Stelvio CARC failure in Oz AND South Africa

[oldbike54]

 Mr Bill says "dear leader mod" , of which only one word accurately describes me 

 Not for one second am I promoting the idea of mobs with pitchforks . However , the ostrich method of dealing with a situation never seems to work out , especially for the ostrich . Now , it may turn out that these two failures are isolated , but if I was riding either Stelvio that had this catastrophic failure , well , someone would certainly get an earful .

  Dusty

[canuguzzi]

Since it seems this is very easy to check for, maybe the best way forward is for those who know about it now to check at earliest opportunity, report is evidence if cracking is found and maintain some diligence in checking for it often? If a crack is found, recommend to stop riding the bike until repair/replacement?

So far it doesn't appear to just fall apart but maybe cracks and after a time fails?

Now that we all know about it, we should be properly informed to avoid on the road failures?

All that being said, how much of a crack should be considered enough to warrant parking the bike? I ask because someone might see a small crack and not think enough of it to take more than casual heed. Is any crack sufficient to park it?

[pauldaytona]

Important is that Piaggio in italy knows each that goes wrong, we have seen three here, there might be more, not everyone with a guzzi writes or reads this forum.

[oldbike54]

Important is that Piaggio in italy knows each that goes wrong, we have seen three here, there might be more, not everyone with a guzzi writes or reads this forum.

 Excellent point .

  Dusty

[pauldaytona]

The three failures were in:

Australia
South Africa   MotoZA
Canada         CanuckGoosie

If I'm correct.
So statisticaly if you drive on the wrong side of the road, there is more chance. And live in a country that the English had their say.
 

[brlawson]

I think all were 2012 bikes? would be good to have VIN or engine numbers to see if they belong to the same batch/month in production

Didn't that year have the suspension link recall? Dots connecting maybe?

https://ultimatemotorcycling.com/2013/08/08/moto-guzzi-stelvio-ntx-1200-norge-1200-griso-1200-recall

[Moz]

...
All that being said, how much of a crack should be considered enough to warrant parking the bike? I ask because someone might see a small crack and not think enough of it to take more than casual heed. Is any crack sufficient to park it?

I'm no metallurgist engineer...  but my advice would be a big  fat "YES" 

[boatdetective]

I deal with LOTS of failed metal in my job. Although it's the marine business, metal failure is metal failure. The fracture surface on either side of the hole is roughly perpendicular to the surface. At the same time, the finish of the break near the hole is slightly darker than the fracture surface across the rest of the failure. If you look closely, i'm sure you'll see that the normally "woody" texture of the fracture will appear somewhat burnished. The tips of the asperities will be rounded over slightly. This is from the crack opening and closing over an extended period of time. the darker color is aluminum oxide ground in the surface.

The fracture progressing from this area will tilt back and forth to form sharp, 45 degree edges. This characteristic is termed a "shear lip" and is typical of final, or fast failure. Quite literally, the shear lips were formed as the swing arm tore apart.

Thin wall failure in castings and extrusions can be more difficult to diagnose than failure in a thicker section. Fatigue in thin wall sections may not show the "beach marks" that are so typical of progressive failure.  The following picture is of an unstayed mast where some genius decided to drill a hole for wiring right below the mast partners:

You should be able to see the same characteristics I mentioned showing the transition from progressive failure to final failure.

As for a "bad run", I don't know about that. It's very easy for people to point the finger by claiming latent defect- but defects typically are a physical thing that can be seen. (the exception might be heat treatment, where sectioning the part and looking under high magnification is necessary to look at the grain structure)

Here is a failed aluminum casting with inclusions in the casting. The inclusions (usually dirt) will look like flat planes in the otherwise homogenious casting. The flat planes are actually voids that can act like stress risers. Virtually all castings have inclusions. The problem arises if the inclusions coincide witha highly stressed area of the part. 

In this case, there was an inclusion just under the surface. The prior photo shows three more inclusions in a row- so what we have here is a "zipper" of weak spots that caused the part to fatigue. You can see the beach marks in the part pretty clearly.


The following failure is a crankshaft in a small Volvo diesel. The crank is massive for the low horsepower. Nevertheless, there was a fatigue failure that occurred over 17 years before the poor thing gave up the ghost.


If you look here, you can see a series of little bubbles- entrapped gas- in the casting that coincided with the very fillet of the journal. This, certainly, is a "defect".

 

     

[bad Chad]

Oldbike, what exactly would you like to see done?

[oldbike54]

Oldbike, what exactly would you like to see done?

 Just some workable resolution . The whole mob with torches thing was a figment of someone's imagination 

 Like with any potential safety problem , there is usually a way of mitigating the danger .

  Dusty

[Aaron D.]

I don't see what can be done, as Jonathan/ Boat Detective has so excellently illustrated sometimes things happen with castings in certain applications.

Ever seen a motorcycle swingarm  made of tubing break like that ?

[canuguzzi]

The thing with failures is that its always after the fact. Now that owners will be looking, (only the foolish or uninformed will not) pre failures might start showing up.

It will be interesting to see if this is isolated to one production year but somehow wouldn't that point to MG knowing about it and just correcting the problem later? Is there a difference between say a 2012 and a 2014 swingarm?

[boatdetective]

Aaron-   just to make itt clear- I do NOT think this is a defect issue in this case. I agree that the hole is the stress risr that initiated the fracture.  I cannot see enough to tell if there was something with this hole to make it more likely to start the crack. I would thing that a raised boss in the casting would've been the wise move to provide reinforcement, though.  Given the non critical placement of the hole, I think that a blob of weld material in the area, filed flush, redrilled and tapped, would beef tthe area up considerably. The heat from the weld will not affect the casting. In fact, the weld can bee relatively "cold"- a quickie pass with a mig welder would be fine. The point would be merely to add material in way of the hole. I guess I'd also chamfer the hole and make sure the tapped hole is not too "snug".

[oldbike54]

I don't see what can be done, as Jonathan/ Boat Detective has so excellently illustrated sometimes things happen with castings in certain applications.

Ever seen a motorcycle swingarm  made of tubing break like that ?

 Nope , but I did break the steering head on a Hodaka landing from a jump , went WHUMP on the ground . No permanent damage , although my normal baritone was temporarily replaced by a kind of squeak 

  Dusty

[Vasco DG]

What I would like to see is the VIN#'s for the three machines we KNOW have failed.

When the considerably less photogenic but equally dangerous linkage failure occurred the factory had good records of which bikes had parts that came from the affected batch. I'm hoping that they would have similar records for major castings such as swingarms.

The CARC system was first used on the Breva 11 back in 2005. That's ten years ago. The Stelvio was launched and has been in production since 2008 and many have been flogged mercilessly and probably grossly overloaded since then. Suddenly, quite close together, there has been a batch of failures. Yes! It's deeply worrying and I'd HOPE the factory gets the on to isolating which machines may be affected with some serious urgency! It is a MAJOR safety issue. BUT to start talking about 'Serious design flaws' on a system that has stood the test of time in hundreds, if not tens of thousands of vehicles, is just plain stupid.

Pete

[canuguzzi]

Could this type of failure happen if the hole wasn't there? In other words, they all cracked there but does that mean it had to be the fault of the hole or could those swingarms have had some weakness in that area and that is where the stress was the most so it would have cracked there anyway?

[oldbike54]

 I think Jonathon and Pete are both onto something . Something in fact can be done to protect the owners of any affected Stelvios W/O putting Guido in stocks  Ultimately fixing the problem should be the ultimate goal .

  Dusty

[motrhead]

 Considering how I have loaded and abused my Stelvio, I do not think it is a strength issue. I seem to remember that one of the other failed swingarms was involved in an impact of some kind? This seems to be a freak event, which makes me suspect the casting...it really should be analysed. Castings can definitely be a hit and miss thing.
 The first batch of BMW 650dirt bikes had front forks that would occasionally snap off (causing more than one serious injury), and BMW quickly and quietly redesigned the forks and denied anything ever happened. There are a bunch of pics of detatched BMW final drives floating around the net...and yes, I have seen steel tube swingarms fail too. There is always the chance that parts can fail. Rims can split. Some of the sportbike frames can lose their steering head from too many wheelies. I guess the lesson here is to check things over on occasion. One more good reason to wash your bike! LOL
 I know I won't be tempting fate by launching my Stelvio off of any big jumps. The CARC is a big thin tubular casting, and I am not about to beat on it like a motocross bike, but I am definitely not afraid to ride it in the rough stuff.

[MotoZA]

Could this type of failure happen if the hole wasn't there? In other words, they all cracked there but does that mean it had to be the fault of the hole or could those swingarms have had some weakness in that area and that is where the stress was the most so it would have cracked there anyway?

No, it most probably won't fail if there's no hole there.

The stress at the edge of a hole has a higher value than the remote stress in the same component. Fatigue cracks usually (mostly) initiate at the sites of stress concentrations. Once a crack has formed, the stress concentration plays no part anymore, it was merely the starting point of the crack. This assumes geometry effects only, and disregards material effects (inclusions, voids, surface roughness, surface hardness, etc). For a simple circular (not elliptical) hole the stress can be three times higher at the edge of the hole if the stress is purely tension, i.e., K_t=3, where  K_t is the stress concentration factor. For torsion, K_t = 4. Source: Yukitaka Murakami, Metal Fatigue, Elsevier. The swing-arm sees both tension (and perhaps compression in some cases) and torsion (due to the offset load from the wheel).

A stress concentration is fine in most cases for something that is loaded statically, since the material will strain strengthen (if it's a ductile material, but not if it's a brittle material). If a material is loaded variably, i.e., not statically, you MUST consider the effects of stress-concentrations, as this may very well lead a to crack forming. Once the crack has formed, it will grow over time due to the variable/repeated/fluctuating/alternating load. The Stelvio will experience a higher cycle of fluctuating loads compared to a Breva, Griso and Norge since it is likely that it will be used on gravel roads with corrugations (in South Africa we refer to these roads as "sinkplaat", which refers to the wave shape of old zink roof sheets) and the fact they're obviously not as smooth as tarred roads.

The following is from Shigley's Mechanical Engineering Design (Auth: Budynas-Nisbett), McGraw-Hill:

A fatigue failure has an appearance similar to a brittle fracture, as the fracture surfaces are flat and perpendicular to the stress axis with the absence of necking. The fracture features of a fatigue failure, however, are quite different from a static brittle fracture arising from three stages of development. Stage I is the initiation of one or more microcracks due to cyclic plastic deformation followed by crystallographic propagation extending from two to five grains about the origin. Stage I cracks are not normally discernible to the naked eye. Stage II progresses from microcracks to macrocracks forming parallel plateau-like fracture surfaces separated by longitudinal ridges. The plateaus are generally smooth and normal to the direction of maximum tensile stress. These surfaces can be wavy dark and light bands referred to as beach marks or clamshell marks. During cyclic loading, these cracked surfaces open and close, rubbing together, and the beach mark appearance depends on the changes in the level or frequency of loading and the corrosive nature of the environment. Stage III occurs during the final stress cycle when the remaining material cannot support the loads, resulting in a sudden, fast fracture. A stage III fracture can be brittle, ductile, or a combination of both. Quite often the beach marks, if they exist, and possible patterns in the stage III fracture called chevron lines, point toward the origins of the initial cracks.

My point is this: Even if the bike's swing-arm experienced a hard knock/load at some point during it's life due to abuse (not me) or accidentally going through a pot-hole, or whatever, it may not have failed, but the hole might've caused a crack to form. Once the crack formed, you're in trouble, since it will most likely keep growing. And, aluminium (aluminum if you're in the US) does not have an endurance limit. Source: Shigley (Budynas-Nisbett). So eventually it will fail. Putting a hole in a stressed area (it's a critically stressed area, actually), without having designed for it, is looking for trouble.

Of course I'm hoping that I am wrong and that it's simply a bad casting and not as a result of poor design. I mean, they've been building bikes for over 90 years, I've never designed a bike  . But I have designed a fair amount of marine/offshore structures (locally and internationally) and a few winches, and we design for fatigue, even if we don't know the loading. We don't put holes in critically stressed areas, and if we have have to, we specifically design for it.

But I'm sure the engineers at Moto Guzzi did take the effect of the hole into account.

Regards,
MotoZA

[John Warner]

Maybe they did, maybe not.
Could be they allowed for the hole in their analysis, but not for the fact it has a thread cut in it.
Simple error.

The fact that companies in much more safety-critical fields (such as Aircraft manufacture) can and do still get it wrong occasionally, keeps many of us employed, me included.

[Chuck in Indiana]

Maybe they did, maybe not.
Could be they allowed for the hole in their analysis, but not for the fact it has a thread cut in it.
Simple error.

The fact that companies in much more safety-critical fields (such as Aircraft manufacture) can and do still get it wrong occasionally, keeps many of us employed, me included.

I'm not sure that aircraft are much more safety-critical..  a motorcycle will kill ya faster than an airplane.
Just kidding, of course.. but a structural failure on either is serious business.

[MotoZA]

The fact that companies in much more safety-critical fields (such as Aircraft manufacture) can and do still get it wrong occasionally, keeps many of us employed, me included.

100%, and I accept that people make mistakes, but as in the aircraft industry, and other industries, IF a mistake (or simple error/oversight was made), it should be corrected. That's why we still climb into airplanes, because we know they do something about their mistakes/errors.

Anyway, I'm hopeful that Piaggio comes to the party.

[canuguzzi]

100%, and I accept that people make mistakes, but as in the aircraft industry, and other industries, IF a mistake (or simple error/oversight was made), it should be corrected. That's why we still climb into airplanes, because we know they do something about their mistakes/errors.

Anyway, I'm hopeful that Piaggio comes to the party.

There should be no question. MG needs to be completely transparent on this issue lest we go down the road of bad weather and short trips.

The ultimate goal is the safety of the owners, and if the problem is due to manufacturing, design or assembly defects, repair or replacement at no cost to the owner without any regard for Guido.

A few failures  in even a couple tens of thousands of bikes and some millions of miles without the problem isn't diddly compared to other vehicles selling in the many millions and going hundreds of millions of miles without actual safety component failures. 3 in the first instance isn't something to stand up and say is some good milestone, it isn't.

[FGO]

In Aircraft, if a failure occurs that could risk life, an AD is issued which is a mandatory requirement to address the problem and identify the suspect aircraft ASAP, I guess the DoT and their European counterparts don't have quite so rigorous program

[canuguzzi]

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?

[azguzzirep]

My local Guzzi dealer said he was unaware of the broken CARCs, and would ask his Guzzi rep about it. He was thankful the issue was brought to his attention.

tom

[JeffOlson]

Wow! Glad you are okay!

If I were in the market for an adventure bike, this would really make me stop and think before springing for a Stelvio...

[pauldaytona]

Wow! Glad you are okay!

If I were in the market for an adventure bike, this would really make me stop and think before springing for a Stelvio...

 well you wouldn't buy anything if you ever had a view of what warranty claims are at any manufacturer. I had by coincidence a view on the piaggio warranty webserver.  I have downloaded a few.., but won't post them, most was not guzzi

[rodekyll]

Wow! Glad you are okay!

If I were in the market for an adventure bike, this would really make me stop and think before springing for a Stelvio...

Just because the front and rear wheels fall snap off at speed?  I think you're being unreasonably picky.   

[canuguzzi]

Just because the front and rear wheels fall snap off at speed?  I think you're being unreasonably picky.   

Serious, yes but so long as you check for it before heading out what is the chances of it starting to crack and then coming apart all on the same run?