CYLINDER HEAD/VALVES
9-6
CYLINDER COMPRESSION TEST
Warm up the engine to normal operating tempera-
ture.
Stop the engine and remove the spark plug cap and
spark plug (page 4-8).
Install a compression gauge into the spark plug
hole.
Open the throttle all the way and crank the engine
with the starter until the gauge reading stops rising.
The maximum reading is usually reached within 4 –
7 seconds.
If compression is high, it indicates that auto decom-
pression system problem or carbon deposits have
accumulated on the combustion chamber and/or
the piston crown.
If compression is low, pour 3 – 5 cc (0.1 – 0.2 oz) of
clean engine oil into the cylinder through the spark
plug hole and recheck the compression.
If the compression increases from the previous
value, check the cylinder, piston and piston rings.
• Leaking cylinder head gasket
• Worn piston ring
• Worn cylinder and piston
If compression is the same as the previous value,
check the valves for leakage.
CYLINDER HEAD COVER
REMOVAL
Remove the front body cover (page 3-9).
Disconnect the crankcase breather hose from the
cylinder head cover.
Remove the fuel hose clamp bolt.
Remove the special bolts and cylinder head cover.
INSTALLATION
Make sure the cylinder head cover rubber seal is in
good condition and replace it if necessary.
Install the rubber seal into the grooves on the cylin-
der head cover.
To avoid discharging
the battery, do not
operate the starter
motor for more
than 7 seconds.
COMPRESSION PRESSURE:
1,098 kPa (11.2 kg/cm
2
, 159 psi) at 550 rpm
CYLINDER
HEAD COVER
SPECIAL BOLTS
BREATHER HOSE
FUEL HOSE
CLAMP BOLT
RUBBER SEAL
CYLINDER HEAD COVER
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