If you can find a spare nut, or buy one, make cuts across the thread with a sharp hack saw blade, then carefully screw it on to the yoke. It will do a pretty good job of cleaning up bruised threads. If it won't start on, I have cut a section out of a nut, about a third, and used it to clean up threads by starting with it on the shaft and working toward the end. Works well on bronze, so I suspect alloy too.
Russ