ACL Race Series connecting rod bearings for BMW 135i, 335i, *35i... (N54B30 and N55B30)
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ACL Race Series connecting rod bearings for BMW 135i, 335i, *35i... (N54B30 and N55B30) (part number 6B1584H), designed for engines that will operate under much higher loads and RPMs than stock.
The structure is trimetal, consisting of a steel backing, a copper-lead-tin lining, a nickel barrier, and a soft surface layer that conforms and prevents seizing even under very high loads. On the connecting rod bearings, the surface layer is thinner to better withstand fatigue.
ACL manufactures them with more "crush" (interference fit) than a standard bearing, ensuring they stay securely in place and dissipate heat better, and with more eccentricity, which helps maintain the oil film when the housing deforms at high RPMs.
In standard size, ACL indicates they are for a connecting rod journal of 49.973 to 49.993 mm, with a bearing width of 17.55 mm. For that diameter, they recommend an oil clearance of about 0.053 to 0.063 mm, measured with a micrometer and bore gauge. If the crankshaft is 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 are combined with the HX version, which provides 0.025 mm of additional clearance.
Before ordering, confirm the measurement of your crankshaft (standard or reground); if you have any questions, write to us with your engine code.