Power Unit; Checking The Compression Pressure; Checking The Oil Pressure - Yamaha F25C Service Manual

POWR

Power unit

Checking the compression pressure

1. Start the engine, warm it up for 5 min-
utes, and then turn it off.
2. Remove the clip from the engine stop
lanyard switch.
3. Remove the spark plug caps and all
spark plugs, and then install the special
service tools into a spark plug hole.
1
CAUTION:
Before removing the spark plugs, blow
compressed air in the spark plug well to
clear out any dirt or dust that may fall into
the cylinder.
Compression gauge 1:
90890-03160
4. Fully open the throttle, crank the engine
until the reading on the compression
gauge stabilizes, and then check the
compression pressure.
NOTE:
Since this outboard motor is equipped with
an automatic decompression mechanism,
accurate data may be difficult to obtain due to
differences in the way the starter rope is
pulled.
Minimum compression pressure
(reference data):
810 kPa (8.1 kgf/cm
5-3
Power unit
S6D55050
2
, 115 psi)
5. If the compression pressure is below
5
specification and the compression pres-
sure for each cylinder is unbalanced, add
a small amount of engine oil to the cylin-
der, and then check the pressure again.
NOTE:
• If the compression pressure increases,
check the pistons and piston rings for wear.
Replace if necessary.
• If the compression pressure does not
increase, check the valve clearance, valve,
valve seat, cylinder sleeve, cylinder head
gasket, and cylinder head. Adjust or
replace if necessary.

Checking the oil pressure

1. Place a rag under the oil pressure switch.
2. Remove the oil pressure switch, and then
install an oil pressure gauge 1 to the oil
pressure switch installation hole.
1
NOTE:
Use a general pressure gauge.
3. Start the engine and warm it up for 5 min-
utes.
4. Check the oil pressure. Check the oil
pump, oil leakage, and oil strainer if out
of specification.
Oil pressure (reference data):
80 kPa (0.8 kgf/cm
engine idle speed
S6D55060
2
, 11 psi) at
6D55F11