I just don't see what you are talking about. Any coil I have adjusted the coil is mounted with slotted holes. Install a .012 +/- thick paper card and have the magnet pull the coil plus hold it with one hand and tighten the screws with the other. If you are just talking about a few thousands one way or the other it will not make any difference. Not that I have tryed it but I have read that it could be as far away as .030 and still run. I have yet ever cleaned the rust or dirt off the magnets unless maybe I had a bad buildup of such. If the coil is bad it gets replaced not revived.