How to prevent bearing failure and determine their causes

Engine Bearings depend on a film of oil to keep shaft and bearing surfaces separated (figure A). Bearings fail when the oil film breaks down or when the bearing is overloaded. The oil film is generated by shaft rotation (figure B).

At rest, the shaft and bearing are in contact. On start up the shaft rubs the bearing briefly. Running, the shaft pulls oil from the clearance space into the wedge shape area between the shaft and bearing. The oil wedge lifts the shaft off its bearing and supports it during engine operation. With normal operating conditions and a continuous supply of clean oil the shaft and bearing surfaces will remain separated.

When bearing damage occurs the cause must be determined and corrected before installing new parts.