ACL Race Series main bearings for Mitsubishi Evo X (4B11T)
Fits
Mitsubishi
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ACL Race Series main bearings for Mitsubishi Evo X (4B11T), part number 5M1237H. These support the crankshaft in the block, and in a tuned engine, they are responsible for ensuring oil reaches the entire crankshaft properly.
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 what works against the crankshaft.
The upper bearings have a full 180° oil groove, and the lower ones have a partial groove to avoid cutting off oil flow to the connecting rods; the end of the groove is tapered to prevent pressure spikes. ACL manufactures them with more "crush" (housing interference) than standard bearings to ensure they are held securely and dissipate heat better, along with increased eccentricity, which helps maintain the oil film when the housing deforms at high RPM.
In standard size, ACL specifies them for a crankshaft journal of 51.973 to 51.985 mm and recommends an oil clearance of about 0.055 to 0.065 mm for that diameter. If the crankshaft has been reground, the measurement changes.
They do not have the final silver-tin plating 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, 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 of the required size, please write to us with your engine code before ordering.