commando kickstart rotation

That has all the hall marks of gearbox layshaft bearing failure.

Strip the box down and check, don't ride the bike until you've done this, it can cause the box to seize with disastrous results.

sam

Yes you can do this at home, I repaired my layshaft bearing with the bike parked in the street, the main shaft can stay in and the rest of the gears and layshaft are all removable. You take the layshaft bearing out using a hot air gun on the gearbox shell and use a hammer on a solid piece of hardwood against the outside gearboxof shell from the primary side to shock it out. Not too much different to a C15 gearbox. The replacement bearing is a roller not a ball so you need to shim the endfloat. It's the cage that fails and the balls fall out and jam the gears, I found balls split into 2 in the bottom of my box.

Almost certainly the layshaft bearing indeed.

Although it is more work to remove the box, I can't help thinking that it's the easier way of doing it and if there is any additional damage and the shell has to be removed, it's easier if the primary drive has been loosened first.

I didn't need to hammer the wood against the shell, heated the shell up and the bearing came out with the layshaft.

sam

It is possible that if the layshaft ball bearing has failed, it could have allowed the shaft to move outward enough to crack the casing - quite a common outcome, but not a disaster, as the casing can be welded. That could explain your oil smell? I had found this damage on my Mk 3 casing, but it had also cracked between the two bearings, which is different matter and resulted in a new casing being required.

Andy

I had a layshaft bearing failure on a 650SS I was restoring and it was terrifying. The gearbox locked up and locked the rear wheel. As John Holmes says the cage had broken and I had no warning and it was sudden.

Now, I always change the layshaft bearing to a roller first with any new Norton. There does seem different opinions about the best type of replacement.