Just changed blades on my Rc72, used new bolts and cup washers, tightened to specified torque. Thought I had lined them up to not make contact. When I started it up the right blade, by the chute, and the middle blade ends hit each other. I loosened the right blade adjusted the timing so the ends of all three would never be in the same space at the same time during a rotation and retightened to torque. When I tested it worked fine for about 10 seconds and then started hitting again, none of the blades seem to be in the timing position that I set. I bought the L3430 and mower about 3 years ago and have no idea how old the belt is so my next thought is that maybe the belt is slipping and needs replaced? Thoughts and recommendations would be appreciated.