ACL Race Series main bearings for Mazda B1, B3, B5, Z5-DE
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ACL Race Series competition main bearing set (part number 5M8353H) for Mazda B1, B3, B5, Z5-DE. These are the bearings that support the crankshaft in the block, and in a tuned engine, the proper delivery of oil to the entire crankshaft depends on them.
They feature a tri-metal construction, 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 bearings feature a full 180° oil groove, while the lower bearings have a partial groove to ensure oil flow to the connecting rods is not restricted; the end of the groove is tapered to prevent pressure spikes. ACL manufactures them with more "crush" (housing interference) than a standard bearing to ensure a secure fit and better heat dissipation, as well as increased eccentricity, which helps maintain the oil film when the housing deforms at high RPMs.
In standard size, ACL specifies them for a crankshaft main journal diameter of 49.938 to 49.956 mm, and for this diameter, they recommend an oil clearance of approximately 0.053 to 0.063 mm. If the crankshaft has been ground, the measurement will change.
These bearings do not have the silver-tin final coating of standard bearings, so their dark, brownish-black and bluish color is the factory finish and does not indicate any defect. ACL advises against polishing the surface of the bearings to adjust clearance; if more is needed, they can be combined with the HX version, which provides an additional 0.025 mm of clearance.
Before ordering, please confirm your crankshaft measurement (standard or ground); if you have any questions, write to us with your engine code.