Dura Ace Crank Failure

I've posted pictures here of my failed Dura-Ace crankarm.

http://www.atmosp.physics.utoronto.ca/people/amit/crank.htm

They simply "folded" when I stood to pedal. The arm bent until it hit the chainring pin. The bent
crankarm hit the chainstay and I didn't fall.

It sheared like a pop can (you can see it's hollow), but didn't separate into two pieces.

I can't see what caused the failure. You can see that the crankarm is buffed smooth where my shoe
occasionally touched it, perhaps that initiated a crack ?

Shimano decided not to replace the crankarm since it is older than the 3 yrs. they warranty Dura-Ace
parts for. I didn't pursue the matter further with them (also my frame is dented where the crankarm
struck - I didn't pursue this either).

I can take some better pictures if someone wants a closer look at the damage.

-Amit Ghosh

 

On 29 May 2003 17:07:52 -0700, [email protected] (Amit) wrote:

>I've posted pictures here of my failed Dura-Ace crankarm.
>
>http://www.atmosp.physics.utoronto.ca/people/amit/crank.htm
>
>They simply "folded" when I stood to pedal. The arm bent until it hit the chainring pin. The bent
>crankarm hit the chainstay and I didn't fall.
>
>It sheared like a pop can (you can see it's hollow), but didn't separate into two pieces.
>
>I can't see what caused the failure. You can see that the crankarm is buffed smooth where my shoe
>occasionally touched it, perhaps that initiated a crack ?
>
>Shimano decided not to replace the crankarm since it is older than the 3 yrs. they warranty
>Dura-Ace parts for. I didn't pursue the matter further with them (also my frame is dented where the
>crankarm struck - I didn't pursue this either).
>
>I can take some better pictures if someone wants a closer look at the damage.
>
>-Amit Ghosh

First off, why did you tell them it was more than three years old? That's mistake number one. Number
two is that if you showed them those pics... I bet that's why they said no way. Your bike is filthy.
Not knocking you, but it looks like you don't take very good care of it. I would have removed the
crank and cleaned it first, or taken off the chainrings before I sent those pics to Shimano. If you
ever have to deal with any company's warranty department, you want the stuff you are trying to send
back to look as new as possible. Let the company think you only rode it a few times before that
happened. Your bike.. well, again, I am not trying to be rude, but it's a damn mess! I have seen
cleaner bikes after finishing Paris-Roubaix. You have a picture that looks like you have dried mud
filling one of your chainring bolts.

Like I said, if I was the guy at Shimano who saw that, I would deny your claim too. The fact that
you are not pushing the issue with them proves their point. Take your bike, clean the hell out of
it, make those crank arms shine like the day they were new (minus the shoe rub wear, you can' t do
anything about that) and take just a picture of the failed crank arm. Then send that to them and see
what they say.

But my first impression when I saw those pics (which is why I bet Shimano felt the same way) was
that this guy doesn't take care of his stuff.. it's abused and there is no way that is a
warranty issue.

It's like the resturaunt business.... presentation is everything.

Russ

 

"Russ" <[email protected]> wrote in message
news:[email protected]...
> On 29 May 2003 17:07:52 -0700, [email protected] (Amit) wrote:
>
> >I've posted pictures here of my failed Dura-Ace crankarm.
> >
> >http://www.atmosp.physics.utoronto.ca/people/amit/crank.htm
> >
> >They simply "folded" when I stood to pedal. The arm bent until it hit the chainring pin. The bent
> >crankarm hit the chainstay and I didn't fall.
> >
> >It sheared like a pop can (you can see it's hollow), but didn't separate into two pieces.
> >
> >I can't see what caused the failure. You can see that the crankarm is buffed smooth where my shoe
> >occasionally touched it, perhaps that initiated a crack ?
> >
> >Shimano decided not to replace the crankarm since it is older than the 3 yrs. they warranty
> >Dura-Ace parts for. I didn't pursue the matter further with them (also my frame is dented where
> >the crankarm struck - I didn't pursue this either).
> >
> >I can take some better pictures if someone wants a closer look at the damage.
> >
> >-Amit Ghosh
>
>
> First off, why did you tell them it was more than three years old? That's mistake number one.
> Number two is that if you showed them those pics... I bet that's why they said no way. Your bike
> is filthy. Not knocking you, but it looks like you don't take very good care of it. I would have
> removed the crank and cleaned it first, or taken off the chainrings before I sent those pics to
> Shimano. If you ever have to deal with any company's warranty department, you want the stuff you
> are trying to send back to look as new as possible. Let the company think you only rode it a few
> times before that happened. Your bike.. well, again, I am not trying to be rude, but it's a damn
> mess! I have seen cleaner bikes after finishing Paris-Roubaix. You have a picture that looks like
> you have dried mud filling one of your chainring bolts.
>
> Like I said, if I was the guy at Shimano who saw that, I would deny your claim too. The fact that
> you are not pushing the issue with them proves their point. Take your bike, clean the hell out of
> it, make those crank arms shine like the day they were new (minus the shoe rub wear, you can' t do
> anything about that) and take just a picture of the failed crank arm. Then send that to them and
> see what they say.
>
> But my first impression when I saw those pics (which is why I bet Shimano felt the same way) was
> that this guy doesn't take care of his stuff.. it's abused and there is no way that is a
> warranty issue.
>
> It's like the resturaunt business.... presentation is everything.

I am a disinterested third party here, and I did notice the bike was filthy, but besides advising
him to cheat on the terms of his warranty did you have anything positive to say? How does dirt
constitute abuse of a crank arm? Do you also encourage your own customers to cheat you?

I am no friend of Shimano Corporation but the product is sold with a clear three-year warranty. Who
wants to be a liar for a few bucks?
--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

 

IMHO, that is a bad part - manufacturing defect. It surprises me that Shimano did not warranty it,
regardless of how old the part was.

That flavor of crank shouldn't break in that location unless there was something wrong
with the part.

I would be interested in close-ups of the failure surface, Amit.

BTW, I think your bike looks clean compared to some of my old commuter bikes of days gone by.

--
==================
Kraig Willett www.biketechreview.com
==================
"Amit" <[email protected]> wrote in message
news:[email protected]...
> I've posted pictures here of my failed Dura-Ace crankarm.
>
> http://www.atmosp.physics.utoronto.ca/people/amit/crank.htm
>
> They simply "folded" when I stood to pedal. The arm bent until it hit the chainring pin. The bent
> crankarm hit the chainstay and I didn't fall.
>
> It sheared like a pop can (you can see it's hollow), but didn't separate into two pieces.
>
> I can't see what caused the failure. You can see that the crankarm is buffed smooth where my shoe
> occasionally touched it, perhaps that initiated a crack ?
>
> Shimano decided not to replace the crankarm since it is older than the 3 yrs. they warranty
> Dura-Ace parts for. I didn't pursue the matter further with them (also my frame is dented where
> the crankarm struck - I didn't pursue this either).
>
> I can take some better pictures if someone wants a closer look at the damage.
>
> -Amit Ghosh

 

Russ <[email protected]> wrote in message

> First off, why did you tell them it was more than three years old? That's mistake number one.

I didn't. The parts are date coded. What do you propose ? I somehow forge a reciept and claim I
bought them NOS ?

> Number two is that if you showed them those pics... I bet that's why they said no way.

Obviously I didn't.

> Your bike is filthy. Not knocking you, but it looks like you don't take very good care of it.

I was riding in the rain when the crank broke.

> wI ould have removed the crank and cleaned it first, or taken off the chainrings before I sent
> those pics to Shimano.

I removed the crankarm (and the chainrings) cleaned it as well as I could and returned to Shimano
through a dealer.

> Take your bike, clean the hell out of it, make those crank arms shine like the day they were new
> (minus the shoe rub wear, you can' t do anything about that) and take just a picture of the failed
> crank arm. Then send that to them and see what they say.
>

No shit Einstein. Do you think I didn't think of this ? Plus, they will always want to examine the
part before replacing it.

-Amit

 

Amit wrote:
> I've posted pictures here of my failed Dura-Ace crankarm.
>
> http://www.atmosp.physics.utoronto.ca/people/amit/crank.htm
>
> They simply "folded" when I stood to pedal. The arm bent until it hit the chainring pin. The bent
> crankarm hit the chainstay and I didn't fall.

Wow! That's amazing! I would have expected this sort of failure to cause the crank to snap off and
dump you hard on the ground. You're very lucky, and it's a tribute to the technology of the Dura-Ace
crank that the failure mode was so benign.

> It sheared like a pop can (you can see it's hollow), but didn't separate into two pieces.
>
> I can't see what caused the failure. You can see that the crankarm is buffed smooth where my shoe
> occasionally touched it, perhaps that initiated a crack ?

That would be my guess, that among all the buffing, some feature of the side of your shoe cut a
groove which acted as a stress raiser. Can't see any sign of this in the photos, but a close look
might reveal traces of this.

> Shimano decided not to replace the crankarm since it is older than the 3 yrs. they warranty
> Dura-Ace parts for. I didn't pursue the matter further with them (also my frame is dented where
> the crankarm struck -

Are you sure? Many Cannondales have factory-installed dents in the rather thick chainstays for the
purpose of improving crank clearance.

Sheldon "Narrow Escape" Brown
+----------------------------------------------------------------------+
| It's also worth observing that, if someone walked down the street, | howling and swearing at
| pedestrians demanding that others get out | of their way,they'd be assumed to be on drugs, or
| mentallydisturbed.| This behavior doesn't somehow become "normal" because that person | happens
| to be in a motor vehicle. In fact, it's less acceptable | given that the person involved is
| driving an intrinsically dangerous| vehicle that requires skill and attention. --Tom Revay|
+----------------------------------------------------------------------+ Harris Cyclery, West
Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find
parts shipped Worldwide http://captainbike.com http://sheldonbrown.com

 

you don't have great detail of the fracture surfaces, but from what i can see, you've got a period
of slow fatigue crack growth [dark area on the fracture] followed by brittle failure [bright 'white'
fracture surface].

this is textbook, and almost certainly due to the scratching and wear initiating a minute notch from
which fatigue has propagated over some time.

judging by the poor condition of the piece and the fact that you've clearly had your shoe rubbing
against it for an extended period without bothering to fix the problem, you've only got yourself to
blame imho.

sorry to sound negative, but if you'd looked after the crank and kept it clean, you'd probably have
been able to spot the crack before failure. and if you'd adjusted your pedals/cleats properly to
avoid the rub in the first place, i seriously doubt you'd have had the problem at all.

every single fatigued crank i've ever seen has had the crack initiate at some kind of notch, usually
from damage in [ab]use, just like this. take care of your gear and it'll take care of you. if it
gets damaged, replace it before it damages you.

best

jb

Amit wrote:
> I've posted pictures here of my failed Dura-Ace crankarm.
>
> http://www.atmosp.physics.utoronto.ca/people/amit/crank.htm
>
> They simply "folded" when I stood to pedal. The arm bent until it hit the chainring pin. The bent
> crankarm hit the chainstay and I didn't fall.
>
> It sheared like a pop can (you can see it's hollow), but didn't separate into two pieces.
>
> I can't see what caused the failure. You can see that the crankarm is buffed smooth where my shoe
> occasionally touched it, perhaps that initiated a crack ?
>
> Shimano decided not to replace the crankarm since it is older than the 3 yrs. they warranty
> Dura-Ace parts for. I didn't pursue the matter further with them (also my frame is dented where
> the crankarm struck - I didn't pursue this either).
>
> I can take some better pictures if someone wants a closer look at the damage.
>
> -Amit Ghosh

 

Amit Ghosh writes:

> I've posted pictures here of my failed Dura-Ace crank.

http://www.atmosp.physics.utoronto.ca/people/amit/crank.htm

> They simply "folded" when I stood to pedal. The arm bent until it hit the chainring pin. The bent
> crank hit the chainstay and I didn't fall.

Very interesting. I can't see enough to assess the cause of the failure but from what the pictures
show, it looks suspiciously like a forced fracture rather than a fatigue crack that gradually grew
and then separated when there was insufficient metal remaining. That amount of metal is often 1/3
the original cross section. In these pictures, no fracture waves are visible, only a clean break and
that implies that the fracture was from a side blow. Pedaling would have caused a diagonal fracture
with a dark zone of advancing fracture followed by a clean separation like the one shown.

> It sheared like a pop can (you can see it's hollow), but didn't separate into two pieces.

Investigation such a failure, inspection of the fracture faces would be essential, but as I said,
from what is visible, the cause of failure doesn't follow your scenario. I have seen many crank
failures and their fracture surfaces and this one does not appear to have occurred as you describe.
That it is hollow means that once the outer wall was through, the remainder would fail faster than a
solid crank. This would make a difference and is why we don't need no steenkin hollow cranks.

> I can't see what caused the failure. You can see that the crank is buffed smooth where my shoe
> occasionally touched it, perhaps that initiated a crack?

I doubt it. It buffed off the anodizing making crack initiation more difficult.

> Shimano decided not to replace the crank since it is older than the 3 years for which they
> warranty Dura-Ace parts. I didn't pursue the matter further with them (also my frame is dented
> where the crank struck - I didn't pursue this either).

They may have sensed the same problems I have with the fracture. It may not be valid but then if I
looked at it more closely, I would be able to be more certain. In any case, this is a suspicious
looking failure.

> I can take some better pictures if someone wants a closer look at the damage.

A view of the fracture face (close-up) on both halves would help. I'm looking for crack propagation
to show that it was a fatigue failure. Other than that, it would have to have an inclusion that
caused weakness, but I see not indication of that. I would not warranty a forced failure from a side
force so that should be ruled out.

Jobst Brandt [email protected] Palo Alto CA

 

Amit Ghosh writes:

> I've posted pictures here of my failed Dura-Ace crank.

http://www.atmosp.physics.utoronto.ca/people/amit/crank.htm

> They simply "folded" when I stood to pedal. The arm bent until it hit the chainring pin. The bent
> crank hit the chainstay and I didn't fall.

Very interesting. I can't see enough to assess the cause of the failure but from what the pictures
show, it looks suspiciously like a forced fracture rather than a fatigue crack that gradually grew
and then separated when there was insufficient metal remaining. That amount of metal is often 1/3
the original cross section. In these pictures, no fracture waves are visible, only a clean break and
that implies that the fracture was from a side blow. Pedaling would have caused a diagonal fracture
with a dark zone of advancing fracture followed by a clean separation like the one shown.

> It sheared like a pop can (you can see it's hollow), but didn't separate into two pieces.

Inspecting the fracture faces would be essential to any failure analysis, but as I said, from
what is visible, the cause of failure doesn't follow your scenario. I have seen many crank
failures and their fracture surfaces and this one does not appear to have occurred as you
describe. That it is hollow makes a difference and means that once the outer wall was through,
the remainder would fail faster than a solid crank. This makes a difference and is why we don't
need no steenkin hollow cranks.

> I can't see what caused the failure. You can see that the crank is buffed smooth where my shoe
> occasionally touched it, perhaps that initiated a crack?

I doubt it. The shoe buffed off the anodizing, reducing probability of crack initiation.

> Shimano decided not to replace the crank since it is older than the 3 years for which they
> warranty Dura-Ace parts. I didn't pursue the matter further with them (also my frame is dented
> where the crank struck - I didn't pursue this either).

They may have sensed the same problems I have with the fracture. It may not be valid but then if I
looked at it more closely, I would be able to be more certain. In any case, this is a suspiciously
non-fatigue looking failure.

> I can take some better pictures if someone wants a closer look at the damage.

A view of the fracture face (close-up) on both halves would help. I'm looking for crack propagation
to show that it was a fatigue failure. Other than that, it would have to have an inclusion that
caused weakness, but I see no such indication. I would not warranty a forced failure from a side
force so that is what needs to be ruled out.

Jobst Brandt [email protected] Palo Alto CA

 

On 29 May 2003 17:07:52 -0700, [email protected] (Amit) wrote:

>They simply "folded" when I stood to pedal.

That's a really weird failure. Why has it folded sideways instead of down ? Have you dropped /
crashed the bike and taken a sideways impact on it ?

You'd need to examine the surfaces to know more, but I'd expect a pedalling-related failure to start
from near the top edge and work downwards or diagonally. If propagation here really was
side-to-side, then I'd look for some non-pedalling impact.

Unless there's some obvious casting fault showing up, I think Shimano are quite clearly
off the hook.

You're in a physics department - what does the nearest tame metallurgist reckon ?

 

"Russ" <[email protected]> wrote in message
> First off, why did you tell them it was more than three years old? That's mistake number one.

Sounds like you are telling him to lie if they ask how old the cranks are. Plonk.

JT

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NB: reply-to address is munged

Visit http://www.jt10000.com
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John Forrest Tomlinson wrote:
> "Russ" <[email protected]> wrote in message
>
>>First off, why did you tell them it was more than three years old? That's mistake number one.
>
>
> Sounds like you are telling him to lie if they ask how old the cranks are. Plonk.

I'd have to agree. Don't lie.

But as to the "clean it first", I've seen similar at my LBS. If you bring something in that's
filthy and they don't know you, they can only base how well you care for the bike on it's current
condition. If it's filthy, they're more likely to assume no/poor maintenance and less likely to
consider something to be warranty. (They'll also charge you more if they have to clean it to work
on it ).

David

 

<< was that this guy doesn't take care of his stuff.. it's abused and there is no way that is a
warranty issue.

Dirty doesn't make cranks fail, riding doesn't either. These or any other modern cranks that costs
so much should not fail. I agree that the customer didn't play the game, but I think shimano should
have warrantied these, or at least want to see them...

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302
(303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene"

 

jim beam <[email protected]> wrote:
: and if you'd adjusted your pedals/cleats properly to avoid the rub in the first place, i seriously
: doubt you'd have had the problem at all.

On every single bike I have every owned, by feet rub on the crankarms.

My pedals/cleats are adjusted properly - to be right for my knees.

As others have said, really rubbing the cranks smooth with your feet should smooth out an possible
stress raisers anyway.

Arthur

--
Arthur Clune http://www.clune.org Power is delightful. Absolute power is absolutely delightful -
Lord Lester

 

On Fri, 30 May 2003 [email protected] wrote:

>Amit Ghosh writes:
>
>> I've posted pictures here of my failed Dura-Ace crank.
>
>http://www.atmosp.physics.utoronto.ca/people/amit/crank.htm
>
>> They simply "folded" when I stood to pedal. The arm bent until it hit the chainring pin. The bent
>> crank hit the chainstay and I didn't fall.
>
>Very interesting. I can't see enough to assess the cause of the failure but from what the pictures
>show, it looks suspiciously like a forced fracture rather than a fatigue crack that gradually grew
>and then separated when there was insufficient metal remaining. That amount of metal is often 1/3
>the original cross section. In these pictures, no fracture waves are visible, only a clean break
>and that implies that the fracture was from a side blow. Pedaling would have caused a diagonal
>fracture with a dark zone of advancing fracture followed by a clean separation like the one shown.
>
>> It sheared like a pop can (you can see it's hollow), but didn't separate into two pieces.
>
>Investigation such a failure, inspection of the fracture faces would be essential, but as I said,
>from what is visible, the cause of failure doesn't follow your scenario. I have seen many crank
>failures and their fracture surfaces and this one does not appear to have occurred as you describe.
>That it is hollow means that once the outer wall was through, the remainder would fail faster than
>a solid crank. This would make a difference and is why we don't need no steenkin hollow cranks.

My assessment of the failure also concludes a side (non pedaling) force initiated it. Even if
the crank arm were cleaned up, there would still be a lot of divots and gouges visible from
where the crank had been up against something like a street curb or a rock. Also, look at all
the abrasion around the cap. This crank looks more like it's been on a well used mountain bike
than on a road bike.

And yes, the condition of the chain, spider and chainrings don't do much to assure me this bike
wasn't just thrown down a lot. The big ring is really roughed up at every junction with the spider.
How many of you put that kind of wear on your road bikes?

I suspect the crank damage began from the bike coming down on the pedal one or repeated times. The
grime everywhere would have made discovery of this crack difficult at best.

Finally, my parting shot. Dura-ace is supposed to be a lightweight racing group. Is it really fair
to expect it to survive the kind of abuse this crank has received? How many people have dura ace on
their commuter or cyclo cross bikes?

From: John B. Rees [email protected] http://www.jrees.net/

 

"John Rees" <[email protected]> wrote in message newsine.BSF.4.40.0305301341460.54874-

> Finally, my parting shot. Dura-ace is supposed to be a lightweight racing group. Is it really fair
> to expect it to survive the kind of abuse this crank has received? How many people have dura ace
> on their commuter or cyclo cross bikes?

You're making assumptions about abuse that don't seem evident to me from the photo, apart from the
crank being rubbed by the foot.

But those assumptions aside, I disagree with your suggestion that a racing group is or should
somehow be less sturdy than other material.

It's a road racing group. Not a special record attempt group or something. Three years of hard use
is not a lot -- whether cross, racing, commuting or whatever. I'm not saying the crank should
survive, say, getting bashed against a metal pole everyday from locking the bike up or something.
But road racing is hard. Bike are stored in cars, on racks, raced hard and pedalled hard. Road
racing groups should be tough, not fragile

I suspect the crank was either defective or was damaged by repeated grinding with the foot (my
cranks are similarly guaged out a bit).

JT

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Visit http://www.jt10000.com
*******************************************

 

From my experience with aluminum failures (A/C mishap investigations), there's usually a culprit
that causes a catastrophic failure as illustrated. Could be a nick created a stress raiser, but I'm
more inclined to think that a minute area of intergranular corrosion festered sufficiently to cause
the eventual failure under load. (High strength Al alloys are prone to corrosion, particularly if
exposed to the elements ... even rain water isn't as pure as you might think). If you examine the
fracture under magnification it will often appear as a darkened area in the fracture ... weld
imperfections are a frequent source as are machining errors.

Glad you're all right. Next time Campy?

R / John

 

In article <[email protected]>, "A Muzi" <[email protected]> wrote:

> Who wants to be a liar for a few bucks?

Is that a trick question? ;-)

 

The one time I had a crankarm fail in that location it was a solid Campy Triomphe (the group that marked the beginning of Campy's fall from grace). There was an obvious material flaw that was invisible from outside the crank but looked like a little black rock (about half the size of a raisin) on the cross section of the failed arm. It was classic fatigue but the crack propagation was internal and invisible until it snapped. That's why good photos of the fracture faces would help to determine if your failure may have been fatigue, and weather or not Shimano gave you a defective part to begin with.

As it happens I was taking a mechanical design course at the time and I gave the crank to my visiting professor from Israel who said he might use a photo if it in a Hebrew textbook he was writing on fatigue failure - I told him to mention that the rider who broke it was a strong sprinter.

 

[email protected] (Qui si parla Campagnolo) wrote in message
news:<[email protected]>...
> << was that this guy doesn't take care of his stuff.. it's abused and there is no way that is a
> warranty issue.
>
> Dirty doesn't make cranks fail, riding doesn't either. These or any other modern cranks that costs
> so much should not fail. I agree that the customer didn't play the game, but I think shimano
> should have warrantied these, or at least want to see them...
>
>
> Peter Chisholm Vecchio's Bicicletteria

Peter,

Riding will make all aluminum cranks fail eventually-there is a limit to the number of fatigue
cycles aluminum can go through, and with the current design of the pedal/crank interface and common
axle/crank interfaces, given enough use every crank will fail eventually. Granted we can expect that
newer cranks from reputable manufacturers should last longer than early aluminum cranks due to
improvements in manufacturing techniques but that's a matter of degree.

Bill Putnam

Regularly inspecting his cranks and removing them from service when cracks are visible.