Catastrophic Belt Failure

[Fast Eddie]

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.

The stresses under engine braking that could hypothetically pull the gearbox forward are very low Dave in comparison to the opposite. Thats why it’s always the rear wheel that ‘takes priority’ resulting in a loose final drive chain and a tight primary.

 

[ludwig]

The chain of events, according to OP explanation :
1. however unlikely, the gearbox is pulled forward with enough force to break the adjuster.
2. box moves at least 6 mm forward to disengage the threaded rod.
( this implies an extremely loose rear chain and would make the belt so loose it would no longer engage the pulleys)
3. The threaded part of the adjuster drops down under its own weight.
4. The gearbox is then pulled back, with the known consequences.
??
I believe there is a simpler, more logical explanation:
The adjuster was already broken AND twisted BEFORE he went out for the ride.
This has nothing to do with 'bad luck' ..

 

[marshg246]

Since this has become a theory free-for-all, I suspect that either:

1) The belt didn't track, rubbed a LOT, the particles of belt got between the belt and pully and jerked the gearbox forward (likely).
2) The belt didn't track, rubbed a LOT, and the gearbox didn't move (unlikely considering the adjuster).

Evidence? Look at the belt and primary cases - that shredding did not happen in an instant.

 

[swooshdave]

The chain of events, according to OP explanation :
1. however unlikely, the gearbox is pulled forward with enough force to break the adjuster.
2. box moves at least 6 mm forward to disengage the threaded rod.
( this implies an extremely loose rear chain and would make the belt so loose it would no longer engage the pulleys)
3. The threaded part of the adjuster drops down under its own weight.
4. The gearbox is then pulled back, with the known consequences.
??
I believe there is a simpler, more logical explanation:
The adjuster was already broken AND twisted BEFORE he went out for the ride.
This has nothing to do with 'bad luck' ..

2. Rear chain was set to 1 1/2in play.

Adjuster could have broke the joint when I adjusted it. Highly unlikely anyone would have spotted it from a visual inspection.

How many broken adjusters have you seen?

 

[swooshdave]

Since this has become a theory free-for-all, I suspect that either:

1) The belt didn't track, rubbed a LOT, the particles of belt got between the belt and pully and jerked the gearbox forward (likely).
2) The belt didn't track, rubbed a LOT, and the gearbox didn't move (unlikely considering the adjuster).

Evidence? Look at the belt and primary cases - that shredding did not happen in an instant.

Unfortunately I didn't check it enough times, I ran it once after adjusting and everything looked fine. Tension good. Ran it again. Work fine, did not check. Rode one last time.

I'll check it more frequently in the future.

 

[Ron L]

.............

How many broken adjusters have you seen?

Two! Both failed at the weld as yours. However, both appeared normal until the gearbox mounting studs were loosened. And both showed corrosion below the weld indicating the weld had failed at some point in the past.

 

[Bernhard]

Two! Both failed at the weld as yours. However, both appeared normal until the gearbox mounting studs were loosened. And both showed corrosion below the weld indicating the weld had failed at some point in the past.

If the lollipop hole had been counter sunk slighty the weld would have got deeper penetration, imo.

 

[gortnipper]

Catastrophic failure notwithstanding, what is the normal service life of these type of belts? And CNW primary belts?

Timing belt life on the Duc is two years/15k mi.

 

[Dogsbody]

Ducati’s are now 4 years since they introduced Kevlar belts.

 

[Mart UK]

Ducati’s are now 4 years since they introduced Kevlar belts.

At higher rpm and torque levels.

 

[gortnipper]

According to their.site, CNW "Uses a Gates 21mm Poly Carbon belt. Stronger than what is used in other belt drive kits on the market".

 

[Nortoniggy]

The first Gates belt on my Norvil drive lasted over 20 years, probably 20k+ miles. Still looked good but I changed it as a precaution. Second belt probably now over 10 years and looks fine.

Car/bike dealers make good money changing cam belts. I'm sure that is a factor in the recommended change intervals. e.g I have a Skoda and the factory recommended change interval for cam-belt is 120k Kilometres, there is no time interval. VAG, the UK importers, say must be changed at 5 years regardless of mileage. Form your own opinion why.

 

[ludwig]

Adjuster could have broke the joint when I adjusted it. Highly unlikely anyone would have spotted it from a visual inspection.

Maybe not the break, but you should have seen that the adjuster was sitting in a very awkward angle,
which is what caused it to fail.
That is the ONLY possible explanation.
Marshg246 theory of trapped debris doesn't stick. Debris is flung outwards.
You cannot misalign a belt to cause that much damage in such a short time, even if you tried.
Besides, you said that you checked the belt ( warm) not that long before.
An already broken, AND wrongly installed adjuster failed, the gbox was pulled backwards, overloading the belt.
That's all there is to it..

 

[marshg246]

Maybe not the break, but you should have seen that the adjuster was sitting in a very awkward angle,
which is what caused it to fail.
That is the ONLY possible explanation.
Marshg246 theory of trapped debris doesn't stick. Debris is flung outwards.
You cannot misalign a belt to cause that much damage in such a short time, even if you tried.
Besides, you said that you checked the belt ( warm) not that long before.
An already broken, AND wrongly installed adjuster failed, the gbox was pulled backwards, overloading the belt.
That's all there is to it..

Clairvoyant - got any stock market tips

 

[ludwig]

Clairvoyant - got any stock market tips

Not clairvoyance, but elementary physics.
I once gave a lift to a woman who just ran her Mercedes SL in the back of a truck.
But she wasn't at fault, because:
"that truck braked so hard, it jumped one meter back, hitting my car.."

Your explanation of how SD's gbox moved forward, follows the same kind of 'logic' .
Reversing cause and effect..

 

[marshg246]

Not clairvoyant, but elementary physics.
I once gave a lift to a woman who just ran her Mercedes SL in the back of a truck.
But she wasn't at fault, because:
"that truck braked so hard, it jumped one meter back, hitting her car.."

Your explanation of how SD's gbox moved forward, follows the same kind of 'logic'
i

I had just graduated college with my degree in Electronics Technology. My cousin and I were working on his car that was clearly missing and we were trying to figure out if some of the cylinders were not getting spark. My cousin's high-school dropout friend went to his house to get a "tool" to help. He came back with a neon panel light with a wire attached to one of the two pins and nothing connected to the other. I laughed and said that there was nothing he could do with that. He wrapped the wire around one of the spark plug leads and the light started flashing in his hand.

I learned that day to not be positive you know everything about a subject.

Your assumption that the adjuster was installed wrong is without evidence that I can see. If you look at the pictures, you'll see belt debris in line with the belt, not just flung outwards. I posted two theories, not statements of fact. You cannot back your theories presented as fact any better than I - they are theories!

To me, it's reasonable to think that the adjuster was installed correctly and that the gearbox moved forward to pull the two pieces apart. I can't think of a way to install the adjuster wrong - maybe the nuts not tight or the top gearbox bolt not tight, but the adjuster only goes one why that I can think of. Still, theories - not facts. I suspect that the gearbox was jerked forward and then backward based on it separating and then on how it ended up.

 

[slimslowslider]

The rusted hole in the adjuster boss where the treaded rod used to sit is facing forward in the picture in the first post.
So boss made half a turn.
Curious, that is a lot.
Hard to imagine this came through the movement of gearbox., over time.
Or is it?
Or a loose bolt indeed?

 

[ludwig]

To me, it's reasonable to think that the adjuster was installed correctly and that the gearbox moved forward to pull the two pieces apart. I can't think of a way to install the adjuster wrong - maybe the nuts not tight or the top gearbox bolt not tight, but the adjuster only goes one why that I can think of. Still, theories - not facts. I suspect that the gearbox was jerked forward and then backward based on it separating and then on how it ended up.

A correctly adjusted rear chain (OP statement) will not allow the GB to move that much forward.
I guess it is around 6 mm (1/4 inch for you)
Even 2 mm will lock the rear chain solid.
An how do you explain the angle of the threaded part:

 

[marshg246]

A correctly adjusted rear chain (OP statement) will not allow the GB to move that much forward.
I guess it is around 6 mm (1/4 inch for you)
Even 2 mm will lock the rear chain solid.
An how do you explain the angle of the threaded part:

Just a guess - the gearbox moved forward, then back. On the way back the rod whether all the way out or partly out catches and spins the other part and itself. I doubt that Dave installed the adjuster that way and then somehow used it to adjust the belt with the adjuster installed that way. Also, Dave said drive chain was adjusted correctly but no mention of any change in it after the incident. At any rate, these are large forces and if they happen in an instant, they are VERY large forces.

Dave,

Maybe I missed it. What happened to let you know you had a problem?

 

[Fast Eddie]

Like I said before, looks to me like the square block is loose, not tightened fully to the cradle.

If this is so, it’s gonna vibrate around badly with the weight of the block on the threaded rod.

If it was doing this, that’s very likely what broke the joint.

But I still say the gearbox top bolt was insufficiently tightened to allow such movement in such short time.

The idea that everything was tight and correctly assembled, and the adjuster innocently broke to to old age and caused this is implausible IMHO.