ACL Race Series connecting rod bearings for Mazda 2.3L L3 MZR Duratec
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These ACL Race Series connecting rod bearings, part number 4B8170H, are for the Mazda 2.3L L3 MZR Duratec. They are the standard choice when opening the engine for performance builds.
The structure is tri-metal, featuring a steel back, a copper-lead-tin lining, a nickel barrier, and a soft overlay that conforms and prevents seizing even under very high loads. In the rod bearings, the overlay is thinner to better withstand fatigue.
Race Series bearings have increased crush and a slightly more eccentric shape than standard bearings, two details designed to prevent the bearing from moving and to maintain proper lubrication when the block and connecting rod deform under load.
In standard size, ACL specifies them for a rod journal of 49.980 to 50.000 mm, with a bearing width of 17.0 mm. For that diameter, they recommend an oil clearance of about 0.053 to 0.063 mm, measured with a micrometer and bore gauge. If the crankshaft has been ground, the measurements change.
They do not have the silver-tin finish of 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 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.