ACL Race Series main bearings for Nissan 350Z - 280 and 300 bhp (VQ35DE)
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ACL Race Series main bearing set for Nissan 350Z - 280 and 300 bhp (VQ35DE), part number 4M2633H. These support the crankshaft in the block, and in a tuned engine, the proper delivery of oil to the entire crankshaft depends on them.
These are tri-metal bearings: an 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 bearings feature a full, 180° oil groove, while the lower ones have a partial groove to ensure oil flow to the connecting rods is not interrupted, with a tapered groove end to prevent pressure spikes. ACL manufactures them with more "crush" (housing interference) than standard bearings 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 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 approximately 0.061 to 0.073 mm for that diameter. If the crankshaft has been reground, the measurement changes.
They do not have the silver tin finish of standard bearings, so their dark, brownish-black and bluish color is factory-standard 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 an additional 0.025 mm of clearance.
Before ordering, please confirm the measurement of your crankshaft (standard or reground); if you have any questions, write to us with your engine code.