So what is the secret to keeping the magneto shaft from moving when you tighten the magneto extractor bolt on the sprocket/AAU? I just retimed an Atlas. I have done this this dozens of times on different bikes. Sometimes after I set the points to break open at 28 to 32 btc (depending on which timing theory I happen to be adhering to at the moment) I can tighten the magneto extractor bolt and nothing moves. Other times I have to keep experimenting with setting the points to break retarded more or less as much as the timing moves when I tighten the bolt, until it ends up in the right place. I know Bernie Nicholson in Modern Motorcycle Mechanics recommends giving the bolt a whack to set the sprocket against the taper on the magneto shaft. I confess that I have tried this on occasion, with mixed success, but it strikes me as a very unsympathetic way to treat the magneto bearings. So what is the lost technique? This timing "system" has been around for ever. The old timers in their sheds must have figured out a reliable secret approach. Anyone know?