Main Bearing Noise

Damaged or worn main bearing noise is revealed by dull thuds or knocks which happen on every engine revolution, and this noise is loudest when the engine is under heavy load.

Excessive crankshaft end play is indicated by an intermittent rap or knock sharper than a worn main bearing. On manual transaxle-equipped cars, the disengagement of the clutch can cause a change in the noise. Cause of main bearing noises include:
- Low oil pump pressure
- Thin, diluted or dirty oil and/or filter
- Excessive main bearing clearance
- Excessive crankshaft end play
- Out-of-round crankshaft journals
- Excessive belt tension
- Loose crankshaft pulley
- Loose flywheel or torque converter
- Loose main bearing cap