Millyard Special

[Ducadini]

No, there is a very small key to hold that sprocket.
I think the Amigo/Novio engines had no key but a pressed-on sprocket (and aluminium camshaft).

ciao
ducadini

[Duccout]

The skill of some people is amazing; I came across a You Tube video yesterday of a guy repairing a small Honda crank. The mainshaft had sheared at the bearing, and this guy ( I don't know where he was, possibly India or East Europe) found an old scrap piece of shaft, centred it, turned it, welded it to the broken flywheel, turned it down to dimension, threaded the end and machined the taper for the flywheel, then rebuilt the crank. Stunning.