LO 8-12 Identify and describe the purpose, types, composition, and failures of plain split insert bearings

1.8. Undersize and Oversize Bearings

Undersize and Oversize Bearings

An undersize bearing is thicker than a standard bearing. It does not describe the bearing but rather the shaft it fits. If a crankshaft is worn or ground to undersize, an undersize bearing is used to fit the journal. If a spun main bearing damages a block, the bearing bore can be rebored to an oversize dimension, and an oversize bearing can be installed.

Camshaft bushings can typically outlast two sets of main bearings because there is less loading. However, excessively worn and bleeding cam bearings can starve main bearings of oil and lead to premature crankshaft bearing failure.