ACL Race Series main bearings for Mini 1.6L (06-15, N12, N14, N16, N18)
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ACL Race Series main bearings for Mini 1.6L (06-15, N12, N14, N16, N18), part number 5M7788H. These support the crankshaft in the engine block and, in a tuned engine, are critical for ensuring proper oil delivery to the entire crankshaft.
They feature a tri-metal construction with a steel backing, copper-lead-tin lining, a nickel barrier, and a soft overlay that conforms and prevents seizing even under very high loads.
The upper shells have a full 180° oil groove, while the lower shells have a partial groove to ensure uninterrupted oil flow to the connecting rods, with a tapered groove end to prevent pressure spikes. ACL manufactures them with more "crush" (housing interference) than standard bearings to ensure they are held securely and dissipate heat more effectively, as well as increased eccentricity, which helps maintain the oil film when the housing deforms at high RPMs.
In standard size, ACL specifies this for a crankshaft journal diameter of 44.981 to 45.000 mm and recommends an oil clearance of approximately 0.049 to 0.058 mm. If the crankshaft has been reground, the required size will change.
They do not have the silver-tin final coating 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 clearance is needed, they should be combined with the HX version, which provides an additional 0.025 mm of clearance.
If the crankshaft has been reground or you are unsure of the required size, please contact us with your engine code before ordering.