N5 chopper belt jumps pulley. Please help

Last year during wheat harvest the one of the rubber paddles on the end of the rotor broke and threw itself into the chopper and bent the shaft. Now I have it reassembled and straightened at a machine shop. I can't stop the belt from jumping off the pulley towards the chopper side of the pulley. I am about to start pulling my hair out. one thing I will try tomorrow is maybe the pulleys are misaligned. that is the last thing I can think of. need some help