3-7
Cylinder Leakage Test
The cylinder leakage test pinpoints engine problems including
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-
35667) 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 plugs and
remove spark plugs.
3. Remove air cleaner and set carburetor throttle 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. Listen for air leaks at carburetor intake, exhaust, head
gasket and timing inspection hole. See Table 3-2.
NOTE
If air is escaping through valves, check push rod length.
9. Repeat procedure on rear cylinder.
1
CAUTION
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 or Cylinder Leakdown Test as
described previously. If further testing is needed, remove sus-
pect head(s) and inspect the following:
●
Valve guide seals.
●
Valve guide-to-valve stem clearance.
●
Gasket surface of both head and cylinder.
●
Oil return passages for clogging.
Table 3-2. Air Leakage Test
AIR LEAK LOCATION POSSIBLE CAUSES
Carburetor 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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