Model 50 Gearbox Sprocket - simple question

It's left hand Mike.

This might be teaching you to" suck eggs", Mike, but if the shaft is spinning anti-clockwise a normal nut will tend to tighten and vice versa. Inertia and all that. So a clockwise spinning shaft will have a left hand (anti-clockwise) tightening nut. George

But the gearbox mainshaft spins anti-clock (viewed from the sprocket side) and has a left hand thread......

Ian McD

Trust you Ian!! I got it wrong again. My abject apologies to all of you. Just for my own peace of mind though, surely if the shaft is spinning a/clockwise the nut will try and tighten with a normal right hand thread and loosen with a left hand thread? George

Theory seems fine, but the Norton designers (and maybe the Sturmey Archer guys before them) either didn't know about the theory or had other reasons to give the shaft a left hand thread.

Ian McD

Its like car wire wheel spinners (and goods vehicle wheel nuts?). If you wobble a slightly oversize ring clockwise round a shaft the ring itself rotates anticlockwise. Don't know exactly where that gets us but anyway the result is that the spinners knock off the opposite way to how you might think at first. I wonder who discovered it? And how painful it was...

I notice that whilst the nut may have a left hand thread the designers then fitted a locking plate to stop it undoing. What's that all about? Why not have a right hand thread and save money on the locking plate and screw? The clutch body locking nut is right hand thread on an a/clock spinning shaft (as I would expect) and as Ian and I know to our cost! George

The two cars I owned (many years ago!) with "Knock- on" wheel nuts, had right hand threads one side, and left the other. Don?t ask which!

Many years ago I was a green AA patrol and was temporarily driving a Bedford recovery vehicle. I had a puncture in one of the n/s wheels and after swearing and sweating for half an hour (and bending my wheel brace) I had to make the embarrassing radio call for assistance.

When the sergeant arrived after a little while he said "You do know that the wheel nuts on the n/s are left hand thread don't you?" Well, no........

Haha! Nice one Ian. I think we've all been there! G

I suspect the design difficulty is that the narrower shouldered portion of the shaft that takes the nut is rather short. So it does not stretch very much when the nut is tightened so vibration easily loosens it. Also the nut is too thin to be torqued as much as usual for its size. Left hand thread helps but apparently not enough..hence the lock plate. As Anna is fond of telling us..the Norton design engineers were good at their job.

( PS this editor automatically changes nut to but every time!)