ACL Race Series main bearings for Honda B18A, B20A SOHC
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ACL Race Series competition main bearing set (part number 5M1957H) for Honda B18A, B20A SOHC engines. These support the crankshaft in the engine block and, in a tuned engine, they are responsible for ensuring that oil reaches the entire crankshaft properly.
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 surface that interfaces with 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 restricted, with a tapered groove end to prevent pressure spikes. Compared to stock bearings, the Race series has increased crush for better retention and heat transfer, and greater eccentricity to promote an oil film at high engine speeds.
In standard size, ACL specifies them for a crankshaft journal diameter of 54.980 to 55.000 mm, recommending an oil clearance of approximately 0.057 to 0.068 mm for this diameter. If the crankshaft has been reground, the required size will change.
They do not have the silver-tin final plating found on standard bearings, so their dark, brownish-black-bluish color 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 can be combined with the HX version, which provides 0.025 mm of additional clearance.
If the crankshaft has been reground or you are unsure of the required size, please contact us with your engine code before ordering.