Magnum swapping the 72 Scamp!

The rounded rod should be a little wider than the base of the groove, that way the groove will show you what the belt "sees". Pulleys can have different thickness walls, and any difference will set up a harmonic vibration at various RPMs. I've used washers to shim the alt to the right spot then cut a section of tube to replace the washers and put it in the right place. Hope this helps.