Engine; Adjustment/Testing; General; Compression Test - Buell XB 2008 Series Service Manual

ENGINE

ADJUSTMENT/TESTING

General

When an engine needs repair, it is not always possible to
determine definitely beforehand whether repair is possible with
only cylinder head, cylinder and piston disassembled or whether
complete engine disassembly is required for crankcase repair.
Most commonly, only cylinder head and cylinder repair is
needed (valves, rings, piston, etc.) and it is recommended
procedure to service these units first, allowing engine crankcase
to remain in frame.
See 3.3 ENGINE ROTATION FOR SERVICE
cycle for removal of cylinder head, cylinder, and piston.
After disassembling "upper end" only, it may be found that
crankcase repair is necessary. In this situation, remove the
engine crankcase from the chassis.
If engine is removed from chassis, do not lay engine on primary
side. Placing engine on primary side will damage clutch cable
end fitting. If fitting is damaged, clutch cable must be replaced.
See 1.19 TROUBLESHOOTING
a need for engine repair are often misleading, but generally, if
more than one symptom is present, possible causes can be
narrowed down to make at least a partial diagnosis. An above-
normal consumption of oil, for example, could be caused by
several mechanical faults. However, when accompanied by
blue-gray exhaust smoke and low engine compression, it
indicates the piston rings need replacing. Low compression by
itself, however, may indicate improperly seated valves, in
addition to or in lieu of worn piston rings.
Most frequently, valves, rings, pins, bushings, and bearings
need attention at about the same time. If the possible causes
can be narrowed down through the process of elimination to
indicate any one of the above components is worn, it is best
to give attention to all of the cylinder head and cylinder parts.

COMPRESSION TEST

PART NUMBER
HD-33223-1 CYLINDER COMPRESSION GAUGE
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. Proceed as
follows:
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 spark plug.
2. Connect compression tester to cylinder.
to strip motor-
NOTE
section. Symptoms indicating
TOOL NAME
NOTE
3. With throttle body throttle plate in wide open position, crank
engine continuously through 5-7 full compression 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
cylinder and repeat the compression test. Readings that
are considerably higher during the second test indicate
worn piston rings.
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 consid-
erably when oil is added to cylinder.
Valve trouble Compression low on first stroke; does
not build up much on following strokes;
does not improve considerably with the
addition of oil.
Head gasket leak Same reaction as valve trouble.

CYLINDER LEAKAGE TEST

PART NUMBER
HD-35667A CYLINDER LEAKDOWN TESTER
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 compressed
air to the cylinder at a controlled pressure and volume, and
measures the percent of leakage from the cylinder.
Use a CYLINDER LEAKDOWN TESTER (Part No. HD-35667A)
and follow the 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 temperature.
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. The piston, in cylinder being tested, must be at top dead
center of compression stroke during test.
5. To keep engine from turning over when air pressure is
applied to cylinder, engage transmission in fifth gear and
lock the rear brake.
6. 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.
7. Refer to Table 3-17. Listen for air leaks at induction intake,
exhaust and head gasket.
3.2
TOOL NAME
2008 XB Service: Engine 3-5