Crankshaft main bearing
Supports the crankshaft on a controlled film of oil.
Between crankshaft main journals and the engine’s bearing supports.
Precision shells provide clearance for pressurized oil; they do not normally rely on dry metal contact.
A slippery cradle that lets a loaded shaft turn.
Knocking, oil-pressure problems or bearing material in oil require investigation.
Usually condition-based rather than a routine replacement. Lubrication, overheating and the exact engine affect wear.
Internal-engine work is usually labor-intensive. Diagnosis and the engine code determine the repair scope.
BMW bearing selection and clearances are engine-specific measurements rather than visual guesses.
BMW petrol and diesel engines; petrol-only systems are identified individually.