Serpentine Belt Replacement

[pyoung62]

I'm at 50k on my '08 135i and ready to replace the serpentine belt (not showing any significant wear, but being proactive with my maintenance). My questions are this:
Is this the only belt or is there an AC belt as well (car's at home so I can't look at it)? Realoem doesn't appear to show a second belt and the routing appears to show the compressor in the serpentine belt routing.
Should I plan to replace the tensioner and both idler pulley's as well? I've never proactively replaced them on other vehicles I've owned, but found some youtube videos that show how to replace all at once. Not sure if that's the recommended practice or the video just being a comprehensive DIY.

[Dackelone]

There is only one serpentine belt. Yes, there are two pulleys and one tensioner. I would think you could get by with out replacing those... but you really won't know until you spin one and feel the bearing for play. IF you want to play it safe I would also replace those parts. I would think the serpentine belt should be done around 90K though.

Note: there had been some guys who were launching the car so hard off the line... that the engine would slam against the front subframe. The crankshaft pulley would contact subframe and damage the serpentine belt and/or the crankshaft pulley. You should take a close look when you do yours! There was a post with: "found a snake under the hood"... which was the old serpentine belt!

[Jcrewsn]

Originally Posted by Dackelone

Note: there had been some guys who were launching the car so hard off the line... that the engine would slam against the front subframe. The crankshaft pulley would contact subframe and damage the serpentine belt and/or the crankshaft pulley. You should take a close look when you do yours! There was a post with: "found a snake under the hood"... which was the old serpentine belt!

My car just had this exact issue. I took it to the dealership, and they said that I had to replace belt, pulley, engine mounts, and subframe... They actually said that the crankshaft had damaged the subframe! I guess this is becoming a recurring issue with the N54. As Dackelone mentioned, the pulley/belt are located towards bottom of engine and, do to the play in the engine mounts, the belt is rubbing against front subframe causing this issue. I was curious about how they were going to remedy this so it won't repeat in the future, but my SA didn't have a definite answer, though he did say he thinks they may have new stiffer engine mounts ( I'll follow up with him later).