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Old Sat, Apr-22-2017, 02:39:41 PM   #28
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Default Re: Picked up a blown-engine project E46 M3

Originally Posted by BergA View Post
I read through your thread. All due respect, but you and I have entirely different situations here. Your crankshaft was scored and a bearing had spun! Contrary to popular believe, crankshafts are not "harder than bearings, so the crankshaft can't be damaged by a spun bearing." When bearings spin, the heated abrasion cuts the crankshaft and also cuts the connecting rod. Clearances (and roundness) go to hell.

On my last N55 rebuild, one connecting rod bearing spun. The crankshaft showed evidence of damage and needed to be replaced. The connecting rod LOOKED good, but closer measurement with a bore gauge showed that the cap expanded from heat by about 0.2mm; just enough for the scored & broken joint to not align on one side. For that reason I had to buy a new set of rods.

This particular car did not exhibit rod knock. Best practice is to have the crank polished before it goes back in, but otherwise it's fine.
I just learned something new. Thank you for sharing. It has been a big lesson learned.
2007 Black Sapphire Metallic + Imola Z4 ///M Coupe
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2011 Space Gray + Fox Red ///M3 Coupe
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