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6. ENGINE TUNING Any owner would like his car to perform well i.e. the engine should give good power and drivability with less fuel consumption. Although these two conditions act contradictory to each other i.e. good power and acceleration would make fuel average drop, we can tune the engine to obtain a respectable level of both. An added advantage would be reduced pollution. In CAF 204 and the first 5 lessons of CAF 205 we studied the procedure of dismantling an engine and reassembling it after due inspection of parts when those that needed repair or replacement were attended to as required. We remounted the engine and test drove the car after engine overhaul to ascertain that engine overhaul had been done to perfection. But it is not always necessary to dismantle the engine for improving its performance. Most of the time certain adjustments are all that is needed. This is called engine tuning. In this lesson we will study the steps of engine tuning.



After going through this lesson, you will be able to tune an engine by performing the following checks and adjustments: i) Tappet clearance adjustments. ii) Ignition system checks and setting. iii) Intake system service.



Proper tuning of the engine is extremely important for it to be able to run efficiently. An inadequately tuned engine leads to: • • • • • •

Lack of power – the engine is not able to carry the load efficiently. Excessive fuel consumption – increases fuel bills. Rough idling – the engine does not run smoothly at slow speeds or when the vehicle is stationary and the engine is running without load. Engine missing – proper sparking does not occur, due to which the engine does not deliver full power. Engine over heating – the operating temperature of the engine goes way above normal. Engine run on – the engine does not stop when the ignition key is tuned off. This implies that some air-fuel mixture continues to be supplied to the engine cylinder which gets burned by the heated exhaust valve or hot spark plug electrodes and the engine continues to run for some time before stopping.

To overcome these problems, the following checks are performed under engine tuning:

• • • • • • • • • •

6.2 • • • • •

Tappet clearance High tension leads Contact breaker points Distributor advance mechanisms Spark plug Air cleaner Dwell angle RPM Timing Pollution level using the CO-HC check.

Removing the Air Cleaner and the Cylinder Head Cover Open the nut on air cleaner cap. Remove the rubber hoses from the air cleaner and remove the air cleaner. Remove the high tension leads of spark plug and PCV hose from the cylinder head cover. Unscrew the bolts of the cylinder head cover and remove the cylinder head cover. Lift one front wheel of the car so that it can be rotated.

This is done to help rotate the crankshaft when adjusting tappet clearance. For a front wheel drive car, the crankshaft can be rotated by rotating one front wheel.


Setting the Tappet Clearance

The tappet clearance should be adjusted every 20, 000 km and additionally at the third service or whenever required. For hot conditions, the recommended tappet clearance is 0.23 – 0.28 mm and for cold conditions, it is 0.13 – 0.18 mm. In order to set the tappet clearance of a cylinder: •

Bring the cylinders in compression one by one so that pressure on the rockers is removed and maximum tappet clearance is available. For this, first rotate the flywheel and bring the T.D.C mark on the flywheel in front of the pointer on the engine block and bring cylinder No. 1 in compression.

Fig. 6.1: Using feeler gauge to adjust tappet clearance.

This can be ascertained by seeing that a little rotation of the crankshaft in either direction causes neither of the two rockers to move the valves to open or close. If the rockers move the cylinder is in exhaust stroke and one complete rotation of the flywheel will bring the valves in compression. Now adjust the tappet clearance of both the valves of cylinder No. 1. For adjusting the tappet clearance: •

Loosen the lock nut and rotate the adjusting screws with the help of a screw driver and set the specified clearance with the help of feeler gauge.

Tighten the lock nut with open end spanner.

After adjusting the tappet clearance of cylinder No. 1, bring cylinder No. 3 and then cylinder No. 2 in compression, one after the other, and adjust the tappet clearance. For a 3 cylinder engine, the flywheel is rotated by 240 degrees and then by another 240 degrees and cylinder No. 3 and No. 2 are brought in compression successively and the tappet clearance adjusted as described above.


Tightening the Cylinder Head Bolts

The cylinder head bolts should be tightened every 10,000 km by following the specified sequence: • •

Tighten cylinder head bolts to a torque of 5.5 – 6.0 mkg. Fix the cylinder head cover with the help of bolts torqued at 0.4 – 0.5 mkg.

Self-check Questions 1. List the defects due to an improperly tuned engine. 2. List the items checked and adjusted during engine tuning. 3. The crankshaft can be rotated by rotating the front wheel of the car only if _________________. 4. For hot conditions, the recommended tappet clearance is _____________. 5. Tappet clearance is greater in hot condition because _________________ _________________________________________. 6. Tappet clearance of cylinder No. 1 is checked when that cylinder is in ______________ and the _____________________________________. 7. TDC mark on the flywheel will be aligned with the pointer on the block when the cylinder is in _____________ and ______________. 8. How is it ascertained that the cylinder is in compression when the TDC mark on flywheel is aligned to the pointer on the block? 9. If the cylinder is not in compression when the TDC mark is in position, how do you bring it in compression? 10. How many degrees of rotation of the flywheel are required to bring successively cylinder No. 3 & 2 in compression? 11. Cylinder head bolts are tightened to a torque of __________________

6.5 • •

Checking the High Tension Leads Check the high tension leads, distributor cap electrodes and terminals, ignition wiring etc. for connection, condition and wear. Replace if necessary. Clean the electrodes of the distributor cap.

6.6 • •

Checking the Contact Breaker Points Clean the contact breaker points with an oil stone or a soft file. For checking or adjusting the contact breaker point gap, rotate the crankshaft to get maximum gap at the contact breaker point.

The contact breaker point gap for a Lucas distributor is specified to be between 0.35 and 0.40 mm. •

• • •

Apply a thin layer of grease to the distributor shaft lobe and on the breaker arm heel. Replace contact breaker assembly if Fig. 6.2: Contact breaker. needed. Fix the distributor cap. Fix the centre high tension lead from the cap to the coil.

The contact breaker assembly should be replaced every 10, 000 km, or earlier if required.


Checking the Distributor Advance Mechanisms

In order to check the centrifugal advance mechanism with vacuum pipe disconnected from carburetor, check the ignition advance with rising engine speed. The rise in advance with engine rpm should be as per specification. To check the vacuum advance, read the timing in terms of crank angle when the engine is running at 3,500 rpm. With the engine running, pull the vacuum pipe out from the carburetor and read the timing again. The difference between these two readings is the advance due to the vacuum advancer.


Inspecting and Cleaning the Spark Plug The condition of an engine can be known by looking at the spark plug.

• •

Observe the surface of spark plug electrodes and insulator before cleaning the spark plug. Clean each spark plug in a spark plug cleaner and tester.

The spark plug cleaner and tester sends a high pressure abrasive blast towards the spark plug electrodes and insulator, removing deposits of oil, carbon, soot etc. The abrasive is then cleaned off with a high pressure air blast by throwing the lever to the other side.

Fig. 6.3: Spark plug cleaner and tester.

• • • •

Using a spark plug tool (wire gauge), adjust the spark plug gap between 0.7 – 0.8 mm. Check the strength of the spark using a new plug as a reference. Replace if required. Re-install the spark plugs after cleaning them. Fix the high tension leads.

The normal interval for replacing a spark plug is 10, 000 km. If a spark plug cleaner and tester is not available, the spark plug can be cleaned with a wire and emery paper and then washed in petrol.


Cleaning the Air Cleaner

The air cleaner element should be cleaned in all periodic maintenance checks. •

Open the air cleaner case by removing the clips and remove the air cleaner element. Clean the element by blowing compressed air from the inside.

You will be able to see dust being blown out. The compressed air should never be blown from the outside of the element as this will lead to the dust particles being embedded in the element. • • • • • •

Fig. 6.4: Using compressed air to clean the air cleaner element.

Clean the air cleaner case and cap and reinstall the element. While fixing the cap, match the arrow mark on cap with the mark on the case. Clamp the cap onto the case with the clips. Mount the air cleaner on to the carburetor and clamp it down with nut. Fix the other nut over the air cleaner bracket. Fix the rubber hose.

Self-check Questions 12. Contact breaker points are cleaned with an __________ or a _________ 13. For a Lucas distributor, CB gap should be between ________________. 14. Centrifugal advance mechanism is checked with vacuum pipe of vacuum advancer connected to carburetor. State whether True/False. 15. Spark plug gap is set between ____________. 16. Spark plug gap should not be set with feeler gauge. State whether True/False. 17. Air cleaner element is cleaned by ______________________________

6.10 Adjusting the Dwell Angle, RPM and Ignition Timing 6.10.1 Preliminary Checks Before the dwell angle, RPM, and ignition timing are adjusted, a number of preliminary checks are required to be carried out. It should be ensured that: • • • • •

The coolant temperature has stabilized, with the needle showing a deflection of 1/3 to 1/2 of the scale. The choke valve is in full open position. All the accessories such as air conditioner, stereo etc. are out of service. The air cleaner is in good condition. The engine tappet clearances are as per specifications

6.10.2 Dwell Angle Following is the sequence of steps to measure the dwell angle of an engine that is running: •

• •

Connect the positive clamp of the tach-dwell meter to the distributor contact breaker point terminal and the negative clamp to the negative or ground of the battery. Throw the switch of the analyzer to dwell and start the engine. Read the dwell angle on the scale corresponding to the number of cylinders in the engine.

Fig. 6.5: Measuring the dwell angle using Tach-Dwell Analyzer.

Fig. 6.5 shows a reading of 60° on the dwell angle scale for a three-cylinder engine. Specifications require this value to be 62±3°. Hence it is within specification. If the dwell angle does not comply with the specifications, the contact breaker point gap needs to be adjusted to get the correct dwell. For this: • • • •

Remove the distributor cap and the rotor. Loosen the fixed point and set the gap. Check the gap with feeler gauge. Fix the rotor and the distributor cap.

The dwell angle is then rechecked and the procedure repeated if the value achieved is not within the specified range. 6.10.3 RPM • •

Throw the switch to read RPM. Read the RPM on the scale corresponding to the number of cylinders in the engine.

The idle RPM of the engine should be 900 ± 50 RPM. If required, use the idle speed adjustment screw to bring idle speed within specifications. 6.10.4 Ignition Timing • •

Remove the inspection cover from the transmission case. Connect the timing light to the high tension lead of spark plug No. 1 and check the timing with a stroboscopic light.

The (yellow) mark on the flywheel should seem stationary and it should be in front of the pointer on the engine block. If the timing is not proper, that is, if the (yellow) mark is not in front of the pointer: •

Loosen the distributorhousing clamp bolt and rotate the housing to adjust the timing. Re-check the timing and tighten the bolt.

Fig. 6.6(b) shows the timing mark exactly in front of the pointer. The idle RPM should be rechecked and readjusted if required.

Fig. 6.6: Using stroboscopic light to check the ignition timing.

The preliminary checks are not essential for checking the dwell angle alone. Due to a close interrelation between dwell angle, RPM, and the ignition timing, the adjustment should always be done in the sequence described above, that is, first the dwell angle, then the RPM and finally the engine timing check. The RPM needs to be rechecked after the ignition timing check.

6.11 Checking the Pollution Level The engine is finally checked for exhaust emissions. The CO-HC values of engine exhaust emission should be within the specified limits. The percentage CO and HC ppm (parts per million) should be as per norms*. If these limits are exceeded, it consequences are – higher fuel consumption, higher carbon deposits in engine, loss of engine power and greater pollution.

Fig. 6.7: Four gas analyzer.

Fig. 6.7 shows a four gas analyzer. To use it, put the machine on and wait for at least fifteen minutes before it heats up. Then, start the engine and put the probe in the tail pipe. The readings of CO, CO2, HC and O2 can be read on the electronic display.

S. No. 1. 2.

Table 6.1 Permissible Emission Values Vehicle type Catalytic converter CO Metro Present 0.5 to 1.5 % Non-metro Absent 1.0 to 2.0 %

HC 1200 ppm 1200 ppm

If the four gas analyzer or the CO-HC analyzer is not available, proceed as follows: • • •

Adjust the idle speed to 1, 000 RPM using the idle speed adjusting screw. Adjust the idle mixture screw to get the highest engine speed. Repeat both the steps above: o Readjust the idle speed to 1, 000 RPM using idle speed screw. o Readjust idle speed to 900 ± 50 rpm by closing the mixture screw.

Self-check Questions 18. List the preliminary checks to do before adjusting dwell, rpm, and timing. 19. Dwell for Maruti 800 engine is __________. 20. Dwell can be increased by ______________________. 21. Idle RPM of M 800 engine is ______________. 22. Idle rpm is adjusted by rotating the ________________________. 23. Timing light is connected to the ___________________________. 24. Ignition timing is adjusted by ________________________ and ______________________. 25. Preliminary checks are not essential for checking only _____________. 26. Give the sequence in which dwell, rpm, and timing are checked. 27. _________ needs to be rechecked after the ignition timing check. 28. Higher CO-HC values result in ________________, ______________, _________________ and __________________.

6.12 Activity 1. If you own a vehicle (2- or 4- wheeler), try doing the following by yourself at homei. Cleaning the air cleaner ii. Cleaning and adjusting the spark plug gap

6.13 Summing Up For tuning the engine, we follow a definite sequence and make necessary adjustments and settings in the engine in order to obtain optimum engine performance. If you adhere to these procedures, you will deliver a perfectly tuned engine with a good fuel average, good power output, low pollution and win satisfied customers.

The procedures described in this lesson pertain to a carbureted engine. Now in the next lesson we will study how an MPFI engine is tuned.

6.14 Possible Answers to Self-check Questions 1. Lack of power, Excessive fuel consumption, Rough idling, Engine missing, Engine over heating, Engine run on 2. Tappet clearance, High tension leads, Contact breaker points, Distributor advance mechanisms, Spark plug, Air cleaner, Dwell angle, RPM, Timing, Pollution level using the CO-HC check 3. gear is engaged 4. 0.23 – 0.28 mm 5. the cylinder head, which is of Aluminium, expands more than the valve and the rocker shaft moves upward 6. compression, TDC mark on the flywheel is aligned with the pointer on the block 7. compression, exhaust 8. a little rotation of the crankshaft in either direction causes neither of the two rockers to move 9. by one complete rotation of the flywheel 10. 240O 11. 0.4 – 0.5 mkg 12. oil stone, soft file 13. 0.35 and 0.40 mm 14. False 15. 0.7 – 0.8 mm 16. True 17. blowing compressed air from the inside 18. The coolant temperature has stabilized, with the needle showing a deflection of 1/3 to 1/2 of the scale; The choke valve is in full open position; All the accessories are out of service; The air cleaner is in good condition; The engine tappet clearances are as per specifications 19. 62 ± 3O 20. decreasing the CB point gap 21. 900 ± 50 rpm 22. idle speed adjustment screw 23. high tension lead of spark plug No. 1 24. loosening the distributor-housing clamp bolt, rotating the housing 25. dwell angle 26. Adjustment should always be done in the sequence, that is, first the dwell angle, then RPM and finally the ignition timing check. 27. rpm 28. higher fuel consumption, higher carbon deposits in engine, loss of engine power, and greater pollution

6.15 Terminal Questions 1. Describe the procedure of setting the tappet clearance. 2. How would you check the advance mechanisms for proper functioning?

3. How would you deduce the health of an engine by looking at its spark plug? 4. How are dwell, rpm, and timing checked and adjusted? What preliminary checks need to be performed before checking? 5. If CO-HC analyzer is not available how would set the mixture?

6.16 References 1. Service Training Handbook, Part 1 – Basic Course, Maruti Udyog Ltd.

6.17 Suggested Further Reading 1. Lewis, G., 1986. Engine Service, 2nd Edition. Prentice-Hall, New Jersey. 2. Chhikara, A., 1999. Automobile Engineering, Vol 3: Automotive Marketing & Workshop Techniques. Satya Prakashan, New Delhi.

6.18 Glossary CO-HC check

Checking of CO and HC percentage by volume in exhaust gases. These should be within limit if the car is to get a pollution under control (PUC) certificate.


Degrees of ignition cam rotation when the distributor contact breaker points remain closed. At this time the coil builds up.

Engine missing

Failure of an explosion to occur in one or more cylinders while engine is running. This may be a continuous or intermittent failure.

Engine run on

Engine does not stop running even when the ignition is switched off due to a hot spot in the cylinder, namely heated spark plug or exhaust valve, provided mixture continues to enter.

High tension lead

The wire which goes from the ignition coil to the distributor and the wires which go from the distributor to each of the spark plugs have to convey high voltage but they carry very little current.

Ignition advance

The extent to which the ignition spark is made to occur earlier than set, depending on engine speed etc. The opposite is ignition retard.


6.0 Objectives 6.1 Introduction Proper tuning of the engine is extremely important for it to be able to run efficiently. An inadequately tun...


6.0 Objectives 6.1 Introduction Proper tuning of the engine is extremely important for it to be able to run efficiently. An inadequately tun...