I have a 4200 series garden tractor that has been shreading the belt on the deck and I have replaced it now 3 times i have checked the pulleys for one being loose the bearings all seem free and your able to spin the blades freely taking multiple spins with with one good push any ideas on why the belt on the mower dec would do this according to the kubota mechanic i talked with he felt it had to be a bearing but as i said cant find a problem i do have some pits on the pulleys but dont think this should do it tell me what you think? I have gone by the manuel and adjusted the etension according to factory recommendations 