ACL Race Series main bearings for Audi 1.6L, 1.8L, 2.0L (83-01)
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ACL Race Series main bearings for Audi 1.6L, 1.8L, 2.0L (83-01), part number 5M1644H. These support the crankshaft in the block, and in a tuned engine, they are responsible for ensuring that 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, and copper sliding layer, which is the surface that works against the crankshaft.
The upper bearings feature a full 180° oil groove, while the lower ones have a partial groove to ensure oil flow to the connecting rods is not interrupted, with a progressive groove end to prevent pressure spikes. Race Series bearings have increased crush and a slightly more eccentric shape than standard bearings, two details designed to ensure the bearing does not move and maintains proper lubrication when the block and connecting rods deform under load.
In standard size, ACL specifies them for a crankshaft journal of 53.958 to 53.978 mm and recommends an oil clearance of approximately 0.056 to 0.067 mm for that diameter. If the crankshaft has been ground, the measurement changes.
They lack the silver-tin flash plating of standard bearings, so their dark, brownish-black and bluish appearance is factory standard and does not indicate a defect. ACL advises against polishing the bearing surface 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, confirm your crankshaft measurement (standard or ground); if you have any questions, write to us with your engine code.