I have a 'Value Leader' which is another Chinese version of the basic design. I think the debris swirling around and building up at the base of the gearbox pulley, the hammering from the PTO that box feeds, and the vibration off the unit itself all played into the pulley problem... the allen key would give up before the shaft. They seem to just eat drive roll belts... having the belt exposed and drawing gunk into the pulleys accounts for most of the wear. I bought the heavy duty green ones once, but they didn't last much longer--I have concluded its a wear item. I don't vary the RPM's at all really... my machines torque peaks at just under 1700 rpm, so I run it 1850-2100. If I have bigger stuff I'll crank it up a little to get the flywheel going. Its awfully loud to blast at 2600, and blows fine at the lower speeds.