Thread: Bad lifter?
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      09-13-2012, 10:22 PM   #23
Some dude

Drives: E28 M5, E92 335i
Join Date: Sep 2011
Location: Northern VA

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It's an "overrun" pulley. It only drives the alternator in the forward direction. It allows the alternator to spin faster than the engine if engine RPMs drop suddenly. They do fail, and they are on all kinds of cars since about 2005. That noise is a possibility, but I haven't seen or heard a failed overrun pulley in person.
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E92 335i/6MT Dinan Stage 3: intercooler, oil cooler, intake, flash, exhaust, LW dual-mass flywheel.
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