Honda CRF450X 2005 Service Manual page 178

CYLINDER HEADIVALVES
TROUBLESHOOTING
• Engine top-end problems usually affect engine performance. These problems can
be
diagnosed by a compression test
or by tracing top-end noise with a sounding rod stethoscope.
• If the performance is poor at low speeds, check for white smoke in the crankcase breather hose. If t he hose is smoky,
check for a seized piston ring.
Compression too low, hard starting or poor performance at low speed
• Valves:
- Incorrect valve adjustment
- Burned or bent valves
- Incorrect valve timing
- Weak valve spr ing
- Uneven valve seating
- Valve stuck open
• Cylinder head:
- leaking or damaged cylinder head gasket
- Warped or cracked cylinder head
• loose spark
plug
• Faulty cylinder. piston or piston rings
• Faulty decompressor system
Compression too high
• Excessive carbon build-up in cylinde r head or t op of piston
Excessive smoke
• Worn valve stem or valve guide
• Damaged stem seal
• Cylinder, piston or piston rings problem
Excesslv, noise
• Incorrect valve adjustment
• Sticking valve or broken valve spring
• Worn or damaged camshaft
• Worn or damaged valve lifter
• Worn or loose cam chain
• Worn or damaged cam chain tensioner
• Worn cam sprocket teeth
• Cylinder, piston or piston rings problem
Rough idle
• l ow cylinder compression
9-6
•