Catastrophic Belt Failure

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Not that I'm unsympathetic to your plight, but I've seen more troubles and money spent on belt drives than I ever experienced in 45 plus years of Norton/BSA/Enfield/Triumph chain primary drive usage.
The belts are less forgiving but the advantages can outweigh the risks. Sometimes.
 
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I'm with you there
Precisely! Once the belt distance is set, its good to go. No fuss..., "Set and forget".
What I have seen so far in failures from other ONO Norton owners is the belt is set too tight using the single lollypop set up. I have also seen bad tracking with the wrong belt used.
 
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Yes, check the mainshaft for runout. I had catastrophic failure of the chain primary (grenaded alternator rotor) that bent my mainshaft. Back in those days Old Britts had used parts for sale, Fred found me a shaft with .003" runout.
What do you think of this runout, the best I can tell it's about .005"

 
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What's your 4th gear sleeve bushings like? Loose bushes will add to your run out.
 
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marshg246

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INMHO the thing to check is the runout of the rear pully with the clutch assembled and engaged. Five thou at the mainshaft may not mean anything with everything loose. To me, the bushing should be a tight fit without binding.
 
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I was just checking to see if the mainshaft was not bent. Is there a spec on how much the mainshaft can move?
 

marshg246

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I was just checking to see if the mainshaft was not bent. Is there a spec on how much the mainshaft can move?
Not that I know of.

With all the variables, the only way to truly check the mainshaft itself is with it out of the gearbox and using a flat surface. I had one that looked fine and installed fine but the gearbox would bind when turning by hand. Once I measured it on a piece of plate glass, it had about a twelve thou bend end for end. It was bent in the middle. I didn't do it, but I bet testing the bend like you were would have shown as 2-5 thou.

If you push the mainshaft in one direction and rotate it while checking with a dial indicator and you have five thou, I would take it out and check. Alternatively, while not turning it, push it to the front and back and see how much it moves (roughly checks the two bearings and one bushings). Do that four times - rotating the mainshaft 90 degrees in between. In either case, in a perfect world, there would be less than one thou and I would get suspicious if there were more. That said, since we are supposed to rotate things and set the primary and final drive at their tightest point, it's clear that we're not talking precision equipment here!
 

maylar

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What keyed me to replace the main shaft after my mishap was that the clutch chainwheel had a noticeable wobble to it while rotating it slowly. I would expect that a bend, if it's there, would have happened on the primary side of the gearbox, and not in the middle.
 
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So even though I remember tightening down the top bolt maybe I didn't get it tight enough. I don't know what else could have happened.

I'll go back to the chain and leaky primary for now. I need to get a guide made for the front belt pulley unless someone had a Maney front pulley they aren't using...

It was interesting that the old lollipop was just brazed. The new ones are welded and chromed (although this one was in the chroming tank too long and the threads needs some working to get the nut on). Someone remind me to get the second nut on the adjuster.

Just waiting for the new stator from @marshg246 and I should be back on the road. I'll also get the dual adjuster ordered. Maybe I'll have the belt back on before the end of the summer.
 

marshg246

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I'll go back to the chain and leaky primary for now. I need to get a guide made for the front belt pulley unless someone had a Maney front pulley they aren't using...
Not sure how you would tell if they fit, but Norvil has a variety of front pulleys that they sell individually for Commando. They specify the number of teeth and width. Might be worth asking if they have what you need. I would think you would need to know the diameter, width, number of teeth, and width of the teeth. Alternatively, if you know the belt you use they can probably say if it is compatible with their pulley.

The one Norvil belt drive I worked on had a straight pulley - nothing to keep the belt on - I'll never touch one again unless it has dual adjusters for the gearbox - it was an 8-hour nightmare getting that belt to track on a 650SS.
 

gortnipper

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Bugger. With that rust on the interior of the lollipop's big O, that has been brewing for a while and would have happened even with the chain drive is my guess.
 

Onder

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It is amazing how detailed digital photos can be. You see stuff you would miss by eye even with a strong glass. Perhaps it would be useful for all of us
to use this as an inspection tool.
Brazing can be very strong but full penetration welding is likely a better method.
 

Fast Eddie

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It’s a bad joint, no question about that. The braze should have been drawn into the joint by capillary action, like when you solder plumbing fittings etc. and would then be a very strong joint.

However, it’s not the cause here at all. That adjuster, acting in compression, would work perfectly even if it was assembled with no brazing or welding at all.
 
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It’s a bad joint, no question about that. The braze should have been drawn into the joint by capillary action, like when you solder plumbing fittings etc. and would then be a very strong joint.

However, it’s not the cause here at all. That adjuster, acting in compression, would work perfectly even if it was assembled with no brazing or welding at all.
At some point the gearbox went forward.
 

Deets55

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At some point the gearbox went forward.
Maybe the gear box got cocked sideways, ie drive chain pulling the primary side back, causing the timing side forward. Now the timing side is no longer in compression. I know that would mean a lot of slack in the gearbox/cradle fit, just spitballing a guess.
 

Fast Eddie

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At some point the gearbox went forward.

I assume that’s a working hypothesis rather than a known fact?

As Deets says, it’s really difficult to speculate as to how that could occur unless the top bolt was really loose...

Being pulled forward by engine braking is all I can picture, but only with a super loose bolt.
 
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I assume that’s a working hypothesis rather than a known fact?

As Deets says, it’s really difficult to speculate as to how that could occur unless the top bolt was really loose...

Being pulled forward by engine braking is all I can picture, but only with a super loose bolt.
Well, considering I was looking at the road and not the gearbox at the time it's all a hypothesis. The top bolt was not loose. But it also wasn't tight enough to hold the gearbox in place.

At this point the conjecture isn't too valuable. Dual gearbox adjusters are the solution along with proper torquing of the gearbox bolts. And good luck, which I seem to be devoid of.
 
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