Compression too low, hard starting or poor performance at low speed
- Leaking cylinder head gasket
- Worn, stuck or broken piston ring
- Worn or damaged cylinder and piston
Compression too high, overheating or knocking
- Excessive carbon built-up on piston or combustion chamber
Excessive smoke
- Worn cylinder, piston or piston rings
- Improper installation of piston rings
- Scored or scratched piston or cylinder wall
Abnormal noise (piston)
- Worn piston pin or piston rings
- Worn cylinder, piston or piston ring
- Worn connecting rod small end