ACL Race Series connecting rod bearings for Honda B17, B18A1, B18B
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These ACL Race Series connecting rod bearings, part number 4B1946H, are for Honda B17, B18A1, and B18B engines. They are the standard choice when opening up an engine for a build.
Internally, they feature three layers on a high-strength steel backing: a copper-lead-tin lining, a thin nickel barrier, and a lead-tin-copper sliding layer, which is the surface that works against the crankshaft. In the connecting rod bearings, the surface layer is thinner to better withstand fatigue.
The Race Series have more housing interference and a slightly more eccentric shape than standard bearings—two details designed to ensure the bearing does not move and remains well-lubricated when the block and connecting rod deform under load.
In standard size, ACL specifies them for a connecting rod journal of 44.980 to 45.000 mm, with a bearing width of 19.5 mm. For that diameter, they recommend an oil clearance of approximately 0.049 to 0.058 mm, measured with a micrometer and a bore gauge. If the crankshaft has been reground, the measurement changes.
They do not have the silver tin final plating found on standard bearings, so their dark color—ranging from brown and black to bluish—is the factory finish and does not indicate any defect. ACL advises against polishing the bearing surface 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.
If the crankshaft has been reground or you are unsure which size you need, please email us with your engine code before ordering.