ACL Race Series main bearings for Mini 997cc and 998cc
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ACL Race Series main bearing set for Mini 997cc and 998cc, part number 3M2203H. These bearings support the crankshaft in the block, and in a tuned engine, they are responsible for ensuring oil reaches the entire crankshaft effectively.
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 that works against the crankshaft.
The upper shells have a full 180° oil groove, while the lower shells have a partial groove to ensure oil flow to the connecting rods is not interrupted, with the groove ending progressively to prevent pressure spikes. ACL manufactures them with more "crush" than standard bearings for a secure fit and better heat dissipation, as well as increased eccentricity to help maintain the oil film when the housing deforms at high RPMs.
In standard size, ACL specifies this for a crankshaft journal diameter of 44.463 to 44.475 mm, and for this diameter, it recommends an oil clearance of approximately 0.049 to 0.057 mm. If the crankshaft has been ground, the measurement will change.
They do not have the silver-tin final plating found on standard bearings, so their dark color—a mix of brown, black, and bluish tones—is as intended from the factory and does not indicate any defect. ACL advises against polishing the surface of the bearings to adjust clearance; if more is needed, they should be combined with the HX version, which provides an additional 0.025 mm of clearance.
Not sure if your crankshaft is standard size? Write to us with your engine code and we will help you choose.