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ENGINE DIVISION SERVICE MANUAL
TM 5-4210-230-14&P-1
ADDENDUM NO. 2
COMPRESSION AND CYLINDER LEAKAGE TESTS
Compression Test
The compression test is performed to measure
cylinder compression pressure. The absolute value of
compression pressure is significant but cylinder to cylinder
variation is even more important. Allowable variation from
cylinder to cylinder is:
Lowest cylinder pressure must not be less than 75% of
the highest cylinder pressure. Greater variation from
cylinder to cylinder indicates need for mechanical repair
which should be carried out in accordance with the
appropriate CTS* ENGINE section. Perform engine
compression test as follows:
1. Run engine until normal operating temperature is reached.
2. Remove all spark plugs and install compression gauge in
No. 1 cylinder.
3. Remove coil secondary wire from distributor cap and
ground it to prevent arcing. Block carburetor throttle open.
4. Connect remote starter switch to starter solenoid or have
an assistant available to crank engine.
5. Crank the engine for at least 5 compression strokes or until
compression gauge reaches its highest value. Note the
number of compression strokes required to reach highest
value. Record compression pressure and number of
strokes.
6. Repeat the test for each of the other cylinders.
7. If one or more cylinders produce a low reading, squirt
about a tablespoon of engine oil into low reading cylinders.
Repeat compression test on those cylinders.
a. If compression pressure improves significantly, worn
or broken piston rings are at fault.'
b. If compression pressure does not improve, valves are
at fault or if two adjacent cylinders have low
compression, a leaking cylinder head gasket may be
the cause.
Cylinder Leakage Test (CLT)
The cylinder leakage test is supplemental to the
compression test and can provide diagnostic information as to
the cause for loss of compression. The CLT can identify
leakage past intake or exhaust valves, leaking cylinder head
gasket, worn or broken piston rings, or other cause for loss of
compression.
Perform cylinder leakage test as follows.
1. Run engine until normal operating temperature is reached.
2. Remove spark plugs from engine.
3. Remove air cleaner and block carburetor throttle open.
4. Remove oil filler cap.
5. Remove radiator cap. If coolant is low, fill to prescribed
level.
6. Turn crankshaft until No. 1 cylinder is at top dead center
on compression stroke.
7. Connect and calibrate cylinder leakage tester in
accordance with manufacturer's instructions.
8. Record cylinder leakage (usually in percent) and determine
source of leakage by listening for air escaping through
carburetor, exhaust system, or crankcase (oil filler tube).
Look for air bubbles in coolant (radiator top tank).
9. Carefully turn crankshaft in normal direction of rotation
until the next cylinder in firing order sequence is at top
dead center. Connect CLT to that cylinder and repeat
test.
10. Repeat test for each consecutive cylinder in firing order
sequence.
When the cause for loss of compression has been
identified, repair engine in accordance with the appropriate
*See CTS or CGES
CGES-215 - Page 46
PRINTED IN UNITED STATES OF AMERICA
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