I had exactly the same problem and realised that the metal plate that goes behind the auxillary pulley wheel was the wrong way round, its flat and sharp one side and curved the other to keep the belt from falling of the bottom crank, so it was a case of turning it round, sabotage i think mate, but yeah i put new belt on and instantly started to slice into it u can see very yhin slice marks, i checked it the other day after looking at this what you put on and found same problem mate!!!!!! thanks, done it 16/10/10 runs better aswell as the belt was so thin it was streching and putting timing slightly out on pull of!!!