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 a heavy load.
Excessive crankshaft end play is indicated by an intermittent rap or knock sharper than a worn main bearing. Causes of main bearing noise include:
- Low oil pressure
- Thin, diluted, or dirty oil and/or oil filter
- Excessive main bearing clearance
- Out-of-round crankshaft journals
- Excessive belt tension
- Loose crankshaft pulley
- Loose flywheel or torque converter
- Loose main bearing bolts.