I had a tensioner bolt (bolt five in the diagram attached the the link below) fall out on it's own after I did some work on the car (an R53). I'm certain it was installed and torqued to spec as I actually crossthreaded it in the hole it threads into (side of supercharger) and wanted to make sure it was properly torqued after retapping it. A couple of days ago I noticed it was missing and was a bit perplexed as to how it came out as it seems I can't put a new one in without replacing the tensioner. The old bolt does not seem to have broken off.

 

bump. anyone?

 

Depending how bad it was cross threaded, you could have compromised the integrity of the threads. Short of drilling/tapping for a timesert or similar, I would try a new bolt and some blue loctite.
Not sure why you think you can't replace the bolt without replacing the tensioner.

 

My plan was to do exactly that -- replace the bolt with some loctite and add a mark so I can monitor if it has turned.

My predicament however is that I cannot fathom how the bolt "fell" out of the tensioner if I can't get a new one back in without first removing the tensioner. Does that make sense?

 

Oh, so you're saying there isn't enough room to insert the bolt into the tensioner. That makes sense. Have never removed that bolt, but if it did back out, there is a lot of movement and vibration that could assist it in doing the impossible.

 

Having replacing the tensioner recently in my '03 MCS, I can attest that bolt #5 cannot be removed without removing the tensioner. It will hit the body of the car before the end clears the hole.

Unless the tensioner repositioned itself so that the bolt could move more, something is very weird.

 

You get the right size bolt, for the right size thread dia. and pitch you tapped the new hole out to?
Thats really the only way its going to back out. Chances are it was a error on your part. Try to find the right bolt, for the tap you used and you shouldnt have any issues