ACL Race Series main bearings for BMW 316i, 318i, Z3 (M40, M42, M43, M44)
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ACL Race Series competition main bearing set (part number 5M1538H) for BMW 316i, 318i, Z3 (M40, M42, M43, M44). These support the crankshaft in the block and, in a tuned engine, are essential for ensuring oil properly reaches the entire crankshaft.
The structure is tri-metal, with a steel backing, copper-lead-tin lining, a nickel barrier, and a soft surface layer that conforms and prevents seizing even under very high loads.
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 progressive groove end to prevent pressure spikes. Race Series bearings have higher crush and a slightly more eccentric shape than standard bearings, details designed to keep the bearing from shifting and ensure proper lubrication when the block and rods deform under load.
In standard size, ACL specifies this for a crankshaft journal diameter of 59.971 to 59.990 mm, and recommends an oil clearance of approximately 0.061 to 0.073 mm for this diameter. If the crankshaft is ground, the dimensions change.
They do not have the silver tin top layer of standard bearings, so their dark, brownish-black-bluish color is factory-standard 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.
If the crankshaft has been ground or you are unsure of the required size, please contact us with your engine code before ordering.