ACL Race Series main bearings for Nissan VQ20, VQ25, VQ30
Fits
Nissan
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ACL Race Series competition main bearing set (part number 4M2633H) for Nissan VQ20, VQ25, VQ30. These support the crankshaft in the block and, in a tuned engine, are responsible for ensuring oil reaches the entire crankshaft properly.
Internally, they feature three layers on a high-strength steel backing: a copper-lead-tin lining, a thin nickel barrier, and a lead-tin-copper sliding layer, which is what works against the crankshaft.
The upper bearings have a full 180° oil groove, and the lower ones have a partial groove to avoid cutting off oil flow to the connecting rods, with a progressive groove end to prevent pressure spikes. ACL manufactures them with more "crush" (housing interference) than a standard bearing, ensuring they stay securely in place and dissipate heat better, along with increased eccentricity, which helps maintain the oil film when the housing deforms at high RPMs.
In the standard size, ACL specifies this for a crankshaft journal of 59.951 to 59.975 mm and recommends an oil clearance of about 0.061 to 0.073 mm for that diameter. If the crankshaft has been reground, the measurement changes.
They do not have the final silver tin plating of standard bearings, so their dark color—ranging from brown and black to bluish—is the factory finish and does not indicate any defect. ACL advises against polishing the bearing surface to adjust clearance; if more is needed, they should be combined with the HX version, which provides 0.025 mm of additional clearance.
Before ordering, confirm your crankshaft measurement (standard or reground); if you have any questions, write to us with your engine code.