Lock lube, snake oil?

Aha!

Does that mean that the centre bolt actually pulls an "expander" up the centre of the shaft, so that it expands radially to grip both the drive gear and the individual cams?

If that is the case, then it is effectively very similar to a tapered joint. The point is, a radial interface with sufficient contact pressure

Whereas it is more difficult to get sufficient axial force to make a strong joint. There are all sorts of reasons. For example, the radius at which the friction force acts is normally significantly lower than the radius at which the wheel force is applied. Assuming the wheel has some radial clearance on the shaft, then radial or axial forces at the wheel rim will tend to make the wheel move with respect to the shaft, leading to fretting in the clamped joint.

the end of the cam is flat and round, it sits in a slight (2-3mm) recess in the cam wheel which may be plastic or metal, the bolt is renewed each time and is torqued up, may be hex or reverse torx head, new bolts come with the belt kit.

I think I need a picture!

OK, not what I suggested above then. But I note the comparatively large area of what I take to be the axial face which carries the torque.

No apologies needed at all. Very interesting lecture all the same;)...

Thanks! My wife has special body language for family and social gatherings that says "Sorry about this, please ignore the old fool".

:-)