ensure that your engine is correctly run-in [5.4] and that your kart is safe. It is essential to get advice and help from the dealer who sold you the kart. Don’t expect to get on the track for the first time without help from someone with experience. 2.2 Preparing a new Kart The following adjustments are needed in order to make your kart suit you. 2.2.1 Seat Try the seat that is fitted to the kart, it should hold you firmly. If the seat doesn’t fit then buy one that does. Adjust the seat height so that it is clear of the ground. Seat height can affect handling [8.11]. 2.2.2 Weights The total weight of the kart & driver must exceed the minimum weight requirement at the end of the race. Weigh both kart and driver in full race kit with the tank at least half filled. If you don’t have access to full size scales then find some flat ground, and weigh one wheel at a time with bathroom scales. Ensure that the steering is fixed in one position and that the other three wheels are lifted to exactly level the kart. Add the four readings together with the weight of the driver in racing gear, to give the overall weight. The best place to fix weights is low down on the side of the seat. You must use two bolts and it is best to use large washers and nylock nuts. If you can’t comfortably reach the pedals then go back to the dealer who sold you the kart or the kart’s manufacturer to get professional help. 2.2.3 Race Numbers Your club will normally allocate a racing number to you. Most clubs will allow you to choose your own racing number if you wish. If you join more than one club ensure that you find a racing number that both clubs will accept because it’s a lot of bother to keep changing numbers.
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A Practical Mechanic’s Guide to TKM Karting If the backing squares keep falling off, because they will not stick to the side pods then; •
Clean the surface with brake cleaner,
•
Roughen with fine emery,
•
Use double-sided carpet tape to fix them in place.
2.3 Keeping a Record Keep a detailed record of environmental data, kart settings and performance. It will prove to be an improving and valuable resource. In order to improve it is essential to constantly review your record. Listed below are examples of what your record should include. Environmental data; •
Weather,
•
Temperature,
•
Track state.
Settings; •
Tyre type, Tyre Pressures, Tyre temperature & State at the end of the race,
•
Track width & Toe out/in,
•
Exhaust flexible pipe length,
•
Gearing,
•
Carburettor settings & Fuel consumed,
•
All set-up changes.
Performance; •
Grid positions,
•
Lap times,
•
Events during the race, i.e. spins, contact etc.,
•
Finish positions.
Example record sheets are included at the end of this guide [15].
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A Practical Mechanic’s Guide to TKM Karting 2.4 Pre-Race Checks This assumes that the kart has been fully checked and prepared prior to race day. •
Check the fuel level - bear in mind the overall weight of the kart at the end of the race.
•
Bleed out all air from the fuel line by blocking the air intake and turning the engine over [4.6.1].
•
Remove, clean and check the spark plug. Use a brake cleaner spray to remove any oil [5.12].
•
Check and record tyre pressures [4.9].
•
Check wheel retention nuts are tight. Do not over-tighten the front wheel retention nuts [8.9.3].
•
Check the chain tension [8.4].
•
If the engine has not been run for a week or more then there is a danger that the carburettor’s needle valve may be stuck down. Check that the needle valve is free, by gently pushing up on the diaphragm with a pencil through the small hole in the bottom of the carburettor (Take care!).
•
Check that the brake works OK. You should be able to lock the wheels when the kart is pulled along the ground by the brake pedal. NEVER allow WD40 near the brake pads or disc.
2.5 On the Grid Ensure that you are on the dummy grid and ready to race with time to spare. It can be very upsetting to lose a position at the front of the grid because you discover a soft tyre when you take the kart off the stand or you have forgotten to bleed the fuel pipe. Always have a plug spanner and a spare plug ready in case the kart fails to start. Move your trolley off the dummy grid and into the Trolley Park as soon as possible.
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A Practical Mechanic’s Guide to TKM Karting It is not unusual to see a dramatic change in the track state whilst waiting on the dummy grid, so be prepared to change the tyre pressures or the tyre type while on the grid. Practice fast wheel changes with the kart on the ground. 2.6 Starting the Kart This is always a traumatic event, even when you have done it a hundred times before. 2.6.1 Starting clutch karts The driver must be seated in the kart. The engineer should say “Ignition ON, Brake ON” to the driver before starting the engine. Ensure that the starter socket is fully engaged on the starter nut. The driver may need to place a hand over the air intake in order to choke the engine. The engine should start immediately. Don’t rev the engine! It may overheat the clutch or worse. If you need to ‘rev’ the engine to keep it ticking over then the carburettor is not correctly adjusted [4.2.5]. 2.6.2 Starting non-clutch karts The faster you go before dropping the back wheels the more likely it is to start. It will not start if you are pushing too slowly no matter how far you push it. The driver should use a small amount of throttle and may need to place a hand over the air intake in order to choke the engine. When push starting don’t get hit by the following karts. When the kart engine has started you must keep running at the same speed after the kart. DO NOT STOP! Look round both sides before running off the dummy grid. Push starting on the grid is dangerous - please take care. 2.6.3 If your Kart won’t start If your kart does not start within the length of the dummy grid, something is wrong so don’t keep pushing it. Assuming that you have followed the instructions in the previous paragraphs [2.6.1 & 2.6.2] then:
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A Practical Mechanic’s Guide to TKM Karting •
For Clutch Karts, check that the ignition switch is ON.
•
Ensure that there is no air in the fuel line [4.6.1].
•
Set the jets to the initial settings [4.2].
•
Check that the tick-over is correctly set [4.2.5].
•
Clean the spark plug and check for a spark [4.5]. This may not be possible in bright sunlight. THE SPARK PLUG MUST BE CONNECTED AND EARTHED WHEN THE ENGINE IS ROTATED [5.11]. If you have a rev counter then check for HT (High Tension) to the spark plug by spinning the engine. If the counter counts then the HT is probably OK.
Try to start it again. Ensure that you are pushing very fast before dropping the back wheels. If it still won’t start: •
Remove the Air Intake Box, place the palm of your hand over the air intake and turn the engine over. If there is a normal amount of suction then the piston & rings are OK. If when you remove your hand, fuel dribbles out of the air intake then the fuel pump is OK.
•
Change the spark plug. It may work OK when out of the engine, but be failing under pressure.
•
Change the carburettor.
Try to start it again. If it still won’t start then seek an expert’s advice. 2.7 After Each Race What you do after each race is as important to winning as what you do before it. 2.7.1 In the track run-off area Take a note of the temperature and state of the tyres [4.9] and the maximum rev’s recorded (if you have a rev counter). Listen and take a note of any other drivers’ comments about track conditions etc. Weigh the kart after the practice session on the official scales. There is often a small variation between scales used at various tracks.
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A Practical Mechanic’s Guide to TKM Karting 2.7.2 Back in the pits You should establish a procedure that ensures that nothing gets missed between sessions. The following bullet points show the authors procedure. The items are ordered so that the essential ‘between races’ checks are made first. If you have reason to suppose that your kart may be damaged or potentially unsafe in any way then that should be your first priority, but otherwise; •
Check the tyre temperature, state and pressures [4.9],
•
Check the fuel levels - remember overall weight [4.6],
•
Check the spark plug condition when it has cooled [4.5],
•
Make and record any required set-up changes,
•
Check that nothing is loose - check all nuts and bolts, including the little grub screws in the back axle bearings [8.5.2], are tight!
•
Visually check for any damage to the steering mechanism - check that the track rods are straight.
•
Check the sprocket alignment [8.3] and chain tension [8.4],
•
Check for any damage to the axle assembly by rotating it [8.5],
•
Visually check for any damage to the chassis & body work,
•
Check & clean the air filter. If it’s raining then it will need drying with paper towels. A spare air filter is useful. Check that the two long screws that hold the carburettor to the engine are tight.
Don’t forget to complete your record sheets! 2.8 After a Crash If the kart has collided with the scenery or another kart then perform the checks described in sections 8 & 9. Do not be tempted to race an unsafe kart, you could end up fined or injured and you will certainly be unpopular!
3. Looking After Your Kart This section is an overview of kart and engine maintenance. You will find that for each hour of racing you will need to spend several more looking after
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A Practical Mechanic’s Guide to TKM Karting your kart. You should spend time with your kart and get to know its every detail. 3.1 Cleaning Always strip and clean your kart after each event [8.2]. You will find loose nuts, bent bits and other problems that would otherwise have gone unnoticed. If you do not have the time to completely strip the kart then at least clean and check it. Don't forget to wash the air filter in warm soapy water. Note that it is illegal and dangerous to use petrol for cleaning in the pits. The author never uses petrol for cleaning because of the risk of fire and explosion. 3.1.1 After a Wet Race Special care must be taken to avoid rust. After a wet race both the engine [5.2.2] and the kart [8.2.1] must completely dried. 3.2 Chassis check Make a careful visual check of all chassis joints for cracks. A quick check of chassis alignment can be made by finding a bit of flat ground and with the driver seated set both front wheels strait and check that the weight on each front wheel is the same. Now turn the steering full right and then full left and check that the sides go up and down evenly [8.6 & 9.]. 3.3. Petrol/Oil mix Keep your fuel clean and don’t forget to put 2-Stroke oil in it [4.6]! 3.3.1 Petrol You must use unleaded petrol. ‘Super Unleaded’ is preferred. Note that if you change petrol brand or rating then you may need to change carburettor settings [4.2]. 3.3.2 '2-Stroke' Oil Only use High Performance 2-Stroke engine oil. Castor based 2-Stroke engine oil is best for lubrication but, synthetic oil does not cause as much carbon build up.
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A Practical Mechanic’s Guide to TKM Karting The author has no knowledge about the merits of various brands and types of engine oil, but there is plenty of advice and in-depth opinion about! The common advice is to use the highest quality castor/synthetic mixed oil. If you are in any doubt then get the advice of Tal-Ko. 3.3.3 Mixture Don't change from the 1/16 ratio advised unless you are sure about what you are doing! If you forget to put oil in the petrol (you won't be the first) then you will be taking your engine home in a bucket. 3.3.4 Storage The author stores fuel for up to five weeks without problems. Ensure that when it is stored in the kart tank that the breather is sealed, that there is no fuel in the fuel line and that the carburettor is connected or that the end of the fuel supply line is sealed 3.4 Engine re-builds Try not to run the engine above 15500 revs and get it checked/re-built every 9 hours. Yes - it will run for longer, but its performance may start to decline and the risk of catastrophic failure will increase. If you consistently run above 15500 revs then get you engine re-built more often (every 2 or 3 events if you max-out on revs). If you need to run on a tight budget then keep your revs below 15000, your mixture slightly rich (high & low jets) and your engine can be made to run safely for much more than 9 hours without greatly reducing its power. This guide assumes that best performance is the objective and sticks to 9 hours between rebuilds.
4. Set-up This section covers the engineering procedures that you will require at the track-side and in the pits, in order to get the best performance from your engine and kart.
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A Practical Mechanic’s Guide to TKM Karting Formula TKM - BT82 engines are intended to be raced in standard unmodified form but there are a few bits that can be legally ‘set-up’ to achieve maximum performance. Several books and a truckload of folklore and advice is available covering the subject of kart set-up. The manufacturer designed and tested the chassis to give optimum performance with settings in a mid position. So if you are in any doubt, adjust the settings to a mid position and you will not be far out. Take care with second-hand karts, as parts may not be as the designer intended. e.g. The back axle may have been changed for a length which is different to the design length. You can only improve if you measure the validity of set-up changes against actual track times and finishing positions. Record and analyse settings and results in order to identify the best settings. Keep a detailed record of set-up changes. The sort of things that should be recorded are; •
Reasons for making the change and its effect
•
Times/positions achieved with various set-ups
•
Engine/carburettor combinations used
•
Initial carburettor settings & changes to carburettor settings.
•
Exhaust length used & changes to exhaust length.
When you start racing you will not be able to detect the difference that small set-up changes make, so be bold and experiment with large changes. This will enable you to understand the difference that particular changes can make. Ensure that you keep a detailed record of the changes and their effect. Spend time now and again reviewing your records. 4.1 Tools required Long small diameter screwdriver for adjusting the low jet. Long nose pliers for removing and replacing various springs. Plug spanner
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A Practical Mechanic’s Guide to TKM Karting 13mm extended socket and wrench Torque wrench Toe-out alignment tool [11.2.4] & Tape measure A set of good quality ‘T’-bar Allen keys. 4.2 Carburettor set-up The carburettor must be clean and the Pop-Off must be correctly set [7.7]. The air filter should be clean and dry. The author does not fully understand the science of carburettor adjustment. He has read all available publications and has listened to much advice, most of it contradictory. Set out here is a method that has evolved by trial and error. 4.2.1 Setting the Jets
Figure 4.2.1-1 Carburettor Jets The low jet is a plain screw head and the high jet is a ‘T’ bar [7.2.2]. 4.2.2 Initial settings Turn both jets in until lightly seated. Turn the High jet out to 1/3 turn on cold days, 1/2 turn on hot days. Turn the Low jet out 11/4 turns on cool days and 11/2 turns on hot days.
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A Practical Mechanic’s Guide to TKM Karting 4.2.3 Jet Adjustment The engine should run OK with these initial settings, but will require tuning to achieve best performance. Note that if the mixture is too weak it can result in damage to the engine. •
If the engine smokes and four-strokes at corners then the mixture is too rich. Weaken the mixture by closing the low and high jets together in increments of 1/16 of a turn.
•
If it is slower than others along the straight because it won’t rev high enough (i.e. It flattens out at below 15000 and sounds ‘fluffy’) then it is too rich at the high end. Weaken the mixture by closing the high jet in increments of 1/16 of a turn. If the track temperature is high then turn the low jet out by equal amounts.
•
If the top end fades or pops and spits then the mixture is too weak. Open the high jet in increments of 1/8 of a turn.
•
If it has poor pulling at low revs coming out of corners, but no engine smoke is visible. The mixture is too weak at the low end. Open the low jet in increments of 1/8 of a turn.
4.2.4 Checking the mixture After the engine has run then remove the cylinder head [5.6] and check the top of the piston. •
Wet & oily indicates that the mixture is too rich (smokes a lot out of corners?),
•
Dry & black indicates that the mixture is perfect,
•
Dark Grey indicates that the mixture is a bit too lean,
•
Light Grey indicates that the mixture is so weak that it may result in engine damage.
Always remove and replace the head with great care [5.6] 4.2.5 Setting Tick-over on Clutch Karts Ensure that the carburettor is clean and serviceable, that the Pop-Off is correctly set [7.7] and the jet screws are set to the initial settings [4.2.2].
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A Practical Mechanic’s Guide to TKM Karting You may find it easier to remove the Air Intake Box assembly complete with the Back-plate in order to gain access to the idle adjust screw. If you do, you will need to put spacers in place off the back-plate (8mm Nylock nuts are ideal) in order to prevent the carburettor securing screws from ‘bottoming’. The chain and the back wheels need to be in place and free to rotate. SAFETY - Ensure that the kart stand is steady and secure, that the wheels are clear to rotate, that there is nothing close to snag and that you keep well clear. With the engine running adjust the idle adjust screw until the rev counter shows between 4500 and 5000 rpm. If you do not have a rev counter then •
Pull the brake on lightly,
•
Screw in the idle adjust screw in until the clutch just starts to bite,
•
Back off a touch.
To test the setting: With the engine running depress the accelerator just enough to spin the back wheels. Release the accelerator and as soon as the revs have stabilised but with the wheels still spinning pull the brake hard on. The engine revs should not drop as the back wheels lock. 4.2.6 Throttle Cable Ensure that the throttle cable is adjusted so that the throttle is fully open when the accelerator is down. Also ensure that when the accelerator is fully depressed the pedal stop screw prevents the cable and throttle shaft arm from being stressed. 4.3 Timing Set-up The timing should be set to a level close to maximum, but safe for scrutineering [5.11]. It should require no further adjustment. 4.4 Exhaust length Set-up Increasing the length of the exhaust's flexible pipe will improve power at low revs and decreasing it will improve power at high revs [5.14.5].
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A Practical Mechanic’s Guide to TKM Karting 4.5 Spark Plug After each heat/race, when the spark plug is cool remove it and check its condition [5.12]. Clean it - Spray brake cleaner works well. Check it carefully for damage and wear. Check and adjust the gap (0.025” or 0.64mm). The spark plug is such a critical component that the author will always discard it for a new plug if in any doubt. 4.6 Fuel It is not permitted to use petrol for cleaning in the pits. It’s dangerous to use petrol for cleaning at any time and the author strongly advises against its use. The fuel supply must be kept clean! If it is not, the carburettor will fail. Ensure that all containers and funnels are clean. Store them in a plastic bag and don’t let them touch the ground. Petrol/oil mix is a magnet to grit and grit kills carburettors.. Use the advised fuel oil mixtures [3.3] specified in TKM Regulations [14.3]. 4.6.1 Bleeding air out from the Fuel Line The engine will not run well or may not run at all if there is air in the fuel line. Check the tops of loops in the fuel line for air bubbles. To remove air from the fuel line: •
Remove the spark plug from the engine, reconnect it to the HT lead and lay it on top of the engine. This ensures that the HT is earthed. If the spark is not earthed it may damage the ignition.
•
Turn the engine over with the air intake blocked. This can be done by placing the palm of your hand over the trumpet, but is best done with the Air Intake Box removed by placing your hand directly over the carburettor intake. This also allows you to check that fuel is pumping into the carburettor OK. You should see fuel run out of the low jet bypass outlet [7.2.2] after a couple of rotations.
Karts fitted with a clutch: •
Block the air intake
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A Practical Mechanic’s Guide to TKM Karting •
Turn the engine over using the electric starter until the air bubbles are gone.
Karts not fitted with a clutch: •
As before, but turn the back wheels by hand.
4.6.2 If Bleeding Doesn't Work If this does not work because too much air prevents the pump from priming then; •
Remove the fuel pipe from the top of the carburettor and pinch the fuel pipe shut.
•
Place the end of the pipe into a spare fuel container and release the pinch.
•
Lower the container until the fuel runs through the pipe into the container.
•
If it does not run out because there is not enough fuel in the line to start the siphon then (DO NOT SUCK IT THROUGH) blow down the breather pipe.
•
When the fuels runs out fit it back onto carburettor.
•
Start the bleeding process again [4.6.1].
4.7 Keeping the Inside of the Engine Clean. The engine is made to very close tolerances and carbon deposits within the engine can make a significant difference to performance. Ensure that the inside of the engine is kept free of carbon [5]. 4.8 Other engine adjustments The following items are worthy of attention: •
Ensure that the aluminium trumpet is flush to the inside of the Air Intake Box.
•
Use some additional method of fixing the trumpet and grommet to the air-box. Tank tape is ideal. You will not be allowed to continue racing if it gets knocked off.
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A Practical Mechanic’s Guide to TKM Karting •
Ensure that the H.T. lead is tied down so that it can not be accidentally snagged and pulled off!
4.9 Tyres See also 8.10. This is another area where a lot of contradictory opinion is available and here is some more! 4.9.1 Slicks Slicks need to heat up to work. Cold slicks don't work! The higher the pressure the quicker they heat up and, to some extent, the hotter they will become. Slicks should be inflated to the lowest pressure that allows them to heat up to a good working temperature within 1 or 2 laps. The normal pressure range for slicks is 14 < 36 psi. On an average dry day, on an average racetrack, 22-psi front and 24 psi rear is a good starting point. If they overheat (over 65°C) they will 'go-off' (melt) and bits of rubber will fly off them! For short races or timed laps then the pressure should be higher, to warm the tyres quicker. On long races the pressures should be reduced so that the tyres do not overheat. Older slicks need more heat to work. They develop a ‘hard’ surface and become a lot less grippy than new slicks. Check slicks immediately on leaving the racetrack. They should be hot to the touch (but not uncomfortably so), slightly sticky and slightly grained. If they did not heat up enough they will be cool and have a smooth, glazed surface. If they overheated they will be hot and heavily grained with sticky bits of rubber coming off the edges. 4.9.2 Wets The author has never been completely happy with his understanding of the pressures needed for wet tyres. There is a lot of folk law around and in any wet race the tyre pressure variation between karts is sometimes extreme. It is always a balance between getting the maximum grip and being sure that the tyres will survive.
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A Practical Mechanic’s Guide to TKM Karting Wets need to warm up to work well, but when its very wet you may not achieve the level of grip needed to warm the tyres. Generally; •
28 < 35 psi when it is very wet, but consider that if the tyres are never going to get warm then you may get more grip with softer tyres. Also consider that if the racetrack starts to dry then the tyres may be ruined and the cost of replacement may be a factor. 20 < 28 psi in the wet. 12 < 20 psi for a drying racetrack. They should not overheat at these lower pressures.
Keep a spare set of old wets for times when the racetrack is drying and you don’t want to sacrifice a good set of wets. They can be run at high pressure to provide good grip on a drying racetrack. 4.10 Track width The track width can be adjusted in order to change the amount of grip available and to ‘balance’ the kart.
Figure 4.10-1 Track 4.10.1 Over-steer, Under-steer and Balance. Over-steer: When a kart has too much grip at the front or too little at the back it oversteers. The back wheels slide away putting the kart into a spin.
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Figure 4.10.1-1 Over-Steer Under-steer: When a kart has too much grip at the back or too little at the front it understeers. The front wheels slide straight on and do not move the front of the kart round.
Figure 4.10.1-2 Under-Steer In balance:
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A Practical Mechanic’s Guide to TKM Karting When the kart is correctly balanced it will slide neatly sideways as it goes round the corner. This ideal is not possible for all corners, but a good compromise can be achieved.
Figure 4.10.1-3 Balanced 4.10.2 Effects of Track Adjustment Increasing track width by moving the wheels out, reduces the downward force on the outside wheels thus giving less grip on corners. The result of this is to reduce the amount of lateral force that the grip can support but providing more predictability in the way in which the kart slides.
Figure 4.10.2-1 Track Adjustment Decreasing track width by moving the wheels in, increases the downwards force on the outside wheels so increasing the grip, but it also increases the rolling moment (causing the inside wheels to rise) and increasing the possibility that the kart will lose grip suddenly. This is called ‘skipping’. This will result in the kart sliding more violently and with less predictability. For novice racers the author suggests that the kart is set up for minimum slide, but no skip so that when it does slide it can be controlled.
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A Practical Mechanic’s Guide to TKM Karting 4.10.3 A (Crude) Method of Setting the Track Width. Adjust the track to mid position for both front and back wheels. Making small adjustments move all four wheels in until the back of the kart just starts to skip on the tightest corners and then back out a touch. Move the front wheels in or out to balance kart. 4.10.4 Asymmetric Track Settings. The author has never been tempted to try different track settings on each side. It may be possible to gain a small advantage on some tracks. More experienced racers may do it. If you give it a try please let the author know what was achieved. 4.10.5 Back Axle There is nothing sophisticated about the back axle! The lack of a differential gear means that the inside wheel will always drag and not contribute towards grip on a corner. A Kart will corner faster and carry more speed out of a corner if the set-up allows the inside rear wheel to lift. 4.11 Front wheel Toe-in/Toe-Out. Toe-out means that both front wheels point slightly outwards when the kart is going straight. Toe-in means that they point inwards. When the track is dry they should normally be set parallel so that there is no Toe-in or Toe-out. Setting slight Toe-in (about 1-3mm) will cause the front tyres to ‘scrub’ and warm up quickly, possibly providing more grip at the front and giving better stability especially on bumpy tracks. The drag produced may reduce the top speed of the kart slightly. In the wet setting Toe-out greatly improves the handling [4.14.2]. 4.12 Engine to Axle Gearing The objective is to set up the gearing to provide the best performance. More teeth on the back sprocket lowers the gearing allowing the engine to reach higher revs. This gives better acceleration, but possibly a lower top speed on long straights.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting In time trials a slightly higher gear may provide the best times, but in racing a slightly lower gear may provide the best finishing position. Use results and lap times to arrive at the best gearing, but remember to keep your revs below 15500rpm. If you are racing at an unfamiliar track then find out what gearing the winning drivers use. Sneak up behind them when they are not looking and peek, or just ask! The author has found that new karters may gain more success with 1 or 2 teeth less on the back sprocket than more experienced drivers use. Consider that a new karter may not be able to compete on the corners due to inexperience and therefore may benefit more from a slightly higher gear, which gives more speed on long straights. Experiment to find your optimum ratio by changing the gear ratio up and down by 1 or 2 teeth. Note that it is the gear ratio that matters. If the back sprocket is too large then reduce the engine sprocket by 1 tooth and the back sprocket by ratio. As a rule use the largest practical engine sprocket as this will result in less wear to the engine sprocket and chain, but bear in mind the risk of a large back sprocket hitting the ground. 4.12.1 Gearing in the Wet Wets have a larger diameter than slicks and therefore the gearing needs to be changed in order to compensate for this. To give the same gearing the rear sprocket should be a couple of teeth bigger with wets. You will need to experiment to get the best gear for each track/condition combination. 4.13 Chain Tension Check the chain tension after each race [8.4.2]. Use proprietary chain lubricant to re-grease it after each race.
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A Practical Mechanic’s Guide to TKM Karting 4.14 Kart set-up for Wet Racing There are no hard and fast rules for wet set-up. Most drivers have their own set-up ideas, but there are some general rules, which apply. The following settings are starting points from which you will need to experiment. 4.14.1 Chassis A flexible kart gives better grip in the wet than a stiff kart. To make your kart chassis more flexible; •
Slacken the nerf bars (side pod brackets) front bolts,
•
Slacken top additional seat stay bolts, or remove the stays completely.
•
Slacken front and rear bumper bar bolts.
These bolts should be longer than normal to allow spare thread when slackened. The nuts must be nylock to prevent them from vibrating off. The seat should also be moved up and forward by about an inch. This produces two effects; •
It raises the centre of gravity. This is needed to lift the rear wheel in the wet when less grip is available.
•
It provides better grip at the front end.
This can be achieved by drilling several sets of holes in the seat and by using additional spacers under it. 4.14.2 Wheels Track: In the wet the kart will have a much greater tendency to over-steer. The track settings should be altered to correct this. Make the rear track narrower so that each wheel is further in than for a dry setting by the following amounts. Rear Track Settings: • Very wet
- 15<20 mm
• Wet
- 10<15 mm
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A Practical Mechanic’s Guide to TKM Karting • Drying
- 5<10 mm
(These settings are illustrative. The actual values that you use may differ greatly. You need to experiment to get the best settings.)
Set the front track to balance the kart. This will usually mean making the front track wider than for dry running. Toe-Out: Setting a small amount of Toe-out gives better grip in the wet. This is in part because it warms up the tyres quicker and in part because it changes the steering and front wheel geometry [9.1.3]. To measure the Toe-out the author uses the (rather naff looking, but works OK) special tool [11.2.4] to provide precise measuring points. Avoid lumps. bumps and other defects on the tyre as that will effect the measurement. Measurements should be taken in line with the tyre surface. Toe-out is normally stated as the difference between A and B.
Figure 4.14.2-1 Measuring Toe-Out Toe-out settings: •
Very wet
10 mm
•
Wet
5 mm
•
Drying
2 mm
(These settings are illustrative. The actual values that you use may differ greatly. You need to experiment to get the best settings.)
A more accurate (and more expensive) alternative is to purchase a set of 'Tracking Discs'.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 4.15 Set-up at Various Tracks All tracks differ. The best set-up at one track will not be the best at another. Weather and temperature will also affect the tracks characteristics. Be prepared to alter kart set-up to suit the track, weather and temperature. Don't forget to keep a careful and detailed record of set-up for each track.
5. Engine Maintenance This section covers all of the engineering details that you will require in order to service your engine. It does not attempt to describe how to perform a complete rebuild of a BT82 Engine. For that you will require specialised knowledge and tools. It does however describe stripping, cleaning and rebuilding to a level that is required by, and should therefore be within the ability of, every karter. Scrutineers may require to inspect the head and ports of the engine and therefore you do need to be able to at least remove and refit the head and barrel. There are a few potential problems that are described below but as long as you take care when stripping and reassembling the engine, it is well within the ability of anyone with basic engineering skills. Note: - ALWAYS tighten fastenings to the torque settings specified in the TMK regulations [14.3]. If any problems occur which are beyond your ability to resolve and in any case after about 9 hours of racing the engine should be sent back to Tal-Ko or to a reputable engine re-builder for checking and rebuilding. If you are not sure of your skills or have never rebuilt a two-stroke engine before then use an engine that is about to be sent away for rebuilding to practice on. 5.1 Tools Required A few specialist tools are required to strip and rebuild the engine as far as this guide goes.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 5.1.1 Torque Wrench A Torque Wrench which can be set in the range 4 < 50 lbs./ft. This may require a small and a medium size torque wrench. 5.1.2 Sockets The only special cases here are a long reach 13mm socket for the four Head retaining nuts and a short 13mm socket with the top edge ground away and a flexible drive for the Manifold Bend retaining nuts. 5.1.3 Special Tools Dummy Gudgeon Pin [11.1.3]. Gudgeon Pin Extractor [11.2.6]. Clutch Holding Tool [11.1.4]. Clutch Puller [11.1.5]. Sprocket Extractor [11.1.6]. 5.1.4 Measuring Tools Feeler Gauge. Steel Rule. Small Micrometer. Vernier Calliper. 5.2 Basics When stripping the engine ensure that every nut, screw, bolt or component removed is carefully stored in an organised manner. The author has a selection of biscuit tins and plastic bowls for this purpose. 5.2.1 Basic Checks The following list specifies the basic things that need to be done after a meeting.
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A Practical Mechanic’s Guide to TKM Karting •
First slacken the spark plug and then remove the engine, complete with carburettor and Air Intake box, from the chassis [5.5.1].
•
Clean the outside of the engine and carburettor using white spirit and a brush. Take care to avoid getting cleaning fluid into the crankshaft bearings or cylinder. Do not get WD40 or oil onto the spark plug or into the plug cap. The plug cap is held on by friction and if this friction is diminished by WD40 it may fall off during a race.
•
The carburettor can be left on the engine if it is performing well and does not require servicing, otherwise it should be removed and stored it in a plastic bag [7.4].
•
Remove, clean and check the spark plug [5.12].
•
Clean and check the clutch and grease the sprocket bearing after each event [6.2].
•
Make a visual check for any damage.
5.2.2 After a Wet Race After a wet event it is important to strip and dry the inside of the engine. Water is sucked into the engine along with the fuel/air mixture. If the engine is left wet, the steel components will start to rust. This will reduce engine life and in severe cases, result in engine failure. Remove the cylinder head and barrel and then warm the engine to dry it. This could be done with a hair dryer! 5.2.3 Engine Record Keep a record of engine hours and of the condition of the engine [15.3]. This should include: •
State of the clutch, including the thickness of the Friction Disc.
•
When carbon was removed from the inside of the engine and how bad the build-up was.
•
Degree and nature of engine wear.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 5.3 How the BT82 works The BT82 Engine is a Piston Port Two Stroke engine. This means that the inlet and exhaust ports are blocked and opened by the position of the piston and not by any other valve mechanism.
Figure 5.3-1 Engine - Induction As the piston moves up towards compression the Transfer & Exhaust ports are blocked allowing the air/fuel mixture in the cylinder to become compressed ready for ignition. The rising piston creates a part vacuum in the crankcase. Because the inlet port is opening, air/fuel mixture from the carburettor is drawn into the crankcase.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting
Figure 5.3-2 Engine - Compression When the piston is at the top of its stroke and the mixture in the cylinder is compressed the ignition fires and drives the piston back down. As the piston moves down the exhaust port is opened allowing the pressurised exhaust gases to escape. As the piston moves further down the inlet port is closed and the air/fuel mixture already in the crankcase is compressed.
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Figure 5.3-3 Engine - Exhaust When the piston is fully down the transfer port is opened and the pressurised air/fuel mixture flows from the crankcase into the cylinder driving out the remaining exhaust gasses. Some of the air-fuel mixture is pushed out of the exhaust port into the exhaust expansion chamber. A pulse wave reflected from the exhaust will then force much of it back into the cylinder [5.14]. If you want to know more about this process then read the book “Two Stroke Performance Tuning” [14.8]. 5.4 Running in Read “Getting the best from your Engine” in the TKM Regulations [14.3] & the 'ENGINE' chapter in 'The Complete Guide to Formula TKM Karting' [14.6]. What you do for the first hour of an engine's life will greatly affect the remainder of its life. New or fully rebuilt engines must be run in for a full hour. Ensure that the carburettor is set slightly rich. The engine should smoke slightly. Build up the revs slowly over the hour. Check the mixture by removing and checking the cylinder head between sessions [4.2.4].
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A Practical Mechanic’s Guide to TKM Karting Check the head and manifold bend securing nuts are at the correct torque between each run. 5.4.1 Running a New Piston In If just the piston and rings have been replaced [5.9] then you will need to run the engine in for a short time. Run at low revs (9000 < 10000) and with a slightly rich mixture for at least 5 minutes. 5.5 Removing and replacing the Engine This is a very straightforward task, but if the engine is replaced incorrectly it can result in severe problems. 5.5.1 Removing the Engine •
Remove the Chain Guard and disconnect the fuel pipe taking care to ensure that it is sealed so that fuel does not escape and dirt does not get in (note that a 6mm screw fits well). Disconnect the accelerator cable from the carburettor. Remove the Rev-counter aerial from the HT lead. Disconnect the ignition switch connectors [5.11.5]
•
Slacken the bolts that hold the engine mount clamps to the Chassis frame so that the engine is free to slide on the frame. Remove the four (or eight) bolts which hold the Axle Sprocket to its carrier and then remove the Axle Sprocket and chain.
•
Remove the Exhaust retaining springs and remove the exhaust. Use a small wad of cloth to block the exhaust port ensuring that no dirt or loose threads get in to the engine.
•
The engine can now be lifted clear of the chassis, but do not lift it by the Air Intake box.
5.5.2 Replacing the Engine When lifting the engine it is very tempting to lift it by the Air Intake box and the Manifold Bend. This is fine, but take care that the Air Intake box does not come off leaving you with just the Air Intake box in your hand and a smashed engine on the floor.
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A Practical Mechanic’s Guide to TKM Karting To reinstall the engine, reverse the sequence for removing it [5.5.1] and then; •
Check sprocket alignment [8.3.1],
•
Adjust the chain tension [8.4.3],
•
Check the accelerator cable setting [7.8],
•
Bleed the air out of the fuel pipe [4.6.1].
5.5.3 Engine Mounts The engine mount allows the BT82 Engine to be fitted to the engine mounting tubes on the chassis frame. Chassis differ so that an engine mount must be matched to the chassis type. The engine mount should normally be removed before sending an engine away to be serviced or re-built. 5.5.4 Removing the Engine Mounts Mark the mount to ensure that it goes back on the same way round. Remove the four ‘cap head ‘ screws securing the engine mount to the bottom of the crankcase. 5.5.5 Checking the Engine Mounts The two aluminium clamps are close to the ground and will often get worn and damaged. This should not be so severe that the heads of the clamping screws become damaged. Look for cracks in the grooves, which fit onto the tubing. No cracking is acceptable. Cracks?
Figure 5.5.4-1 Engine Mount Clamps If either of the screw threads strip then replace the mount.
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A Practical Mechanic’s Guide to TKM Karting Replacement cap head screws MUST be the correct lengths. If too long then they may bottom and strip the threads. If too short they will not be strong enough. 5.5.6 Replacing the Engine Mounts Ensure that the screws are tight and the mount goes back on the correct way round. 5.6 Cylinder Head The aluminium cylinder head is a critical component and must be treated with respect. It is quite soft and will distort or crush if it is not treated with appropriate care. 5.6.1 Removing the cylinder Head The Cylinder head must be cool before it is removed. It is important to remove the two cap head screws first and then the four 13mm brass nuts in a diagonal order as shown. This will prevent the risk of warping the head.
1
3 Cap Head screws
2
4
Figure 5.6.1-1 Cylinder Head Nuts •
Remove the Cap head screws first.
•
Loosen the nuts slowly in a diagonal order. Loosen (1) first by a 1/4 turn and then (2) etc. returning to (1) after (4). Do not remove any one nut before the others are slackened.
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A Practical Mechanic’s Guide to TKM Karting •
Collect the 4 nuts, 2 screws and 6 washers and store them safety.
•
Note that the barrel will now be free to be lifted off the crankcase.
5.6.2 Replacing the cylinder Head It is important to re-tighten the four 13mm brass nuts in a diagonal order as shown in figure 5.6.1-1. If you do not you may warp the head. Set the torque wrench to about 6lbs/ft first and then 10 lbs./ft and then 13lbs/ft to finish. The two cap head screws should be replaced last. Check the Squish Band Clearance [5.7.6], as it may decrease when the head is re-tightened. 5.6.3 Cleaning the cylinder head. A discoloration of the head due to a small amount of carbon deposit is OK and makes very little difference to performance. If it starts to get thick it could in theory cause an engine to fail scrutineering due to the reduced capacity of the cylinder. Chip off the carbon lumps using a shaped piece of hard plastic. You may finish off removing the carbon with fine wetted emery paper, but if you do then use it with great care and - DO NOT REMOVE ANY METAL! Do not use any form of oven cleaner. Most contain caustic soda (Sodium Hydroxide) or similar substances that will erode aluminium. The author never uses chemical cleaners, but if you must use a chemical cleaner then test it first. Drill a hole in a spare piece of aluminium and take the curly swarf that comes off the drill bit and put half of it into the chemical cleaner. Leave it for a few hours and then compare it with the untreated swarf. - You may be surprised at the degree of erosion. 5.6.4 Checking the cylinder head. After cleaning the head use a magnifying glass and a good light to examine the head for cracks, pitting and any other sign of damage. 5.7 Cylinder Barrel You may be required to remove the barrel for scrutineering.
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A Practical Mechanic’s Guide to TKM Karting The barrel will be free to be lifted from the crankcase when the head is removed. 5.7.1 Removing the barrel Take care with the base gaskets. They can be reused if undamaged. When removing the barrel, support the piston so it doesn't fall on to the crankcase. In order to ensure that no dirt or loose components fall into the crankcase place a clean cloth over the exposed hole. 5.7.2 Replacing the barrel This requires practice. Like many things when you have done it a few times it becomes easy, but the first time you try it may seem to be almost impossible. •
Place the engine on its side on a clean surface. If you leave it upright you will find it difficult to support the head, compress the rings and push the piston into place without running out of hands!
•
Ensure all internal parts are spotless and lightly oiled with 2-Stroke oil.
•
Ensure that it's the right way round. The exhaust port faces the rear!
•
Align the ends of the piston rings with the pins in the slot [5.9.4].
•
Using finger and thumb to compress first, the top ring and then the lower ring, gently insert the piston into the cylinder. Never force it. The piston and rings must be oiled. The rings must be aligned with the pins in the piston. The piston will slide easily into the barrel when everything is correct.
•
Turn the engine over by hand to check free movement and, using a thumb on the top of the piston, 'wobble' the piston about to ensure that the rings are not stuck.
•
Always check the Squish Band Clearance after replacing the barrel [5.7.6].
5.7.3 Cleaning the barrel Remove any carbon from the ports using a plastic scraper.
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A Practical Mechanic’s Guide to TKM Karting Never use chemical cleaners or oven cleaner. Removing the black anodising from around the ports may make the engine illegal. You can use white spirit and then WD40 on the outside of the engine but the cylinder must be lightly oiled with Two-Stroke engine oil. 5.7.4 Checking the barrel The cross-hatching caused by honing the bore should still be clearly visible. The surface should not show vertical wear lines (Scoring). Check for scoring - especially below the ports.
Figure 5.7.4-1 Scoring below a port It is beyond the scope of this manual to completely check the bore. If you have any doubts you should send the engine away to be fully checked by TalKo or a reputable engine re-builder. 5.7.5 The Squish Band Clearance The Squish Band clearance is the gap between the top of the piston and the cylinder head. It is critical to good combustion within the cylinder. The book “Two-Stroke Performance Tuning” provides an excellent explanation [14.8]. This clearance is normally adjusted by the total thickness of the base gaskets (between the barrel and the crankcase). These gaskets come in various sizes and it is permitted to use up to three to achieve the correct Squish Band
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Clearance. These gaskets can be reused, but they must be replaced if they become brittle or damaged in any way. The Squish Band Clearance should be less than 0.914mm (0.036") and greater than 0.762mm (0.030"). As a general rule the best performance will be achieved by setting the minimum clearance. It should be checked often as the gaskets can become compressed so reducing the clearance. Reducing the Squish Band Clearance further than these limits may cause the engine to fail scrutineering by causing a reduction in the head volume below the legal minimum. It may also place excessive stress on the piston assembly and may even cause the engine to overheat. Machining of the head or barrel will result in a reduced Squish Band Clearance. 5.7.6 Measuring the Squish Band Clearance To measure the Squish Band Clearance tighten the head down to its correct torque [5.6.2]. Insert a length of soft solder wire towards the sprocket side of the engine. It should be inserted far enough through the Spark Plug hole that a good length will be crushed against the cylinder head when the piston rises. (The type of solder with a flux core is ideal. The solder wire used by the author has an original diameter of 1.27mm). Turn the engine over by hand until top-dead-centre is passed and the solder is crushed.
Figure 5.7.6-1 Squish Band Clearance
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Remove the solder wire and carefully measure the width of the crushed end. Repeat this, using fresh solder inserted towards the ignition side of the engine. If the measurements are not the same then replace the base gaskets and try again. If it is still uneven then something is seriously wrong and the problem should be referred to an expert. If the measurements are both the same, but not correct then change the gaskets to achieve the correct clearance. 5.8 Piston Assembly You will need to remove the piston assembly in order to clean and check it. The author always replaces the circlips. Replace the small end bearing rollers if they show any sign of damage. 5.8.1 Removing the Piston assembly
Figure 5.8.1-1 Removing the Circlips-1 If you do not own a proprietary tool then removing and replacing the ear-less circlips used to keep the gudgeon pin in place requires practice. â&#x20AC;˘
Place the engine on its side so that bits do not fall into the crankcase.
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A Practical Mechanic’s Guide to TKM Karting •
Grease the dummy gudgeon pin [11.1.3].
•
Push the gudgeon pin down away from the circlip so that a small gap is evident between the circlip and the gudgeon pin.
•
Using a small Instrument screwdriver with a blade width of about 1.5mm carefully move the circlip around the groove until the gap in the circlip is aligned with the edge of the slot in the piston.
•
Insert the screwdriver under the end of the circlip.
Figure 5.8.1-2 Removing the Circlips-2 •
Using the inside edge of the gudgeon pin as a fulcrum, raise the screwdriver handle lifting the free end of the circlip up so that it is just out of the groove.
•
Grip the freed end of the circlip with snip-nose pliers (The points need to be small enough to fit into the groove) and rotate and pull it clear so that the gripped end turns in pulling the remainder of the circlip out of the groove.
•
Remove the other circlip and discard them both.
Insert the Dummy Gudgeon Pin into the piston (rotate it to stop it sticking) until it starts to displace the Gudgeon Pin. Insert the threaded bar from the Gudgeon Pin Extractor [11.2.6] through the Gudgeon and Dummy Gudgeon pin and fix it in place with the two nuts with the domes facing inwards.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Dummy Gudgeon Pin
Figure 5.8.1-3 Removing the Gudgeon Pin Push the assembly through until the dummy gudgeon pin supports the needle Rollers and Thrust Washers in place. Take care not to place any load on the crank. If the gudgeon pin is tight then assemble the remainder of the Gudgeon Pin Extractor [11.2.6] and use it to jack the gudgeon pin out. Very little force will be required unless something is wrong so do not use a hammer or drift.
Figure 5.8.1-4 Gudgeon Pin Extractor Remove the Gudgeon pin removal tool. The Piston and the con-rod can now be separated without the Needle Rollers flying in all directions.
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Dummy Gudgeon Pin inside Conrod Figure 5.8.1-5 Removing the Con-Rod Assembly Use a cable tie to secure the dummy gudgeon pin, 25 rollers, 2 aluminium and 2 steel thrust washers in place. 5.8.2 Replacing the Piston Assembly Take your time and ensure that everything is very clean. Have your tools and new parts ready to hand. •
Assemble the rings on to the piston [5.9.4].
•
Lay the engine down (inlet port facing down) so that any dropped component does not fall into the crankcase. It is also easier to work on in this position.
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A Practical Mechanic’s Guide to TKM Karting 1.85mm Alluminium Washer 1.0mm Steel Washer
25 Rollers
Figure 5.8.2-1 Small End Bearing. •
Assemble the 25 bearing rollers and dummy gudgeon pin into the crank shaft small end. Use 2-Stroke oil to hold them in place. Ensure that there are 25 pins.
•
Oil the four thrust washers and place them on to the dummy gudgeon pin. (Note that the steel Washers may have a pressing flash around the edge. If so ensure that it does not interfere with the aluminium washer or the con rod.)
•
Push the Gudgeon pin part-way into the piston.
•
Oil the surfaces on the inside of the piston against which the Trust Washers bear.
•
Carefully place the assembled small end bearing into the piston. Ensure that the gap in the top piston ring faces towards the front of the engine and the gap in the bottom ring faces the rear (exhaust port). [5.9.4]. Note that older pistons may have the gaps in both rings facing the rear of the engine.
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Front (Carburettor)
Peg for top ring
Back (Exhaust)
Peg for bottom ring
Figure 5.8.2-2 New Piston Ring Alignment
Front (Carburettor) Peg for top ring
Back (Exhaust)
Peg for bottom ring
Figure 5.8.2-3 Old Piston Ring Alignment •
Ease the Alignment Spring [11.2.7] though the gudgeon pin and into the dummy gudgeon pin to bring both into alignment. Take care not to allow the spring to push the dummy gudgeon pin out of position. Hold the dummy gudgeon pin in place
Figure 5.8.2-1 Aligning the Dummy Gudgeon Pin •
When the spring is in place use finger pressure to push the gudgeon pin home and the Dummy Gudgeon pin out. If finger pressure is not
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A Practical Mechanic’s Guide to TKM Karting enough then first ensure that a thrust washer has not slipped down between the dummy and real gudgeon pins and that nothing else is wrong before using the Gudgeon pin extraction tool to press it in [5.8.14]. Do not use a hammer! Check that about 0.25mm (0.098”) of clearance exists between the thrust washers and the conrod. That’s the easy bit done! If you found it difficult to get the ear-less circlips out then replacing them needs to be practised using an old piston before you try it on the new one, or see the note about eared circlips below. •
Adjust the position of the gudgeon pin so that a small amount of clearance is available below the groove into which the circlip sits.
•
Place one end of the circlip into the groove so that the end of the circlip is aligned with the centre of the slot. Ensure that it is in the groove and not below it.
•
The protruding half of the circlip can now be pushed down into the groove with your thumb. If it is too tight then use an aluminium drift to push it home. End of circlip aligned to centre of slot.
Aluminium Drift
Figure 5.8.2-2 Fixing the Circlip in Place •
Have a few spare circlips ready! Do not crush the circlip or scratch the piston.
•
When both circlips are in place, use a good light and a magnifying glass to re-check that both circlips are fully home.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Eared Circlips Eared circlips are easy to insert and remove, but care must be taken to ensure that they do not wear due to the end of the gudgeon pin rubbing against them! Check them frequently. When inserting eared circlips ensure that they are not crushed. Only compress them as much as is essential in order to insert them. Use a magnifiing glass to ensure thet they are well seated. A reduced gap between the ears indicates a poorly seated circlip.
Gap
Figure 5.8.2-3 Fixing the Eared Circlip in Place Do not re-use circlips. 5.8.3 Small-End Bearing Surface The con rod should easily last between rebuilds, but check the small-end bearing surface (inside the hole) for any damage. A worn or damaged roller can damage the bearing surface. 5.9 Piston The piston is a critical component and must be treated with respect. It is made from aluminium which can be easily damaged. It can tell a story about mixture and engine temperature. If the piston is replaced then the piston rings must be replaced. New piston rings require a small amount of 'Running In' [5.4.1].
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A Practical Mechanic’s Guide to TKM Karting 5.9.1 Cleaning the Piston Remove the piston rings [5.9.3]. Using a shaped plastic scraper remove any carbon that has built up on the top of the piston or in the piston ring grooves. It is possible to clean the top of the piston with fine wet emery, but this practice has no great merit. 5.9.2 Checking the Piston The piston will not normally require replacing more often than every 9 hours, but if the piston is damaged in any way, or you suspect that it may be damage then replace it. The author has had an engine destroyed by a piston breaking at over 15000 rpm. The piston would have cost £50 to replace, the engine cost over £800! The author now checks pistons very carefully and replaces them when any damage or wear is evident. No degree of damage is acceptable! If you use higher than normal rpm then the piston will be absorbing excessive amounts of stress. This will result in premature failure so replace it more frequently. •
Use a magnifying glass under a good light to check for hairline cracks, scuffing (around the skirt) and scratches (from tools and cleaning). A scratch will act as a focal point for stress and may cause premature failure.
•
Check the piston ring location pegs with care. They are prone to damage.
•
Check the Aluminium Thrust Washers and the mating surfaces on the inside of the piston for wear. The aluminium surfaces can become worn which will increase the end-float of the piston on the conrod/gudgeon pin. This can be heard at tick-over as a 'clicking' sound.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 5.9.3 Removing the Piston Rings
First finger Thumbs
Figure 5.9.3-1 Removing Piston Rings Ease the rings open with your thumb nails until the ring can be lifted clear without scratching the piston. 5.9.4 Replacing the Piston Rings Piston rings can be changed more frequently if you suspect leakage due to wear. The most likely cause of 'blow by' (shown by blackening down the side of the piston) is carbon in the slots causing the rings to stick. Using nothing but your fingers and thumb nails, gently ease the rings open until they can be placed onto the Piston. [5.9.3-1] Take great care to avoid scratching the piston with the sharp ends of the rings.
Figure 5.9.4-1 New Piston Ring Alignment
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A Practical Mechanic’s Guide to TKM Karting Note that the ring alignment may be different in older pistons. [5.8.2-3] The ‘gaps’ in the piston rings must be aligned to the pegs. Use a magnifying glass to check that the pegs are OK (they are very small). The piston rings must be free to move freely within the slot cut into the piston. 5.9.5 Cleaning the Piston Rings Piston rings are made from high quality steel and are resistant to most chemical cleaners. The author however still prefers to use a plastic scraper to remove carbon. It is essential to ensure that the ring is free to move within the slot cut into the piston. 5.9.6 Checking the Piston Rings The pistons and rings need to be cleaned and inspected frequently. If scoring is evident then replace the rings. No damage of any kind is acceptable on the piston rings. 5.9.7 Measuring the piston ring gap Piston rings come in various sizes as defined by the bore size into which they will correctly fit.
Figure 5.9.7-1 Piston Ring Size The way to check the size of a piston ring is to place it into the cylinder, taking care to align it with the top surface of the cylinder and then measure the gap with a feeler gauge. If a ring of carbon exists around the top of the cylinder then ensure that the ring is below it.
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The gap should be greater than 0.006"(0.15mm)
Figure 5.9.7-2 Measuring the Piston Ring Gap Note that the gap measured on a new Tal-Ko supplied engine was 0.011" (0.23mm) and on a (so called) tuned engine was 0.015" (0.38mm). Do not crush an oversized ring to achieve a smaller gap, as this may cause the ring to 'lock' when the engine gets hot resulting in the engine seizing. It may also allow leakage around the ring because if the ring is deformed it will not form a good seal against the cylinder wall. Gaps
Figure 5.9.7-3 Crushed Piston Ring 5.10 The Bottom End There are a few checks that can be made without expert knowledge or special tools. If any problems are found then refer it to an expert. 5.10.1 Crank Alignment Never hold the ignition side nut in order to remove the starter nut. If you do you will cause a misalignment of the crank by rotating one ‘half crank’ against
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting the other around the crank pin. This problem may also occur with normal running and therefore the crank alignment needs to be checked frequently.
Figure 5.10.1-1 Crank Misalignment-1 When the crank is correctly aligned the axis of the two Half Cranks are coincident.
Figure 5.10.1-2 Crank Misalignment-2 If one side of the crank is held whilst torque is applied to the other this will result in one half crank rotating about the crank pin with respect to the other.
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Figure 5.10.1-3 Crank Misalignment-3 The axis of the sprocket side half crank is no longer coincident with the axis of the ignition side half crank, but the crankshaft bearing centres remained fixed by the crankcase.
Figure 5.10.1-4 Crank Misalignment-4 This results in each end of the crank shaft prescribing a circle as shown in exaggerated form [5.10.1-4]. This can cause vibration leading to engine failure. The best way to identify a misaligned crankshaft is to carefully observe the gap between the ignition rotor and the stator whilst turning the engine over. With a good light and a magnifying glass you will see very small changes. Alternatively take four measurements, using a feeler gauge, at the same point on the stator whilst turning the rotor 90 degrees between each measurement. If any misalignment is detected send the engine back to a specialist (Tal-Ko)
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting to be re-aligned. It should not be an expensive job, but it will lead to an expensive failure if it is not fixed. 5.10.2 Big End Bearings If any vertical movement (a soft click) can be felt in the Big End Bearing when the crankshaft is gently pushed and pulled vertically then it is time to get it checked. 5.10.3 Oil Seals Check the condition of the oil seals frequently. Their major function is to provide an 'air' seal so that a vacuum can be held in the crankcase. Should a seal leak air then this could result in poor running. This will be particularly evident at tick-over. 5.11 Ignition Modern ignition systems, both PVL and Motoplat, are very robust and reliable. Other than cleaning and adjusting the timing there is not a lot to be done with them. Ensure that the HT lead is always earthed when turning the engine over or you may cause a spark to damage the internal electronics. This is best done by reconnecting the spark plug and laying it on top of the engine. 5.11.1 How the Ignition works The author lost track of how ignition systems worked when magnetos went out of fashion, but luckily this doesn't matter. It is a sealed unit and no repairs can be made to it. 5.11.2 Looking After the Ignition Keep the magnetic rotor clean and oil free. It attracts small bits of steel, which then get caught between the rotor and stator causing scratches or worse damage. Check that connectors are clean and make a good connection. If the connectors get worn or broken then renew them using the correct parts and a crimping tool. Do not solder the connectors on as this will lead to early failure.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Fix all cables in place with cable ties. Ensure that no load is on the HT cable at the coil end. Do not allow cables to flap! The coil's rubber mount is essential and must not be damaged or perished. It is possible to replace the Plug cap and HT lead on new PVL ignition systems, but if you do, ensure that you use the correct Tal-Ko part. 5.11.3 Setting the Ignition Timing The value quoted for ignition timing is the 'lead' before Top-Dead-Centre (TDC). This equates to the vertical distance travelled by the piston between when the ignition fires and the highest point reached by the piston. Turn the crankshaft until TDC is achieved. Rotate the dial on the dial guage to read zero at TDC. Turn the crankshaft back and forth a few times in order to check that the dial is zeroed at TDC. Rotate the crank until the timing marks are aligned. The dial gauge will now show the ignition timing setting (lead).
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Figure 5.11.3-1 Setting the Timing Best performance will be achieved by setting the lead to a maximum value (most advanced) that will guarantee that it will be between the limits if tested during scrutineering. A typical setting for the Motoplat ignition is 2.9 mm. The limits for both types of ignition (Motoplat & PVL) are specified in the TKM regulations (15.3). 5.11.4 Checking that the Ignition works Generally if there is a spark across the plug gap then the ignition works. If the sunlight is too bright to see the spark then use a rev counter: If it gives a reading then the ignition works.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 5.11.5 Wiring the Ignition Switch It is a requirement of the regulations that all clutch karts have an ignition switch. The switch must be of a suitable type (Get it from Tal-Ko) and it must be correctly connected as described in the TKM Regulations [14.3]. Connect the earth side of the switch to the ignition earth on the engine. Connect the switch wiring to the ignition wire and earth using good quality snap connectors so that it can be disconnected when the engine is removed. 5.12 Spark Plugs This is another subject that causes amateur engineers to go into spasms of in-depth opinion. The author uses the spark plugs recommended in the TKM Regulations [14.3]. Using an inappropriate plug or plug lead can cause overheating and engine seizure. 5.12.1 Checking and Cleaning Spark Plugs When the plug is cool, clean any carbon deposit from it. Spray Brake cleaner and a toothbrush will do the job. Check the gap. It should normally be 0.64mm or 0.025 inches. If it has worn so that the gap has increased or it shows any sign of damage then dump it. Since fitting a new plug, which turned out to be duff, the author never uses a new plug for a race. Keep a tested, but almost new plug for important races. As a rule of thumb the author discards plugs after about two hours of running time, but this has no scientific basis. 5.13 Engine Sprocket All of the power generated by the engine passes through the 9, 10 or 11 teeth of the Engine Sprocket. Change it if it shows signs of excessive wear. If you can see any distortion of the sprocket teeth then you should consider that to be excessive. It should never get so bad that cracks are evident. An old worn sprocket is less efficient than a new one and will absorb more energy.
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Excessive wear
Cracks
Figure 5.13-1 Worn Teeth The rear sprocket is covered in paragraph 8.3.4. 5.14 Exhaust The exhaust must be standard and marked TKM on the Chrome end. The only permitted modification is adjustment to the length of the flexible pipe and the fitting of noise reducing devices specified by local clubs. 5.14.1 How the Exhaust works The exhaust is a normal 2-Stroke exhaust. The expansion chamber is encased in a parallel cylinder. The shape and size of the expansion chamber is critical to the function of the exhaust. It produces positive and negative pressure waves which move up and down the exhaust at the speed of sound resulting in the exhaust gases being evacuated from the cylinder
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A Practical Mechanic’s Guide to TKM Karting and forcing the escaped mixture back into the cylinder. The book “TwoStroke Performance Tuning” [14.8] provides an excellent explanation of this .
Figure 5.14.1-1 the Exhaust 5.14.2 Cleaning the exhaust The build up of carbon on the inside of the exhaust will reduce performance. Most of this carbon can be removed with a wire brush. Chemical cleaners can be used, but great care must be taken as they normally contain Sodium Hydroxide (Sometimes called caustic soda or caustic acid) which is dangerous. If any chemical cleaner is used then take care to follow the instruction provided with the product. The chrome end cap is filled with fibreglass and must be remove before cleaning the exhaust. Leave the exhaust lightly oiled, inside and out, to prevent rust.
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A Practical Mechanic’s Guide to TKM Karting 5.14.3 Assembling the exhaust Take care when replacing the three self-taping screws as these will strip if over tightened. Be prepared to replace lost screws if they do come out. Alternatively place a jubilee clip around them to hold them in place. This is especially true if an End Can is fitted.
Figure 5.14.3-1 Assembling the Exhaust 5.14.4 Fitting the exhaust correctly The exhaust and the flexible pipe need to be a good fit in order to reduce noise levels. When cutting flexible pipe ensure that the end is square and makes a good seal. You may also need to bind the joint with heatproof webbing held in place with wire to achieve required noise levels. Use good springs of the correct size and type. If you can pull the joints apart by hand, they are not tight enough. Cross pairs of springs over if required. Due to noise limit regulations it is essential that you carefully check the exhaust system; •
Ensure that there are no cracks and that there is no slack in the spiral joints in the flexible pipe.
•
Renew the flexible pipe frequently.
•
Rotate the exhaust so that the holes in End Can face down and back.
5.14.5 Setting the Exhaust Length The Tuned Length (L) of an exhaust affects the peak power output of the engine. The longer the exhaust the lower the revs will be at which peak power output occurs.
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Figure 5.14.5-1 Measuring the Tuned Length Keep a selection of flexible pipe lengths in the range 60 to 100 mm. An ideal set would include the following lengths; 60, 65, 70, 75, 80,90 & 100 mm. The author has no set rule for selecting the correct exhaust length for any track/engine combination; 80 mm is a good starting point. Be prepared to change lengths and record changes in performance in order to develop your own table of lengths to suit each circuit/ engine/ conditions combination. For example; with an 80mm flex fitted, peak power may occur at 12500 rpm and with a 60mm flex fitted peak power may occur at 13500. Discard any flexible pipe that has started to leak due to cracking. The engine vibration will ensure that any flexible pipe has a limited life. When removing or inserting flexible pipe always rotate it in the direction which closes the loops or it will break.
6. Clutch The TKM clutch is a centrifugal clutch, which engages at about 6000 rpm. Many karters are unfamiliar with clutches and many drivers believe that they will reduce performance. The author has found that since fitting a clutch the practice lap times have not changed, but positions have improved. The driver explains this as being due to having increased courage going into contended corners. Read the following pages in the ‘TKM Regulations' [14.3]: •
‘Clutch Fitting & Service’,
•
The Clutch fiche.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 6.1 How the Clutch Works Pressure Plate Sprocket Drum Starter Nut
Drive Hub
Levers
Fixed Plate Friction Disc
Figure 6.1-1 Free running Clutch When the engine is at rest, springs pull the Pressure plate back towards the Drive Hub and away from the Friction disc.
Levers turned out by centrifugal force, push the Pressure Plate forward to clamp the Friction disc to the Fixed Plate
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A Practical Mechanic’s Guide to TKM Karting Figure 6.1-1 Driving Clutch When the engine runs it rotates the Drive Hub, Fixed Plate and Pressure plate Assembly. The Levers are weighted and have a cam shaped face, which rests against the Pressure Plate. As the engine accelerates above 6000 rpm, the levers rotate outwards under centrifugal force so that the cams force the Pressure Plate against the Friction Disc (clamping the friction disc between the Pressure Plate and the Fixed Plate). The Friction Disc drives the Sprocket Drum via the tabs on the circumference of the Friction Disc, which fit, into the slots in the back of the Sprocket Drum. 6.2 After each Event The clutch should be cleaned, checked and the sprocket drum roller bearing re-greased after each event. This can be done with the engine still mounted in the kart. •
Remove the clutch/coil safety cover and coil assembly.
•
Clean all round the engine crankcase and any other dirty bits.
•
Prevent the Crankshaft from rotating with the Clutch Holding Tool [11.1.4] and remove the Starter Nut.
•
The Sprocket Drum, roller bearing and two Thrust Washers can now be removed.
•
Clean the clutch Friction Disc and other components of the Drive Hub assembly remaining on the Crankshaft, with brake cleaning spray [13.15]. Take care to avoid getting cleaner near the Crankshaft Oil Seal.
•
Inspect the Sprocket Drum teeth [5.13]. Check the machined hole that forms the bearing outer in the Sprocket Drum for damage and lightly grease it with lithium grease. If the Sprocket is damaged then replace the Sprocket Drum and the bearing.
•
Check the roller bearing and if any doubt replace it.
•
Re-assemble the Sprocket Drum and other component [6.7].
•
Re-assemble the clutch cover and coil.
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A Practical Mechanic’s Guide to TKM Karting 6.3 Removing the Clutch Removing the clutch from the engine is a simple procedure, which does not require any special skills. It does however require the following special tools; •
Clutch Holding spanner, [11.1.4]
•
Clutch Puller, [11.1.5]
•
24mm Ring Spanner.
The clutch can be removed whilst the engine is mounted in the kart, but it is easier to work with the engine on a bench. •
Remove the Sprocket Drum, Thrust Washers and Bearing. [6.2].
•
Prevent the Crankshaft from rotating by holding the clutch with the special Clutch Holding spanner [11.1.4] and remove the large securing nut using a 24mm ring spanner. Remove the coned safety washer.
•
Using the special Clutch Puller [11.1.5], remove the Drive Hub Assembly. It should come of the tapered shaft with a crack! If it does not come free try tapping (very carefully!) the head of the jacking bolt with a steel hammer.
•
Lift out the Woodruff key from the crankshaft. Push one end in and the other will rise out.
•
Clean and check the crank shaft for damage. Lightly grease the shaft to protect it from rust.
•
Whilst the Clutch is removed it is a good opportunity to check that the Crankshaft oil seal looks OK.
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A Practical Mechanic’s Guide to TKM Karting 6.4 Dismantling the Drive Hub Assembly
B C
D
E
G
F A H
I
Figure 6.4-1 the Drive Hub Assembly A – Three counter sink hex’ socket screws which secure the Fixed Plate (B) to the Drive Hub (G). B-
Fixed Plate.
C-
Friction Disc.
D-
Pressure Plate.
E-
3 x sets of three Levers.
F-
3 x Dowel Pins.
G - Drive Hub. H-
3 x Pressure Plate Springs.
I-
3 x Spring Retainer Nuts.
•
Remove the three socket head, counter-sunk screws (A) which secure the Fixed Plate to the drive hub. They should not be tight.
•
Hold the Drive Hub Assembly with the Clutch Holding Tool [11.1.4] and loosen the three green Spring Retaining Nuts. – Remove the nuts (I) together, one turn at a time.
•
The components of the Drive Hub assembly can now be separated.
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A Practical Mechanic’s Guide to TKM Karting 6.5 Servicing the Clutch Clean all of the clutch components using spray Brake Cleaner [13.15]. (This will remove all grease from the roller bearing!) •
Inspect the Sprocket Drum and Bearing [6.2].
•
Measure and record the thickness of the Friction Disc. This will give a means of predicting when the Friction Disc will need replacing. The minimum thickness is specified in the TKM Regulations [14.3] as 2.90mm.
•
Remove and inspect the three Dowel Pins. If any wear, scoring or damage is visible then replace all three pins. Because the Dowel Pins are highly stressed they should be replaced whenever the Friction Disc requires replacement.
•
Separate the 9 Levers and check them for damage. Moisture often gets trapped between them causing rust. Check the pivot holes for wear and elongation due to stress. If you have any doubts then replace them.
•
Check the Friction Disc tabs for cracking.
•
Check that the free length of the Pressure Plate Springs exceeds 12mm. If not replace them.
•
Check and clean all other components.
6.5.1 Checking the Friction Plate Remove the friction plate [6.4] and inspect it for impact damage and cracking.
Figure 6.5-1 Impact Damage
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A Practical Mechanic’s Guide to TKM Karting 6.6 Reassembling the Drive Hub Ensure that all parts of the clutch are clean and that minimum amounts of grease are used. Under no account allow grease, oil, WD40 or any similar contaminant onto the Friction Disc or the ground surfaces of the Pressure Plate and Fixed Plate. •
Place the Drive Hub down with the Dowel slots facing up. Lightly grease the Dowel Pins and the Dowel Pin slots with anti-seize copperslip [13.15]. Assemble the Pins and Levers into the Drive Hub. They will just drop into place.
Triangular Corners
Figure 6.6-1 Pins and Levers in place •
Apply a small amount of copper slip [13.15] to the triangular corners to ensure that the Pressure Plate will move freely on the Drive Hub. Place the Pressure Plate over the Drive Hub and Lever assemblies. Ensure that the studs are correctly engaged and wipe off any excess grease.
•
Holding the Drive Hub, lift the assembly, ensuring that the Pressure Plate falls fully into place, turn the assembly over and place it down onto the Friction Disc and Fixed Plate, so that the Pressure Plate studs are held up proud of the Drive Hub.
Pins Levers
Figure 6.6-2 Springs and Retaining Nuts
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A Practical Mechanic’s Guide to TKM Karting •
Apply Blue Loctite to the Pressure Plate Studs. Place the three springs over the studs and screw on each of the spring retaining nuts, by just a turn (They will be tightened later).
•
Turn the assembly over and apply a small amount of copper-slip [13.15] to the three countersink screws. Screw in the three countersink Fixed Plate securing screws. These should not be tightened, just lightly touched home. They will not come out because the Large Coned Safety Washer will hold them in place.
•
Turn the assemble over and hold the Drive Hub with the Clutch Holding Tool [11.1.4]. Tighten the Spring Retaining Nuts down to about 2-½ lbs./ft
•
If you have changed any components then check the height of the Spring Retaining Nut as required by the fiche. (Item 4 in the clutch fiche. [14.3]).
Figure 6.6-3 Checking the Clutch Nut Height 6.7 Refiting the Clutch •
Ensure that the Crankshaft is clean and very lightly greased. Replace the Woodruff Key into the Crankshaft and install the Drive Hub assembly. Ensure that it is well seated on to the tapered part of the Crankshaft. (Note that the Woodruff key is not the same as for the nonclutch Crankshaft. The clutch keyway is 3mm wide and the non-clutch keyway is 2.5mm wide.)
•
Install the Coned Safety Washer with the dome facing outwards. Install the large clutch retention nut.
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Figure 6.7-1 Coned Safety Washer •
The nut needs to be tightened to 45 lbs./ft. Use the Clutch Holding Tool [11.1.4].
•
Lightly grease the Internal Thrust Washer and place it onto the crankshaft with the inner radiused edge facing inward [6.8].
•
Apply a small amount of lithium grease to the part of the Crankshaft that forms the bearing inner and slightly more grease to the bearing itself before installing it.
•
Install the Sprocket Drum. Ensure that the tabs on the Friction Disc are correctly inserted into the slots on the peripheral of the Sprocket Drum.
•
Lightly grease the small Thrust Washer and place it onto the crankshaft with the inner radiused edge facing inward [6.8].
Figure 6.7-2 Sprocket Drum & Bearing
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A Practical Mechanic’s Guide to TKM Karting •
As the Starter Nut is tightened to 15lbs/ft keep checking the Sprocket Drum free play. If it becomes clamped then stop and locate the problem. If you tighten the starter nut with the Sprocket Drum slots not engaged with the Friction Disc tabs so that the Sprocket Drum is pressing on the Friction Disc tabs then you might crack the Friction Disc.
•
The Sprocket Drum should move freely in and out along the crankshaft with about 0.3 mm of free-play [6.7-2]. If it does not, then check the orientation and size of the thrust washers [6.8].
6.8 Thrust Washers The two thrust washers are not just ordinary washers; they are very accurately ground and must never be replaced with anything but the correct Tal-Ko part. The Internal Thrust Washer is supplied in three thicknesses to allow for adjustment of the Sprocket Drum clearance. Both Thrust Washers have a chamfered inner edge. Chamfered
Ground Square
Figure 6.8-1 Thrust Washer Chamfer The crankshaft manufacturing process leaves radiuses in the seat of the shoulders.
Figure 6.8-2 Shoulder radiuses
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A Practical Mechanic’s Guide to TKM Karting The thrust washers MUST be installed onto the crankshaft so that they are seated against the shoulder and not installed back-to-front so that they are resting on the chamfer. correct
Gap!
Figure 6.8-3 Thrust Washer - Correct The internal radiused edges on the washers are very small and you may need a magnifying glass to see them. This is true for both the internal (big) and the external (small) thrust washers. 6.9 Sprocket Drum Clearance If you have not changed the Sprocket Drum or the Thrust Washers then the Sprocket Drum clearance should be OK. If the end float is much less than expected then you have assembled it incorrectly! To measure the Sprocket Drum clearance, use a feeler gauge. Check the free play and adjust it by changing the thickness of the Internal Thrust Washer. 6.10 Clutch: Major Overhaul The term 'Major Overhaul' simply means replace the parts that need to be replaced. The clutch needs to be overhauled when the thickness of the Friction Disc wears to less than 2.9mm or in any event after about 20 hours of running. You will always need to replace: •
Roller Bearing
•
Friction Disc
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A Practical Mechanic’s Guide to TKM Karting •
Three Dowel Pins.
The Sprocket Drum should be replaced if the sprocket is worn [5.13]. Replace any damaged, worn or suspect component.
7. The Carburettor This section covers all of the engineering details that you will require in order to service a carburettor. The only carburettor permitted is the Walbro WB19 marked with the TKM logo. It is robust and adequate. If the fuel is kept clean the carburettor should not require frequent maintenance. No Choke is provided on the WB19 for TKM.
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A Practical Mechanic’s Guide to TKM Karting 7.1 How the Fuel Pump Works
Figure 7.1-1 How the Carburettor works The Walbro carburettor has an integral fuel pump which works well as long as the Pulse pipe (short pipe running from a connector on the top of the carburettor to the crank case) is the correct part (fuel pipe is too soft), is in good condition and makes a good air seal at each end. The fuel pump occupies the top of the carburettor. The fuel comes in at ‘A’ to fill the fuel input chamber ‘C’. The Fuel Pump Diaphragm separates the pumping chamber 'E' from the Pulse chamber 'F'. The vacuum/pressure pulse from the crankcase comes in at ‘B’ and causes the Fuel Pump Diaphragm to expand and contract into the pumping chamber ‘E’. This pulls fuel from the input chamber ‘C’ through the one way valve ‘C/D’ and pushes it out through the one way valve ‘G/H’. This pressurised fuel supply is then forced down through the filter ‘I’ to the metering valve ‘J’.
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A Practical Mechanic’s Guide to TKM Karting 7.1.1 Physical Layout of the Fuel Pump It is not immediately obvious how the fuel pump works from the physical layout of the chambers. This diagram shows the view down on to the Fuel pump gasket and diaphragm after the top of the carburettor has been removed.
C
C/D E&F I G/H
Figure 7.1.1-1 Fuel Pump Layout • • •
C C/D E&F
• •
G/H I
Fuel input chamber One way valve from C below to D above Pumping Chamber E below diaphragm & Pulse chamber F above. One way valve from G below to H above Filter chamber below diaphragm
7.2 Carburation The carburettor functions are located at the bottom of the carburettor.
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A Practical Mechanic’s Guide to TKM Karting 7.2.1 Metering the fuel
Figure 7.2.1-1 Fuel Pump Layout The pumping action increases the fuel pressure enough to cause the inlet valve needle ‘J’ to be pushed off its seat. Fuel then passes into the metering chamber ‘L’. As the pressure in the metering chamber builds up the metering diaphragm ‘M’ starts to move down. Note that the lower side of the diaphragm is open to atmosphere. As the diaphragm moves down it causes the paddle lever ‘K’ to push the inlet valve needle back up thus reducing the fuel flow and maintaining a fuel supply, at a steady pressure, to the jets. 7.2.2 The Jets The jets are like taps; as they are screwed out, the hole through which the fuel passes, gets bigger. High Jet: - Fuel passes through the filter and one way valve ‘N/O’ to the High jet screw. The High jet screw controls the flow to outlet ‘S’. Low Jets: - Fuel passes directly from the metering chamber ‘L’ to the Low jet screw. The Low screw controls the flow to the Low jet feed chamber ‘T’.
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A Practical Mechanic’s Guide to TKM Karting
Figure 7.2.2-1 Position of Jet Outlets When the shutter is closed the vacuum within the crankcase provides a pressure differential so that air is forced into the holes ‘R & Q’, mixing with the fuel in the chamber ‘T’ before being sucked out through the Low Jet Bypass outlet ‘P’. As the shutter starts to open then the hole at ‘Q’ becomes the main Low jet and fuel will also pass out through the hole ‘Q’. The high jet provides most of the mixture at high revs and the low jet is predominant at low revs when the butterfly valve is almost closed. However, it can be seen that adjustment of the high jet will also affect the fuel flow at low revs and adjustment of the low jet will have an affect on the fuel flow at high revs. This interaction is important to bear in mind when adjusting the jets. [4.2.1]. 7.2.3 Positions of the Jets This diagram shows the positions of the various Jet holes from within the metering area with the circuit cover, diaphragm and gasket, removed [Figure 7.6.1-4].
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R Q P
S
Figure 7.2.3-1 Position of Jets (From underneath) 7.2.4 The Shutter Small gap
34-65 Figure 7.2.4-1 The Shutter The shutter is a butterfly valve which when open allows air to be drawn through the body of the carburettor into the engine. The top of the shutter is slightly ground away so that when it is shut a small gap is still evident. This prevents the shutter from sticking shut. Force applied by spring
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A Practical Mechanic’s Guide to TKM Karting Figure 7.2.4-2 Throttle Shaft Actuator arm Take care when re-assembling a carburettor to ensure that the spring applies force to close the butterfly valve and press the Actuator Arm against the Idle Adjust Screw. 7.3 Tools You will require: •
A selection of nail and tooth brushes for cleaning.
•
A selection of cross point and flat point screwdrivers which exactly fit the various screws. (Never use an inappropriate screwdriver!)
•
Carburettor pressure tester [11.1.10]
7.3.1 Work area; Work on a clean particle free surface. A melamine kitchen surface that has been carefully wiped is ideal. A wooden garage bench that’s been brushed clean is not. Acquire a few small dishes for parts and a larger dish for cleaning. 7.4 Removing & Servicing the Carburettor Servicing of the carburettor is a straightforward and simple process. 7.4.1 Frequency of Servicing The carburettor will require an internal clean after about three events and a full service after six events. Note that in-line fuel filters between the tank and the carburettor are not permitted, but a weighted filter used as the fuel pick up within the kart’s fuel tank is essential. The Pop-Off [7.7] must be checked whenever the metering cover is removed. 7.4.2 Removing the Carburettor •
Disconnect the Fuel pipe and Pulse pipe at the carburettor.
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A Practical Mechanic’s Guide to TKM Karting •
Seal both open pipe ends to ensure that dirt does not get in and petrol or vapour does not escape. A clean 6mm screw will fit well!
•
Remove the accelerator cable from the actuator arm.
•
Remove the Air Intake Box.
Figure 7.4.2-1 Mounting the Carburettor •
Slacken and remove the two (long) screws which secure the carburettor to the Barrel.
•
Remove the carburettor from the engine taking care not to damage the 3 gaskets.
•
Using a safe cleaner (Halfords Carburettor cleaner works well) and a small stiff bristle brush clean the outside of the carburettor before servicing it.
7.4.3 Sequence The author has found that the best sequence is: •
Dismantle the fuel pump.
•
Dismantle the metering mechanism.
•
Clean the main body casting and all parts to be re-used.
•
Check and assemble fuel pump
•
Check and assemble metering mechanism.
•
Check the Pop-off.
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A Practical Mechanic’s Guide to TKM Karting 7.5 Servicing the Pump
Figure 7.5.1-1 Fuel Pump The fuel pump is under the top cover of the carburettor. 7.5.1 Dismantling the Fuel Pump •
Using the correct size and type of cross-point screwdriver remove the four screws securing the fuel pump cover in a diagonal order [7.5.1-1].
•
Remove the cover, the gasket and the diaphragm.
7.5.2 Cleaning the Fuel Pump •
Using a carburettor cleaner [13.15] thoroughly clean all of the orifices thus revealed. The filter can be removed and replaced or just cleaned. Ensure that the filter is positioned correctly.
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A Practical Mechanic’s Guide to TKM Karting Peg holes which match the pegs in the fuel pump cover
Figure 7.5.4-1 Locating the Pump Gasket & Diaphragm 7.5.3 Checking the Fuel Pump •
Check the gasket and the diaphragm and if they show any sign of damage then replace them.
•
If the diaphragm is stretched or baggy then replace it.
7.5.4 Assembling the Fuel Pump •
Ensure that the gasket is above the diaphragm and that the pegs in the fuel pump cover are located into the peg holes in both the gasket and the diaphragm before tightening the four screws to a sympathetic loading in a diagonal order. Half tighten the screws on the first pass and then fully tighten.
7.6 Servicing the Metering Mechanism The metering mechanism end is a bit trickier. 7.6.1 Dismantling the Metering Mechanism •
Remove the high and low jet screws taking care to retain the various springs and washers.
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A Practical Mechanic’s Guide to TKM Karting
Figure 7.6.1-1 High Jet Screw Assembly
Figure 7.6.1-2 Low Jet Screw Assembly The rubber grommet on the high jet screw is required to prevent leakage because the fuel is at full pressure behind the high jet screw. •
Remove the four screws securing the metering cover in a diagonal order [7.6.1-3].
When removing the cover take care to ensure that the metering diaphragm stud disengages from the paddle lever [7.6.1-4] before lifting it clear.
Figure 7.6.1-3 Removing the Metering Cover
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Figure 7.6.1-4 Paddle Lever Arm •
Remove the two screws securing the circuit cover, diaphragm and gasket. The small gauze filter can be cleaned without being removed.
•
Remove the single screw which holds the metering lever pin in place and taking care to keep the spring under control, remove the metering lever, spring and inlet needle valve.
Figure 7.6.1-5 Removing the Circuit Cover, Diaphragm, Gasket, Paddle Lever & Inlet Valve assembly
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A Practical Mechanic’s Guide to TKM Karting 7.6.2 Cleaning the Metering Mechanism All three of the holes associated with the Low jet [7.2.3-1] can be visually checked and cleaned using a jet of pressurised air or carburettor cleaner from an aerosol. If necessary, it is possible to carefully clear the holes with a length of fine copper wire. The High jet outlet is blanked at one end and cannot be checked or cleared except with compressed air or carburettor cleaner. The Carburettor and all of its components must be spotless. 7.6.3 Checking the Metering Mechanism The author always replaces the components that come in the Full Carburettor Service pack [7.12], but this is not essential. Any damaged or worn part must be replaced. Carefully check the sealing surface of the tapered part of the needle valve. 7.6.4 Reassembling the Metering Mechanism Screws should be tightened to a sympathetic torque. •
Spray a small amount of WD40 onto the metering valve assembly.
•
Replace the Paddle Lever & Inlet Valve assembly. Ensure that the Pin, spring and metering arm are correctly located before tightening the single screw [Figure 7.6.1-5].
•
Select the correct Circuit Gasket from the two provided in the Service Kit. The one on the right [Figure 7.6.4-1] has an extra hole in the low jet feed which allows more fuel to pass to the low jets. This is the Gasket normally used. Discard the spare gasket.
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A Practical Mechanic’s Guide to TKM Karting Figure 7.6.4-1 Selecting the correct Circuit Gasket •
Assemble the Circuit Gasket, diaphragm and cover so that the one way valve flap in the diaphragm is directly under the filter hole in the cover. [Figure 7.6.1-5] Tighten the two single slot screws.
•
Adjust the height of the Paddle Lever Arm [7.7.3].
•
Fit the Gasket, Metering Diaphragm and Cover ensuring that the stud on the Metering Diaphragm is correctly engaged with the Paddle Lever fork. Tighten the four cross point screws [Figures 7.6.1-3] in a diagonal.
7.7 Checking the Pop-Off The Pop-Off should be checked whenever the metering diaphragm is disturbed and at regular intervals. The metering valve must lift (Pop Off) between 11 and 13 psi. As the pressure bleeds away the valve should re-seal and hold the pressure steady between 5 and 8 psi. 7.7.1 Checking for Leaks Before checking the Pop-Off you must be sure that there are no air leaks in the carburettor or test equipment. Brush on a mixture of washing-up liquid and water to check for leaks; •
Connect the Carburettor tester to the Pulse Pipe connection and pump the pressure up to 15psi. Check for leaks in the Carburettor Testor, the connecting pipe, the fuel inlet connector and around the top of the carburettor.
•
Connect the Carburettor tester to the Fuel Input connector and pump the pressure up to 11psi. If it Pops-Off before 11psi is reached, adjust the Pop-Off pressure first [7.7.4] and then re-test for leaks from the Pulse Pipe connector and around the top of the carburettor.
7.7.2 Measuring the Pop-Off The Pop-Off pressure should be between 11-13psi and the stabilised pressure after Pop-Off should be between 5 - 8psi. •
Connect the Carburettor Tester to the fuel inlet on the carburettor.
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A Practical Mechanic’s Guide to TKM Karting •
To ensure that the valve is not sticking, operate the pump until it ‘PopsOff’ and then release the pressure to zero.
•
Operate the pump at a steady even rate and note the Pop-Off pressure (11-13 psi).
•
After Pop-Off the pressure should drop very quickly and then remain steady at 5-8psi .
Repeat this process a few times. The readings should be the same each time. If the Pop-Off pressure requires adjusting [7.7.4] then first check the height of the Paddle Lever Arm. 7.7.3 Adjusting the Paddle Lever Arm If the Pop-Off pressure is too high or too low then check that the Paddle Lever Arm is set to the correct height. It must be set to 1mm from the bottom of the carburettor body to the paddle lever fork.
Bottom face of carburettor body casting 1mm
Figure 7.7.3-1 Adjusting the Paddle Lever Arm Height This can be checked using the special gauge sold by TAL-KO or measured using a steel rule placed across the bottom face of the carburettor base and a small piece if 1mm diameter wire. It is important to set the Paddle Lever Arm at the correct height so that it does not load the Metering Diaphragm when it's engaged with the stud. [Figure 7.6.1-4]. If the Paddle Lever arm is not set to the correct height when assembled the diaphragm will be pushed up or pulled down by the Paddle Lever Arm.
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Figure 7.7.3-2 Raising & Lowering the Paddle Lever Arm If the Paddle Lever arm is too low (more than 1.1mm) then gently lever it up. If the Paddle Arm is too high (less than 1mm) then gently bend it down by pushing on both ends. 7.7.4 Adjusting the Pop-Off If after setting the Paddle Lever Arm to the correct height the Pop-Off does not occur between 11-13psi then the force provided by the spring will need to be adjusted. There are two ways in which this can be achieved; •
Very small changes in Pop-Off pressure can be achieved by slightly bending the Paddle Lever Arm, but the clearance must remain close to 1mm.
•
Larger changes can be achieved by altering the closing force provided by the spring.
•
If the Pop-Off pressure is too high then compress the spring between finger and thumb, or try another spring (Keep a few spare springs).
•
If it is too low then extend the spring a little.
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A Practical Mechanic’s Guide to TKM Karting If the the Pop-Off pressure is more than a few pounds out or when set correctly the stabilised pressure is not correct then something is wrong! •
Ensure that the four screws holding the diaphragm cover are correctly tightened.
•
Ensure that the Diaphragm and Diaphragm Gasket are in good order and correctly assembled.
•
Ensure that the Metering Valve and its seat are clean and undamaged.
7.8 Re-fitting the Carburettor Ensure that the 3 gaskets are in place and in good condition [Figure 7.4.2-1]. The two carburettor securing screws should be tightened to the correct torque [14.3]. Note that these need to be rechecked frequently as the engine vibration and the length of the screws may cause them to slacken. Fit the Air filter and tighten the jubilee clip to the absolute minimum required to keep it in place. If you over-tighten it the rubber will stretch and it will become harder to fit. When fitting the Air Intake Box, ensure that it, and the jubilee clip which holds it in place, are perfectly lined up. If it is miss-aligned then the black plastic housing will crack when you tighten the jubilee clip. The trumpet should be high enough to clear the side pod or, if it's raining, positioned in the side pod [7.11]. The Air Intake Box can be fixed to the Back-plate using self-taping screws. If you choose to do this then take care to not crack or split the Back-plate. Ensure that when the accelerator is pressed fully down the throttle is fully open, but that the throttle actuator arm is not under load against its stop. This needs careful adjusted because the carburettor will be damaged if it is over-stressed. Adjustment is usually provided on the front end of the cable outer and to the accelerator pedal stop.
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Figure 7.8-1 Carburettor The carburettor includes a return spring on the throttle actuator arm, but it is essential to supplement this with a spring (or two) between the arm and the cylinder head. This will give the accelerator a more 'controllable feel' and will improve safety by reducing the chance of the accelerator sticking open. This will require a small hole to be drilled into a fin on the head. Check other TKM carts to see how it is fitted. 7.10 Fuel line and petrol tank Ensure that the fuel line is not kinked in any way. Maximise the radius of any curve in the pipe. It is a good idea to arrange the fuel line to rise from the carburettor so that any air in that end of the line is held away from the carburettor fuel intake. Air in the fuel intake may prevent the fuel pump from working. The fuel pick-up must be free to move from side to side with the fuel when cornering. Make the pipe to the pickup just long enough so the pickup just touches the bottom of the tank. You need to keep at least 150mm of fuel in the tank to avoid the fuel surging in the pipe and to prevent air getting into the fuel pickup on cornering. Change the pipe often, including the pipe to the fuel pick-up inside the tank. Never use an old yellow pipe that has gone hard with age as this may result in the pipe not sealing fully when replaced on to the carburettor, resulting in air getting in.
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A Practical Mechanic’s Guide to TKM Karting Regularly check the tank, fuel line and connections for leaks. Replace any doubtful of failed component. Another potential cause of leaks is a loose pump cover on the top of the carburettor. Leaks can result in both fuel escaping and air getting in. 7.11 Preventing water from entering the carburettor Prevent large quantities of water from getting into the Air Intake Box because if the filter gets soaked it can greatly reduce the amount of air getting to the engine. Cover the holes at each end of the side pod. Old plastic number plates cut to size and fixed into place with cable ties work well. Cut a slot in the Side Pod so that the Air Intake Box can be rotated down until the Trumpet is inside the Side Pod. (When racing in the dry, ensure that the trumpet is above the Side Pod). 7.12 Carburettor service kits The service kit D10-WB 618 contains all of the parts that you will normally require to service the carburettor. You may sometimes need to replace one of the components found in the K19-WB 618 Service Kit. You may also need to replace components which do not appear in either kit, e.g. the spring which goes under the Paddle Lever, and for that you may have to approach TAL-KO direct. 7.12.1 D10-WB 618 D10-WB 618 - contains replacement gaskets and diaphragms. For a normal service you need only replace the gaskets and diaphragms. 7.12.2 K10-WB 618 K10-WB 618 - contains the same as D10-WB 618 but with the addition of the following parts:
Paddle Lever (Metering Lever)
Paddle Lever Pin
Needle Valve (Inlet)
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Screen (for check valve) & Retainer
Screen (for fuel inlet)
Two Blanking plates
You may sometimes need to replace the Paddle Lever or the Needle Valve, but the other parts are rarely needed.
8. Kart Maintenance This section covers all of the engineering details that you will require back at the garage to service the kart. The author has observed a racer who chucks his kart into a trailer after each race meeting and does not get it out again until he arrives a week or two later for the next meeting. He then works frantically to prepare it for the days’ racing and goes out and either gets placed, breaks down or crashes! This is one approach to racing, the other is specified in this guide. 8.1 Special Tools Required Strait Edge [11.2.3], Tyre Press [11.1.8] Tyre Levers [11.2.5] Valve Extractor [11.1.9] 8.2 Basics When stripping the kart for cleaning ensure that every nut, screw, bolt or component removed is carefully stored in an organised manner. The author has a selection of biscuit tins and plastic bowls for this purpose. Sequence; •
Place the kart up onto a stand,
•
Remove all four wheels,
•
Remove the side pods [8.7.1],
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A Practical Mechanic’s Guide to TKM Karting •
Remove the back sprocket and chain,
•
Remove the engine [5.5],
•
Remove the back axle [8.5.1],
•
Remove the kingpin bolts [9.4] and the steering centre bolt - freeing the two Track rod & Stub axle assemblies.
Clean and check the remaining chassis assembly and the removed components as specified in the following paragraphs. 8.2.1 After a wet race; A wet kart will rust within hours if it is left wet. If you do not have time to completely strip and clean it immediately then you must protect it from rusting. Remove the rear wheels and the brake calliper assembly from the chassis, but do not disconnect the hose. With the calliper still connected by the hose place it into the seat and cover it. Lightly spray WD40 over the back axle including the brake disc. Remove the front wheels and spacers and spray the stub axles and steering components with WD40. Ensure that all traces of WD40 are removed before re-assembling the brakes and NEVER get WD40 near the pads! Don't forget to dry-out the engine [5.2.2] 8.3 Sprocket Alignment & Wear All of the power from the engine is transmitted through the chain and sprockets. It is essential that the are maintained in perfect alignment and good condition. 8.3.1 Engine Sprocket Alignment The engine mount must hold the engine in alignment. A damaged mount or chassis may result in misalignment. No degree of engine sprocket misalignment is acceptable
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Figure 8.3.1-1 Misalign Engine Sprocket If the engine sprocket appears to be misaligned then check that the engine mounts are correctly seated and undamaged also check that the chassis is undamaged. The Engine Mount must be the correct part for the chassis [5.5.3]. 8.3.2 Rear Sprocket Alignment Check the sprocket alignment and chain tension after each race. Any unexpected change in settings could indicate serious problems requiring a full check of the kart for damage. Rear sprocket misalignment can be caused by any of the following: •
Loose rear sprocket carrier.
•
Axle bearing supports bent [8.6.2].
•
Bent back axle (8.5.3).
•
Axle slipped through bearings (8.5.2).
Figure 8.3.2-1 Sprocket Alignment
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A Practical Mechanic’s Guide to TKM Karting To align the rear sprocket, remove the wheel and the chain. Place a steel ruler (strait edge) onto the rear sprocket and slid it forward so that it just touches the outside edge of the front sprocket. (Note that the front and rear sprockets may not be exactly the same thickness) This should be done four times turning the back sprocket through 90 degrees each time. If the alignment changes for each measurement then the axle, rear sprocket or sprocket carrier is bent. 8.3.3 Effects of Sprocket Misalignment •
Excessive chain & sprocket wear,
•
Breaking chains,
•
Slight loss of power.
8.3.4 Sprocket Damage & Wear Engine sprocket wear is covered in paragraph 5.13. The loading on the rear sprocket is spread among many teeth, which allows it to be made from aluminium. Look for physical damage to the teeth. To check that the sprocket is not bent, rotate the back axle and check that the toothed edge does not move laterally. Don't try to straighten a bent sprocket, replace it. The Sprocket or Sprocket Carrier could also be damaged if the sprocket has hit the ground. 8.4 Chain Only buy the best quality chain. It is too important to skimp on. Use the newest chain possible for racing and keep older chains for practice. Replace chain as often as your budget will allow. Only use Chain Lubricant formulated for racing. Cheaper lubricants are not as good. Lubricate the chain each time you go on to the track. 8.4.1 Selecting Chain Length Keep a range of chains to avoid the need to split them. Ideally you should have an appropriate length chain for each sprocket size used.
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A Practical Mechanic’s Guide to TKM Karting 8.4.2 Chain Tension 20 < 25mm
Back Sprocket
Engine Sprocket
Figure 8.4.2-1 Chain Tension Check chain tension after each race - it should deflect up freely by between 10-15 mm and down by slightly less. Ensure the two clamp bolts which hold the engine mount to the chassis are tight and the chain tension screw which holds the engine mount forward in the chassis is locked into position. Do not tighten the chain tensioning screw against the engine mount so that it is under compression. As the engine is run this compression will push the engine forward and tighten the chain no matter how tight the engine mount bolts are. If the Chain Tension Changes Between Races? •
Engine mounts are not securely attached to the chassis.
•
The chain tension adjustment screw was too tight/lose.
•
Sprocket misalignment is causing excessive chain wear.
If the Chain Tension changes as the Sprocket is rotated? •
The axle is bent [8.5.3].
•
The sprocket or sprocket carrier is bent.
8.4.3 Adjusting Chain Tension •
Slacken the two engine mount clamping bolts and push the engine forward until the chain is tight. Pinch the clamping bolts down, front bolt first, so as to avoid placing the chain under excessive tension.
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A Practical Mechanic’s Guide to TKM Karting • Turn the chain-tensioning bolt forward until it just touches the engine mount and then turn it back 2 flats. Lock it in position with the lock nut. An 8mm screw has a pitch of 1.25mm, therefore each flat is equal to 1.25mm / 6 = 0.21 mm) The recommended movement due to slack is 10<15mm. It can be calculated that this equates to the engine being moved back by just 1.5 < 2.5 flats or 0.32 < 0.53mm.
•
Pull the engine back so that it just touches the chain tension bolt and tighten it down.
Note that it is important to never tighten the engine down first and then screw the tension adjustment bolt tight because when the engine is run any compression in the bolt will push the engine forward. It is easy to tighten this bolt against the mounting with enough compression to move the engine forward by 0.5 mm, placing the chain under tension and causing damage to it. 8.4.4 Cleaning Chains Immerse the chain in a bowl of white spirit. Use a brush to clean the chain. After drying the chain place it into a container and soak it in Chain Lubricant. 8.4.5 Checking Chains for Wear How much wear can a chain take before it should be discarded? That is a very subjective judgement. Some drivers wait until the chain breaks before discarding it! The author normally uses a chain for 4/5 meetings and then for practice until it looks too worn. Measuring the wear in a chain is also a bit imprecise. An experienced engineer can often just pick it up and shake it to assess the degree of wear, but here are two practical methods. Ensure that the chain is clean and grease free. Method 1. •
Lay the chain on a flat surface with the rollers horizontal and with one half of the chain on top of the other.
•
Do the same with a new chain.
•
Push both chains into a curve until the slack is taken up. Touch the ends of the two chains together.
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New
Figure 8.4.5-1 Worn Chain (Method 1.) •
The old chain will curve more than the new chain. The gap between the chains indicates the degree of wear.
Method 2. With the engine forward so that the chain is tight, attempt to pull the chain away from the back of the rear sprocket. If more than 1 mm of daylight can be seen then consider dumping the chain. A new chain should be tight against the sprocket.
More than 1mm of daylight Back Sprocket
Engine Sprocket
Figure 8.4.5-1 Worn Chain (Method 2.) As the chain stretches the number of links in contact with the sprocket decreases rapidly to just 1 taking the load! 8.4.6 Checking Chains for Damage Inspect the chain for chips and cracks
Look for cracks
Look for damage Figure 8.4.6-1 Checking the Chain
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting The links should rotate freely and not 'stick'. To check this hang the chain over the end of the axle and rotate the axle until all of the chain has passed over it. Each link should run smothly over the end of the axle and through the bottom loop without sticking.
Figure 8.4.5-1 Chain runs free? 8.5 Back Axle Assembly The back axle on any 100 cc kart is a critical item that deserves much attention. On a TKM kart it is either a solid 30 mm steel bar or a 30mm tube with a minimum wall thickness of 5mm. It looks very strong, but it is in fact vulnerable to damage and along with the components that it supports, needs to be carefully inspected after each race. 8.5.1 Removing the axle assembly Slacken the (usually 6) bolts fixing the brake disk to its carrier and slacken the carrier screw. Ensure that the carrier slides on the axle. Alternatively remove the brake calliper [8.8]. Remove the (3 on each bearing housing) bolts that secure the two bearing housings to the axle support brackets. The axle can be lifted out complete.
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A Practical Mechanic’s Guide to TKM Karting Figure 8.5.1-1 Back Axle Assemble 8.5.2 Positioning the Axle in the Bearings
Figure 8.5.2-1 Axle Bearing The grub screws in the axle bearings prevent the axle from sliding through the bearing. If these grub screws come loose the whole axle will move left or right. If this happens then remove the grub screws completely and move the axle back into position so that the small holes are lined up with the grub screw holes. Replace the grub screws using blue Locktite. [8.5.5] 8.5.3 Bent Axle After an accident on the track you may dash back to the pits to check for damage. If you see marks on one of the back wheels you may look along the back axle to ensure that it is straight. The chances are it will look OK, so off you go again. This may be OK in the heat of the moment, but a bit more science is required when time permits. For an example assume that the kart has been hit from behind on the back left wheel. No bend is visible, but when the kart is on the stand and with the wheels removed a very slight movement is detected at the left-hand side when the axle is rotated. It does not cause a vibration and no damage was caused to the right (sprocket) side. You may assume that the axle is OK, but there is more to the problem than meets the eye! Why the axle may look straight, but isn’t;
Impact
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Figure 8.5.3-1 Bent Axle. The impact will have bent the axle at the left-hand bearing but will have also caused the axle to bend in a curve between the bearings. The misalignment is exaggerated here in order to show the effect.
Figure 8.5.3-2 Bent Axle Rotated 180 Degrees. As the axle rotates it can be seen that the curve between the bearings also causes displacement of the right hand end of the axle. Assume for example that the impact has caused the axle to curve between the bearings so that the right hand end is 0.5 mm out of true resulting in a total movement of 1.0 mm when the axle is rotated. This will not be visible on inspection of the static axle, but it will result in a movement of about 0.7 mm at the edge of the sprocket. This amount of lateral movement would result in the chain tension changing by more than 10mm as the axle is rotated.
Figure 8.5.3-3 Chain Tension Changes In this example the author would recommend replacing the axle.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 8.5.4 Checking for a bent axle; Remove the chain, rear wheels and hubs. Attach a 'moll grip' to the back bumper so that it just touches the end of the axle. Rotate the axle until it only just touches the axle lightly in one spot. Rotate the axle until the gap between the axle and the moll grip it greatest. Measure the gap using a feeler gauge.
Figure 8.5.3-4 Checking for a bent axle A more accurate method is to use a dial gauge to measure the movement at the end of the axle. Any movement of more than 0.5 mm will produce a noticeable change in chain tension as the axle rotates. Consider replacing the back axle if any more than 1mm movement is evident. Note:- If the axle is bent you may also see the brake disk move from side to side between the brake pads when the axle is rotated. Any curve or bend in the axle will also have a detrimental effect on bearing wear.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 8.5.5 Replacing an Axle If possible, replace a damaged axle with an original part from the chassis manufacturer. If this is not possible then buy one that is the same length as the original. Ensure that keyways match. Also ensure that it meets TKM Regulations [14.3]. The axle will need to be drilled with two small holes to receive the tips of the axle bearing grub screws [8.5.2]. Assemble the axle into the bearings and tighten the bearing plates. Move the axle alone its axis until it is central within the chassis. Do not use a centre punch through the bearing grub screw holes, as this will raise a small lip making it impossible to slide the bearing off the axle. Use a hand-held drill bit to mark the position to drill. Remove the axle to drill the holes, but don't drill the hole too deep (1-1.5mm is enough). Use new circlips on the end of the axle. 8.5.6 Checking Sprocket & Brake disc alignment Attach a 'moll grip' to the back bumper so that it just touches the side of the brake disc or sprocket and adjust its position until it only just touches the sprocket lightly in one spot. Rotate the axle until the gap between the axle and the moll grip it greatest. If the gap is more than 1mm remove the sprocket and check the carrier. Dispose of any carrier, sprocket or brake disc that is out of true by more than 1mm.
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Figure 8.5.6-1 Checking Sprocket/Brake disc alignment 8.6 Chassis Check the chassis for damage and misalignments after every impact no matter how slight and after each meeting. Remove all components from the chassis, clean it thoroughly and carefully inspect it for cracks in the welded joints, dents and any other form of damage. The chassis has been engineered to keep the wheels apart in a very precise fashion. A small misalignment, which cannot be seen on an assembled kart, can make a significant difference to handling. The following checks are intended to give an indication of chassis alignment, but the only way to be sure is to return the chassis to the manufacturer for re-jigging. This will not cost a great deal and in the authors experience is a very good investment. If you perform these checks regularly and record the results you will know when and by how much it has been bent! How much of a bend is acceptable is subjective. The author has found that you may not be able to tell that a slight bend has occurred until it is fixed and then the driver notices an improvement in handling. If in doubt get it re-jigged.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Before starting these checks remove the bodywork, engine, seat, fuel tank, wheels and any other bits that are in the way, but leave the back axle and steering mechanism in place. 8.6.1 Back end parallel to front Measure from back axle to Steering bolt on both sides. Ensure that you measure at 90 degrees to the back axle taking the shortest distance. Measurements A & B should be the same. A
B
Figure 8.6.1-1 Back & Front Parallel? 8.6.2 Rear axle Bearing Supports Check that they are upright by using a small builders level to first level the frame and then check that the Supports are upright. Small errors are OK as the bearing will run with a small tilt, but it may indicate other problems. 8.6.3 Chassis Twisted? Place a straight edge [11.2.3] across the tops of the front stub axle lugs. From the front of the kart, view the straight edge and the back axle. Raise and lower your viewpoint until a thin sliver of light can be seen between the axle and the straight edge. Any twist in the chassis will be clearly visible.
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Figure 8.6.3-2 Chassis Twisted? 8.6.4 Front Stub axle lugs The front stub-axle lugs are an integral part of the steering and are covered in paragraph 9. 8.7 Body-work The plastic Side Pods and Nose cone take most of the battering in the close racing that makes the TKM class so competitive. They can be straightened if slightly dented, but should be replaced if badly crushed or split. The front bumper can be softened for straightening by filling it with very hot water. If you need to replace the front bumper fixings then ensure that they meet the TKM regulations. Side-pods should be mounted well forward on clutch Karts and will require a hole to be cut in order to use the starter. Plastic bodywork comes in different weights. The heavier it is the stronger it is! 8.7.1 Removing the Side-Pods The side pods can be removed with the Nerf Bars attached. The Nerf Bar is normally attached to the chassis by a nut and bolt at each end.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 8.8 Brakes More overtaking manoeuvres are won by good braking than by better acceleration. Many karts fail scrutineering for brake problems, most due to contaminated or worn pads. 8.8.1 How the Brake System Works
Figure 8.8.1-1 How the Brakes Work
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A Practical Mechanic’s Guide to TKM Karting A - Master cylinder filler cap B - Piston return spring C - Master cylinder piston D - Direction of peddle pressure E - Actuator piston F - Brake pad securing screws G - Brake disc H - Brake pads I - Bleed screws J - Brake Pipe When the brake pedal is depressed the Master cylinder piston drives a column of brake fluid down the brake pipe to the calliper. The total area of the two actuators exceeds the area of the master cylinder piston so providing a lever effect. This combined with the mechanical levers built into the brake pedal mechanism, results in a much higher pressure being applied to the brake pads than that applied by the driver. 8.8.2 Removing the Complete Brake System In order to remove the Master Cylinder and Calliper assemble without losing brake fluid; •
Remove the brake cable from the lever on the master cylinder,
•
Remove the bolts securing the master cylinder to the chassis and place the master cylinder on the seat,
•
Remove the securing fixing bolts.
The complete assemble can now be removed. 8.8.3 Cleaning the Brake System Never allow WD40 or petrol near the brake pads. The only cleaner that you should use on, or near, the pads is Brake Cleaner [13.15]. If the calliper assembly needs cleaning then it may be best to remove the brake pads first. It is possible to use wire wool to remove rust from the disc, but it is better to not allow the disc to rust. If it's wet then dry it. It you must store it for any length of time then remove it and protect it with WD40. Make sure that you
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A Practical Mechanic’s Guide to TKM Karting remove all traces of WD40 with Brake Cleaner [13.15] before reusing the disc. It is best to remove the calliper assembly complete, leaving the brake pipe connected, and clean it away from the brake disc. It can then be sealed in a plastic bag to protect it and placed on the seat when cleaning the Kart. Brake pads can be cleaned by placing fine sandpaper on a flat surface and rubbing the pad against it. 8.8.4 Checking the Brake System These checks should be made frequently and do not require the removal of the brake system. •
Wear on the brake pads is indicated by the depth of the slot in the pads. Braking efficiency does decline as the pads age so consider replacing them before the slot is completely worn away!
•
If the brake disc is 'blue' or 'glazed' due to overheating then use very fine emery to remove the glaze.
•
Check the peripheral of the brake disc for chipping, dents, or cracks. It can hit the ground!
•
Ensure that both brake cables are not frayed, that the cable clamps are secure and that all joints and pivots are undamaged and lubricated.
•
Check the brake pipe for cuts and abrasions.
•
The brake fluid should show clean and clear through the pipe.
•
Ensure that the master cylinder is fully topped up with DOT5 brake fluid and that no air is in the system [8.8.7].
•
Ensure that the Brake Disc in centred in the calliper.
•
Check that the Brake bleed and filler screws are tight.
8.8.5 Replacing the Brake Pads Always replace pads in pairs. •
Remove the Brake Pad securing screw and springs.
•
Remove the pad.
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A Practical Mechanic’s Guide to TKM Karting •
Insert the new pad and using red loctite on the pad securing screws, secure the pad.
8.8.6 Draining Old Brake Fluid If the fluid is no longer clear it may be wise to flush the system through with fresh fluid by refilling and re-draining. •
Remove the calliper from the chassis and then remove the Brake pads [8.8.5].
•
Place the calliper in a bowl as low as possible and remove the bleed screw from the Calliper.
•
Remove the master cylinder filler cap and allow the brake fluid to seep out. Pump the remaining fluid out by pulling the pump actuator out, place a finger over the filler cap hole and slowly depress the actuator. Allow all of the fluid to drain.
8.8.7 Refilling & Bleeding the Brake System Ensure that all components are clean. Dirt and dust causes hydraulic systems to fail. Use only the best DOT 5 brake fluid. Kart brakes can become very hot and heat degrades brake fluid and in extreme cases can cause it to boil. •
Replace the bleed screws in the Calliper. Carefully pour the new fluid into the master cylinder. Keep 'jiggling' the pipe and calliper until no more fluid goes in.
•
Leaving the calliper low down and in the bowl, turn the calliper so that the bleed screws face upwards. Slacken and carefully remove each screw in turn. Hold the screw over the hole so that the air can escape, but prevent large amount of fluid coming out. Replace the screw when only fluid comes out. Check the fluid level in the master cylinder before removing the second bleed screw.
•
Check the fluid level in the master cylinder and then carefully depress the brake pedal. Observe the brake actuators in the calliper. Do not allow them to come out too far. Using fingers and thumbs alternately depress the actuators in a rocking motion - one in - one out. At first you will feel air in the system and will see air coming up the brake pipe.
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A Practical Mechanic’s Guide to TKM Karting Keep this up whilst turning the calliper over and back, until no more air comes out. Keep checking the fluid level in the master cylinder. •
Check that the bleed screws are tight and leave the system as it is, with the calliper low until no air is evident in the pipe.
•
Place a cloth around the master cylinder filler hole and press the actuator pistons into the calliper until they are flush. This will push excess fluid out of the master cylinder. Replace the master cylinder filler cap without letting air in.
8.8.8 Adjusting the Brake System Adjust the gap between the pads to be about 2mm wider than the disc. The calliper mechanism is designed to take up small amount of misalignment, but you should take care to ensure that the gaps between the pads and the disc are parallel.
Figure 8.8.8-1 Brake Adjustment Centralise the disc between the pads by moving the disk along the axle and lock it firmly in place. Screw in the stabilising screw and lock it in place. It should not be used to force the calliper in or out. It should be locked into position. Adjust the brake cable to remove excess slack. A small amount of slack should remain.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 8.8.9 New Brake System? If you need to replace your braking system with another then ensure that you replace it with the correct homologated brake system for your chassis. You will not be permitted to race with a braking system that is not homologated. 8.9 Wheels Wheels are normally cast aluminium and sometimes machined aluminium. The author has always tended to buy budget priced wheels and has never had a problem with them. Replace wheel nuts frequently because the Nylock inserts wear and it is important for the nuts to stay on! When wheel nuts are in place a minimum of 11/2 threads should show. Narrow front wheel nuts may need to be purchased to ensure this. 8.9.1 Checking Wheels Wheels are very sturdy in normal use, but if the metal rim hits anything solid it will fail. The cheaper type of wheel will crack and the more expensive wheels will bend, but either way the wheel must be discarded. The best way to check the true-ness of wheels is to spin them on their axle with the tyre removed. Any misalignment will be evident. 8.9.2 Wheel Sizes
Figure 8.9.1-1 Wheel Sizes A = Overall width B = Inner Bead width
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Some manufacturer's quoted sizes are measured overall (dimension 'A') which is several mm greater than than the inner bead size. The maximum legal wheel sizes for TKM are; B
A
Front
< 120mm
< 131mm
Rear
< 210mm
< 217mm
8.9.3 Front Wheel Spacers The front wheel spacers are used to adjust the front track width [4.10].
Figure 8.9.3-1 Front Wheel Spacers The spacers between the inside bearing and the stub axle shoulder dictate the front track. The spacers on the outside must protrude over the thread a small amount or the front wheel nut will lock onto the shoulder and leave the wheel loose. Tighten front wheel nuts until the spacers are becoming stiff to turn. Never tighten them further. Never tighten the nut and then ease back until the spacers are free as you will have already damaged the bearings. Over-tightening the front wheel nut will damage the bearings.
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A Practical Mechanic’s Guide to TKM Karting Figure 8.9.3-2 Gap Under Spacers 8.9.4 Checking and changing front wheel bearings If the front wheel bearings grumble or drag when the wheel is spun then change them. They don’t cost much. To remove bearings use an aluminium drift or a screwdriver and a lot of care. The wheels are made from soft aluminium and the bearing housing is easily damaged by a screwdriver blade. Ensure the housings are undamaged and then clean them with WD40. When inserting new bearings push them in as far as possible by hand ensuring that they are going in evenly (not tilted). Use a large socket that rests only on the bearing outer race to tap them in. If you must use a drift ensure that it does not slip off the outer onto the thin metal seal, as this will destroy the bearing. 8.9.5 Rear Hub Carriers The Rear Hubs can be slackened and moved along the axle in order to adjust the rear track. The only part that may fail is the thread in the aluminium casting. The locking screw threads may fail if the locking screw is overtightened or they may wear out due to use. Use red locktite to hold the studs in place. 8.9.6 Rear Wheel Hubs Be aware that the fixing point ‘A’ for rear wheels can differ between makes of wheels. Therefore when changing wheels you need to re-check the setting of the rear track.
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A Practical Mechanic’s Guide to TKM Karting Figure 8.9.6 Rear Wheels 8.10 Tyres Tyres keep the kart stuck to the ground, so take care of them! Tyre pressures are covered in paragraph 5.3. There may be some variation in the circumference of Maxxis tyres. New tyres are marked 'A3', 'C4' etc. to indicate their circumference. You need to match tyres in order to be sure to have the same size tyres on an axle. 8.10.1 Looking after Tyres After an event, remove the wheels and store them in a tyre bag. Do not store them where they may freeze or get too hot. Tyres harden with age (especially slicks). New slicks need to be scrubbed in. This can be done by running for 2 laps at less than racing speed and then store them in a bag for at least 24 hours, 'curing' time. When inflating tyres never exceed 40psi as tyres will stretch! and at over 60psi they may burst. After each event release the tyre pressure to less than 10psi. If tyres are left for long periods inflated to pressures above 10psi, they will become permanently stretched. It may be possible to gain advantage on some tracks by using larger tyres on the outside (Like INDY cars). A 1cm increase in circumference makes a difference to handling. A 2cm difference in circumference of the back tyres equates to about 2%. Assuming that a 2% difference equates to a 1% drag this could slow you by half a kart length at the end of a 100 metre straight.
8.10.2 Tyre wear Most tracks result in the front outside tyres wearing more than the others, but each track has it's own characteristics. These include; •
types of corners,
•
surface material and texture
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amount of rubber deposited on the surface
•
Temperature and humidity
Kart set-up and tyre pressures need to account for these factors. Bad setup can result in extreme tyre wear. Older tyres will give less grip and will wear less because they have hardened with age. Kart frame stiffness effects grip and hence tyre wear. The lack of a differential will cause the rear inside tyre to drag on corners, but if the frame has enough flexibility to allow it to come off the ground then the drag will be reduced and so will tyre wear. The author swops tyres around to extend their life. Slicks have dimples to indicate the wear. In the authors experience slicks start to lose grip long before the dimples have been worn away. 8.10.3 Removing tyres •
Fully deflate the tyre.
•
Using a Tyre Press [11.1.8] push the tyre away from the wheel rim around the full circumference and on both sides. This may require a fair amount of force.
Figure 8.10.3-1 Removing a Tyre
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Place the tyre onto the wheel holder [11.2.5] and insert the two tyre levers [11.2.5] so that they cross in front of the peg. Taking care not to damage the rims, rotate the tyre levers around the circumference of the tyre lifting the tyre wall off the rim. The old tyre can now be separated from the rim. Clean the wheel with WD40. Ensuring that you do not get excessive amounts on to the bearings. Note that WD40 can wash the lubricant out of sealed bearings! 8.10.4 Replacing Valves The valve will not normally need replacing, but if it does now is the time to do it. Screw the valve extractor [11.1.9] on to the valve and lever it out. Ensure that the valve hole is clean. Lubricate the rubber valve with water and push the new valve in from the inside of the Wheel and screw on the valve extractor. With care lever it through until it is firmly in place. Take a close look and ensure that the rubber seal on the inside is correctly in place. 8.10.5 Replacing Tyres Work on the ground so that you can get a good grip and use your weight. You will need to use a lot of force. Check the direction arrow on the tyre. Ensure that you end up with a left and right wheel and not two lefts or two rights. Place the wheel onto the holding tool [11.2.5]. Take a good grip on the tyre and then push the tyre wall on to the wheel forcing the tyre over the rim. The first side will go over easy, but the second will be harder. A small amount of WD40 around the rim will greatly assist this and will also result in a slightly better air seal.
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Figure 8.10.5-1 Replacing a Tyre A compressor with a reservoir is ideal and will inflate the tyre without problems. It is possible, but more problematical to inflate the tyre with a little electric pump from Halfords. If its not inflating because the air is escaping from around the wheel rim then squeeze the top of the tyre to push the tyre wall out onto the rim. Tyre wall moves out
Push
Figure 8.10.5-2 Making an Air Seal While running the pump push the tyre with the palm sharply or bounce the tyre onto the ground. The force will suddenly increase the pressure in the tyre and cause the tyre wall to seal on the wheel rim. When it seals leave the pump running until the tyre wall is up against the rim for the whole circumference, on both sides.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting It may jump into place with a loud crack, this is normal. Do not exceed 60psi [8.10.1] or you will damage the tyre. Another method is to use a 'Tyre Band'. A heavy-duty nylon band wrapped at least twice around the tyre when it is deflated, buckled in place it will hold the tyre wall against the rim.
Figure 8.10.5-2 Making an Air Seal This has the potential to be dangerous. The band could break and fly off at speed if the tyre is inflated to a pressure which exceeds the strength of the band. 8.11 Seat height adjustment Seat height affects handling. Generally the lower it is the better. The flat bottom of the seat should be parallel to the ground and above the bottom of the chassis in order to minimise the risk of hitting the ground.
Ground Clearance
Figure 8.11-1 Seat Position
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Always use large washers and rubber spacers between the stays and the seat. For narrow seats use extra spacers. Do not bend supports in to meet the seat. Use extra long bolts for the seat stay so that they can be slackened in the wet. When fitting the seat have the engine and airbox installed. Move the engine fully forward to ensure clearance with the seat and then fully back to ensure clearance with the seat stay.
9. Steering This section covers the engineering details that you will require in order to check and maintain the steering mechanism. The steering mechanism may look simple at first sight, but closer examination will reveal greater complexity and a lot of opportunity for damage to cause problems. No amount of engine tuning or driving skill can compensate for damaged or badly adjusted steering. 9.1 How the Steering Mechanism Works The steering is a simple rod & lever mechanism. The steering gearing is much higher than in a car so that a small movement of the steering wheel produces a large movement at the front wheels. This provides rapid manoeuvrability, but also produces heavy steering loads especially in the dry with warm slicks. Note that in Formula TKM the axis of the stub Axle must pass through the axis of the kingpin.
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Figure 9.1.1-2 Stub-Axle/King-Pin Axis 9.1.1 What is Castor angle? The castor angle is the angle between a notional line drawn from the centre of the axle to the tangential point where the wheel touches the ground and the axis of the kingpin. Castor angle Axis of rotation of the King Pin
Lead
Figure 9.1.1-1 Castor Angle & Lead The Castor angle dictates the lead and thus the steering weight. If the lead increases then the steering gets heavier and the tendency for the steering to return to centre increases. If the lead decreases, the steering gets lighter and the tendency for the steering to return to centre decreases. Should the lead become negative then the forward momentum of the kart will cause the steering to flip left or right and it will have no tendency to return to centre.
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 9.1.2 What is Camber angle? The Camber Angle is the angle that the stub axle subtends to the horizontal. It can be seen from the front of the kart as the angle that the wheel tilts in or out from the vertical.
Figure 9.1.2-1 Camber Angle Normally the Stub Axle lug tilts upwards and the Stub axle shaft tilts downwards so that when the steering is centralised the Camber angle is close to zero.
Figure 9.1.2-2 Zero Camber when going straight. 9.1.3 How the Stub Axle and Lug geometry work The Castor and Camber angles cannot be altered on a Formula TKM kart, but they do change as the kart is steered. As the steering is turned from left to right large changes in the Camber angle occur. The left and right relative ride height at the front of the kart also changes dramatically
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Figure 9.1.3-1 Camber Angle and Height Changes The following diagrammatic sketches are notional views of the front wheels from the driver's point of view, from behind the steering wheel. The rear axle and wheels are indicated as dotted lines. Going straight; When going straight the front wheels have almost zero camber and the front ride height is symmetric.
Turning Right When the kart turns right Centrifugal force increases causing the effective centre of gravity (CofG) to move towards the left side of the kart.
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A Practical Mechanic’s Guide to TKM Karting Effectiv CofG
Figure 9.1.3-1 Individual forces In order to counteract this the camber angle of the front wheels change. For the left-hand wheel it increases and for the right hand wheel it decreases to become negative. Intuitively it can be seen that this results in the wheelbase moving left bringing the effective centre of gravity back towards the centre of the kart. This change in camber also allows more surface rubber to stay in contact with the track. The asymmetric change in ride height of the front wheels creates a 'twisting' force in the chassis which together with centrifugal force will act to lift the inside rear wheel off the ground. This is desirable because otherwise the lack of a differential will result in drag when both back wheels have grip in a corner. 9.2 Tools required Stub Axle Lug Alignment Bars [11.2.1]. Centring Bar [11.2.2] Straight Edge [11.2.3] 9.3 Centring the steering with the front wheels parallel It is essential to be able to set the steering exactly straight and central for checking and setting adjustments. Don’t rely on the steering wheel spokes being central or the track rod lugs on the bottom of the steering column being central. The track rods may differ slightly in length or setting. Note that Toe-Out adjustment is covered in “Kart Set-Up” [5.5].
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting 9.3.1 To Set the Steering Straight and Central Place a strait edge [11.2.3] across the top of the KingPin bolts.
Figure 9.3.1-1 Centre Steering The steering is exactly central when both stub axles are parallel to the strait edge and the track rods on both sides are set to exactly the same length Note that a proprietary 'Tracking Bar' can be purchased that may achieve the same alignment with greater accuracy. 9.3.2 Centring Bar When the steering is accurately centred, cut a rod to fit exactly between the swivel bolt heads as shown [11.2.2]. If the steering is exactly centred then it will fit both sides! This can then be used to quickly centre the steering by adjusting the length of each track rod until the centring bar fits exactly between the bolt heads on both sides.
Figure 9.3.1-2 Centre Bar 9.4 Checking the King Pin Bolts & Bearings Always remove and check the Kingpin bolts after every event. They take a pounding and often bend or crack. If they are damaged then replace them. The bearings should not need to be replaced very often
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Figure 9.4-1King Pin Bolts & Bearings The spacers above and below the stub axle bearings and the tubing between them must not touch the bearing outers. Use appropriate sizes of spacers and washers to adjust the ride height and to minimise the vertical clearance of the stub axle in the lug. Tighten the kingpin bolt to clamp the bearing inners tight against the spacers and bearing inners. Ensure that the bearing outers are not fouled. 9.5 Checking the Stub Axle This method of checking compares one Stub-Axle with another. It is most unlikely that you will bend both Stub-Axles at the same time so it should pick up most problems. 9.5.1 Stub Axle Bent Vertically If one of the stub axles is bent up or down then this will be apparent when they are compared.
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Figure 9.5.1-1 Stub axle bent vertically Bolt them together as shown using the King pin bolt. The distance ‘A’ should be the same along the length of the shaft. 9.5.2 Stub Axle Bent Horizontally If one of the stub axle shafts is bent forward or back then this will become apparent when they are compared.
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Figure 9.5.2-1 Stub axle bent horizontally Remove one of the Stub-Axles from the kingpin bolt and replace it the other way round so that the steering arms are together. Place the assembly down so that the steering arms are aligned.
Figure 9.5.2-2 Checking Stub axle for horizontal alignment
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting A surface plate is ideal or flat surface will be good enough. Any bend in the Stub Axle shaft will be apparent by the misalignment of the ends of the shafts. 9.6 Checking the Stub-Axle Lugs Remove the front wheels and spacers from the Stub-Axles. Replace the kingpin bolts with the Stub Axle Alignment Bars [11.2.1] and lock them in position with the locking nuts. 9.6.1 Checking the camber angle of the lugs. This visual check uses threaded bars [11.2.1] to magnify any misalignment. This is only a rough test, but more accurate than just looking at the assembled kart.
8mm threaded Bar A
bars B C
C
Straight Edge Figure 9.6.1-1 Checking the lugs (1) Stand away from the front of the kart and view the assembly. Even small errors will be apparent. A second check is to measure the camber angle of the Stub Axle Lug. Ensure that the length of threaded bar above the lug (C) is the same both sides. The distance from the outside of the King Pin bolt head to the top of the threaded bar on the other side should be the same for both sides (A=B). 9.6.2 Checking the castor angle Check that the caster angle is the same both sides by ensuring that the threaded bars are parallel.
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Figure 9.6.2-1 Checking the castor angle 9.7 Checking the Track rods 9.7.1 Track rod ends The Track rod and Swivel assemblies must be free to rotate by the maximum possible amount. The track rod swivels must be aligned at each end of the track rod to provide maximum movement. Spring washers placed between the swivels will provide more space in which the joints can swivel.
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Spring Washer
Swivels must be aligned. Figure 9.6.1-2 The swivel joints should be clean and lightly oiled. 9.7.2 Checking that track rods are straight A quick and accurate way of checking that track rods are straight is to take a sheet of thin aluminium and place the track rod onto it.
Figure 9.7.2-1 Bent Track Rod ?(1) Bend the sheet up each side and roll the track rod by rocking the bent sheet to and fro!. If you hear a steady whoosh sound then it is straight, but if you hear a bomp-bomp-bomp sound then it is bent! This will identify very slight bends.
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Figure 9.7.2-1 Bent Track Rod ?(2) Another method is to put the Track Rod against a straight edge and hold it up to the light. The light shining through the gap will show any bend clearly. 9.8 Checking the Steering column Check the height of the lower steering boss to ensure that it has not been bent (up or down). Remove the trackrods and any other impediments from the Steering Column so that it will rotate freely. Rotate it to check that it isn’t bent. If it is then slight bends can be straightened, but not so that it weakens the structure. It is not critical to get it perfectly straight, but it should not foul the fuel tank.
10. Buying a Kart Before you buy a TKM kart ensure that it is legal. You will not be able to race an illegal kart. Carefully read the ‘Formula TKM Regulation & Technical Guide’ [14.3] and chapter 14 of the MSA Kart Race Yearbook [14.4] which are the definitive regulations for Formula TKM. These notes only supplement the regulations. You must also ensure that the kart is safe and undamaged. If you are new to karting then buy your kart from a well-known dealer and ensure that you get an agreement from the dealer to provide assistance on your first practice. 10.1 Chassis Ensure that the chassis is an homologated chassis and that there are NO modifications of any sort.
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A Practical Mechanic’s Guide to TKM Karting Chassis are made with differing levels of stiffness to suit various track conditions and driver skills. It is a good idea to contact the manufacturer of a chassis that you are considering buying to ask about its suitability for your needs. Carefully check the chassis and if in doubt negotiate a deal that includes a check and re-jig of the chassis by the manufacturer. Check the identification plates riveted to the left-hand rear-bearing hanger. There should be a manufacturers ID plate and it must also have a TKM sequential plate. If it does not, but does have a ‘100UK’ stamp then it was made before 1994 and may be too old to be worth much. Remove all plastic bodywork, engine, fuel tank, seat, wheels etc. If any stickers on the tubing look new or are in an odd position then also remove them! The original paintwork would normally be heat-cured enamel. If it has been repainted then ask to see the bill. If it was not repainted after being rejigged by the manufacturer then don’t buy it. Ensure that there are no cracks in the tubing or welded joints. Pay special attention to the area near the stub axle lugs (i) and the upper (ii) and lower (iii) steering column stays.
Figure 9.6.1-2 Checking Chassis Condition Turn the chassis upside-down and check the underneath for ground impact damage. 10.2 Transmission Rotate the back axle and look for movement that would indicate that it is bent [8.5.3]. Ask the vendor if the axle is the correct part supplied by the chassis
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A Practical Mechanic’s Guide to TKM Karting manufacturer. If not, it may be a different length to the original, which will affect kart set-up. 10.3 Brakes Check the brake disc for damage around its circumference. It may have struck the ground and sustained damage. Check the level of wear on the pads and ensure that they are not contaminated with oil or WD40. Establish when the fluid was last changed. Ensure that it is the correct braking system as homologated with the chassis. 10.4 Wheels & Tyres Check for damage around the rims and establish how many and what size wheels are included. 10.5 Engine Get a written statement about how many hours the engine has run since it was last rebuild and if you are in any doubt then negotiate a deal which includes an engine rebuild by Tal-Ko or a reputable engine rebuilder. If you wish to run with a clutch then buy an engine with a clutch fitted. This will cost considerably less than buying a none-clutch engine and having it modified. If the engine is old then ensure that the cylinder bore is not over (or close to) the legal limit [14.3]. Generally no changes are permitted to the BT82 engine. The one exception is a hole in the cooling fins to accept a carburettor return spring.
11. Tools A wide selection of good quality tools is essential to good kart maintenance. This section describes the tools which may not be normally available. A list of the ordinary tools that you will normally require can be found in ‘The Complete Guide to TKM Karting’ [14.4].
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A Practical Mechanic’s Guide to TKM Karting 11.1 Special Tools The following tools are special tools required by the TKM Mechanic. They can be purchased from specialised suppliers. 11.1.1 Folding Plug Spanner Small enough to fit in your pocket along with a replacement spark plug. This is essential on the grid. (Halfords; £3.00) 11.1.2 Dial Gauge & Adapter The purpose of this is to enable the position of the piston to be found when setting the timing. The Dial Gauge fits into the adapter which in turn is screwed into the Spark Plug hole. (Dartford Karting; £20 for the dial gauge and £8 for the Adapter.) 11.1.3 Dummy Gudgeon Pin Used to hold the small end bearing rollers in position when the piston is removed. (Tal-Ko; £3.50) 11.1.4 Clutch Holding Spanner Prevents the clutch and crankshaft from rotating when the starter or Clutch retaining nuts are being slackened or tightened. (Tal-Ko; £8.50) 11.1.5 Clutch Puller Tool For removing the clutch drive hub from the crankshaft. (Tal-Ko; £9) 11.1.6 Sprocket Extractor For removing the sprocket from the crankshaft. (Dartford Karting; £10) 11.1.7 Tyre Pressure Gauge Any good quality tyre pressure gauge which operates in the range 8-50 psi. (Dartford Karting; £13)
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A Practical Mechanic’s Guide to TKM Karting 11.1.8 Tyre Press For pushing tyre walls off the aluminium rims. (Dartford Karting; £23) 11.1.9 Valve Extractor Lever for removing & replacing the air valves from wheel hubs. 11.1.10 Carburettor Tester For checking the carburettor's Pop-Off pressure. (Dartford Karting; £28) 11.2 Home-made Tools These are a useful set of special tools that are simple to make. They have all been manufactured and used by the author. All of the raw materials are available from large DIY stores. Each tool is designed to be constructed with minimal engineering skill and using the basic tools that any karter should own. If you have access to more sophisticated tools like Lathes, Pillar Drills and the skills to use them you do not need these designs. 11.2.1 Stub Axle Lug alignment bars. Two lengths of 8mm threaded bar of identical length. They must be straight and should be about 200-250mm long. They will require 2 x 8mm nuts on each bar [9.6.1]. They replace the KingPin bolts to allow the Stub Axle Lug alignment to be checked. 11.2.2 Centring Bar A metal bar of about 5mm diameter cut to an exact length [9.3.2]. It is used to set the track rods length so that the front wheels are parallel. 11.2.3 Straight edge A length of ‘L’ shaped aluminium extrusion slightly longer than the front track width. The cross-section should be about 10mm x 15mm and it must be straight. It is used for checking the chassis alignment and for centralising the steering.
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A Practical Mechanic’s Guide to TKM Karting 11.2.4 Toe-Out alignment tool Two 300mm lengths of ‘L’ shaped aluminium extrusion 10mm by 15mm. Drill a hole at each end of both pieces of aluminium and tie a 3-5mm bungy rubber to each.
Figure 9.6.1-2 The bungy holds the bars against the inside of the front wheels. 11.2.5 Tyre Replacement Tools Two tyre levers each 500mm long made from flat steel bar about 20mm x 3mm. Ensure that the ends are well rounded and smoothed with fine emery.
Figure 11.2.5-1 Tyre Levers A flat steel base about 300mm x 300mm made from 2mm(or more) plate. With a 300mm long 15mm diameter peg welded on to it.
Figure 11.2.5-2 Wheel Support The peg holds the wheel in place while the tyre is removed and replaced [8.10.3]. The peg also provides purchase for the tyre levers.
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A Practical Mechanic’s Guide to TKM Karting 11.2.6 Gudgeon Pin Extractor. When removing or replacing the Gudgeon pin it can become stuck so that when pushed harder it jumps through. Some publications suggest that you can use a mallet, but the author finds this a bit nerve racking. This tool will enable you to move the Gudgeon pin and dummy gudgeon pin, slowly but in perfect control.
Materials •
A 120mm length of 6mm treaded brass rode.
•
40mm long sturdy plastic tube. Diameter approx’ 20mm. should be sturdy enough to support the pull provided by the wingnut
•
2 x 6mm Wing nuts, 1 plain 6mm nut, 2 x 6mm Nylock nuts & a large washer with a 6mm hole.
Construction •
Drill out the nylon inserts from the Nylock nuts, taking care not to damage the threads. Place them onto the bar so that the domed top of the nuts both face inwards.
Figure 11.2.6-1 Threaded Brass Rod •
The plastic tubing must be cut square at one end and shaped at the other end to sit well on the side of the piston. The washer should be fixed (glued) to the flat end. Plastic Tubing
Washer
Figure 11.2.6-2 Plastic Tubing
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A Practical Mechanic’s Guide to TKM Karting 11.2.7 Gudgeon Pin Alignment Spring A ordinary spring (Exhaust securing spring is OK) of about 60mm in length that fits snugly into the hole down the centre of the gudgeon pin. It is used to hold the gudgeon pin and dummy gudgeon pin in alignment. 11.2.8 Chain Measure A strip of aluminium marked with numbers of links at one end so that when the chain is hung over the axle and pushed down with the chain measure the number of links can be read off the measure.
115 114 112 110
Figure 11.2.8-1 Chain Measure
12. Jargon Buster This list details the components which have jargon names, obscure names or names which are not immediately obvious. The names used in this guide are in the title. The other names shown are common alternatives. 12.1 Engine, Carburettor & Exhaust 12.1.1 Air Intake Box •
Induction Box
•
Intake Box
•
Homologated Box
•
Noise box
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A Practical Mechanic’s Guide to TKM Karting All refer to the Air intake box and include; Backplate, Air filter element, Trumpet & Rubber grommet, Black plastic housing, and 3 jubilee clips.
12.1.2 Axle Sprocket •
Rear Sprocket
The large, chain driven, sprocket mounted on the axle. 12.1.3 End Can •
Deci-bell
•
End Canister
The aluminium can which goes over the end of the exhaust and claims to reduce the noise level. 12.1.4 Engine Sprocket •
Front Sprocket
The 9, 10 or 11 tooth sprocket which drives the chain. 12.1.5 Exhaust Silencer •
Exhaust muffler
•
Exhaust Pipe
•
Expansion Box
The main body of the exhaust
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A Practical Mechanic’s Guide to TKM Karting 12.1.6 Flexible pipe •
Flex
•
Flexible coupling
The 60<100mm length of flexible pipe which connects the Manifold Bend to the Exhaust Silencer. 12.1.7 Manifold Bend •
90 degree bend
•
Manifold
The bent pipe which bolts to the engine exhaust port at one end and connects to the Flexible Pipe at the other. 12.1.8 Pop-Off The pressure which, when applied to the carburettor's fuel inlet pipe, will cause the metering valve to lift thus releasing (Pop-Off) the pressure. 12.2 Chassis & Bodywork 12.2.1 Bearing Supports •
Axle Hangers
•
Axle Uprights
The uprights welded to the chassis into which the Rear Axle bearing housings are bolted 12.2.2 Bearing Retention Plates •
Retention Plate
Two or three hole pressed steel plates that hold the rear axle bearings. 12.2.3 Bodywork Any part of the body which is not the chassis.
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A Practical Mechanic’s Guide to TKM Karting 12.2.4 Brake Disc Carrier Fixture, which clamps the Brake, disc to the back axle. 12.2.5 Chain Guard •
Chain Strip
•
Chain Cover
Cover (usually plastic) to catch oil which comes off the chain. It is also intended to be a safety cover, but most would not meet this requirement if tested! 12.2.6 Chassis •
Frame
The welded steel tubing Frame. (Does not include any part that is not welded in place). 12.2.7 Front Bumper •
Front Spoiler
•
Nose Cone
The plastic box mounted on the front of the kart, usually used as a pushing device! 12.2.8 Front Panel •
Nassau Panel
The sloping front panel which covers the steering column and on which the number is stuck. 12.2.9 Rear Bumper Tubular metal bar, usually chrome plated, needed to fend off Front Bumpers (see above)! 12.2.10 Seat Stay •
Additional Seat Stay
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A Practical Mechanic’s Guide to TKM Karting Removable seat stays which connect between the seat and the Bearing Hangers. Can be slackened or removed to increase chassis flexibility. 12.2.11 Side Pods •
Side Bumpers
•
Side body work
•
Nerf Box
•
Nerf Pods
The large square plastic boxes on each side of the kart. (Used for 'nerfing' opponents out of the way!) 12.2.12 Sprocket Carrier The fixture which clamps to the axle, on to which the axle sprocket is bolted. 12.2.13 Track Distance (width) between the front wheels, (Front track) or rear wheels. (Rear track) 12.2.14 Wheel hubs •
Hubs
The aluminium fittings on to which the rear wheel rims are fitted. 12.2.15 Wheel Rims •
Rims
The aluminium wheel without the tyre, but normally includes the valve assembly and for front wheels, the bearings. 12.2.16 Wheel Studs The studs (bolts with no head!) which are permanently fixed into the Wheel Hubs.
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A Practical Mechanic’s Guide to TKM Karting 12.2.17 Wheelbase The distance between the centres of the front Stub axle and rear axle. 12.3 Steering and Wheels 12.3.1 King-Pin •
King-Pin bolt
The main steering bolt which holds the stub axle to the Stub Axle yoke. [9.4]. 12.3.2 Stub Axle •
Axle Stub
The axle onto which the front wheel is fixed [9.5]. The Stub Axle Yoke is the bit on the chassis to which the Stub Axle is attached by the King Pin. 12.3.3 Castor Angle See paragraph 9.1.1. 12.3.4 Camber Angle See paragraph 9.1.2
13. Spares & Products The author travels to meetings in a large van, usually towing a caravan and often with two children, two dogs, and several friends. The following items also find a corner to hide in. This inventory is appropriate to a single kart and is listed in the order in which the parts have most frequently been required. 13.1 Wheels [8.9] & Tyres [5.3] The minimum required is one set of Slicks and one set of Wets.
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A Practical Mechanic’s Guide to TKM Karting The author carries the following; •
Newest slicks on best wheels for racing.
•
Second best slicks on wheels for practice.
•
Spare slicks in case of damage. (Check the race rules before changing tyres!)
•
Newest wets on best wheels for racing.
•
Second best wets on wheels for racing in drying conditions
13.2 Chains [8.4] & Sprockets [5.13] & [8.3] Rear sprockets:- Carry two of the most frequently used sizes for each track at which you race, plus a few sizes larger and smaller. Chains:- Carry a range of chain sizes to match the range of sprockets. 13.3 Spark Plugs [5.12] Carry a spare of each type used. Also keep a spare HT lead and plug cape. 13.4 Nuts, Bolts and springs You can never have enough or a wide enough range of nuts and bolts. The author buys them by the dozen from www.kart-nuts.co.uk. A few special bolts can only be purchased from specialist Karting suppliers. You will pay 500% more for bolts at the trackside. Having a good selection of nuts and bolts will make you many friends! Keep a good range of springs - The exhaust springs can sometimes get knocked off. 13.5 Track rods [9.7] These frequently get bent. They can be straightened, but it is quicker to just change them and straighten them later. Keep a few spares. 13.6 Carburettor [7.] Keep at least one spare carburettor, set up ready to go and sealed in a plastic bag (Self-Sealing Freezer bags are ideal). Ensure that the fuel is
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A Practical Mechanic’s Guide to TKM Karting removed from the carburettor or it will evaporate and leave a sticky residue to gum up the works! The author also carries the following:•
Carburettor rebuild kit. (You may need it)
•
Gaskets of the sort that go between the carburettor and the engine.
•
Throttle cable - complete.
•
Petrol pipe - pre-cut to the correct length and sealed in a plastic bag to keep it clean.
•
Air intake Box (Complete) - These have a habit of getting knocked off.
13.7 Exhaust & Flexs [5.14] A range of Flexible pipes. A complete spare exhaust. 13.8 Cable ties A good range of cable ties is essential. 13.9 Steering column [9.8] Steering column - drilled ready to be fitted. Ideally keep a spare steering column with a steering wheel already fitted. 13.10 Bearings - all types At least one of each type of bearing. 13.11 Body-work and number plates [8.7] Spare numbers and backing square are essential as they often get removed from the side bumpers when nerfing. Front bumber with fittings or at least ready drilled to take fittings.
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A Practical Mechanic’s Guide to TKM Karting 13.12 Back axle[8.5] Ideally a complete Back axle assembly. If this is not possible then just the axle. 13.13 Engine Your spare engine should be complete with carburettor, air-box etc, and be ready on engine mounts. 13.14 Useful Products In no particular order. •
Carburettor cleaner from Halfords. (Thin nozzle tube with high pressure to clean jets.)
•
Red & Blue Loctite from Halfords.
•
Electrical Tape from Halfords. (Various colours.)
•
Tank Tape
•
Brake fluid (DOT 5) from Karting shops
•
Cable ties from Electricians suppliers - Various sizes
•
WD 40 from Halfords
•
Fine emery paper from Halfords
•
Copper Slip (Grease) from Motorcycle shops
•
Lithium Grease from Halfords
•
2-Stroke oil from Karting shops
•
Bicycle oil from Halfords - For cables
•
Brake Cleaner from Karting shops
•
Racing Chain Lubricant from Dartford Karting - Must be formulated for racing!
Karting shops - Black and strong!
14. Publications In no particular order;
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A Practical Mechanic’s Guide to TKM Karting 14.1 ‘Karting’ Magazine Includes a Formula TKM page by Sidney Sprocket. It’s worth getting the magazine just for Sidney’s articles! Available from newsagents or direct from Lodgemark Press 01689 - 897123 14.2 The ABkC Racing Reg’s (The Association of British Kart Clubs Kart Racing Regulations). Essential reading. Some good stuff for new karters at the back. Available from The ABkC, Kart Clubs and Lodgemark Press. 14.3 Formula TKM Regulations & Technical Guide Published by Tal-Ko. - New version issued each year. 14.4 MSA Kart Race Yearbook Published by the MSA Is specific to Karting. 14.5 MSA Competitors' Yearbook Published by the MSA Contains much important information. 14.6 The Complete Guide to Formula TKM Karting By Grahame Butterworth of Impact Karting. - Essential introduction to TKM karting. Available from Lodgemark Press. 14.7 Maintaining 100cc Kart Engines By P Evrard of Scorpion Engineering. - Very good guide to rebuilding 100cc kart engines Available from Lodgemark Press.
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A Practical Mechanic’s Guide to TKM Karting 14.8 Two-Stroke Performance Tuning By A. Graham Bell. - Very detailed. Available from Lodgemark Press. 14. 9 Videos Formula TKM Video (£19.00) Official TKM video. Winning Engine Maintenance (£27.00) - American, but otherwise OK. Both available from Lodgemark Press.
15. Forms & Records This section shows examples of the various forms and records that have been mentioned throughout this guide. These are only suggestions and the author would advise the reader to develope and carefully maintain their own set of records. This is not real data. It is just there to illustrate the point! 15.1 Track Record Example:Location/Date Event Engine No Tyre/set Pressures Carb Toe-out Engine No 54.60 49.80 48.80
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Practice Slick/2 26/28 1.25/.33 0 8456 51.2 48.65 48.65
Time Carb No Track Gears Exhaust Flex Fuel Carb No 50.20 48.20 48.20
10:15 2.0/7.2 10/82 80 6.5 3 50.00 48.72 Spin
Chris Compton (compark) 2001
A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Event Engine No Tyre/set Pressures Carb Toe-out Engine No 54.60 49.80 48.80
Heat 1 Slick/2 26/28 1.25/.33 0 8456 51.2 48.65 48.65
Time Carb No Track Gears Exhaust Flex Fuel Carb No 50.20 48.20 48.20
10:15 2.0/7.2 10/82 80 6.5 3 50.00 48.72 Spin
15.2 Best Settings Summary This idea has proven to be extremely useful. When conditions change it can be a bit of a panic to get the cart set-up correctly. These tables are constantly updated as we learn more about conditions at various tracks. They are fixed to a card backing and sealed in plastic and stuck on the inside of the van for an immediate reference. The values shown are not real values - you must derive your own from your records! You should have a card for each track and for each chassis (if you have more than one).
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting
Shenington Dry & Gearing Tyre Pressures F/B; Carburettor Settings L/H;
V-Hot 82/10 20/23
Hot 82/10 22/25
Mild 82/10 24/27
Cold 82/10 27/31
1.3/0.8
1.25/.4
1.0/.25
Exhaust Flex Spark Plug Toe Out Track F/R Wet & Gearing Tyre Pressures F/B; Carburettor Settings L/H;
80
80
1.25/.3 3 70
0 2/2.5 Damp 81/10 18/20
0 2/2.5 Wet 80/10 22/26
0 2/2.0 Soak 80/10 32/38
0 3/2.0
1.3/0.8
1.25/.4
Exhaust Flex Spark Plug Toe Out Track F/R
65
65
1.25/.3 3 65
-5mm 4/1.5
-10mm 4/1.0
-15mm ?
70
15.3 Engine Record Each engine needs it own record. It is essential to record the engine run time: Engine number 1234 Last Rebuilt 2-June-1999 This event Since piston Since re-build 1-00 1-00 1-00 Running in at Blackbushe 14-June-97 - OK
0-23
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1-23
1-23
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A Practical Mechanicâ&#x20AC;&#x2122;s Guide to TKM Karting Blackbushe 28 June 97 - Cold & Wet - Carb 02 used Not running well - (Note - Dirty carb?) 0-30 1-53 1-53 Shenington 20 Aug 97 - Hot and dry. Carb 03 used OK! Good with 70 mm flex? Why? Friction disc replaced & carbon removed from head. (Not much carbon!)
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