Main Bearing Noise

Damaged or worn main bearing noise is revealed by dull thuds or knocks which happen on every engine revolution; 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. Causes 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.