My Mk3 E/S failed while out on a run two months ago. Several presses of the starter after stalling at a junction and it not firing properly. I think there was a backfire and I heard a loud clonk. But it still kickstarted and I ran for another 100 miles. The starter motor would just run freely with no drive. I did wonder if metal fragments of something or other might be moving around the chaincase.
When I stripped it down this week I found that the nut on the anti-backfire device, that applies pressure to the belleville washers, had shattered into seven pieces. At the bottom of the chaincase were the six pieces of nut hex plus the six ball bearings normally in the middle of the anti-backfire device. I was relieved that it was such a low-cost and simple to repair breakdown.
Why did the nut break apart? It seems it was a stress breakage with a crack visible in one of the pieces. I had set the torque of the anti-backfire to around 50-70 ft/lbs many years and some 10,000 miles ago. Wear on the gear shows that the balls had been running around on the 'release' track so perhaps vibration shock built up?
The attached photo shows the broken nut and a new one to compare.
I will add a good word for Andover Norton. I ordered new parts from the web at 2:00 pm on Thursday, paid £1 extra to have Royal Mail 24 hours delivery, received a confirmation email at 3:00 pm to say it was being despatched, and the envelope arrived at 1:00 pm Friday.
Never seen a failure like…
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Yes, totally agree with you…
Yes, totally agree with you about the nut annoyingly moving as you test the torque. For that reason I will copy your locknut idea - thank you!
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Never seen a failure like that one Norm. If you had reset the release torque on the device your 'peening' of the locknut could have damaged it. I dislike the method of locking the nut to stop it revolving on the shaft. as when you test the breakaway torque the action of the balls lifting the plates apart turns the plates and the lock/adjusting nut so 'unsetting' the desired torque setting.
I lock the nut differently. Much easier to set and adjust.
I machine the 'peening' edge off the nut and screwcut a thin locknut to replace it. Once set to the desired torque, remove the locknut, apply Loctite and refasten the locknut. Tighten securely.
I can get two locknuts from a standard 1/2" UNF nut cut in half with a junior hacksaw. Cut ends faced up true to bore.