Group10 - Pre-delivery, delivery and after-sales inspections
Group 15 - Lubrication and periodic service
Group 20 - Engine and tractor tune-up and adjustment
Group 25 - Separation
SECTION 20 ENGINE
Group S General information, diagnosing malfunctions
Group 10 - Cylinder head and camshaft
Group 15 - Cylinder block, liners, pistons and connecting rods
Group 20 - Crankshaft, main bearings and flywheel
Group 25- Timing gear train
Group 30 - Oil pump, oil pressure regulating valve and oil filter
Group 35 - Engine cooling system
Group 40 - Speed control
SECTION 30 FUEL SYSTEM
Group 5- Diagnosing malfunctions
Group 10 - Fuel tank, transfer pump, fuel filters
Group 15 - BOSCH injection pump
Group 20 - ROTO DIESEL injection pump
Group 25- ROOSA MASTER MODEL CBinjection pump
Group 30 - ROOSA-MASTER injection nozzles
Group 35 - BOSCH injection nozzles
Group 40 - Cold weather starting aids
SECTIOh 40 ELECTRICAL SYSTEM
Group 5 - Diagnosing malfunctions
Group10 - ”BILUX” lighting system
Group 15 - Sealed-beam lighting system (from tractor serial no. 77054 L)
Group 16 - Sealed-beam lighting system (up to tractor serial no. 77053 L)
Group 20 - Starting motor
Group 25 - Alternator and regulator
Group 30 - Generator and regulator
SECTION 50 POWER TRAIN
Group 5- Engine dual stage clutch and clutch linkage
Group 10 - Collar-shift transmission
Group15 - Differential assembly
Group 20 - Final drives
Group 25 - PTO shafts
SECTION 60 FRONT AXLE, STEERING SYSTEM AND BRAKES
Group S Front axle
Group 10 - Manual and power steering
Group 15 - Brakes
SECTION 70 HYDRAULIC SYSTEM
Group 5- General information, diagnosing malfunctions, pressure tests
Group 10 - Oil reservoir, filter and valves
Group 15- Hydraulic pump and transmission oil pump
Group 20 - Rockshaft
Group 25- Selective control valve
SECTION 80 MISCELLANEOUS
Group 5 - Belt pulley
Group 10 - DE LUXE seat
Group 15 - Front wheels
INTRODUCTION
This technical manual for the 820 tractor is a concisely written publication for the service personnel. It contains procedures and specifications which an individual cannot be expected to remember.
The table of contents on the first page of this manual lists the individual sections and their groups. A table of contents on the first page of each section lists the groups in the section and the page number of the major subjects found in each group. Coloured tabs make it easy to locate the individual sections.
Coverage for each components includes:
General information, diagnosing malfunctions checks, removal, disassembly, repair, assembly, installation, adjustments, specifications and special tools. Specifications and special tools are always listed at the end of each group.
The section ”GENERAL INFORMATION” includes instructions for ”Pre-delivery, delivery and after-sales inspections” as well as ”Engine and tractor tune-up” torestorefull performance.
Tractor service and lubrication as well as lubricants required are described in the Operator's Manual.
Little explanation is given about theory of operation in this manual unless the theory is peculiar only to the component in this machine. Basic theory of operation and general information about the systems or components of the tractor will be found in the ”JOHN DEERE F,undamentalsof Service’ manuals.
Keep this ”Technical Manual” in the shop where it is readily accessible and refer to it whenever in doubt about correct procedures of servicing the 820 tractor. Using it as a guide for any and all service problems will reduce error and costly delay.
Model 820Tractor
TM-42 2 70) 1
SPECIFICATIONS
SERIAL NUMBERS
Theengine serial numberisstampedintothename plate at thelowerright ofthefrontcylinder block.
NOTE: I f ordering engine parts, indicate all digits
Engine horsepower on tractors eqnipped u›ith BOSCH or ROTO DIESEL injection pump.
Flywheelhorsepower )at2100rpm incl. accessories2) 32 HP (32PS) withoutaccessories2)...................34 HP(34 PS) of the serial number on the name plate.
The name plate showing the tractor serial number is located on the right-hand side of the front support.
NOTE: I{ ordering trac tor parts, (excluding engine parts), indicate all digits of the serial number on the name plate.
MODEL NUMBERS
Theinjection pump, injectionnozzles,the generator, starter and the main hydraulic pump have model numben to facilitate identification of different makesofagivenunit.
2) Water pump, fan, generator, air cleaner and muffler.
3) With the engine run in (above 100 hours of operation) and having reached operating
Working speedrange . 1400to2100rpm temperature(engineandtransmission);measured by means of a dynamometer. Permissible variationz 5%.
COL LAR-SHIFTTRANSMISSION
8-speed transmission with helical-cut gears. This transmission isavailable inthreevariations:
8-speed transmission with parking lock, without independent hand brake, 8-speed transmission without parking lock and with independent hand brake; 8-speed transmission without parking lock, with blocked 8th gear and independent hand brake.
Withthistransmission8or7forwardand4reverse speeds are available.
DIFFERENTIAL ANDFINAL DRIVES
Planetary reduction gear and differential with spiral bevel gears.
DIFFE RENTIAL LOCK
Hand or foot operated; spring-loaded out of engagement.
POWERSHAFTS
Single, 540 rpm rear powershaft or dual 540 and 1000 rpm rear powershaft. Conversion from 540 rpm to 1000 rpm and vice •rersa is made by interchanging the stub shaft. In addition, a front 1000 rpm powershaft may beinstalled.
The powershafts are independent of the transmission as the tractor is equipped with a dual-stage engine clutch.
Pomersha(I Speeds engine
HYDRAULIC SYSTEM
Open center, constant oi1 flow system; also includesrockshaft andselective control valves.
The steering is a recirculating ball bearing, worm and nut type. A number of steel balls between ball nut and steering wheel shaft provide for positive engagement ofsteering wheelandsteeringlinkage.
HYDRAULIC BRAKES
The disk brakes run in an oil bath and are hydraulically controlled.
Every new JOHN DEERE tractor leaves the factory in such a condition that it can be delivered to the customer after a minimum of service.
To promote complete customer satisfaction, proper predelivery service including mending of possible shipping damage and giving the finishing touches to the tractor, are of prime importance to the dealer.
A tag pointing out the factory-recommended procedure for predelivery service is attached to each new tractor before it leaves the factory. The reverse side of this tag is filled in by the factory after the tractor has undergone a thorough inspection prior to shipping.
After completing the factory-recommended dealer checks and services listed on the predelivery. tag, remove the tag from the tractor and file it with the shop order for the job. The tag will then serve as a basis for certifying that the unit has received the proper predelivery service.
TEMPORARY TRACTOR STORAGE
Check radiator for coolant loss and antifreeze protection (gravity of antifreeze and rust inhibitor mixture)
CAUTION: On tractors shipped with dry-charged batteries or without battéries which are to be started by means of a slave battery, do not remove insulating tape on terminal of cable to starter under any circumstances. Also, do not remove contrary to earlier statements wire between terminals D+ of regulator and D+ of generator. If this advice is disregarded, damage to generator andregulator may result.
Remove batteries, drain and store electrolyte.
Reduce shipping pressure of tires
Cover tractor and tires for protection and cleanliness
Coolant level should be midway between radiator core and bottom edge of filler neck
CAUTION: If the tractor is to be started by means of a slave battery, do not remove insulating type on terminal of battery cable to starter under any circumstances. Also, do not remove contrary to earlier statements wire between terminals D+ of regulator and D+ of generator. If this advice is disregarded, damage to generator and regulator may result.
If thebatteries areto beinstalledinthe tractor,removeinsulatingtapeonterminal of batterycableif tractorwasshipped with dry-charged batteriesorwithout batteries.
”Fundamentals of Service, Electrical Systems” manual under ”Batteries”
Operator's manual
Operator's manual
’top mark on dipstick
Operator's manual
Operator'smanual
OperatorsmanuM
S ervice
ENGINE
Check oi1bath air eleaner
Check dry type air cleaner
Fill fuel tank and start engine
BEFORE DELIVERING TRACTOR -
Continued
Specifieations R eference
Fill withoi1to ”Fiill” mark
Capacity: 13.75 Imp. (16.5 US) Gals = 62.5 lit.
Check lighting system, indicator lamps and instruments for proper operation
Check if speed control linkage moves easily
Check engine idle speeds
Check injection timing
TESTING OPERATION
Check dual-stage clutch operation
Shift transmission through all speeds
Check differential lock operation
Check powershaft operation
Cheek 3-point hitch operation
Cheek hydraulic system operation
Cheek brake system
Approx. 1 in. (25 mm) clutch pedal free travel
Operator's manual
Operator's manual
Operator's manual
Section 20, group 40
Section 20, group 40
Section 30, group15 und 25
Section 50, group 5
Operator's manual
Operator's manual
Operator's manual
Operator's manual
Seetion 70, group 5
Section 60, group 15
Check steering Section 60, group 10
Check seat adjustment
GENERAL
Tighten accessible nuts and attaching screws
Clean tractor and touch up paint
Operator's manual
Seetion 10, group 20
Model 820 Tractor TO-4212 (Jan-70)
DELIVER Y INSPECTION
A thorough discussion of the operation and service of the tractor at the time of its delivery helps to assure complete customer satisfaction.
Proper delivery should be an important phase of the dealer's program.
It is a well-known fact that many complaints have arisen simply because the owner was not shown how to operate and service his new tractor properly.
Enough time should be devoted, at the customer's convenience, to introducing him to his new tractor and explaining to him how to operate and service it.
Using the tractor operator's manual as a guide, be sure that the owner understands the following points properly.
1. Adjusting the seat
2. Operation of control levers and instruments
3. Starting and shutting off the engine
4. The importance of the tractor break-in period
5. Use of counterweights and proper inflation pressure as well as filling of tires with water and magnesium chloride, if required.
6. Operating the complete hydraulic system
7. Operating the powershaft
8. The importance of the safety rules
9. The importance of lubrication and periodic service
AFTER-SALES INSPECTION
In the interest of the purchaser and the dealer an after-sales inspection should be carried out by the dealer after the first 100 hours of using a new John Deere tractor.
The purpose of this inspection is to make sure that the customer is receiving satisfactory performance
Through this inspection a needless volume of service work can be eliminated by preventing minor difficulties from developing into serious problems later on. It also will promote stronger dealercustomer relations and give the customer an opportunity to ask questions that may have arisen during the first few days of use. from his tractor. At the same time, the inspection should reveal whether or not the tractor is being Thereby the dealer has the further opportunity of operated, lubricated and serviced properly. promoting the possible sale of other new equipment.
The following inspection program is recommended:
AFTER-SALES INSPECTION
COOLING SYSTEM
Check coolant level
Coolant level should be midway between radiator core and bottom edge of filler neck
Operator's manual
Clean exterior of radiator
Check hose connections
FUEL SYSTEM
Check sediment bowls and elements of fuel filter as well as bowl of fuel transfer pump for water or sediments
Check line connections
ELECTRICAL SYSTEM
Check gravity of battery electrolyte
Check electrolyte level of batteries
Check tension of fan belt
Start engine and check operation of lights, indicator lamps and instruments
LUBRICATION
Check crankcase oil level
Checktransmission oillevel
Checkoillevelofsteering gearhousing
Cheek oil level of belt pulley housing
Lubricate dual-stage clutch throw-out
Lubricate 3-point hitch
Gravity should be 1.260 at an electrolyte temperature of 80OJ (27°C)
For brands of oil and lubricants to be used as well as for lubricating and servicing the model g20 tractor, seeoperator's manual.
ENGINE AND TRACTORTUNE-UP
GENERAL INFORMATION
Beforetuninguptheengine,determine whether a doubt, the following preliminary tests will helpto tune-up will restore operating efficiency.If thereis determine iftheengine canbetunedup.
After the engine has been tuned up as explained Compare measured performance in HP with output above, determine powershaft horsepower by means measured before carrying out “Enginetune-up”. of a dynamometer, see “Fundamentals of Service, Engine” manual.
TRACTOR TUNE-UP
After carrying out engine tune-up, adjust tractor as follows:
ENGINE DUAL-STAGE CLUTCH
Adjust clutch pedal free travel
FRONT WHEELS
Cleanandlubricatefrontwheel
Approx. 1 in. (25 mm)
Section 50, group 5
Section 80, group 15 bearings
Adjust front wheel bearings
Check toe-in
1/8 to 3/8 in. (3 to 9.5 mm)
Check torque of front wheel 85 ft.lbs (12 mkg) bolts
Recommended torques inft. lbs. and mkg for UNC and UNF cap screws
Headmarking (identifying strength)
NOTE: Avariattonof+ 10%is permissible forall torques indicated in tiiisciiart.
Torque figures indicated above and in the repair data sections of this manual are valid for non-greased or non-oiled threads and heads unless otherwise specified.
Regular bolts and cap screws
Tempered steel high strength bolts and cap screws *** Tempered steel extra high strength bolts andcap screws
Fig.1 Separating between Tractor Front End and Engine Remove pipe clamps 3 (fig. 2). Remove cap screw 5 and retainer 2 for attaching suction line l to
1 Cap screws
2 Distributor
3 Cable of fuel gauge sending unit
d Fuet return line
6 Upper water hose
6 Air intake pipe front of clutch housing. Disconnect pressure line 4 at connector.
Disconnect air intake pipe 6 at intake manifold of engine.
Drain coolant and disconnect upper and lower water hose at radiator.
NOTE: Plug lines and openings immediatel y with plugs or caps.
Disconnect drag link at bell crank. Securely support rear of tractor under clutch housing.
Insert wood blocks between front axle and front support to prevent the latter from tipping sideways.
Attach front of tractor to a suitable hoist.
Remove cap screws 1 (fig. 1) of front support and separate front end from engine. Take measures to prevent front of tractor from tipping to the front. If tank contains too much fuel, drain it or safely support front of tractor.
CAUTION: Move front end forward out of tractor until pump drive shaft comes loose of front or rear coupling of pump drive.
INSTALLATION
Install hydraulic pump drive shaft into front coupling. Make sure both dowels are in place on front support.
Move front of tractor toward engine. Be sure to install hydraulic pump drive shaft in rear coupling, and to install suction line1 (fig.2) inclutch housing.
Attach front end of tractor to engine, using cap screws 1 (fig. 1). Tighten screws to the specified torque.
Model 820 Tractor TM-4212 (Jan-70)
Install retainer 2 (fig. 2) of suction line 1 and tighten cap screw 5 of retainer to the specified torque. Connect pressure line 4.
NOTE: yor proper sealing o[ suction line, place a newO-ringinclutchhousing bore.
Install fuel transfer pump and connect fuel lines. Make sure transfer pump inlet line is below and behind fuel pressure line.
Open fuel shut-off valve.
Connect wire to fuel gauge sending unit.
Connect headlight wires to junctions.
Attach water hoses to radiator.
Attach air intake pipe to intake manifold.
Install clamps of hydraulic lines
Attach drag link to bell crank and tighten slotted nut to the specified torque.
Install hood and radiator side grilles.
Fill radiator with clear, soft water, adding an antifreeze-rust inhibitor mixture (see Operator's Manual).
Connect ground cable to batteries.
CAUTION: Always connect ground cable to negative (-) polesof batteries.
Start engine and check fuel lines, hydraulic lines and water hoses for possible leaks.
REMOVINGANDINSTALLING ENGINE
NOTE: for most engine service operations the engine need not be removed. Hou›ever, i[ the crankshaft has to be removed or in case o/ mojor overhaul, remove engine.
REMO¥’AL
Porsafety disconnect groundcableatbatteries.
Separate front of tractor ftom engine, as explained above.
Disconnect all cables to dashboard at regulator andall cables 4(fig.3) at starter.
Remove flexible shaft 2 (fig. 3) of tachometer from clutch housing and cam shaft. Replace rubber seal of flexible shaft, if required (seal will possibly remaininhousing bore).
Remove cap screws S attaching dash to flywheel housing.
Disconnect wireatsignalhorn.
On tractors wit A starting ftuid adapter: Disconnect startingfluidlineatintakemanifold.
in tractors uiith Thermostart aid: Disconnect cableatheaterof intakemanifold.
On trocfors with BOiSCH or ROTO DUBEI injection putrip: Disconnect shut-off cable at the pump.
On tmetors with ROOiSA MAS!TER model CB i•ieetiOn R* p1 Disconnect shut-off cable at the pump.
Screw retaining screw of flexible tube of coolant temperature gauge out of cylinder head and withdraw flexibletubefromcylinder head.
Remove left dashpanel as well as both batteries.
Remove cap screws attaching dashboard to flywheelhousing.
Attach JD 244-1 and 244-2 engine lifting eyes to cylinder head and attachenginetoasuitablehoist.
Remove cap screws 1 (tigs. 3 and 4) attaching flywheelhousingtoclutchhousing.
Liftengine outfront by meansof thehoist.
CAUTION: Move engine properly in line with drive shaft and hollow drive shaft until these shafts come loose of the driven disks of the engine dual-stage clutch.
INSTALLATION
Align engine properly with drive shaft and hollow drive shaft and move toward rear Of tractor. Align splines of both shafts with internal threads of driven disks. Also align screw holes of flywheel housing with screw holes of clutch housing. Slide engine evenly toward clutch housing, inserting two dowels of flywheel housing in bores of clutch housing until engine fully contacts clutch housing.
CAUTION: Make sure flywheel housing is flush against clutch housing before tightening screws. Then tighten attaching screws to the specified torque.
Secure dash to flywheel housing.
Connect speed control rod to injection pump.
On tractors with BOSCH or ROTO DIESEL in/ection pump: Attach shut-off cable to pump.
On tractors with ROOSA MASTER model CB iriJectioti pump: Connect shut-off cable to pump.
Model 820 Tractor TM-4212 (Jan-70)
lnsert flexible tube of coolant temperature gauge in cylinder head and tighten retaining screw.
Connect cables to regulator and starting motor and connect cable to oil pressure switch.
Connect cable to signal horn.
Install both batteries.
CAUTION: Connect battery cable to positive poles of batteries.
Lubricate rubber seal of tachometer flexible shaft and attach shaft to clutch housing (see 2, fig. 3). Make sure driving tab of flexible shaft engages in slot of camshaft. Do not tighten excessively to avoid damage to the seal resulting in leakage.
On tractors north starting fluid adapter: Connect starting fluid line to intake manifold.
On tractors with Thermostart aid: Connect Thermostart aid wire to heater in intake manifold.
Attach front of tractor to engine.
CAUTION: Connect ground cables of batteries to negative (-) poles.
NOTE: I f engine has been overhauled, tune up engineasexplained ingroup 20.
REMOVALAND lNSTALLATlON OFCLUTCH HOUSING
NOTE: !Separating and attaching o/ engine and Separate engine from clutch housing as explained clutch housing as uiell as of clx tcJt housing and under ”REMOVING ENGINE”; the tractor front transmission case is explained below. JPhere the end may remain attached to the engine. tractor is to be separated depends on the individual repair operation. I{, e.g., repair worn has to be carried out on the transmission, separation Remove clamps 3 (fig. 2), cap screw 5 and retainer between the clutch housing and the transmission 2 for fastening suction line 1 to front clutch case will besufficient. housing. Disconnect pressure line 4 (fig. 2) at connector.
REMOVAL
Disconnect battery ground cables.
Drain transmission oil.
Disconnect drag link at bell crank.
Insert wood blocks between front axle and front support to prevent front support from tipping sideways.
Safely support rear end of tractor.
Attach tractor front end and engine to a suitable hoist and remove attaching screws 1 between engine and clutch housing (see figs. 3 and 4).
Roll engine and tractor front end away from clutch housing.
Remove oil line of front quick coupler (if provided). Remove right footrest.
Disconnect brake lines at brake valve and cylinder. Remove transmission shield.
Remove clamp of pump pressure line at clutch housing.
Fig. 5 Separating between Glutch Housing and Transmission Case, L.H. Side
1 Attaching screa's
2 Wiring barness
Remove both harnesses to rear fenders at connectors. Disconnect cable at starter safety switch and cables at brake light switch.
Remove transmission shift cover 3 (fig. 5).
Remove transmission oil filter.
Remove cap screws 1 (fig. 5) on both sides and both inner cap screws. Separate clutch housing from transmission case.
Discard seal rings provided between the two housings.
NOTE: Be sure ball and spring provided on some po wersho/f t y pes do not get lost (see section 50, group25).
INSTALLATION
Install new seal rings in clutch housing front facing transmission case.
Slide clutch housing against transmission case.
Slide PTO drive shaft into bore of front PTO shaft or (if front PTO is not provided) into bore of quill. Make sure spring and ball provided on some powershaft types are installed in PTO drive shaft or quill or front powershaft. Align clutch housing with centerline of PTO drive shaft and slide against transmission case. Mesh powershaft gears with splines of hollow PTO drive shaft.
Make sure clutch housing is flush against transmission case before tightening cap screws to the specified torque.
NOTE: If clutch housing has also been separated from engine, assemble a8 explained under ”Installation of Engine.”
Install suction line 1 (fig. 2) in bore of clutch housing and secure by means of screw and retainer. Tighten cap screw to the specified torque. Connect front section of pressure line 4 (fig. 2) to rear section. Then install both pipe clamps 3.
NOT£: For proper sealing of suction line, insert new O-ring inboreo[clutchhousing.
As regards further installation operations reverse removal procedure.
CAUTION: Connect ground cable of batteries to negative (-) poles.
REMOVAL
REMOVAL AND INSTALLATION OF FINAL DRIVES
NOTE. The removal o[ both final driues is explained below. I f onI y one final drive is to be removed, remove only one wheel, wiring harness etc.
Forsafetydisconnect groundcableatbatteries.
Lift up rear of tractor by means of a car jack or hoistandremoverearwheels.
CAUTION: Support transmission safely to prevent tipping of tractor.
Disconnect both rear wiring harnesses at connectors.
Removerearfender.
Disconnect cables at brake warning switch located inleft-handrearaxlehousing.
Disconnect brake lines on bothrear axlehousings.
Disconnect pilot line 5 (fig.6) at dump valve and rockshaft and remove. Remove clamp 7.
Disconnect both pressure lines 3 and 4 at elbows and return line 8 oil manifold 1. On tractors with selective control valve disconnect line to quick coupler at control valve. Remove two cap screws 6 attaching oil manifold 1 to right final drive housing. Lift off oil manifold with pressure control valveandselectivecontrol valve(ifequipped),
Cover connections and exposed openings with plastic plugs or caps to keep out foreignparticles.
Final ‹lrive shaft
Attach tinal drive to hoist. Remove finn dnve attaching screws and pull final drive housing from transmission case. Withdraw housing evenly until final drive shaft gear is no longer in mesh with planetary gearsof finaldrive.
INSTALLATION
NOTE: I f the bra he dish and the ”Roofing” facing mere removed, install bonded two-layer {acing so that the brass- interwoven upper layer faces the brake curface of the transmission case.
Position new gasket between final drive housing andtransmission case.
Attach final drives to transmission case by means of asuitable hoist. Make sure finaldriveshaftgear 2 Pcessuze
indexes with planetary gears and that thedowels areproperlyaligned.
Tighten final drive attaching screws to the specifiedtorque.
Attachoilmanifoldwithpressurecontrolvalve and Install rear fenders. Connect lines of wiring selective control valve (if equipped) to final drive harnesses toconnectors. housing.
Install rear wheels and tighten to the specified torque.
CAUTION: Tighten ground cable to negative (-) poles of batteries.
REMOVAL ANDINSTALLATION OFROCKSHAFT
IMPORTANT: Work on the hydraulic system requires extreme care and cleanliness. Minute dirt or foreign particles, scratches, nicks or burrs may put the hydraulic system out of function. Before removingtherockshaft,checkhydraulicsystemfor leaks.
For safery, disconnect ground cable from batteries.
Remove transmission shield. Disconnect line l (fig. 8)of starter safety switch.
Remove operator's seat. Disconnect both lift links at lift arms.
Loosen clamp of oil return hose S (fig, 8) facing rockshaft andmoveaside.
Disconnect lines of rear quick couplers (if equipped) atselectivecontrolvalves.
Disconnect pilot line 2 (big. 8) at elbow on rockshaft.
Free both rear wiring harnesses.
Move selector lever in position ”L” so that the control linkage roller slides along the cam of the controlarmwhenremoving therockshaft.
Attach engine lifting eye No. JD 244-2 to top of rockshaft housing.
Removerockshaftattachingscrews(seearrowsin fig. 8). Lift rockshaft assemblé off transmission case by means of a hoist. Withdraw oil return line 3 from rockshaft adapter.
Take care not to damage two rear harnesses.
NOTE: A[ter removing rochsha[t, couer transmission case to prevent (oreign particles /rotn [alling into the transmission.
INSTALLATION
Use a new gasket between transmission case and rockshaft. Make sure dowels in transmission case and seal ring of oü înlet passage are installed.
Move selector lever in position ”L” so that the control linkage with roller can be slided over the cam.
