Crankshafts
The crankshaft converts the up-and-down movement of the pistons into the rotation that drives the vehicle. It runs in main bearings within the engine block and carries counterweights to balance the load.
What it does
Connecting rods attach to offset journals on the crankshaft, so each downward piston stroke turns the shaft. The crankshaft then drives the flywheel, the timing system and the ancillary belt.
Signs a crankshaft is failing
- A deep knocking from the bottom of the engine, worst under load
- Low oil pressure, particularly when hot
- Metallic particles in the oil or filter
- Crankshaft position sensor faults caused by a damaged reluctor ring
When to replace them
Not a wear item in normal service. Replaced after bearing failure, oil starvation, or during a major rebuild.
What to confirm before ordering
Have these ready and the counter can usually confirm the part in under a minute.
- Engine code from the block
- Undersize required, if journals have been reground
- Whether main and big-end bearing shells are supplied with it
- Reluctor ring type, which must match the crankshaft sensor
Crankshafts questions
Can a crankshaft be reground instead of replaced?
Often yes, if the journals are within regrind limits and there is no cracking. Regrinding requires matched undersize bearing shells, so order those together.
What causes crankshaft bearing failure?
Loss of oil pressure or contaminated oil. Both let the journal contact the shell directly instead of riding on a film of oil, and the damage follows quickly.