Thread: Bad lifter?
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      09-13-2012, 09:22 PM   #23
JamesM3M5
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Drives: E28 M5, E92 335i
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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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