Stelvio CARC failure in Oz AND South Africa

[Triple Jim]

Possibly the casting is being pushed to it's limits off road and any slight structural flaw during manufacture can result in cracking.

Any decent safety related part should be designed for several times the load it will ever see in real life.  Automotive components often use a factor of three times the expected maximum load.  This is specifically to prevent a part from being pushed to its limit.

[Wayne Orwig]

This part would be impossible to forge in one piece. The Aprilia swing arms appear to be extruded in several pieces, then welded.

I agree, not practical.
It would be an easy thing to add a rib, or just more metal, near that highly stress point.

[canuguzzi]

The bikes that go 60k plus miles without a failure doesn't mean much, 3 that went went down and had catastrophic safety related failures does mean a lot.

It means that anyone with a Stelvio of those model years, for the most part, is thinking about it and anyone thinking about buying or selling one is probably going to either pass on the purchase or have a hard time selling it at a good price, depending on how fast word travels.

The Stelvio that goes 60k miles on mixed roads including non paved roads is great. Doesn't mean a thing unless information is available to determine that swingarm isn't affected. Right now, no one knows but those who are aware of the three failures are thinking about it, they'd be crazy not to.

There are paved roads that make gravel roads look and feel like ribbons of pristine asphalt, so far Norge's haven't been affected, maybe the Norge uses a different swingarm? Some owners to load up their bikes and hitting some rough paved roads can easily setup worse conditions than some gravel roads.

No doomsday for sure but this isn't something that should wait until the next one. Thank goodness none of these failures happened as the owner was headed down some road, two up at 80mph and pray it never happens.

[WitchCityGuzzi]

This part would be impossible to forge in one piece. The Aprilia swing arms appear to be extruded in several pieces, then welded.

Galvanic corrosion- I don't think so. You would see the threads packed with aluminum oxide.

Honestly, I think that the hole was an add on that was drilled and tapped after designing the plug for the mold. The hole is in the bold face of the casting- so it really is a weak spot- or at least an anomaly- in the rest of the surface. Normally, you'd have a thickened section, or boss, which then would be drilled and tapped.

It's very hard to predict fatigue and it doesn't mean all units must fail in order to be a design issue. The onset of fracture initiation can be a real coin toss. 

So Doug- tell me you didn't rush up to the garage and shimmy under your bike to check your swing arm??? :)

Nope. Not yet. May glance at it tomorrow when I get to work, but honestly, if it hasn't failed yet in the 63,000 miles of crap I've put it through, it probably isn't going to.

[Demar]

There are a lot of factors at play here. Nobody has mentioned resonant frequency. It's most likely a combination of a number of factors that all combine to cause a failure; casting variables (pour temp, inclusions, insufficient venting), hole drilling and tapping, base metal, load (static load, cyclic load, torsion).

It may be that a washboard road set up a resonant frequency to start the crack. The road could appear and in fact be "a mild gravel road" without large pot holes but the 3 cases may have just hit the right combination of load and vibration to reveal a potential problem.

[Arizona Wayne]

So far it hasn't happened in the USA (?) because I doubt the NTSA would overlook it in the current climate. Do we know if any of the failures have been reported to government agencies? Perhaps the reports have gone only to dealers. If the dealer takes care of it in some handshake agreement with the factory, it wouldn't go past that would it?

NTSA expects failures to be reported by owners of the failed vehicle.   Do you really think a dealer or mfg. is going to let NTSA know every time they have a failure?  No customer complaints, no interest by the NTSA.

[canuguzzi]

NTSA expects failures to be reported by owners of the failed vehicle.   Do you really think a dealer or mfg. is going to let NTSA know every time they have a failure?  No customer complaints, no interest by the NTSA.

None of my points in that post even hinted that the dealers or anyone but the owners would or should report the incidents.

The point you missed was that there could possibly be other failures but depending on how they were handled, no one but the owner, dealer and factory would know. After all, not all Stelvio owners read or participate on this forum and if a cracked swingarm was simply replaced by the dealer with factory supplied parts, that owner might not report it at all. Thus, there could be failures that did happen, did not get reported and no one would hear about it.

Read what I wrote once more, it will become clear.

[Rough Edge racing]

I agree, not practical.
It would be an easy thing to add a rib, or just more metal, near that highly stress point.

 If designed different it could be forged . Cost is always a factor of course... But I believe no one who wants a Guzzi would blink at a 100 buck increase in price.

  And what triple Jim says about safety factor leads up to perhaps poor engineering.....Unl ess the bike is making insane stunt jumps no kind of road going abuse should cause such a failure..

[canuguzzi]

Nope. Not yet. May glance at it tomorrow when I get to work, but honestly, if it hasn't failed yet in the 63,000 miles of crap I've put it through, it probably isn't going to.

True enough. This is probably limited to certain swingarms being used in certain riding conditions. I imagine it could even be that one suspension setup would allow the failure to happen yet another, different setup would not. Maybe even the rider that sits on the seat over ripples vs the one that stands up, changing where the most load is transferred.

Hopefully, MG figures it out and doesn't remain silent, just fixing them as failure occur. That would do zilch to instill confidence in the model years affected. Their best bet is to figure it out, issue clear communications to owners of all Stelvio or those bike models that use the same swingarm explaining the problem, solution and costs to owners if any.

[Wayne Orwig]

There are a lot of factors at play here. Nobody has mentioned resonant frequency. It's most likely a combination of a number of factors that all combine to cause a failure; casting variables (pour temp, inclusions, insufficient venting), hole drilling and tapping, base metal, load (static load, cyclic load, torsion).

It may be that a washboard road set up a resonant frequency to start the crack. The road could appear and in fact be "a mild gravel road" without large pot holes but the 3 cases may have just hit the right combination of load and vibration to reveal a potential problem.

Or preload adjustment. If the preload is not set properly, and the shock is being bottomed out, that might add a lot of impact type stress. I found the spring on the stock 2009 pretty weak when loaded.

[Vasco DG]

Their best bet is to figure it out, issue clear communications to owners of all Stelvio or those bike models that use the same swingarm explaining the problem, solution and costs to owners if any.

AFAIK only these three bikes we've heard about but I'm checking the service site regularly, if and when there is any announcement I'll let people know. Safety notices are always red flagged.

Pete

[Peter from Sch'dy]

Or preload adjustment. If the preload is not set properly, and the shock is being bottomed out, that might add a lot of impact type stress. I found the spring on the stock 2009 pretty weak when loaded.

What limits the travel of the arm? Coil binding? CARC rotation within the case? There's no "hard stop", is there?

Best,
Peter

[Arizona Wayne]

None of my points in that post even hinted that the dealers or anyone but the owners would or should report the incidents.

The point you missed was that there could possibly be other failures but depending on how they were handled, no one but the owner, dealer and factory would know. After all, not all Stelvio owners read or participate on this forum and if a cracked swingarm was simply replaced by the dealer with factory supplied parts, that owner might not report it at all. Thus, there could be failures that did happen, did not get reported and no one would hear about it.

Read what I wrote once more, it will become clear.

What I said here was not pointed at what you said. It is just a general statement of all X failures and the NTSA knowing about them. 

A number of 500 MP3s have had their pistons break up and Piaggio has not made good on this occurance to the customers.   

[Triple Jim]

  And what triple Jim says about safety factor leads up to perhaps poor engineering.....Unl ess the bike is making insane stunt jumps no kind of road going abuse should cause such a failure..

It could be poor engineering or it could be flaws in the castings that result in the part being 1/3 as strong as the engineer(s) expected it to be (for example).  It's really all speculation until a real analysis is done.

If this were happening to an engineering design I was responsible for, I'd probably be building a test rig to do dynamic testing on every assembly before it's put into use, at least until the cause of the problem is determined and a solution found.

[canuguzzi]

It could be poor engineering or it could be flaws in the castings that result in the part being 1/3 as strong as the engineer(s) expected it to be (for example).  It's really all speculation until a real analysis is done.

If this were happening to an engineering design I was responsible for, I'd probably be building a test rig to do dynamic testing on every assembly before it's put into use, at least until the cause of the problem is determined and a solution found.

All hypothetical of course, if the test rig revealed that the swingarms had defects and were used across multiple models but only one model had shown in actual use failures, is the appropriate solution to fix only the models where they are anticipated to be used in similar conditions as the failed representatives or do you apply the fix to the entire mix regardless of application?

That seems like it would get very expensive for the factory unless the parts were sourced from a third party and then the money follows the problem back to its origin, assuming the design was good and the casting was not.

With the airbags for example, initially Dodge didn't recall airbags for trucks that weren't operated in humid conditions but then decided to recall them regardless of where the trucks were registered, apparently because someone clued them in that trucks,  like cars can move around.

[Triple Jim]

All hypothetical of course, if the test rig revealed that the swingarms had defects and were used across multiple models but only one model had shown in actual use failures, is the appropriate solution to fix only the models where they are anticipated to be used in similar conditions as the failed representatives or do you apply the fix to the entire mix regardless of application?

If they didn't prove to be as strong as they were designed to be, 3x max load for example, due to defects, design or manufacturing errors, or whatever, I wouldn't use them.  But then I'm not in charge of this problem, so what I think or would do isn't very relevant, I guess.

[johnr]

I understand that aluminium will crack when holes have flash left around the edges. The edges of holes need to be smoorthly chamfered.

The earliest incident related to this is possibly the disastrous failure of pressure skins on the 50s De Havilland Comet Jetliners, which mysteriously fell out of the sky after some use.  After 6 months testing in an over-sized bath tub ;-) they found a crack appeared at a hole used for mounting a window frame, and traced the cause to the hole having not been cleaned around after drilling.

At the risk of high jacking the thread, that snippet about the Comet is very interesting. I knew about the cracks developing around a window but not why. The Comet was a tragedy really. It was a wonderful design and deserved to be successful, but it was breaking new ground and there in lie the risks.  It reminds us how close to destruction some of our more extreme machines are, or might be.

[boatdetective]

They were corner cracks as i recall. Classic field case of fatigue.

If anyone here wants a truly great book about materials and failure for the non scientist, I would highly recommend J/E. Gordon's New Science of Strong Materials -or why you don't fall through the floor.  He's a dotty Brit engineer who worked, amongst other things, on the Mosquito program during WWII.  His explanations of how things work and why they break is as entertaining as it is seminal. 

I just saw it for $1.00 on ABE books:
http://www.abebooks.com/servlet/SearchResults?an=j.+e.+gordon&sts=t

[bad Chad]

This conversation is what happens when men give up all hope of getting laid.

[oldbike54]

This conversation is what happens when men give up all hope of getting laid.

 Or don't care anymore 

  Dusty

[canuguzzi]

Or have hope, do care and work hard toward the goal only to realize the deep breathes are those of deep sleep.

[Arizona Wayne]

Or have hope, do care and work hard toward the goal only to realize the deep breathes are those of deep sleep.

Except such knowledge assumes the couple still sleeps in the same bed or bedroom.   

[Rough Edge racing]

It could be poor engineering or it could be flaws in the castings that result in the part being 1/3 as strong as the engineer(s) expected it to be (for example).  It's really all speculation until a real analysis is done.

If this were happening to an engineering design I was responsible for, I'd probably be building a test rig to do dynamic testing on every assembly before it's put into use, at least until the cause of the problem is determined and a solution found.

 Casting flaws can still be  bad engineering...The Italian industry is capable of state of the art alloy vehicle parts. If it's a dozen swingarms made at the same time you can say it's casting flaws..But if it's random failures, that's something else...

 Yes.. boring... but mentioning the sexual habits of old men on an internet motorcycle sites is a bit scary.....

[boatdetective]

This conversation is what happens when men give up all hope of getting laid.

OK Chad, why don't you drift the thread with a discussion of how to establish your own sense of fashion with a sidelight on eyebrow waxing. 

[WitchCityGuzzi]

So I looked at the bottom of my CARC (sounds dirty.  ) and this is what I found.



It looks like this is a type of plastic/nylon push fastener. Doesn't look like it's a threaded bolt or anything else at all. Is this what the new ones look like too? I'm curious.

[MotoZA]

Hmmm, is it my imagination or is that different to the pics on the first page posted by Green1000s? I agree, don't see why a tapped hole is required, unless that little plastic clip somehow screws in? Intriguing.

Could we have some more pictures by Stelvio owners, please!

[canuguzzi]

Hmmm, is it my imagination or is that different to the pics on the first page posted by Green1000s? I agree, don't see why a tapped hole is required, unless that little plastic clip somehow screws in? Intriguing.

Could we have some more pictures by Stelvio owners, please!

Looks the same on the Norge, at least 2013 & forward. Maybe including tabs in the casting was more difficult than drilling and tapping holes?

[brlawson]

The plastic clip has threads more or less but is simply pushed into the whole.

[Chuck in Indiana]

The plastic clip has threads more or less but is simply pushed into the whole.

Yeah, that is commonly done on automotive fasteners. Makes it removable without destroying it, but still stays put.

[canuguzzi]

The plastic clip has threads more or less but is simply pushed into the whole.

  how it works. They are the one time use clips although you could probably remove it and reuse. If it breaks off, what is left behind is likely a real bugger to remove and crazy if it ends up inside. They seem to hold up well though, well, the plastic thingy anyway

Over time, they get brittle and they hold until you remove them at which time they break into very small pieces, if they are anything like those used on cars, the ridged portion falling behind the panel never to be found again.