TOPIC 5. ENGINE TUNE-UP

TM 10-3930-644-14&P

TOPIC 5. ENGINE TUNE-UP

Engine tune-up is an orderly process of restoring the

D. CYLINDER LEAK TEST

engine to satisfactory performance.

in addition,

preventive maintenance and corrective operations

Perform cylinder leak test by removing one spark plug at

should be accomplished so that engine serviceability will

a time, (ensure high tension coil wire is disconnected)

be unimpaired.

The following outlines simple

and insert leak tester in spark plug well; build up

adjustments, inspections and tests, and should be

pressure as recommended. Record reading and record

performed in the order given.

any appreciable pressure fall-off. If pressure loss is

indicated, check cylinder head for hissing noise, (head

A. BATTERY SERVICEABILITY

gasket), carburetor, (intake valve), exhaust pipe and

manifold, (exhaust valve), and oil fill tube, (piston rings).

Be sure that battery tray is clean and level and that

Check all cylinders in like manner and repair as required.

battery hold-down clamps are snug. Ensure battery

posts and cables are clean and free of corrosion. Apply

E. IGNITION TIMING

a light coat of grease to terminals.

The ignition system consists of the battery, ignition coil,

Make certain that battery cables are not reversed.

distributor, condenser, spark plugs, alternator and high

Connect negative to ground, positive to starter solenoid.

and low tension wiring.

The system produces and delivers high voltage surges

Check electrolyte level regularly, and add clean water if

of up to 20,000 volts to the correct plug, at the correct

necessary, but do not overfill Keep battery clean and

intervals in exact time with the engines' sequential

wash with baking soda solution if corrosion is evident.

mechanism.

Do not allow soda solution to enter cells. Inspect cables,

To maintain efficient, economical engine operation, the

clamps and hold-down bracket regularly. Replace if

electrical and mechanical sequencing must be exactly

necessary.

matched or timed.

The distributor warrants particular attention in relation to

B. INSPECT AND ADJUST SPARK PLUGS

this sequencing and the following procedure is

recommended as a comprehensive alignment:

Blow dirt from spark wells, then remove plugs Clean

spark plugs. Inspect for cracked or broken insulators,

1. At 500 hour intervals, remove the distributor cap

broken electrodes or excessive carbon deposits.

and dust seal and inspect contact points, rotor

Replace any faulty plugs. Adjust gap to specifications.

and cap for evidence of wear, arcing, cracks or

corrosion. Repair or replace as required. Label

Test cylinder compression before reinstalling plugs.

spark plug wires for correct installation.

C. COMPRESSION

2. Pitted or burned points must be re- placed.

Warm up engine to operating temperature. Blow dirt out

NOTE

of pockets around spark plugs. Remove all plugs and

If points are burned or pitted, replace

insert compression gauge in first spark plug hole and

the condenser, too.

hold it firmly. Crank engine until the highest gauge

reading is obtained. (Approximately four compression

3. The distributor may be removed for servici ng or

strokes.)

replacement at this time.

Check all cylinders in this manner. If readings are low in

NOTE

two adjacent cylinders, a blown head gasket is indicated.

When the distributor is removed and

If readings are low and vary widely (more than 10 PSI),

replaced, the original position of the

pressure is being lost either at the pistons, rings or

distributor must be observed. Refer

valves. To determine where pressure loss is occurring,

to ELECTRICAL SYSTEM MANUAL

insert about one tablespoon of SAE 30 engine oil

for proper removal and replacement

through the spark plug hole. Take a new reading. If this

procedures.

reading is higher than the initial reading, the piston rings

are faulty. If reading is the same as the initial reading,

the valves may be leaking or the cylinder head gasket is

damaged.

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