ACL Race Series main bearings for Honda K20A3
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ACL Race Series main bearings for Honda K20A3, part number 5M1959H. These support the crankshaft in the block and, in a tuned engine, are responsible for ensuring oil effectively reaches the entire crankshaft.
These are tri-metal bearings: a SAE 1010 steel backing, a 0.3 mm copper-lead-tin intermediate layer, a nickel barrier, and a lead-tin-copper overlay that conforms to the crankshaft surface and resists seizing.
The upper bearings feature a full 180° oil groove, while the lower ones have a partial groove to avoid interrupting oil flow to the connecting rods; the end of the groove is tapered to prevent pressure spikes. Compared to stock bearings, the Race series has increased crush for better seating and heat transfer, as well as greater eccentricity to promote an oil film at high engine speeds.
In standard size, ACL specifies them for a crankshaft journal 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 machined, the measurements will differ.
They do not have the silver-tin finish found on standard bearings, so their dark, brownish-black and 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, combine them 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.