Compression Pressure - HYOSUNG COMET 125 Service Manual

2-19 PERIODIC MAINTENANCE

COMPRESSION PRESSURE

The compression of a cylinder is a good indicator of its
internal condition.
The decision to overhaul the cylinder is often based on
the results of a compression test. Periodic maintenance
records kept at your dealership should include compres-
sion reading for each maintenance service.
Compression pressure
Standard
Service limit
Low compression pressure can indicate any of the fol-
lowing conditions :
Excessively worn cylinder wall
Worn-down piston or piston rings
Piston rings stuck in grooves
Poor seating of valves
Ruptured or otherwise defective cylinder head gasket
COMPRESSION TEST PROCEDURE
NOTE
Before testing the engine for compression
pressure, make sure that the cylinder head
bolts are tightened to the specified torque
values and valves are properly adjusted.
Have the engine warmed up by idling before test-
ing.
Be sure that the battery used is in fully-
charged condition.
Remove the parts concerned and test the compression
pressure in the following manner.
Loosen the oil cooler mounting bolts from the frame.
Remove all the spark plug.
Fit the compression gauge in one of the plug holes,
while taking care that the connection is tight.
Keep the throttle grip in full-open position.
Crank the engine a few seconds with the starter, and
record the maximum gauge reading as the compres-
sion of that cylinder.
Compression gauge : 09915 - 64510
2
14~16 kg/cm (at 500 rpm)
2
12 kg/cm (at 500 rpm)
Compression pressure
Standard 11~13 kg/cm
Service limit
2
(at 500 rpm)
2
10 kg/cm (at 500 rpm)