Inspection Of Compression Pressure - TOHATSU MFS 25D Service Manual

14) Inspection of Compression Pressure

1. Start the engine to warm up for 5 minutes, then stop the
engine.
2. Shift the gear into the Neutral (N) position.
3. Remove lock plate (stop switch lanyard) from stop switch.
Remove lock plate (stop switch lanyard)
f r o m s t o p s w i t c h b e f o r e m e a s u r i n g
compression pressure. This will prevent
engine from accidental starting.
4. Remove all plug caps and then all spark plugs.
Clean the areas around the spark plugs
on the cylinder before removing the spark
plugs to prevent dirt from entering the
cylinder.
Install the compression gauge 1 into the plug hole.
5.
Compression Gauge 1:
P/N. 3AC-99030-0
6. Fully open the throttle and crank the engine until the
compression gauge indication stabilizes, then measure the
compression pressure.
Compression Pressure (Reference): at 500 r/min
with decompresser
without decompresser: 1.40 MPa (203 psi) [14.3 kgf/cm
• Compression pressure is greatly affected by the
cranking speed, and normally varies by about
10% to 20%.
• For remote control model: Remove the cable
joint and fully open the throttle cam with your
hand, then measure the compression pressure.
7. If the compression pressure is below the specified value
or varies a lot among the cylinders, pour a small amount of
engine oil into the cylinders and perform the compression
test again.
• If the compression pressure increases after the
above measure, check the pistons and piston
rings for wear. Replace if necessary.
• If the compression pressure does not increase
after the above measure, check the valve
clearances, valves, valve seats, cylinder
sleeves, cylinder head gasket and cylinder
head. Adjust or replace if necessary.
4st 25/30 2022
CAUTION
CAUTION
: 0.50 MPa (73 psi) [5.1 kgf/cm ]
²
]
²
A Basic Tiller Handle Model
B Multi-Function Tiller Handle Model
C Remote Control Model
3
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