Tri-metal crankshaft main bearings ACL Subaru EJ20 EJ22 EJ25 housing OS2

The Subaru EJ four-cylinder engines

ACL lists main bearing set 5M8309HOS2 for the Subaru EJ18E, EJ20E, EJ20G, EJ20Y, EJ205, EJ206, EJ207, EJ208, EJ22E, EJ25D, EJ251, EJ252, EJ253, EJ255, EJ257 flat-four engines. They share the same crankshaft journal diameter: a single set covers the whole family. This OS2 version has an outside diameter increased by 0.002 inch, with the thrust half shell at main bearing no. 5.

The crankshaft of these engines runs on five main bearings. Each journal turns between two half shells, one seated in the block and the other in the main bearing cap: they carry the crankshaft. The ACL Race Series tri-metal set shown here replaces them on built engines.

Tri-metal main bearings

A tri-metal bearing stacks three layers: a steel back, a copper-lead intermediate layer with high load capacity and an anti-friction running surface that protects the journal. The complete set covers the five main bearings of the crankshaft. The upper and lower half shells are different: each goes in its own position.

An aluminium bi-metal takes around 8,000 psi, a performance tri-metal up to 12,000 psi, 50% more. Hence better resistance and better durability on turbocharged, supercharged and high-revving engines.

Technical specifications

Technical guide

The ACL main bearings shown here are trimetal bearings, designed for engine building and racing. Compared with an original bearing, they handle far higher loads: they cope with increased power, high rpm or the addition of a turbo or supercharger, where a standard bearing quickly reaches its limit.

The brand

ACL Bearing Company, an Australian manufacturer of high-performance engine bearings since 1949, offers with its Race Series precise trimetal bearings, available in many sizes and proven on built engines worldwide.

Vehicle compatibility

This main bearing set fits the following vehicles, by engine code: