2006 Buell Lightning: Engine 3-7
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COMPRESSION TEST PROCEDURE
Combustion chamber leakage can result in unsatisfactory
engine performance. A compression test can help determine
the source of cylinder leakage. Use CYLINDER COMPRES-
SION GAUGE (Part No. HD-33223-1).
A proper compression test should be performed with the
engine at normal operating temperature when possible. Pro-
ceed as follows:
NOTE
After completing the compression test(s), make sure that the
throttle plate is in the closed position before starting engine.
Engine will start at an extremely high RPM if throttle plate is
left open.
1. Disconnect spark plug wire. Clean around plug base and
remove plug.
2. Connect compression tester to cylinder.
3. With induction module throttle plate in wide open posi-
tion, crank engine continuously through 5-7 full compres-
sion strokes.
4. Note gauge readings at the end of the first and last com-
pression strokes. Record test results.
5. Compression is normal if final readings are 120 psi
(827 kPa) or more.
6. Inject approximately 1/2 oz. (15 ml) of SAE 30 oil into cyl-
inder and repeat the compression test. Readings that are
considerably higher during the second test indicate worn
piston rings.
Cylinder Leakage Test
The cylinder leakage test pinpoints engine problems includ-
ing leaking valves, worn, broken or stuck piston rings and
blown head gaskets. The cylinder leakage tester applies com-
pressed air to the cylinder at a controlled pressure and vol-
ume, and measures the percent of leakage from the cylinder.
Use a CYLINDER LEAKDOWN TESTER (Part No. HD-
35667A) and follow the specific instructions supplied with the
tester.
The following are some general instructions that apply to
Buell motorcycle engines:
1. Run engine until it reaches normal operating tempera-
ture.
2. Stop engine. Clean dirt from around spark plug and
remove spark plug.
3. Remove air cleaner and set induction module throttle
plate in wide open position.
4. Remove timing inspection plug from crankcase.
5. The piston, in cylinder being tested, must be at top dead
center of compression stroke during test.
6. To keep engine from turning over when air pressure is
applied to cylinder, engage transmission in fifth gear and
lock the rear brake.
7. Following the manufacturer’s instructions, perform a cyl-
inder leakage test on the front cylinder. Make a note of
the percent leakdown. Any cylinder with 12% leakdown,
or more, requires further attention.
8. See Table 3-17. Listen for air leaks at induction intake,
exhaust, head gasket and timing inspection hole.
NOTE
If air is escaping through valves, check push rod length.
9. Repeat procedure on rear cylinder.
NOTE
After completing the compression test(s), make sure that the
throttle plate is in the closed position before starting engine.
Engine will start at an extremely high RPM if throttle plate is
left open.
Diagnosing Smoking Engine or High Oil
Consumption
Perform COMPRESSION TEST PROCEDURE or Cylinder
Leakage Test as described previously. If further testing is
needed, remove suspect head(s) and inspect the following:
●
Valve guide seals.
●
Valve guide-to-valve stem clearance.
●
Gasket surface of both head and cylinder.
Table 3-16. Compression Test Results
DIAGNOSIS TEST RESULTS
Ring trouble Compression low on first stroke;
tends to build up on the following
strokes but does not reach normal;
improves considerably when oil is
added to cylinder.
Valve trouble Compression low on first stroke;
does not build up much on follow-
ing strokes; does not improve con-
siderably with the addition of oil.
Head gasket leak Same reaction as valve trouble.
Table 3-17. Air Leakage Test
AIR LEAK LOCATION POSSIBLE CAUSES
Induction module intake Intake valve leaking.
Exhaust pipe Exhaust valve leaking.
Timing inspection hole Piston rings leaking.
Worn or broken piston.
Worn cylinder.
Head gasket Leaking gasket.
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