Yamaha F40BED, Service Manual, Page: 108 / 537

CHK
ADJ
3-16
POWER UNIT
E
4. Install:
• Cylinder head cover
• Spark plugs
• Flywheel magnet assembly cover
5. Connect:
• Blowby hose
• Fuel hoses
• Spark plug leads
MEASURING THE COMPRESSION
PRESSURE
CAUTION:
Before removing a spark plug, use com-
pressed air to blow away dirt accumulated
in the spark plug well to prevent it from fall-
ing into the cylinder that is being tested.
1. Check:
• Valve clearance
Out of specification
→
Adjust.
Refer to "ADJUSTING THE VALVE
CLEARANCE" on page 3-14.
2. Warm-up:
• Engine
3. Remove:
• Spark plug(-s)
4. Install:
• Compression gauge
(into the spark plug hole)
5. Measure:
• Compression pressure
Below minimum compression pres-
sure
→
Inspect valve clearance,
valve face, valve seat, piston rings,
cylinder sleeve, piston, cylinder
head gasket and cylinder head.
1
Compression gauge
YU-33223 / 90890-03160
Compression pressure
Minimum
1,210 kPa (12.1 kgf/cm
2
, 175 psi)
1