ACL Race Series main bearings for Nissan RB25/28/30
Fits
Nissan
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ACL Race Series competition main bearing set (part number 7M2394H) for Nissan RB25/28/30. These bearings support the crankshaft in the engine block and, in a tuned engine, they are critical for ensuring proper oil delivery to the entire crankshaft.
These are tri-metal bearings: a SAE 1010 steel backing, a copper-lead-tin layer approximately 0.3 mm thick, a nickel barrier, and a surface layer of lead, tin, and copper that conforms to the crankshaft surface and resists seizing.
The upper shells feature a full 180° oil groove, while the lower shells have a partial groove to ensure uninterrupted oil flow to the connecting rods, with a tapered groove end to prevent pressure spikes. ACL manufactures them with more "crush" (housing interference) than a standard bearing to ensure a secure fit and better heat dissipation, as well as greater eccentricity, which helps maintain the oil film when the housing deforms at high RPM.
In standard size, ACL specifies this for a crankshaft journal diameter of 54.951 to 54.975 mm, and recommends an oil clearance of approximately 0.057 to 0.068 mm for that diameter. If the crankshaft has been ground, the dimensions will change.
They do not have the silver-tin finish of standard bearings, so their dark color—ranging from brown and black to bluish—is the factory finish and does not indicate a defect. ACL advises against polishing the bearing surface to adjust clearance; if more is needed, combine them with the HX version, which provides an additional 0.025 mm of clearance.
Not sure if your crankshaft is standard size? Send us your engine code and we will help you choose.