Main Bearings

What are Main Bearings?

Main bearings are used to support the crankshaft within the engine block and allow it to rotate freely so it can convert the reciprocating motion of the pistons into rotational motion to power the vehicle. The bearings are located between the crankshaft and main caps and journals in the engine block. Main bearings are machined to tight tolerances to ensure the crankshaft rotates securely, and reduces the friction between the engine's crankshaft journals and the bearings using motor oil. In some cases, oversized bearings may be necessary if the crankshaft journals have been machined to remove imperfections or damage. Over time, main bearings can wear out or be damaged by dirt or debris in the engine, low oil pressure, or poor oil quality. This can lead to engine knocking, increased noise, and reduced performance. Failing main or rod bearings can also cause knocking when you accelerate, which is a sign that they are excessively loose or otherwise damaged. If you hear knocking when you start the engine, or your low oil pressure light is on, check the condition and level of the oil. If it's full and clean, the knocking might be caused by worn or damaged main bearings or rod bearings. For your engine overhauls, repairs, and more, shop O'Reilly Auto Parts, where we carry replacement main and rod bearings, oil pumps, oil pan gaskets, and more to help you complete your engine rebuilding project.