Dura Ace Crank Failure

[Jay Beattie]

"John Carrier" <[email protected]> wrote in message news:[email protected]...
> 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?

The Campy recommendation begs the question of whether the hollow crank arm design materially
contributed to the cause of the failure. I doubt that Shimano has a higher rate of forging-related
defects than Campagnolo and would guess that brand-switching would get the OP nowhere unless the
failure were design related. For example, the design of the Campagnolo NR cranks 20 years ago
resulted in many failures, and I switched to Shimano after breaking four or five crank arms. If the
hollow crank arm design presents the same kind of problems, then switch -- and do it now before
getting locked into the latest Dura Ace BB set up. -- Jay Beattie.

 

[Jobst Brandt]

Bill Putnam writes:

> 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.

That doesn't explain a failure at a low stress point such as the one we see. Your statement may be
true in what it states but it is not related to the crank failure we are seeing. This is the kind of
statement one could call a smoke screen to divert attention from the problem at hand.

Jobst Brandt [email protected] Palo Alto CA

 

[John Forrest To]

<[email protected]> wrote in message news:[email protected]...
> This is the kind of statement one could call a smoke screen to divert attention from the problem
> at hand.

Are you suggesting Putnam is intentionally trying to confuse the issue? That's a rather big
assumption. Just because someone says something that is not 100% on target does not mean necessarily
mean they are trying to mislead others.

JT

--
*******************************************
NB: reply-to address is munged

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

 

[Jobst Brandt]

John Forrest Tomlinson writes:

>> This is the kind of statement one could call a smoke screen to divert attention from the problem
>> at hand.

> Are you suggesting Putnam is intentionally trying to confuse the issue? That's a rather big
> assumption. Just because someone says something that is not 100% on target does not mean
> necessarily mean they are trying to mislead others.

No. but it is a distraction and can lead discussion of the subject off course. I think contributors
should review what they are trying to contribute to the thread at hand. In this message, I was not
clear on what was intended except that I got the feeling that analysis was a waste of time and that
we should be happy it is broken and out of service.

Jobst Brandt [email protected] Palo Alto CA

 

[John Carrier]

> The Campy recommendation begs the question of whether the hollow crank arm design materially
> contributed to the cause of the failure.

Honestly don't know. Certainly a hollow arm can create the strength and stiffness desired for less
weight, but when you weld it up you introduce a potential for flaws in the structure.

You're right about the old NR cranks (an easily corrected design flaw that would probably not have
escaped computer stress analysis ... had they used it on bike stuff 20+ years ago). Then again the
C-Record was everything you'd want a crank to be ... except light.

My preference for Campy is based on having better experiences with their components over the years
... fewer failures/problems, easier maintenance. But I was also throwing bait onto the waters of the
eternal Campy vs. Shimano debate ... best concluded with "Which shifting system do you prefer?"

R / John

 

[Amit]

[email protected] wrote in message news:<4%BBa.18130

>
> 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.
>

The crank may have taken a blow from the side in the past. I have fallen or crashed on this bike,
but not in the last 8 months prior to the failure. It failed while riding as I described. Could a
side impact cause a failure sometime later even if any damage isn't evident ?

> > 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.

I'll take a picture of the fracture face when I get the part back. I might have to saw through the
remaining portion of the crankarm to get a good view.

-Amit Ghosh

 

[Amit]

jim beam <[email protected]> wrote in message news:<QRBBa.1093

>
> 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.
>

My shoe doesn't (didn't) rub it constantly, only sometimes (when I ride out of the saddle and tilt
my bike a bit). But three years of that is enough to wear off the anodizing.

> 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.
>

I use this crank with Time pedals and Sidi shoes. Unless I'm prepared to do some minor surgery to
the shoe or hardware, there is no provision for lateral adjustment of the cleat (though the Time
cleat can move laterally in the pedal a few mm).

> 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.
>

There is no scratch or notch evident, if rubbing caused cranks to fail I think we'd see a lot more
failures like this than we do.

-Amit

 

[David L. Johnso]

On Fri, 30 May 2003 05:19:44 +0000, jim beam wrote:

> this is textbook, and almost certainly due to the scratching and wear initiating a minute notch
> from which fatigue has propagated over some time.
>
No argument there.

> 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.

This is a bit past the line. For one thing, a shoe rubbing on the cranks is a very common, and
unavoidable circumstance. It really depends more on how wide your feet are than anything else. IMO
that should not cause such a failure, at least not for many years.

The only real "problem" the photo showed was that the bike wasn't clean. I think it's incredibly
anal to think that he ought to clean up a bike with a broken crank for the pictures. The dirt --
which may have been just from the last ride, and certainly could have been from a few rides in the
weather we've been having here in the East -- did not precipitate the crack. Keeping the bike clean
is not really a warrantee requirement.

OTOH, the crank was several years old, and out of warrantee. Failures happen. You get stuff with a
3-year warrantee, you should expect failures before, say, 10 years. It did look like you got a lot
of miles out of it. You got your money's worth. If you want to avoid this in the future, you'll have
to get stronger cranks. Dura-Ace equipment is mostly known for being lightweight, not for being
particularly durable.

> 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.

So you are suggesting that the worn-off anodizing layer was the cause? Doubtful.

--

David L. Johnson

__o | It is a scientifically proven fact that a mid life crisis can _`\(,_ | only be cured by
something racy and Italian. Bianchis and (_)/ (_) | Colnagos are a lot cheaper than Maserattis
and Ferraris. -- Glenn Davies

 

[David L. Johnso]

On Sat, 31 May 2003 14:13:36 +0000, Amit wrote:

> The crank may have taken a blow from the side in the past. I have fallen or crashed on this bike,
> but not in the last 8 months prior to the failure. It failed while riding as I described. Could a
> side impact cause a failure sometime later even if any damage isn't evident

Yes, it can.

--

David L. Johnson

__o | This is my religion. There is no need for temples; no need for _`\(,_ | complicated
philosophy. Our own brain, our own heart is our (_)/ (_) | temple. The philosophy is kindness.
--The Dalai Lama

 

[Chris Zacho "Th]

OMG! That bike looks like you used it off road! Sorry, Charlie, but I would see that as user abuse
(or at least neglect).

Nothing personal, but you should have neatened things up a bit, so at least looked like you take
care of the bike.

Or claimed it caused you to veer onto the shoulder and landed in the dirt, if nothing else (that may
have even strengthened your case)

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner

 

[Chris Zacho "Th]

Muzi, I wouldn't consider it cheating at all! If the crank simply spilled it's guts after only a few
year's use, that has nothing to do with warrantees, that's a clear cut manufacturing defect!!

I have a Shimano Tourney on my MTB, certainly not a high end crank, it's lasted ever since I got it
with my first MTB back in 1986! It's still on my current MTB. It's so scratched it actually
glitters! But it still works, no problem.

Now, if a low end crankset can last that long, I would think a Dura Ace, Shimano's "flagship" line,
could be depended on NOT to fail after only three years!

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner

 

[Mark Hickey]

"John Carrier" <[email protected]> wrote:

>> The Campy recommendation begs the question of whether the hollow crank arm design materially
>> contributed to the cause of the failure.
>
>Honestly don't know. Certainly a hollow arm can create the strength and stiffness desired for less
>weight, but when you weld it up you introduce a potential for flaws in the structure.

One thing that occurred to me was that the hollow construction of the crank arm may have actually
saved the OP going down in a heap.

The part of the crank that failed was the U-shaped upper, to which is welded a flat back plate. It
seems to me that the crack didn't propagate into the back plate, but I would expect a crank forged
or CNC'd from a billet would tend to fail catastrophically before the crank would deform enough to
be noticed.

Any opinions?

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame

 

[Sheldon Brown]

Mark Hickey wrote:

> One thing that occurred to me was that the hollow construction of the crank arm may have actually
> saved the OP going down in a heap.
>
> The part of the crank that failed was the U-shaped upper, to which is welded a flat back plate. It
> seems to me that the crack didn't propagate into the back plate, but I would expect a crank forged
> or CNC'd from a billet would tend to fail catastrophically before the crank would deform enough to
> be noticed.
>
> Any opinions?

Ditteaux

Sheldon "Me Too" Brown +--------------------------------------------+
| We hardly find any persons of good sense |
| save those who agree with with us. |
|- Francois, Duc de la Rouchefoucauld |
+--------------------------------------------+ 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

 

[Jobst Brandt]

Amit Ghosh writes:

>> 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.

> The crank may have taken a blow from the side in the past. I have fallen or crashed on this bike,
> but not in the last 8 months prior to the failure. It failed while riding as I described. Could a
> side impact cause a failure sometime later even if any damage isn't evident?

Possibly. The side impact could have cracked through the outer wall to the edge of the hollow. After
that, crack propagation would progress easily without needing overload. As I said, "we don't need no
steenkin hollow cranks" there are good reasons not to do this, and no good ones AT ALL!... other
than wealthy Americans who need to believe that it's worth every cent you pay for it.

>>> 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.

> I'll take a picture of the fracture face when I get the part back. I might have to saw through the
> remaining portion of the crankarm to get a good view.

That may help.

Jobst Brandt [email protected] Palo Alto CA

 

[Andrew Webster]

[email protected] (Chris Zacho "The Wheelman") wrote in message
news:<[email protected]>... <cut>
>
> Now, if a low end crankset can last that long, I would think a Dura Ace, Shimano's "flagship"
> line, could be depended on NOT to fail after only three years!
>
<cut>

My experience reflects your own. Lifetime of "low end" Shimano drive components is generally high on
all bikes I have had them on. Higher than mid range Shimano components.

From this I draw the opposite conclusion to your own. Namely:

Lifetime of "higher end" drive components is lower. I assume that the Shimano "high end" stuff is
built more for lightness than for durability and therefore likely to last less well.

By paying more you are getting smoother operating, nicer looking and lighter components, not more
durable ones.

It just goes to show how the same data can be looked at in different ways.

Caveats

1)My sample size is too small to be statistically significant.
2)This experience for drive components does not aply to Shimano hubs.

 

[Jasper Janssen]

On 31 May 2003 23:07:39 -0700, [email protected] (Andrew Webster) wrote:

>Lifetime of "higher end" drive components is lower. I assume that the Shimano "high end" stuff is
>built more for lightness than for durability and therefore likely to last less well.

To take a random example, chainwheels in steel versus aluminium. Aluminium ones are more expensive,
last much shorter, and are slightly lighter.

Give me the steel any day. Once you factor in my way-above-average weight, whether my bike weighs 10
kilos or 20 is really no big deal.

Jasper

 

[Rick Warner]

[email protected] (Amit) wrote in message
news:<[email protected]>...

I'll let Jobst and the rest of the more engineering inclined comment on the failure. On another
note, you need to find out why your foot is buffing the crank so much; that is not 'occasional',
that looks like it is rather frequent. I have a 3 yr old Shimano crank on a bike I ride 4-5000 miles
per year and my foot occasionally buffs the crank; it has barely buffed off part of the writing! I
ride with Speedplay X pedals, so my foot can rotate rather freely, and I consciously had to work to
get the shoe to hit the crank very much, and then it my heel hitting near the crank bolt; yours is
much more severe and has worn quite a bit down half the length of the crank arm. My foot is average
(42) as are the cranks (172.5mm). If I had to guess, you have a wide foot. Perhaps you need to
consider a pedal with a longer spindle to move your foot away from the crank.

- rick warner

 

[A Muzi]

"Chris Zacho "The Wheelman"" <[email protected]> wrote in message
news:[email protected]...
> Muzi, I wouldn't consider it cheating at all! If the crank simply spilled it's guts after only a
> few year's use, that has nothing to do with warrantees, that's a clear cut manufacturing defect!!
>
> I have a Shimano Tourney on my MTB, certainly not a high end crank, it's lasted ever since I got
> it with my first MTB back in 1986! It's still on my current MTB. It's so scratched it actually
> glitters! But it still works, no problem.
>
> Now, if a low end crankset can last that long, I would think a Dura Ace, Shimano's "flagship"
> line, could be depended on NOT to fail after only three years!

Oh, we all have seen things that worked well for thirty or more years and we've all seen things fail
prematurely. This wasn't about the crank, really.

I may have overreacted, but I was taken aback that someone would knowingly lie, or encourage someone
else to lie, in a public forum no less, over a few dollars.

(What a hue and cry there would be other way if Shimano falsified something to screw a guy out of a
legitimate warranty!)

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

 

[A Muzi]

> Mark Hickey wrote:
>
> > One thing that occurred to me was that the hollow construction of the crank arm may have
> > actually saved the OP going down in a heap.
> >
> > The part of the crank that failed was the U-shaped upper, to which is welded a flat back plate.
> > It seems to me that the crack didn't propagate into the back plate, but I would expect a crank
> > forged or CNC'd from a billet would tend to fail catastrophically before the crank would deform
> > enough to be noticed.
> >
> > Any opinions?

"Sheldon Brown" <[email protected]> wrote in message
news:[email protected]...
> Ditteaux Sheldon "Me Too" Brown

I cut open the first hollow crank here that was destined for recycling. The LX models are made in
one large closed-bottom cylinder like a Tom Collins glass and then punched flat at the pedal end.
The two halves are threaded through as one and there isn't a weld at all. One interesting part is a
2mm hole near the bottom for air to escape when the crank is flattened ( covered by a sticker.)
Overall ,a very impressive exercise in of material forming.

Anyway, is there a weld in a Dura Ace crank? If not , the end result if their material selection and
processing is even more impressive after the front side failure.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

 

[David Damerell]

Kraig Willett <[email protected]> wrote:
>BTW, I think your bike looks clean compared to some of my old commuter bikes of days gone by.

Remember, a clean bike is a stolen bike. Keep 'em filthy. The OP's bike is a fair bit cleaner than
mine is right now.
--
David Damerell <[email protected]> Kill the tomato!