Posted by Mark Rand on 30/12/2017 22:56:34:
As for the belt slipping, check that the belt is riding between the pulley sheaves and not sinking down to the bottom of the pulley groove. It it's doing that, then the pulley is too large for the belt, the belt is worn or r the pulley is worn. Solution as above.
^^^^ This.
The original Myford belt is a Z section, smaller than the more common A section used on the Myford headstock to countershaft belt. Check the new pulley you fitted is not the wider A section and the old Z section belt is not sitting in the groove seating on the bottom instead of the angled sides. If so, the solution is to fit an A section belt, it will ride up on the tops of the Z pulley but will still work OK. I've been doing this for some time with a Z countershaft pulley and A motor pulley. No problems.
You say it only happens when hot. Check the countershaft and headtstock bearings are not getting hot and nipping up after a bit of use. Loosen the belt tension lever and rotate both shafts and the motor by hand to make sure you don't a have a tight bearing somewhere.
Edited By Hopper on 31/12/2017 03:15:37