Honda CRF450R 2009 Service Manual page 248

CYLINDER HEADNALVES
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 the hose is smoky. check for
seized piston rings.
Compression t oo low, hard starting or poor pertonnance at low speed
Valves:
- Incorrect valve adjustment
- Burned or bent valves
- Incorrect valve timing
- Broken valve spring
- Uneven valve sealing
Cylinder head:
- leaking or damaged cylinder head gasket
- Warped or cracked cylinder head
loose spark plug
Faulty cylinder, piston or piston rings (page 10-6)
Faulty decompressor plunger
Faulty decompressor weigh t
Compression too high, over-heating or knocking
• Excessive carbon build-up on piston head or oornbustion chamber
Excessive smoke
Worn valve stem or valve guide
• Damaged stem seal
• Faulty cylinder, piston or piston rings (page 10-6)
Excessive 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
Faulty cylinder. piston or piston rings (page 10-6)
Worn crankshaft bearings (page 13-24)
Worn or damaged connecting rod big end bearing (page 13-22)
Worn connecting rod small end (page 10-8)
Worn balancer shaft bearings (page 13-26)
Improper balancer installation (page 13-7)
Worn. seized or chipped transmission gear (page 13-15)
Worn or damaged transmission bearing (page 13-26)
Rough Idle
• Low cylinder compression
9-6