[fourdee]

Welp, pulled the covers today after the motor went out on the highway, and it would appear I'm screwed. Belt has broken on the horizontal cylinder.
So what damage am I possibly looking at? Valves, guides, etc? I'm new to working on the desmoquattro (LT's guide is on it's way), these are interference motors, correct? Possibly a chomped up piston?
Give it to me straight, doctors.

 

[Yorik]

You can pretty much count on valves. But one thing I notice in your picture - the tensioning pulley looks too close to the fixed pulley. It appears whoever did the belts last turned the tensioner in the wrong direction. At least that's what it looks like from the angle shown.

 

[fourdee]

Yep, noticed the same thing.
Also posted this in the wrong forum- mods, feel free to delete this thread, I'm going to repost it in the ST forum. Thx

 

[Yorik]

I'm curious as to what brand of belt it is. Any markings on it? I know that breakage may not have anything to do with the manufacturer. Just curious.

 

[fourdee]

I'm curious as to what brand of belt it is. Any markings on it? I know that breakage may not have anything to do with the manufacturer. Just curious.

California Cycleworks Part TBST4

 

[Corse1]

Wow Bad luck. Not a common occurrence so following this with interest. Do you know how old the belts were and what mileage they had on them?

 

[fourdee]

No honest idea. Recently got the bike at 39,000 miles, I've put maybe 500 or so on it. Knew the belts needing checking soon, this was honestly the last ride before I planned to pull the covers and change them. Last owner did some... questionable... maintenance to say the least.

 

[belter]

if the cams don't turn the valves are bent. generally no piston damage, etc. it just bends the valves out of the way and that's it.

we had a 916 once that the cams turned on, so we fitted a new belt, did a comp check and away it went. only once though.

 

[socalnative]

Maintenance is key on these. Oil change and filter, air filter, spark plugs, belts, valve adjustment, coolant, brake and clutch fluids. Unless you know the person and have receipts or first hand knowledge just plan on doing all of these things. If the tires are 5 years old or more junk them. Chain and sprockets need to be in good shape. Then you can be sure of your starting point. And start to ride with confidence.

 

[Duccout]

Bummer.

 

[dewcatty]

Off with the head. What's involved Belter? A special spanner I think. A new head gasket. Head to go for new valves. Replace valve guides/ seals? And then of course a good shim job. Any change out of $2K? Or if you do it yourself maybe $5-$600 ?

 

[ducvet]

Damage can be anywhere from a broken belt and no damage, I have seen it a few times if the belt breaks when the valves are close you should be good. Most of the time people are not so lucky so as Belter said you are likely to have at least belt valves and probably a cracked valve guide or two. Intake guides are more prone to crack so look close, but check them both. Since it happened on the highway I have to ask how long you ran it after it broke the belt?

worst case is the valve bent and then if it could not close enough bent again and then bent some more. at a certain point the valve head either comes off or goes 90 degrees and you drive it through your piston while creating deep head damage. while this extreme compression is going on the big end rod bearings are taking a beating and might even be enough to bend a connecting rod.

After the broken valve and bent rod breaks a hole in your piston all the parts fall into the still spinning lower end and play pinball with broken chunks of forged piston and some times steel valve head (after it snaps off). the rod bearing being shot from all of this then then is loose and a rod bolt breaks off dropping into the mix adding some more steel to your Ducati cocktail. By now the rod will break the skirt off the lower part of the cylinder and large chunks will be smashed through the windage portions of your cases. some aluminum pieces may go through gears in the gearbox but the often do not lock things up just weaken them.

Yeah so you are somewhere between no damage and new motor, no way to tell until you take it apart. No special tools I can think of to remove the head so start there and hope the damage is light , most common is as belter said bent valves and guides but ask yourself this, how long did you run the motor after the belt broke?
Followed by how lucky are you?

As to reason it broke.
Yes a miss adjusted belt could have done it 100%
Also a spun rod bearing or bad main bearing could have allowed the piston to hit a valve as it floats the piston closer to the valve. Often you will see marks on the head /piston where they contacted.
Any part CAN break even a aftermarket timing belt, In my experience with them it has never been the fault of the belt when I do teardown and diag. postmortem . any belt would break under the reasons listed above. what happens after is usually a relation to how long you continue to drive with ducati parts in a blender.

 

[Strega]

This ...

 

[tonered]

Welp, pulled the covers today after the motor went out on the highway, and it would appear I'm screwed. Belt has broken on the horizontal cylinder.
So what damage am I possibly looking at? Valves, guides, etc? I'm new to working on the desmoquattro (LT's guide is on it's way), these are interference motors, correct? Possibly a chomped up piston?
Give it to me straight, doctors.
View attachment 982849

Sorry to hear this!

I had a broken CA CW belt. I tried extending my service intervals to 10,000mi. It snapped and I rode Thumper home another 3.5mi. The only damage was the intake valves on the horizontal cylinder.

I'm still running the CA CW belts, but this is about the fourth break that I have heard of.

There wasn't a silver lining though. About 4k after I the belt break, the horizontal con rod bearings lunched themselves. I found the crank scored, so it was cheaper to get a used motor off of eBay. The positive side there is that I saved enough doing all my own work that the replacement motor was no big deal.

Hopefully your fix is easy and lasts a long time.

Have a good one.

 

[fourdee]

Alright, so the horizontal cylinder head has been pulled. Preliminary inspection, it looks like just the intake valves got bent. You can see where they contacted the piston- they left scuff marks on the piston face right at the valve reliefs. Beyond a small bit of the carbon buildup being removed, there appears to be no actual damage to the piston. You cannot feel any rough edges where the scuff appears on the two top valve reliefs- it's really just 'cosmetic' for lack of a better term. Intake valves are definitely bent. I'll be pulling the cams, etc to check everything out.

 

[fourdee]

I have to ask how long you ran it after it broke the belt?

Less than 30 seconds, maybe?
Motor went out completely on I-85. Coasted with motor off across 6 lanes (thank god traffic's light with the pandemic), got to exit ramp.
Once on the ramp, attempted to start it, got it cranked (but running on one cylinder) and tried to limp it up the ramp but it was running so badly on one cylinder I shut it off.
I had it full throttle cranked once I got it started, wouldn't go past 5k rpm and as such I realized shit had hit the oscillating unit.

 

[belter]

i'd say the exhaust valves hit the piston too, with that line across them.

 

[fourdee]

i'd say the exhaust valves hit the piston too, with that line across them.

Yah, noticed that a minute ago. About to go pull everything apart and see the real damage.

 

[tonered]

Alright, so the horizontal cylinder head has been pulled. Preliminary inspection, it looks like just the intake valves got bent. You can see where they contacted the piston- they left scuff marks on the piston face right at the valve reliefs. Beyond a small bit of the carbon buildup being removed, there appears to be no actual damage to the piston. You cannot feel any rough edges where the scuff appears on the two top valve reliefs- it's really just 'cosmetic' for lack of a better term. Intake valves are definitely bent. I'll be pulling the cams, etc to check everything out.

View attachment 983297 View attachment 983298

The test that I used once it was all lapped was to see if it holds gas poured in to the head. You could check your exhaust valves this way.

 

[davidcumbria]

Sorry to hear this!

I had a broken CA CW belt. I tried extending my service intervals to 10,000mi. It snapped and I rode Thumper home another 3.5mi. The only damage was the intake valves on the horizontal cylinder.

I'm still running the CA CW belts, but this is about the fourth break that I have heard of.

There wasn't a silver lining though. About 4k after I the belt break, the horizontal con rod bearings lunched themselves.

I am about to do a belt change and pretty concerned by this. Surely the supposed stronger exact fit belts ought not to be snapping at 10k. Sounds like staying with OEM is worth the cost. My Ducati specialist here in uk said he had hardly ever come across a belt failure.