ACL Race Series main bearings for Honda D16
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ACL Race Series competition main bearing set (part number 5M1957H) for Honda D16. These support the crankshaft in the block, and in a tuned engine, they are responsible for ensuring oil reaches the entire crankshaft properly.
These are tri-metal bearings: a SAE 1010 steel backing, a copper-lead-tin layer of approximately 0.3 mm, a nickel barrier, and a lead-tin-copper surface layer that conforms to the crankshaft surface and resists seizure.
The upper shells feature a full 180° oil groove, while the lower shells have a partial groove to avoid interrupting oil flow to the connecting rods, with a tapered groove end to prevent pressure spikes. ACL manufactures them with more "crush" (housing interference) than a standard bearing to ensure they stay firmly seated and dissipate heat better, along with 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 54.980 to 55.000 mm and recommends an oil clearance of approximately 0.057 to 0.068 mm for this diameter. If the crankshaft has been ground, the dimensions will change.
They do not have the silver tin finish of standard bearings, so their dark color—a mix of brown, black, and bluish tones—is the factory finish and does not indicate any defects. ACL advises against polishing the bearing surface 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.