Service Manual

ENGINE TOP END 5-7
Cylinder Head
Compression Measurement
•
Before measuring compression, do the following.
○
Be sure the battery is fully charged.
○
Thoroughly warm up the engine so that engine oil be-
tween the piston and cylinder wall will help sealing the
compression as it does during normal running.
○
Stop the engine.
•
Disconnect the spark plug caps of each cylinder and re-
move the spark plugs.
•
Attach the compression gauge assembly firmly into one
plug hole.
Special Tools - Compression Gauge, 20 kgf/cm²: 57001-221
[A]
Compression Gauge Adapter, M14 × 1.25:
57001-1159 [B]
•
Ground the spark plugs to the engine.
WARNING
To avoid fire, do not ground the spark plugs in prox-
imity to the plug holes. Keep the plugs as far away
as possible from the plug holes.
•
Open the throttle fully. Run the engine by turning the en-
gine switch key several times until the compression gauge
stops rising. Read the highest compression value.
Cylinder Compression (MIN) 440 kPa (64 psi) @ Engine
Oil Temperature 50 ∼ 60°C (122 ∼ 140°F), Cranking
Speed 450 rpm/5 Seconds
•
Repeat the measurement on the other cylinder.
If the compression 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 and/or worn piston oil rings. This may be
indicated by white exhaust smoke.
If the cylinder compression is lower than the (MIN), check
the following.
1. Gas leakage around the cylinder head - replace the
damaged gasket with a new one 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.