Remove the magneto from the machine following the instructions in your
machine's service manual.
If fitted with an automatic timing device (ATD) for advance and
retard, undoing the ATD retaining screw more than a few turns should
engage its self-extract mechanism, and a further turn of the retaining screw should release the taper.
If fitted with a fixed drive pinion/sprocket, a puller will be
required. With some pinions/sprockets, a sleeve of the puller is screwed
into the pinion/sprocket, and an extractor screw is then tightened against
the end of the magneto drive shaft to release the taper. With others, a
universal two-legged puller can be employed, or there may be provision for
attaching a bridge puller. Resist the temptation to crowbar the
pinion-sprocket off by levering against any mating surfaces of the timing
With magdynos, it is, of course, also necessary to remove the dynamo
and its drive train.
Some of fixing nuts/screws may be difficult to access and specially
adapted tools may be required. If in doubt and your service manual doesn't
help, ask on the appropriate web forum for your machine.