Lecture 3, 4: Unit 6: PE 312, Automobile Engineering: tuning up on engine,

fault finding and their remedies

The engine tuning:

The engine tuning is a procedure to bring an engine in good mechanical

condition to operate at peak efficiency and power. Every unit of the engine is
made to function at its best.

 The engine tuning is more frequently required in modern high

compression engines which are more sensitive to variations from
specifications than the earlier slow speed, low output engines
 Often during the engine tuning, several conditions will be found which
must be corrected to restore the engine to like new condition.

Tuning Procedure:

Below is given a typical tuning or tune up procedure (some of the checks

are not related to the engine but should be done for the safety purpose):

1. After making the spark plugs loose, start the engine to blow out carbon
and dirt, shut off engine and remove plugs.

2. Test engine compression. If the compression ratio is not upto

secifications, perform engine services that will eliminate the trouble. If
the compression is in order re-install the spark plugs.

3 Remove distributor cap. Clean it, and visually check it for carbon
tracks, chips and corroded terminals. Replace it, if it is not in good
condition.

4. Clean and inspect rotor. Replace it if it is not in good condition.

5. Inspect the high tension leads. If they have cracks, or frayed insulation
or wires are damaged, replace them.

6. Check distributor centrifugal advance.

7. Test the vacuum advance.

8. Check distributor contact points and clean them. Read just the point
opening.
9. Re-install distributor cap and replace wiring

10. Check battery state of charge, water and hold-down clamps.

11. Check battery cables for damage, corrosion and loose connections and
make necessary corrections.

12. If the battery has been overcharged or undercharged, check the

alternator and regulator.

13. Check drive belts and tighten or replace them as required.

14. Check the condition of the manifold heat control valve, making sure
that it is free to operate.

15. Check the intake manifold bolts for tightness to proper specifications.
Even a slight leak will reduce engine performance.

16. Check fuel lines for tight connections and kinks, beads or leaks.

17. Check the cooling system for leaks, weak or collapsed hoses, correct
coolant level and antifreeze protection.

18. Check and adjust the accelerator linkage, if necessary.

19. Check crankcase ventilation system

20. Check intake manifold and air injection system.

21. Remove carburetor, air cleaner, and check choke valve to make sure
choke is working normally. Clean or replace air filter element, if
necessary.

22. Check and adjust contact point dwell and ignition timing.

23. Adjust idle speed and mixture to specifications.

24. Check the doorjamb sticker to see if lubrication is required.

25. Check the working lights and horn. Check headlight adjustment.

26. Check steering system for looseness and ease of action.

27. Check suspension system and shock absorbers for looseness,

excessive play and wear.
 28. Check front wheels and ball joints for excessive wear or loose
bearings.

29. Other tests that can be done include:

(i) Cylinder balance test to find a weak cylinder;

(ii) Cranking motor operation

(iii) Conditions of ignition coil and condenser;

(iv) Tightness of mounting bolts;

(v) Oil level in engine

(vi) Air pressure in tyres;

(vii) Condition of tyres

(viii) Efficiency of the brakes.

 Engine vibrations:
The engine vibrations may be due to the following possible causes

(i) Too stiff engine supports.

(ii) Misaligned engine-transmission-propeller shaft.

(iii) Crankshaft out of balance.

(iv) Clutch out of balance.

(v) Defective carburetion

(vi) Defective ignition.

(vii) Maladjusted valves.

(viii) Connecting rods and pistons of unequal weight.

Crankshaft thumping. "Crankshaft thumping" means metallic, heavy and dull

knocks which increase in frequency by the increase of rotational speed.

Most commonly, thumping is caused by excessive clearance at one or

more main bearings. An excessive axial play of crankshaft gives a
sharper and higher noise at irregular intervals
 Following are the causes of crankshaft thumping;

(i) Excessive main bearing clearance.

(ii) Excessive crankshaft axial play

(iii) Crankshaft out of balance.

(iv) Out-of-round or ovalized bearings.

(v) Loose flywheel.

(vi) Low oil pressure.

(vii) Insufficient lubrication.

 Piston noise. The piston noise, usually the "thumping," is due to the
oscillation of piston in barred.

It is heard as a dull and low sound.

It is more evident at low r.p.m. rates under load.

If the noise is slight when the engine is cold and disappear as the
engine warms up, pistons do not require replacement.

 Piston pin noise. The piston pin noise is the sharp and metallic knock
easily heard when engine idles.

The various causes of piston noise are

(i) Excessive clearance between pin and piston boss bore.

(ii) Excessive clearance between pin and bush.

(iii) Bush loose in connecting rod small end.

Connecting rod noise:

The noise due to connecting rod is usually more intense than that
originated by main bearings.

The noise is more evident with engine idling and transmission in neutral
and becomes high as the engine speed increases.

The following are the possible causes of connecting rod noise

 (i) Misaligned connecting rod.

(ii) Excessive big end bearing clearance.

(iii) Ovalized or tapered crankpins.

(iv) Low oil pressure.

(v) Insufficient lubrication.

Valve and tappet noise:

The valve and tappet give ‘clicking' noise. Its frequency is lower
than that of any other noise of engine. If only one or two valves are
noisy, the sound will be intermittent, otherwise it may be
continuous.

The following are the possible cauuses of valve and tappet noise :

(i) Broken valve springs.

(ii) Excessive tappet clearance.

(iii) Excessive push rod-to-guide clearance.

(iv) Excessive wear of one or more cams of camshaft.

(v) Worn thread of set screws.

(vi) Excessive valve stem-to-guide bore clearance.

Oil low pressure:

Normal oil pressure in a new or overhauled engine must be 2.5 to 3

bar. No pressure at all indicates a defective pump or oil leakage.

 ROAD TEST
Engine:
Ease of starting Oil pressure when hot
Idling Acceleration
Maximum speed Fuel Consumption
Oil consumption Engine temperature
Exhaust : noise ; restriction
Blue smoke
General noise Fumes
Clutch:
Slip Fierceness
Spinning Unusual noise
Gear box:
Noisy gears Synchromesh operation
Pre-selector operation Vibration on gear lever
Gears jumping out of mesh
Propeller shaft:
Vibration Noise
Back axle:
Noise on drive Noise on over run
Noise on over-run
Instruments:
Functioning Accuracy
Suspension:
Comfort Roll on corners
Brakes:
Power Balance
Smoothness Judder or squeal
Binding
Example:
Sl Troubles Causes Remedies
No.
1. Engine does not start (i) No fuel in tank. (i) Fill Fuel
(ii) Choked fuel (ii) Clean and clear
supply. the obstruction in
(iii) Loose or leaking fuel line.
fuel line connection. (iii) Tighten loose
(iv) Sticking needle connection or
valve in carburetor. move leakage.
(v)Flooded (iv) Release.
carburetor.
(v) Release sticking
(vi) Ignition on.
float.
(vii) Spark plugs
Repair or replace
dirty or bridged
punt float.
by soot or oil.
Repair or replace
(viii) Damaged defective needle
spark plugs. valve.
(ix) Loose or dirty Check and adjust
battery terminals. float level
(x) Discharged Open choke valve if
battery. close.
(xi) Loose or Remove liquid petrol
leaking H.T. lead
From induction
from ignition coil. manifold.
(xii) Defective or (vi) Switch on
missing rotor. ignition/replace
(xiii) Dirty, burned defective switch.
C.B. points.
(vii) Clean, check
(xiv) C.B. points not and adjust gap.
opening.
(viii) Replace.
(xv) Defective
(ix) Clean and
ignition coil or con-
tighten battery
denser.
terminal.
(x) Recharge.
(xi) Tighten or
replace
(xii) Replace/fix on
rotor.
 (xiii) Clean or
replace.
(xiv) Adjust gap.
Repair or replace
defective C.B. arm
(xv) Replace.

*For more troubles and their remedies Refer some good book on I C
Engine