I have an older Craftsman tractor model 944.602200 20hp Kohler Magnum with a 50" deck. For the last few years its had a habit of chewing up the deck belt and throwing it off the pulleys. The 3 blade bearings are tight and the tensioner seems ok. If I take the guard off and run it the belt is bouncing and jumping all over the place. This unit will go through a couple belts a season if not more and throw them off the pulleys I dont know how many times. Am I useing the wrong belts maybe? Im out of ideas. Hello all and thanks in advance for any input.