Compression Pressure - HYOSUNG 2010 ST7 Service Manual

2-27 PERIODIC MAINTENANCE

COMPRESSION PRESSURE

The compression pressure reading 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 pressure reading for each maintenance service.
Compression pressure
Standard
Service limit
Difference
COMPRESSION TEST PROCEDURE
NOTE
Before testing the engine for compression
pressure, make sure that the cylinder head
bolts are tightened to the specified torque val-
ues and valves are properly adjusted.
Have the engine warmed up by idling before
testing.
Be sure that the battery used is in fully-charged
condition.
Remove the parts concerned and test the compres-
sion pressure in the following manner.
Loosen the radiator cover mounting bolts from the
frame.
Loosen the radiator mounting bolts.
WARNING
The hot radiator and the hot engine can burn you.
Wait until the radiator and the engine are cool
enough to touch.
CAUTION
Be careful not to damage the radiator fins.
Do not extract the radiator hose.
Remove the seat and fule tank. (Refer to page 5-2)
Remove all the spark plugs.
Fit the compression gauge in one of the plug holes,
while taking care that the connection is tightened.
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 cylinder.
Compression gauge : 09915-64511
2
14 kgf/cm (at 500 rpm)
2
12 kgf/cm (at 500 rpm)
2
2 kgf/cm (at 500 rpm)
Low compression pressure can indicate some of the
following 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
NOTE
When the compression pressure goes below
specification, check the engine for conditions list-
ed above.
Overhaul the engine in the following cases :
Compression pressure in one of the cylinder is less
than 12 kgf/㎠.
The difference in compression pressure between two
cylinder is more than 2 kgf/㎠.
All compression pressure readings are nearly 12 kg/㎠
even when they measure more than 12 kgf/㎠.