Cylinder Head/Valves Troubleshooting - Honda 2010 CRF250R Service Manual

CYLINDER HEADNALVES
TROUBLESHOOTING
Engine top-end problems usually affect engine performance. These problems can be diagnosed by a compression test or by
tracing lop-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 too low, hard starting or poor performance at low speed
Valves:
- Incorrect valve adjustment
- Burned or bent valves
- Incorrect valve liming
- Broken valve sprmg
- Uneven valve seating
Cylinder head:
- Leaking or damaged cylinder head gasket
- Warped or cracked cylinder head
Loose spark plug
Faulty cylinder, piston or piston rings (page 9-5)
Faulty decompressor plunger
Faulty decompressor weight
Compression too high , over-heating or knocking
• Excessive carbon build-up on piston head or combustion chamber
ExcessIve smoke
Worn valve stem or valve gUide
• Damaged stem seal
• Faulty cylinder, piston or piston rings (page 9-5)
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 cham tensioner
Worn cam sprocket teeth
Faulty cylinder, piston or piston rings (page 9-5)
Worn crankshaft bearings (page 12-26)
Worn or damaged connecting rod big end bearing (page 12-24)
Worn connecting rod small end (page 9·7)
Worn balancer shaft bearings (page 12·10)
Improper balancer installation (page 12·9)
Worn. seized or chipped transmi ssion gear (page 12-18)
Worn or damaged transmission bearing (page 12-28)
Rough idle
• Low cylinder compression
8-6