ACL Race Series main bearings for Honda B16A
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ACL Race Series main bearing set for Honda B16A, part number 5M1959H. These support the crankshaft in the block, and in a tuned engine, they are responsible for ensuring oil reaches the entire crankshaft properly.
The structure is tri-metal, with a steel backing, copper-lead-tin lining, a nickel barrier, and a soft overlay that conforms and prevents seizing even under very high loads.
The upper shells have a full 180° oil groove, while the lower shells 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 range features more crush for improved seating and heat transfer, as well as greater eccentricity to promote an oil film when the engine is revving high.
In standard size, ACL specifies them for a crankshaft journal diameter of 54.980 to 55.000 mm, and for that diameter, they recommend an oil clearance of approximately 0.057 to 0.068 mm. If the crankshaft has been reground, the measurement will change.
They do not have the final silver tin plating of standard bearings, so their dark, brownish-black-bluish color is factory-standard and does not indicate any defect. ACL advises against polishing the surface of the bearings to adjust clearance; if more clearance is needed, they should be combined 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.