Main & rod bearings come in standard, undersized, and oversized. An undersized bearing has extra material thickness on the inside of the bearing facing the crankshaft journal. Undersized bearings are used when a crankshaft has been machined or ground undersize.

How do I know what size main bearings I need?

Measuring the inside diameter of a main or rod bearing will require a dial bore gauge. The best ones to use are accurate down to 0.0001-inch. With these two tools you can quickly determine the clearances in any engine. Measuring bearing clearance is only valuable if the numbers are accurate so use quality tools.

What is the standard rod bearing size?

Main bearings and rod bearings are typically available in standard size and . 010,” . 020” and . 030” undersizes for passenger car and light truck engines.