Engine Crankshaft Main Bearing

What Are Engine Crankshaft Main Bearings?

Engine crankshaft main bearings are among the most critical — and most overlooked — components in any internal combustion engine. A main bearing is a bearing that holds the crankshaft in place and allows it to rotate within the engine block. Without them, the crankshaft would have no stable support surface, and the rotating assembly would quickly destroy itself.

Each bearing consists of two semi-cylindrical shell halves — an upper and a lower — that together cradle the crankshaft journal. Once the engine starts and oil pressure builds, the crankshaft begins to rotate and oil is forced into the narrow gap, creating a hydrodynamic film that lifts and separates the journal from the bearing surface, enabling the crankshaft to "float" and rotate with minimal friction. This oil film also acts as the primary medium for heat removal, protecting both bearing and crankshaft from thermal stress.

Why Main Bearings Matter

Main bearings take a tremendous beating during normal engine operation. Very heavy loads are applied to the bearing surface through the oil film — including the firing load transmitted through the piston and connecting rod as each cylinder fires, and inertia loads resulting from the rotation of the crankshaft assembly. If lubrication fails due to low oil pressure, contamination, or oil breakdown, the protective film collapses, leading to metal-to-metal contact and rapid, catastrophic wear.

The layered construction of a quality main bearing is designed to handle these conditions: a strong steel backing provides structural support, while a softer overlay alloy provides a conformable, embeddable surface. This design helps protect against surface imperfections in the crankshaft journal and allows the bearing to accommodate small debris particles by embedding them — preventing them from scoring the crankshaft. Bearing clearance is equally critical: insufficient clearance causes excessive friction and overheating, while excessive clearance creates instability and accelerated wear.

Choosing the Right Main Bearing

When selecting crankshaft main bearings, consider the application: a daily driver undergoing a routine rebuild has very different needs than a turbocharged or naturally-aspirated race engine pushing thousands of horsepower. For stock rebuilds, standard-size or undersized OEM-spec bearings restore proper clearances. For high-performance builds, upgraded tri-metal or coated bearings offer greater load capacity, seizure resistance, and fatigue life. Always verify journal diameter and consult the manufacturer's size chart — many brands offer standard, .001", .010", .020", and .030" undersizes to accommodate reground crankshafts.

Top Brands in Engine Crankshaft Main Bearings

Clevite is widely regarded as the benchmark in engine bearing technology. Since developing the first precision insert-type bearing in 1929, Clevite has become the bearing of choice for engine builders from daily drivers to NASCAR and IndyCar programs. Their signature TriMetal™ construction — a hardened steel back, copper-lead alloy substrate, and electroplated white metal overlay — delivers an ideal combination of conformability, embeddability, and fatigue resistance. Their newer F-Series raises seizure resistance significantly over the conventional H-Series design, making them a top pick for serious performance builds.

King Engine Bearings has become a major force in both the performance aftermarket and OEM supply chain, earning a strong reputation for tight tolerances and innovative materials. King is known for their pMaxKote and pMaxBlack coated bearing lines, which reduce friction and improve wear characteristics — particularly valuable in high-performance and racing applications.

ACL Bearings is an Australian-founded manufacturer with a long history supplying bearings to both OEM and aftermarket customers worldwide. ACL's Race Series main bearings are a popular choice among engine builders who want precision-fit, high-performance bearings at a competitive price point, with options available for a wide range of domestic and import applications.

Federal-Mogul brings decades of OEM-level engineering to the aftermarket, manufacturing main bearings that meet or exceed original equipment specifications. Their broad application coverage makes them a go-to for professional shops performing high-volume engine rebuilds.

MICHIGAN 77 rounds out the lineup with a focused selection of main bearings covering popular domestic engines, offering reliable OEM-replacement quality for technicians and rebuilders seeking straightforward fitment and dependable performance.