Just replaced my power steering pump in my 2001 330Ci AT. It all went pretty well except dealing the __________ _________ (choose any two swear words) tensioner. What a pain that T50 is. Why BMW chooses to use TORX when both the bits and the bolts can be so easily stripped out, I have no idea. I stripped out one of the bracket bolts on this effort too, but that's not the main point of the story...
Anyway, sooo, after being able to use the T50 into the tensioner bolt (surprisingly) to get the belt off, I fought for an hour trying to get the belt back on. On hour 3 of this project, and about an hour into trying to make the T50/pulley method work, I started looking for other solutions.
The answer came in the form of the 5/8 nut-like protrusion that's part of the tensioner arm. You can see it to the left of the tensioner pulley itself. Clearances on the bottom of the car and behind the fan were pretty narrow on my AT equipped 330Ci. I managed to wrangle a 5/8 spark plug changing socket onto that nut and then put a wrench on that, and a breaker bar on that. At that point I was able to move the tensioner, but the upper radiator hose prevented me from moving that tensioner enough to get the belt on. So...I disconnected the upper radiator hose, leaking coolant into a bucket I put under the car, but then I could actually move it enough to get the belt on and then slowly let it go.
Man, it was supposed to be easier than that...