Just about pulling my hair out on this one. I changed [traded ] transmissions from a Raider 10 to a newer unit from an unmarkerd12 horsepower 8 speed. After i hooked it up, the belt was too loose to drive the machine at about 83" i then bought a new 83" belt and it was still too loose. An 82" belt will drive it fine, but will not loosen enough with the clutch applied to shift gears. I am either doing something wrong with the clutch side or i need to change the idler pulley on the throwout arm from 4" to something smaller. There is only so much adjustment anyway until the clutch hits its limit
The original belt on the Raider is 83'" although it is old enough to have some wear. I have checked all the drive pulleys from each transmission and they are the same size. I used a 5/8ths x 82" belt and wonder if a half inch belt might sink into the pulleys just enough to compensate for the mis-match.
Those are all the ideas I have and do not know what else to try..