Service Manual

5-6 ENGINE TOP END
Cylinder Head
Compression Measurement
•
Before measuring compression, do the following.
Thoroughly warm up the engine so that engine oil be-
tween the piston and cylinder wall will help seal compres-
sion as it does during norm al running.
Stop the engine.
•
Disconnect the spark plug cap of and remove the spark
plug.
•
Attach the compression gauge assembly firmly into spark
plug hole.
Special Tools - Compression Gauge: 57001–221 [A]
Compression Gauge Adapter: 57001–1159
[B]
•
Ground the spark plug to the engine.
WARNING
To avoid fire, do not ground the spark plug in prox-
imity to the plug hole. Keep the plug as far away as
possible from the plug hole.
•
With the throttle fully open, turn engine over with the recoil
starter knob several times until the compression gauge
stops rising, the compression is the highest reading ob-
tainable.
Cylinder Compression (MIN)196 kPa (28.4 psi)
If the compressi on is higher than the specified value, the
piston rings, cylinder and valves are probably in good con-
dition.
If the compression is too high, check the following:
1. Carbon build-up on the piston crown and cylinder head
- clean off any carbon on the piston crown and cylinder
head.
2. Cylinder head gasket - use only the proper gasket. The
use of a gasket of incorrect thickness will change the
compression.
3. Valve guides and piston rings - rapid carbon accumula-
tion in the combustion chamber may be caused by worn
valve guides or worn piston oil ring. This may be indi-
cated by white exhaust smoke.
If cylinder compression is lower than the (MIN), check the
following:
1. Gas leakage around the cylinder head - replace the
damaged gasket and check and check the cylinder head
warp.
2. Condition of the valve seating.
3. Valve clearance.
4. Piston/cylinder wear, piston seizure.
5. Piston ring, piston ring groove.