Catastrophic Belt Failure

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As you can see the gearbox adjuster failed. I had planned on getting the second adjuster but wanted to try it with one first. Well that didn't work. Top bolt was tight, maybe not tight enough? The adjuster is original and a little rusty.

We had a good ride yesterday to the club meeting, but I didn't check the belt after the ride. I had checked it after the previous ride and even hot there was the correct play.

A call to AAA and the bike was picked up and safely home. I have it on the morgue table now and will get in there to clean it up.

And no, I'm not going back to a chain.
 
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Yeah, looks like that belt was tracking outwards on both pulleys. You'd think that the upper trans nut/ bolt would have still kept the adjustment even after the adjuster broke, but that's what probably broke it.
 
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Had that happen with an RGM kit (nothing wrong with the kit, the bearings/alignment need to be 'just so' and mine weren't).
Bits of wire shards clustered around the alternator rotor, fur everywhere and other internals looked as if they'd been laminated with clear plastic....
 

Fast Eddie

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That’s a bummer swoosh!

I’m struggling to think why the adjuster would snap. The rear chain always pulls the primary and not vice versa, so your adjuster would be in compression. I can’t see why / how being in compression would make it snap?

But then I notice how it seems to have rotated after breaking. Is this becasue it’s not tightened fully to the cradle? If so, I guess vibration could have caused it to break.

Also, some adjusters I have seen are not symmetrical, they have to be mounted the right way to line up properly with the square locating part, if fitted the wrong way the threaded rod will be under huge tension, which would be an obvious potential to cause it to snap.

But, even without the adjuster, if the gearbox mounting bolts are properly tight and a proper fit, they should hold the gearbox adequate for a short run and at a sensible pace... Unless you’ve been doing drop clutch drag starts or mixing with the stunting / wheelie boys again....?
 
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That’s a bummer swoosh!

I’m struggling to think why the adjuster would snap. The rear chain always pulls the primary and not vice versa, so your adjuster would be in compression. I can’t see why / how being in compression would make it snap?

But then I notice how it seems to have rotated after breaking. Is this becasue it’s not tightened fully to the cradle? If so, I guess vibration could have caused it to break.

Also, some adjusters I have seen are not symmetrical, they have to be mounted the right way to line up properly with the square locating part, if fitted the wrong way the threaded rod will be under huge tension, which would be an obvious potential to cause it to snap.

But, even without the adjuster, if the gearbox mounting bolts are properly tight and a proper fit, they should hold the gearbox adequate for a short run and at a sensible pace... Unless you’ve been doing drop clutch drag starts or mixing with the stunting / wheelie boys again....?
I will admit to giving it a handful of throttle before it let go so I doubt the bolts alone would have held.
 
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swooshd,
I've been down that road too with a CAA trailer but my belt was just old. looks like the whole upper bolt shifted aft judging by the witness marks on the paint in front of the lollypop holders.
Not the fault of the belt as it just became too tight and got miss-aligned. just be positive and work out the bugs. I use the RGM twin Lollypop system which I bought from Frank (RIP) at Clubman Racing. Works for me. Or you can try ludwigs design.
Cheers.
Tom
 
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baz

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I have a belt drive with two adjusters
On two occasions I've found the top gearbox bolt had come loose but the gearbox/primary belt still fine
I'm really not sure what causes it to work loose? I did have a maney outrigger at that time,now removed
Sorry to see your carnage
But it coulda been worse if it had been a primary chain!!
 

SteveA

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My Rickman has two fixed plates, one each side of the gearbox/engine plates! Work out the shaft centres for correct tension and 'fix it'.
 

Fast Eddie

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Ludwig uses plates behind the fixing nuts that he secures to the cradle, thus creating fixed centres.

An alternative I've been pondering is making some inserts to go in the slots, either side of the stud, thus allowing no (or very little) movement.
 
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SteveA

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That’s a bummer swoosh!

I’m struggling to think why the adjuster would snap. The rear chain always pulls the primary and not vice versa, so your adjuster would be in compression. I can’t see why / how being in compression would make it snap?

But then I notice how it seems to have rotated after breaking. Is this becasue it’s not tightened fully to the cradle? If so, I guess vibration could have caused it to break.

Also, some adjusters I have seen are not symmetrical, they have to be mounted the right way to line up properly with the square locating part, if fitted the wrong way the threaded rod will be under huge tension, which would be an obvious potential to cause it to snap.

But, even without the adjuster, if the gearbox mounting bolts are properly tight and a proper fit, they should hold the gearbox adequate for a short run and at a sensible pace... Unless you’ve been doing drop clutch drag starts or mixing with the stunting / wheelie boys again....?
My guess would be that the adjuster threaded section into the lollipop head was already cracked, probably from the top gearbox bolt rotating the lollipop head on final tightening!
 
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img-2186.jpg


https://shop.kingpincomponents.co.uk/norton/transmission/norton-primary-chain-adjuster-threaded-hole

I was planning on getting one of these but they were out of stock when I was putting it back together. RGM wants $26 per item for shipping. :rolleyes:

I hope that fits a Commando. With my luck it's for the older bikes.

Primary chain adjuster in stainless steel. These have a 5/16 x 26TPI male thread and a 9/16 x 26TPI hole to take the gearbox bolt where adjusters are to be fitted to both sides. Designed to be fitted on the drive side of the bike, you will also need the plain version on the other side.
 
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That’s a bummer swoosh!

I’m struggling to think why the adjuster would snap. The rear chain always pulls the primary and not vice versa, so your adjuster would be in compression. I can’t see why / how being in compression would make it . . .
The short answer is the orginal setup was for a 500 and here we are some 50 years on with people being ask of it to cope with even bigger engines. . . . .
 

Onder

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Once the belt is correctly adjusted, it doesn't stretch so you adjustment should be final and FE's idea of a piece to fill the
empty area in the cradle is great if you can make the pieces. Make a tracing of the cradle area and cut and file away on a piece
of stock. After seeing the carnage makes me think I ought best get to work.
 

Craig

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Good luck with your repair Swoosh ! Several years ago I had a similar event , only I was running chain , a terrible mess , new stator , rotor , inner half of primary and a tri-plex chain .... unlike your situ though I rode the damn thing all the way home right into shed before I shut it down , figured damage was done and would see how close I could get before using the cell phone .... surprised still that the bike took me all the way ..... hope your fix turns out to be permanent and the next time you in there you are replacing worn belt !
 

gortnipper

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I got a stainless lollipop from Rockypoint a few years ago. I think Matt might have bought out his stock?
 
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