CYLINDER HEAD/VALVES
9-5
TROUBLESHOOTING
• Engine top-end problems usually affect engine performance. These problem can be diagnosed by a compression test,
or by tracing top-end noise with a sounding rod or stethoscope.
• If the performance is poor at low speeds, check for white smoke in the crankcase breather hose. If the hose is smoky,
check for a seized piston ring (page 10-7).
Compression too low, hard starting or poor performance at low speed
• Valves:
– Incorrect valve adjustment
– Burned or bent valve
– Incorrect valve timing
– Broken valve spring
– Uneven valve seating
– Valve stuck open
– Weak valve spring
• Cylinder head:
– Leaking or damaged cylinder head gasket
– Warped or cracked cylinder head
– Loose spark plug
• Cylinder/piston problem (page 10-3)
Compression too high, overheating or knocking
• Excessive carbon build-up on piston head or on combustion chamber
• Decompressor system problem (page 9-12)
Excessive smoke
• Worn valve stem or valve guide
• Damaged stem seal
• Cylinder/piston problem (page 10-3)
Excessive noise
• Incorrect valve adjustment
• Sticking valve or broken valve spring
• Excessive worn valve seat
• Worn or damaged camshaft
• Worn or damaged cam chain
• Worn cam sprocket teeth
• Worn rocker arm and/or shaft
• Worn or damaged cam chain tensioner
• Worn cylinder (page 10-4)
• Worn piston or piston rings (page 10-7)
Rough idle
• Low cylinder compression
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