In a search for increased smoothness at high speed, I recently splashed out on a Fenner Powertwist V belt for the motor to countershaft drive on my Super 7. Unfortunately my experience so far is not good.
The old v belt is z section, nominally 10mm wide at the top of the wedge. My pulleys have v grooves which are about 9.4 mm wide at the top, so the belt outer surface sits a little above the pulley rim. The Powertwist belt, supplied as z section, is 11.2 mm wide at the top, and barely enters the v of the pulleys. It stands so high above the outer rim of the pulley that it rubs on the belt cover. (N.B. Before anyone says I've been sent an A section belt by mistake, I also have an A section Powertwist belt, and it measures 13 mm wide at the top.)
I am in discussion with the supplier about this problem, but in the meantime I wondered if anyone else in the group had encountered similar problems with Powertwist belts.
Mike