Catastrophic Belt Failure

baz

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My experience with a belt drive on my A65 was brief and expensive. Belts were $100 and lasted weeks no matter how meticulously adjusted. It simply removed two chunks of teeth till it lost drive and I was stuck at the side of the road. I only did it twice to realize the triplex was problem free with the crank and G/box shafts with extra bearings to keep the run in line. No failings from the chain even with 73ftlb of engine torque, for the last 18 years.
You can't compare a belt drive on an a65 with fixed centers (centre's were machined at the factory and may not have been precise !!) To a pre unit design such as the pre MK3 commando
 
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On the A65 how did you adjust the tension on the belts? It's a unit construction so the crank and mainshaft are fixed, right?
You use a tensioner with the lining removed, this belt was designed to run in oil. When it gets hot the shafts move apart a little so you adjust it for hot, and the motor does get quite hot. This is a big 883cc motor, it could get damaged just kick starting. It did snap the shaft of a kick lever once. Not that I'm very heavy.
 

Burgs

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My two bob's worth, I have considered belts, but the design of a Norton primary drive is based on compact drive shaft dimensions, a belt drive exasperates this by moving the bending moments of the crankshaft and gearbox shaft, out further than the original design, add in the more HP you chaps are putting in over the original design will, in engineering terms add more stresses. and result in misalignment of shafts and sprockets.
The Norton engine plates will bend and flex as they are basically the same strength as that of a 500cc Dominator :) all this will not be good for a belt that has been designed for everything being strong enough to maintain alignment without shaft bending and frame deflections.
A chain will withstand most of these issues so long as lubrication is maintained.

Burgs
 

robs ss

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A belt is fundamentally sound on a Norton if all is well. There are plenty out there giving good service as proof of this.
Totally agree - I think the bending moment argument is a bit of a Furphy.
If you're set up correctly (as you should be) belts (and chains) work as intended.
 
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Yes I agree with the misalignment causing the failure. But been following this post and do not recall anyone describing the belt's structure. The belt drives I have seen came with an entry level belt, rayon- fiberglass cords. There are Kevlar as a middle load and carbon fiber for the max. I believe the Torque load is more important then HP. What was the cord material?
I have a couple of BNR belt drives and an RGM belt drive
Those all have multiple endless steel cables to carry the load. The Rubber/kevlar is just there to form the drive teeth and hold the cables in their place.
Chain drive primaries are excellent overall. The negatives are
-They are a much heavier drive system.
- They can be leaky- really leaky with the Dominator tin cover.
- When the chain does let go, the destruction is tremendous.
I believe that the main reason many vintage racers prefer belt drives. They tend to stand up very well to race engines and racing.
Bob Newby hasn't made a business out of failed belt drives.
With belts it seems the main problem is getting the alignment correct. Once it's there , they work for a very long time.
One of the Newby's is on the 1360 Vincent, fixed centres.
That one carries a lot of power without any problems so far.
So either drive will work, one is way lighter and does not require oil in the primary.

It's a bit like the stainless steel/ steel discussion.
When someone posts a photo of a broken part made from stainless, ten people post up explanations of how the part broke because it is made of stainless, which is , as is well known, too brittle, too soft, too hard, too flexible, difficult to weld and prone to cracks from vibration.
The same part made in steel breaks and the response is "when that broke on my bike I ordered a new one here, they had the best price"

Glen
 
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My two bob's worth, I have considered belts, but the design of a Norton primary drive is based on compact drive shaft dimensions, a belt drive exasperates this by moving the bending moments of the crankshaft and gearbox shaft, out further than the original design, add in the more HP you chaps are putting in over the original design will, in engineering terms add more stresses. and result in misalignment of shafts and sprockets.
The Norton engine plates will bend and flex as they are basically the same strength as that of a 500cc Dominator :) all this will not be good for a belt that has been designed for everything being strong enough to maintain alignment without shaft bending and frame deflections.
A chain will withstand most of these issues so long as lubrication is maintained.

Burgs
I'd like you to explain the "moving the bending moments of the crankshaft and gearbox shaft, out further than the original design" part please. The belt runs in approximately the same location and if anything diminishes the forces on the parts due to the lighter weight.
 

concours

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"Those all have multiple endless steel cables to carry the load."


43 years using these belts in industrial & automotive. I'd not yet seen steel cables.
 
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RGM describe theirs as: 'Steel backed polyurethane'.... When they abrade they can wear the alternator stator as the debris clings to the rotor... (Been there... done that )
 

Fast Eddie

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This just popped up in ‘random media’....

83E87DAC-85FD-41F5-9913-043D3E0261CF.jpeg
 

concours

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I wouldn't put that (above shown) belt on a sewing machine.

 
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This is a badly stored synchroflex at10, possibly stored in something acidic.
I purchased the NOS RGM belt drive on eBay.
The seller did not include a photo of this damaged portion.
You can clearly see the steel cables.

Glen
 

concours

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This is a badly stored synchroflex at10, possibly stored in something acidic.
I purchased the NOS RGM belt drive on eBay.
The seller did not include a photo of this damaged portion.
You can clearly see the steel cables.

Glen
Don't use it.
 

Burgs

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I'd like you to explain the "moving the bending moments of the crankshaft and gearbox shaft, out further than the original design" part please. The belt runs in approximately the same location and if anything diminishes the forces on the parts due to the lighter weight.
It's pretty simple, the belt is wider than the chain, so the centre of the bending moment moves out accordingly.
Burgs
 

Fast Eddie

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It's pretty simple, the belt is wider than the chain, so the centre of the bending moment moves out accordingly.
Burgs
That’s why a belt should always be set up to run as far inboard on the clutch pulley as possible.
 

Burgs

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That’s why a belt should always be set up to run as far inboard on the clutch pulley as possible.
Yes it should, many years ago, I designed a belt drive system (75mm wide belt) for a prototype flying boat and learnt a hell of a lot out of that one especially noise, and bending moments on the shafts if you can keep them in line, no bending they work well :).
But what we ended up with was a hell of a lot more beefier than any Norton set up you are looking at here.
Admittedly the power was from a supped up WRX Subaru engine, funny thing about that project was the aero dynamic design made it dive rather fly above the water :D.

It is rather simple, move the centre of moment out you introduce bending moments, yes I agree there are a lot of successful belt drive systems out there, but there are as many unsuccessful systems.

Burgs
 

Fast Eddie

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yes I agree there are a lot of successful belt drive systems out there, but there are as many unsuccessful systems.

Burgs

Hmmm, I definitely agree there are many unsuccessful INSTALLATIONS... I’m not sure there are many / any unsuccessful SYSTEMS on the market today ?
 
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