So I have finished rebuilding my cylinder head after I bent all my exhaust valves from over reving the engine on my GSR motor. I got the parts put back together. I was installing the timing belt that I had on the car when I over reved the engine and I noticed a lot of slack in the belt. I installed the belt and then tighted the spring loaded belt tensioner. Then I turned the crank by hand to get the timing belt to seat properly. Well as I turned the crank, slack would develope and the cams would skip teeth on the belt. I don't know if over reving the engine stretched the belt or if the tensioner spring is shot. I'm not sure and it's the only things that I can think of but the belt looks in great shape and the tensioner pulley and spring also look good and are holding tension. What am I doing wrong? Any input would be helpful.