cffisher makes a very good point, snap a picture so all the above folks will be able to have a better idea of your set up, otherwise it is just a crap shoot. Good alignment is a key, notice how the belt sets in the groves, is it even or pulled to one side. This will show itself without running the engine. Lots of cars and truck for that matter run without belt tensioners, and like Pat said shorter belt, can the tensioner could be the way to go.....