Yamaha F90D, Service Manual

Page: 69 / 241

POWR
Power unit
5-3
6D81G11
Power unit
5
Checking the compression pressure
1. Start the engine, warm it up for 5 min-
utes, and then turn it off.
2. Remove the engine stop lanyard from the
engine stop lanyard switch on the remote
control box.
3. Remove the spark plug wire cover and all
spark plugs, and then install the special
service tools into a spark plug hole.
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.
4. Fully open the throttle, crank the engine
until the reading on the compression
gauge stabilizes, and then check the
compression pressure.
5. If the compression pressure is below
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 head gasket, and cylin-
der head. Adjust or replace if necessary.
Checking the oil pressure
1. Remove the flywheel magnet cover.
2. Place a rag under the oil pressure switch.
3. Remove the oil pressure switch, and then
install an oil pressure gauge
1
to the oil
pressure switch installation hole.
NOTE:
Use a general pressure gauge.
4. Start the engine and warm it up for 5 min-
utes.
5. Check the oil pressure. Check the oil
pump, oil leakage, and oil strainer if
below specification.
Compression gauge
1
: YU-33223
Compression gauge extension
2
:
YB-06563
Minimum compression pressure
(reference data):
860 kPa (8.6 kgf/cm
2
, 124.7 psi)
S6D85110
1
2
Oil pressure (reference data):
510 kPa (5.1 kgf/cm
2
, 74.0 psi) at
engine idle speed
S6D85120
1