Main Bearings

What Main Bearings Do in Your Engine

Main bearings support the crankshaft where it rides in the engine block. They also hold the oil clearance that keeps a pressurized film between the journal and the bearing surface. Each main journal sits in a saddle in the block, clamped by a main bearing cap that holds the bearing shell in place. As the crank spins, these crankshaft main bearings carry combustion and rotating loads while the oil film prevents metal-to-metal contact. Too much clearance drops oil pressure; too little wipes the overlay and scores the crank. Main bearings work alongside the other engine bearings in your rotating assembly. The connecting rod bearings ride between each rod and its crank journal, while the camshaft bearings support the cam. Together they keep the crankshaft centered, control endplay through the thrust bearing, and route oil through the engine. Getting main bearing clearance right is the foundation of a durable rebuild.

Main Bearing Types and Materials

Main bearings come in a few construction types, and the right one depends on your power level and how hard the engine runs. Traditional bearings use three layers: a steel back, a copper-lead center, and a thin babbitt overlay. Here are the constructions you will find in this category:

• Tri-metal bearings: copper-lead alloy, steel backing, and a babbitt overlay for durability and conformability
• Aluminum-silicon (bi-metal) bearings: high-strength steel bonded to an aluminum alloy for high-load performance
• Coated race bearings: an added surface layer for extra protection under high RPM and load
• Standard vs. narrowed race sets: options for street rebuilds or dedicated race engines

Tri-metal sets suit most street and street/strip builds. Aluminum-silicon and coated race sets handle the higher RPM and cylinder pressure of a dedicated race engine. Clevite 77 bearings use a copper-lead alloy on a steel backing with an electroplated babbitt overlay. ACL Race Series sets use a trimetal design on a hardened steel back for high-RPM loads.

How to Choose the Right Main Bearing Size

Choose your main bearing size by measuring the crankshaft main journals and comparing them to the manufacturer spec. A crank with journals still at factory diameter takes a standard main bearing set. If the crank has been reground to clean up wear or damage, you need undersize main bearings that match how far the journals were cut. Common steps are -.010, -.020, and -.030 in. on domestic cranks, plus .25 mm and .50 mm metric undersizes on many import cranks. Oversize main bearings cover blocks or cranks machined in the other direction. Confirm the grind stamped on the crank, or measure it yourself, rather than guessing. Then check main bearing clearance during assembly with Plastigauge or a bore gauge and micrometer. Target the clearance your manufacturer calls out, often near .0010 to .0025 in. depending on the platform. A set of accurate engine rebuild tools makes that measurement repeatable and keeps the bearings matched to the journals.

Shop Main Bearings by Brand

This category carries engine main bearings from four suppliers with different strengths. Clevite MAHLE makes the Clevite 77 line, a tri-metal bearing with a copper-lead alloy, steel backing, and electroplated babbitt overlay. It is a long-time pick for high-performance main bearings in street and race builds. Sealed Power offers replacement-grade sets for stock rebuilds and daily drivers. ACL Bearings supplies both standard sets and the ACL Race Series, a trimetal bearing with a hardened steel back built for high-RPM and high-load engines. Enginetech rounds out the lineup with value-priced full sets for common domestic and import platforms. You will also find JEGS-brand sets and ACL race series options here. Match the brand to your goal: a stock refresh, a street/strip combination, or a full race engine. Every set is sold to cover all the main journals for the engine you select.

Main Bearings for Popular Engine Platforms

Main bearing sets are cataloged by engine family, so you shop by the platform you are building. For small-block Chevy, sets cover the 350, 327, and 400 and their aftermarket variants. Big-block Chevy sets fit the 396, 427, and 454 with their larger journals. Ford builders will find sets for the Windsor small-blocks along with the 351C, 351M, and 400. Chrysler/Mopar coverage spans the B and RB big-blocks and the 318 small-block. Import options include the Nissan RB, Toyota 1JZ, Subaru FA20, and Honda engines, with metric undersizes available. Because journal diameters, block saddles, and thrust locations vary between families, a set built for one platform will not fit another. Confirm the engine family, the crank's journal size, and any prior regrind before you order. If you are planning the whole rotating assembly, choosing the right short block first tells you which main bearing set and size you need.