Why wont my serptine belt stay on after alternator change?

I had my alternator replaced on my 2000 1.8L Turbo VW Bettle and now since that has happened my serpentine belt has fallen off 3 times. This last time that I put it back on I noticed that the roller at the bottom of the spring loaded tension setter is not in line with the rest of the pulley track. It sets to the inside of the track and is wearing a ridge on the inside of that roller. I was wondering if when they put my tension setter back on after changing the alternator if they for got to put a piece back in like a spacer. If not, what would be an explanation for the tension setter roller to be off track.
Why wont my serptine belt stay on after alternator change?
your belt tensioner should be bolted and torqued properly, generally there's no spacer that i know of that holds it on the side of the block but who knows.



it is possible they didn't tighten all the way and the belt is riding off the pulley on it enough to throw it. Have them take it back off and make sure it is properly aligned.
Why wont my serptine belt stay on after alternator change?
Sounds like they put a spacer in the wrong spot, like on the wrong side of a bracket or something. Take it back and demand that they fix the problem free of charge.
The tensioner is probally bad, they dont cost much and arent that hard to change. However, I would go back to the mechanic and complain, he should help you out with it a lil bit. He shouldve seen it when he changed the belt.
Both of the top posters are correct, look to make sure the pulley on the tensioner or the alternator is in line with its neighbors.

You should probably replace the belt too since its been damaged by repeatedly coming off.
you need to replace the tensioner. it is spring loaded, and the spring can wear. a tensioner onn most vehicles should be less than $50.00. you probably should replace the pulleys as well, as they can wear too. tensioner/pulley combos can be purchased. As for your mechanic, he had to have noticed!!!! He's just lazy! Find a new one
take it back they installed it wrong its not lining up with the other pulleys.Its got to be presicely straight with the other pulleys