ACL Race Series connecting rod bearings for BMW M20, M50, M52, M54B22, M54B25, M54B30
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These ACL Race Series connecting rod bearings, part number 6B1490H, are for BMW M20, M50, M52, M54B22, M54B25, and M54B30 engines. They are the standard choice when opening an engine for performance upgrades.
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 overlay that runs against the crankshaft. In connecting rod bearings, the overlay is thinner to better withstand fatigue.
The Race Series have more crush and a slightly more eccentric shape than standard bearings—two details designed to keep the bearing from shifting and ensure proper lubrication even when the block and connecting rod deform under load.
In the standard size, ACL specifies them for a connecting rod journal of 44.975 to 44.991 mm, with a bearing width of 18.0 mm. For this diameter, they recommend an oil clearance of about 0.049 to 0.058 mm, measured with a micrometer and bore gauge. If the crankshaft is reground, these dimensions change.
They do not have the silver-tin final plating found on standard bearings, so their dark color—ranging from brown and black to bluish—is normal from the factory 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 dimensions of your crankshaft (standard or reground); if you have any questions, write to us with your engine code.