Catastrophic Belt Failure

Burgs

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Indeed. In fact the belt on my 11:1cr / 920cc Commando is 21mm wide...
Hi you are all correct, I am thinking of a single chain, not triplex, but one wonders, a belt that is thinner and lighter than a chain why so many failures, I have been riding motorcycles since 1965, most have had chain primary drive, one has had duplex chain, T120 Triton (1958 Featherbed 1959 Bonneville Engine?), triplex (Combat), and never had a failure?
Most of my bikes have been standard I must agree, but if you look at the later engines and their primary drive systems they have huge strong cranks, primary drive shafts ect compared to that of a Norton engine, so from an engineering view it doesn't look good.
Out rigger bearings and stronger engine plates, might keep things straight.
Burgs
 

mean gene

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Nobody seems to recognize the lighter weight difference especially the centrifugal load being reduced dramatically at 9000 rpm!!! Proper sized and aligned belt has to be better. Have had them on Harleys, a lot less noise and vibration. Still waiting to install Bob Newby on my 850, just not enough time. I'm glad you have pics of steel cords, seen a lot of belt drives in Industry but never steel cords.
 
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RoadScholar

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I read the initial posts about a day after the thread was born; I became increasingly less interested as I saw the momentum build. Tonight I caught up and read all the posts from day 1 to current. What I read coupled with my experience leads me to the following thoughts:

1) The pictures on the adjuster appears (was) what set off the events that shredded the belt.
2) The adjuster assembly was/is so corroded it should have been at the top of the parts shopping list much earlier, all the parts of this assembly show a high degree of neglect.
3) Going with dual adjusters may easily cause more problems than it solves.
4) Going at maintenance, piecemeal, without an eye to the system(s) affected quickly leads to repairs, which if done without system(s) awareness quickly leads to a lot of walking/pushing and much greater expense.

I have seen plenty of tired motorcycles, owned by well meaning people, that finally succumbed to a corollary of "don't fix it it ain't broke". Truth is that if you renew one system you move the stress to another which, probably, "ain't broke" by will be much sooner now that it has to bear the stress that it used to share as designed.

Best to all.
 
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Hi Road Scholar

Please could you explain why you think a dual adjuster may easily cause problems than it solves?

Thanks
 
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I read the initial posts about a day after the thread was born; I became increasingly less interested as I saw the momentum build. Tonight I caught up and read all the posts from day 1 to current. What I read coupled with my experience leads me to the following thoughts:

1) The pictures on the adjuster appears (was) what set off the events that shredded the belt.
2) The adjuster assembly was/is so corroded it should have been at the top of the parts shopping list much earlier, all the parts of this assembly show a high degree of neglect.
3) Going with dual adjusters may easily cause more problems than it solves.
4) Going at maintenance, piecemeal, without an eye to the system(s) affected quickly leads to repairs, which if done without system(s) awareness quickly leads to a lot of walking/pushing and much greater expense.

I have seen plenty of tired motorcycles, owned by well meaning people, that finally succumbed to a corollary of "don't fix it it ain't broke". Truth is that if you renew one system you move the stress to another which, probably, "ain't broke" by will be much sooner now that it has to bear the stress that it used to share as designed.

Best to all.
That’s is the question, at what point do you keep repairing verses a complete tear down to restore?


If you think the adjuster was due for maintenance can you tell me the last time you saw one fail?
 
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I have been running a belt drive for about 35 years on my 850 with no problems. I use two adjusters to maintain alignment of the belt. I was back in England visiting my parents so I took advantage, and the day off to drive up to Staffordshire and bought a lot of stuff from Norvil. Les Emery came to the counter for a chat and told me how to set up his kit. Run the belt at idle with no side plate on and adjust it to run true. that way you aren't relying on the belt being held in place by the side plates, then install the plate. On the way home I felt like dropping into a pub for a pie and a pint only to discover that they still closed the pubs from 2-5! Bless 'em :)
Nobody has mentioned that the way to set up the tension of the primary drive be it chain or belt is to make the primary too tight and then adjust if forward to the desired tension. This takes up all of the slack in the set up otherwise the gear box will get torqued backwards and tighten the belt or chain. The only problem I've had was last year a piece of the clutch tab washer broke off and ended up in the belt. I found it on a maintenance check before there was too much damage but I do need a new front pulley. I have had problems over the years with the original set up and now use a belleville washer (spring) with the nut torqued to 45 ft/lbs and blue loctite. I find it amusing that a broken part could lead to 7 pages of discussion on all of the engineering variables of belt and chain drives when the answer is to replace it and move on.
I hope I don't sound too pi**y but I've spent the last few days refurbishing the rear disc brake of a 1978 Triumph. There should be a special place in hell for whoever designed that piece of *&#$#%.
 
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I have been running a belt drive for about 35 years on my 850 with no problems. I use two adjusters to maintain alignment of the belt. I was back in England visiting my parents so I took advantage, and the day off to drive up to Staffordshire and bought a lot of stuff from Norvil. Les Emery came to the counter for a chat and told me how to set up his kit. Run the belt at idle with no side plate on and adjust it to run true. that way you aren't relying on the belt being held in place by the side plates, then install the plate. On the way home I felt like dropping into a pub for a pie and a pint only to discover that they still closed the pubs from 2-5! Bless 'em :)
Nobody has mentioned that the way to set up the tension of the primary drive be it chain or belt is to make the primary too tight and then adjust if forward to the desired tension. This takes up all of the slack in the set up otherwise the gear box will get torqued backwards and tighten the belt or chain. The only problem I've had was last year a piece of the clutch tab washer broke off and ended up in the belt. I found it on a maintenance check before there was too much damage but I do need a new front pulley. I have had problems over the years with the original set up and now use a belleville washer (spring) with the nut torqued to 45 ft/lbs and blue loctite. I find it amusing that a broken part could lead to 7 pages of discussion on all of the engineering variables of belt and chain drives when the answer is to replace it and move on.
I hope I don't sound too pi**y but I've spent the last few days refurbishing the rear disc brake of a 1978 Triumph. There should be a special place in hell for whoever designed that piece of *&#$#%.
Going back to the chain is only a temporary solution. The chain is more forgiving. The answer is that upgrades often expose weakness. You correct any weaknesses and continue on.
 

RoadScholar

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Please could you explain why you think a dual adjuster may easily cause problems than it solves?

If you have trouble with the factory adjuster you can easily compound the difficulty in getting and keeping the transmission square to the crankshaft. The additional left side adjuster is hard to get at and given the, roughly, 180 degree difference in orientation between the two it almost begs to cock the transmission. Virtually all belt failures are caused by lack of attention to detail. Jim Comstock made a post about belts a long time ago where he says that he changed out a belt at, I believe, 80K miles because he figured it was time to do so...

When installing a belt drive or even a new chain you have to get used to frequent checking/adjusting; either will settle down at some point. Proper torque on the central bolt is essential, but don't forget that the lower stud also presents enough clearance to be a factor in properly squaring the g/b. For street riding the second adjuster shouldn't be needed; diligent and timely inspection will win the day.

With a belt drive you can observe the "line" that the belt is running in, with a running engine, and correct accordingly, with a chain you look for shiny plates and teeth that shouldn't be showing signs of abrasion.

Best.
 
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I don't think I would use a belt drive without the dual adjusters, every time you tighten up the top and bottom bolts it's going to move a bit without them. Not really sure why you would feel for a street bike it's not needed?? The box needs to be square no matter what it's running on or it's going to fail. As triumph2 says it needs to be setup so the box cannot move back and pull the belt tighter. Belts are fine and last a long time if set up correctly.
 

RoadScholar

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If you think the adjuster was due for maintenance can you tell me the last time you saw one fail?

I believe that your's is the first one I've seen that failed and, frankly, I have also never seen one that even comes close to looking as gnarly as the one that, in all likelihood, triggered the events leading to shredding the belt. Additionally I noticed that the upper right side of the cradle in the picture shows what appears to be rust erosion pained over that insures that proper torque can't be distributed evenly. I'd go one step further and suggest that the corroded cradle should be thoroughly examined before considering returning it to active service, but it's hard to judge the extent of the full corrosion damage from the picture; someone did paint it over and whether that was an attempt to stop the rusting and/or to allay a buyers eyes I can't say.

I like reading your posts and your videos and always learn from them, and/or the attendant responses. Keep up the good work.

Best.
 

Fast Eddie

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I don't think I would use a belt drive without the dual adjusters, every time you tighten up the top and bottom bolts it's going to move a bit without them. Not really sure why you would feel for a street bike it's not needed?? The box needs to be square no matter what it's running on or it's going to fail. As triumph2 says it needs to be setup so the box cannot move back and pull the belt tighter. Belts are fine and last a long time if set up correctly.
Well I use double adjusters myself, but nevertheless I can relate to Roadscholars point. If the cradle and gearbox shell etc are all good condition, with good faces and good alignment then a road bike (ie something that does not have 100bhp and does not get revved to the max all the time) simply should have no need for a second adjuster.

However, due to the difficult access, it is quite easy for a second adjuster to fail to be adjusted perfectly, in which case it could cause an issue.
 
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Well I use double adjusters myself, but nevertheless I can relate to Roadscholars point. If the cradle and gearbox shell etc are all good condition, with good faces and good alignment then a road bike (ie something that does not have 100bhp and does not get revved to the max all the time) simply should have no need for a second adjuster.

However, due to the difficult access, it is quite easy for a second adjuster to fail to be adjusted perfectly, in which case it could cause an issue.
So you feel that it's not as critical for the belt on a road bike? I myself want to be sure it's as close as I can get it, and have a better chance at it lasting longer. Thanks for your opinions guys.
 
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I believe that your's is the first one I've seen that failed and, frankly, I have also never seen one that even comes close to looking as gnarly as the one that, in all likelihood, triggered the events leading to shredding the belt. Additionally I noticed that the upper right side of the cradle in the picture shows what appears to be rust erosion pained over that insures that proper torque can't be distributed evenly. I'd go one step further and suggest that the corroded cradle should be thoroughly examined before considering returning it to active service, but it's hard to judge the extent of the full corrosion damage from the picture; someone did paint it over and whether that was an attempt to stop the rusting and/or to allay a buyers eyes I can't say.

I like reading your posts and your videos and always learn from them, and/or the attendant responses. Keep up the good work.

Best.
As far as I know the cradle as never been out of the bike and never repainted. You're just seeing typical wear and slight corrosion from the lack of paint in a couple areas. It's just surface rust and nothing to worry about. The bike has been in the family since the early 90s and while maintenance has been constantly done the only major repair was an engine rebuild. This is what an unrestored ridden bike looks like.

If anything the gearbox could stand a rebuild and I have that on my list for next winter along with the forks. When you have multiple bikes in your stable it's hard to get to all of them. I certainly have more projects than time at it was the same when my brother had the bike. It's like having multiple kids, you have to share your attention and someone is going to feel neglected.
 
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Fast Eddie

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So you feel that it's not as critical for the belt on a road bike?
Correct.

Remember, they are called ‘tensioners’ not ‘hold in place devices’ !

If a everything is in line, then there is just no ‘need’ for any extra ‘belt and braces’. The clamping forces of the top and bottom fixings being more than enough for the 40 ish horses involved.

However, as already said, an owner who does not always use the necessary care and attention could easily miss-adjust the second adjuster which can be very difficult to get at. Or, the difficulty of getting at it may prevent fine tuning of belt adjustment after initial bedding in. Swoosh‘s brothers bike comes to mind, he would have to remove his e start motor to adjust the belt. Now, maybe HE will, but that’s the kind of thing that might make many owners think ‘nah... it ain’t so bad... I’ll do that another day’.

Thats not to say that some road bike users do not WANT extra belt and braces... like you... and me...! I’m not saying they should be banned, just that they are not strictly necessary, and agree with the notion that they could therefore cause more harm than good for some owners.
 
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I agree that the trans adjuster(s) are for static adjusting rather than holding during acceleration.
If you look at the rear wheel which I believe has 2x the force acting on it, the single axle bolt/clamp holds the fort.
The wimpy sheet metal chain adjusters wouldn't hold much if the axle clamp ever failed to hold.

Glen
 

gortnipper

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I agree that the trans adjuster(s) are for static adjusting rather than holding during acceleration.
If you look at the rear wheel which I believe has 2x the force acting on it, the single axle bolt/clamp holds the fort.
The wimpy sheet metal chain adjusters wouldn't hold much if the axle clamp ever failed to hold.

Glen
These wimpy adjusters are not present on pre mk3 bikes. If the axle bolt comes loose there is nothing to keep the wheel from moving aft...one side...then the other...back...and forth...
 
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