ACL Race Series main bearings for Honda B18C
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ACL Race Series main bearing set for Honda B18C, part number 5M1959H. These support the crankshaft in the block and, in a tuned engine, are essential for ensuring oil properly reaches the entire crankshaft.
The structure is trimetal, featuring a steel backing, a copper-lead-tin lining, a nickel barrier, and a soft overlay that conforms and prevents seizing even under very high loads.
The upper bearings have a full 180° oil groove, while the lower bearings feature a partial groove to avoid restricting oil flow to the connecting rods, with a tapered groove end 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 support the oil film at high engine speeds.
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 that diameter. If the crankshaft has been reground, the measurement changes.
They do not have the silver tin finish of standard bearings, so their dark, brownish-black-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.
Not sure if your crankshaft is standard size? Write to us with your engine code and we will help you choose.