I had my stock SC pulley machined from 74 mm to 70 mm. This was done at Carrs Machine Shop between Danville and Bloomsburg Pa. Tim is a friend and charged me $60. The limit is about 67 but with a 181 main pulley, 70 was as low as I wanted to go to keep the SC from exceeding the safe limits. Tim Carr is an excellent machinist, he is an instructor at the local Vo-Tech school. This is the same guy who produced my two piece front wheel bolts.