MKIII start failure

Helping a friend with his estart that suddenly just went whirrr.
Turned out to be the special nut that clamps the Bellville springs on the anti-backfire shaft (see part 9, lower left, below)
The body of the nut was fine but the "hexed" flange was broken off into 5 pieces meaning that it could no longer clamp the bellvilles.
Probably a previous history of backfires weakened this nut.

My questions to you are:
1. Has anyone else seen this failure and care to comment?
2. That "hexed" flange is quite thin (and weak), another under-engineering by Norton. Has anyone found a stronger after-market one?
Cheers
PS: I do know that that nut has to be tightened until the ball-clutch just clicks over at 50 ft ib (both directions)

Yes the nut #9 broke on mine earlier this year, it may have been partially seized and looked as if it had canted i.e. not lifted squarely.
I will be rechecking mine next week as even though I had torqued it the correct way, Loctite and peened it gives the occasional "clatter" on start up.

possm said:

I will be rechecking mine next week as even though I had torqued it the correct way, Loctite and peened it gives the occasional "clatter" on start up.

Click to expand...

That shows the anti-backfire device is working so don't adjust it so it doesn't slip.

Well - parts arrived (new special nut and balls) so will be assembling tomorrow.
My method last time was to clamp the large cog in a (soft jaws) vise and clamp a large vise-grip, with 1mm ally insulator, onto the "inner" odd spline.
My neighbour had welded 1/2" key steel either side of the vise-grip.
That way I could attach a torque wrench and tighten the nut until I got 50ft.lb in both directions.

Anyone got a better method?
Cheers

robs ss said:

Well - parts arrived (new special nut and balls) so will be assembling tomorrow.
My method last time was to clamp the large cog in a (soft jaws) vise and clamp a large vise-grip, with 1mm ally insulator, onto the "inner" odd spline.
My neighbour had welded 1/2" key steel either side of the vise-grip.
That way I could attach a torque wrench and tighten the nut until I got 50ft.lb in both directions.

Anyone got a better method?
Cheers

Click to expand...

I got the splined #17 thrust washer from AN and welded it to a socket for the torque wrench. Afterword, I followed the "Old Britts" tech article on this. I only checked the torque clockwise.

Don't lose or forget to put back the #16 e-clip at the outboard end. Pictured is the Napa replacement. It was too big for the recessed area in the aluminum alternator housing. That would not have worked. Luckily, I finally found the original e-clip.

Edfury828 said:

I got the splined #17 thrust washer from AN and welded it to a socket for the torque wrench. Afterword, I followed the "Old Britts" tech article on this. I only checked the torque clockwise.

Don't lose or forget to put back the #16 e-clip at the outboard end. Pictured is the Napa replacement. It was too big for the recessed area in the aluminum alternator housing. That would not have worked. Luckily, I finally found the original e-clip.

View attachment 114593

Click to expand...

Sorry rob ss, but I am now obsessing about torqueing the the unit in both the CW and CCW directions.
Is there a reference, or link, or simple explanation for this?
Wouldn't the device only need to operate in one direction?
Does a correct setting in the CW direction generally also work in CCW, or is it always a concern to check both ways?
I have not yet started my bike since adjusting my device. I hope nothing explodes!

I had miss unstood the 50 lbs torque. Maybe I misunstood you. The clutch is to release at 50 lbs torque, you don't torque the nut to 50 lbs