Some back and forth from there:
The large speedo drive gear is a shrink fit on the hub. To remove it simply heat with a blow torch and it will drop off. To refit, heat again and drop it on, making sure that it abuts the shoulder on the bub. Phelps. 4/21/09
How exactly do you heat the large speedo gear without heating the alloy hub? Applying heat will only expand the alloy more than the steel gear ring and the gear will be a tighter fit. It is a better bet to get the hub as cold as possible or, if not possible, apply no heat at all. Remove the gear with a gear puller and replace by tapping back into place. I always replace with a little Loctite which keeps the gear tight. Derek J. Peters. 4/21/09
I would certainly not advise using intense heat to a speedo drive gear, it is entirely unnecessary. If you look in Paul Richards's "Vincent" you will see that he says that the gear ring is only a press fit on the hub and he suggests removiong it with a 3 arm sprocket puller. I do feel his idea of refitting it by using an old piston to tap it into position is an excellent one. The staking after fitting that he recommends is no longer necessary if Loctie is used. Derek J. Peters. 4/22/09
Speedo drive gear removal: By using an oxy-acetylene torch which has an intense flame that can be directed locally. Heat the teeth edge of the gear quickly and it will fall off. If in doubt, place a short piece of tube over the hub to protect it from the flame. Phelps. 4/22/09