Inspection Of Compression Pressure - TOHATSU MFS25 Service Manual

Maintenance

15) Inspection of Compression Pressure

1. Start and run engine for 5 minutes to warm up, and then
stop.
2. Shift gear into neutral (N).
3. Remove lock plate (stop switch lanyard) from stop switch.
Remove lock plate (stop switch lanyard)
from stop switch before measuring
compression pressure. This will prevent
engine from accidental starging.
4. Remove all plug caps and then all spark plugs.
Clean areas around spark plugs on the
cylinder before removing spark plugs to
prevent dirt from entering cylinder.
5. Install compression gauge to plug hole.
Compression Gauge :
P/N. 3AC-99030-0
6. Fully open throttle, crank engine until compression gauge
indication stabilizes, and then measure compression
pressure.
Compression Pressure (Reference) :
1.13 MPa ( 164 PSI ) [ 11.5 kgf/cm2 ] ± 10 %
Compression pressure is affected much by
cranking speed, and normally changes in the
range from 10 % to 20 %.
7. If compression pressure is below specified value or varies
much among cylinders, put small amount of engine oil into
cylinders, and perform the test again.
• If compression pressure increases after the
above measure, check pistons and piston rings
for wear. Replace if necessary.
• If compression pressure does not increase
after the above measure, check valve
clearances, valves, valve seats, cylinder
sleeves, cylinder head gaskets and cylinder
head. Adjust or replace if necessary.
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CAUTION
CAUTION
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25/30 2006