Tailpipe butterfly valve rattling.

GenePoole · 06-10-2016, 08:59 AM

I've got a recently purchased CPO 2012 F30 and my service manager says exhaust related problems are not covered under CPO. Bummer.

I have a nasty rattle from the butterfly flapper in the 2nd muffler outlet. I'm not sure of the purpose of the flapper. My previous BMW (2006 E90 330i) had it, but I believe it only opened in wide-open-throttle, or in sport mode. Some searching seems to indicate the the N20 turbo requires some backpressure at cold startup, then the flapper is always open.

Looking at the tailpipe, it appears that a nut or bushing or something is missing. I don't know if this is serviceable, but dealership wants to replace the entire muffler. The axle shaft protruding appears to be threaded, but not enough protrudes for me to be sure, and if so, it doesn't appear that a nut would grab more than half a thread or so.

My first thought was to spot weld it so that it is always open (I have MIG and TIG welders), but the prospect of damaging the turbo made me rethink that approach.

Has anyone had this issue? Can somebody take a picture of the same spot on a normally functioning part? I'm curious what might be missing.

Here's the photo of the culprit. If I hold a screwdriver or something against the axle, the rattling stops:

GenePoole · 06-15-2016, 08:36 PM

Followup: It was a small spring clip (called a "fixing bow") that came loose. The dealer fixed it for me at no charge since the car is only 1 month out of primary warrantee. The part is #9 below, a $5 part:

06-10-2016, 08:59 AM	#1
GenePoole Lieutenant 46 Rep 541 Posts Drives: 2012 F30 328i Join Date: Apr 2010 Location: Brighton, IL iTrader: (0)	Tailpipe butterfly valve rattling. I've got a recently purchased CPO 2012 F30 and my service manager says exhaust related problems are not covered under CPO. Bummer. I have a nasty rattle from the butterfly flapper in the 2nd muffler outlet. I'm not sure of the purpose of the flapper. My previous BMW (2006 E90 330i) had it, but I believe it only opened in wide-open-throttle, or in sport mode. Some searching seems to indicate the the N20 turbo requires some backpressure at cold startup, then the flapper is always open. Looking at the tailpipe, it appears that a nut or bushing or something is missing. I don't know if this is serviceable, but dealership wants to replace the entire muffler. The axle shaft protruding appears to be threaded, but not enough protrudes for me to be sure, and if so, it doesn't appear that a nut would grab more than half a thread or so. My first thought was to spot weld it so that it is always open (I have MIG and TIG welders), but the prospect of damaging the turbo made me rethink that approach. Has anyone had this issue? Can somebody take a picture of the same spot on a normally functioning part? I'm curious what might be missing. Here's the photo of the culprit. If I hold a screwdriver or something against the axle, the rattling stops:
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06-15-2016, 08:36 PM	#2
GenePoole Lieutenant 46 Rep 541 Posts Drives: 2012 F30 328i Join Date: Apr 2010 Location: Brighton, IL iTrader: (0)	Followup: It was a small spring clip (called a "fixing bow") that came loose. The dealer fixed it for me at no charge since the car is only 1 month out of primary warrantee. The part is #9 below, a $5 part:
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