I have a 81 Express SR NX50 that is belt driven. After I many moth search I found a new belt for it. Now less then 100 miles later it is shot. The damn thing got worn down on the sides and now is slipping. What caused this? Which pulley is doing it? Looks like the rear pully on the clutch side is. ANyone good with these? Anywhere with in 200 miles of Cioncy that can work on this bike???