ACL Race Series main bearings for Honda K20A2, K20Z1, K24
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ACL Race Series main bearings for Honda K20A2, K20Z1, K24, part number 5M1959H. These support the crankshaft in the block, and in a tuned engine, they are responsible for ensuring that oil reaches the entire crankshaft properly.
These are tri-metal bearings: a SAE 1010 steel backing, a 0.3 mm copper, lead, and tin layer, a nickel barrier, and a lead, tin, and 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 ensure oil flow to the connecting rods is not interrupted, with a tapered groove end to prevent pressure spikes. Compared to stock bearings, the Race series has higher crush for better retention and heat transfer, and increased eccentricity to improve the oil film at high engine speeds.
In standard size, ACL specifies them for a crankshaft journal diameter of 54.980 to 55.000 mm, and for that diameter, recommends an oil clearance of approximately 0.057 to 0.068 mm. If the crankshaft has been ground, the measurements change.
They do not have the silver tin finish of standard bearings, so their dark, brownish-black and bluish color is factory-standard and does not indicate any defect. ACL advises against polishing the bearing surface to adjust clearance; if more clearance is needed, combine them with the HX version, which provides an additional 0.025 mm of clearance.
Before ordering, please confirm the measurements of your crankshaft (standard or reground); if you have any questions, write to us with your engine code.