ACL Race Series connecting rod bearings for BMW M3 E36 3.2L S50B32
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These ACL Race Series connecting rod bearings, reference 6B1497H, are for the BMW M3 E36 3.2L S50B32. They are the standard choice when opening the 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 sliding layer, which is the one that works against the crankshaft. In connecting rod bearings, the surface layer is thinner to better withstand fatigue.
ACL manufactures them with more "crush" (housing interference) than a standard bearing to ensure they are held securely and dissipate heat better, and with more eccentricity, which helps them maintain the oil film when the housing deforms at high RPMs.
In standard size, ACL specifies them for a connecting rod journal of 48.975 to 48.991 mm, with a bearing width of 18.0 mm. For that diameter, they recommend an oil clearance of about 0.052 to 0.062 mm, measured with a micrometer and bore gauge. If the crankshaft has been reground, the dimensions change.
They do not have the final silver tin plating of standard bearings, so their dark color—ranging from brown and black to bluish—is factory-standard and does not indicate any defect. ACL advises against polishing the bearing surface to adjust clearance; if more is needed, they are combined with the HX version, which provides 0.025 mm of additional 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.