Just snapped 20-yr-old crank arm...

[Jeff Potter]

I've been riding an Exel crank on my commuter for 20 years now.
Actually, it was on my first racing bike. Today it snapped. My foot
hit the ground on a bumpy dirt road uphill, with the pedal still
clipped to it. No crash. Man, that was a first. I suppose it's
something you don't want to happen too often. I wonder if this kind of
thing is going to start happening with all this 20-year-old alloy
stuff I'm using right now... Oh well! I must have another crank in a
box around here somewhere...

--JP

[[email protected]]

Jeff Potter writes:

> I've been riding an Exel crank on my commuter for 20 years now.

Was it standing in your garage that long or did it get any mileage?
How much? Where did it break and how does the break look? If it was
bad material, the fracture will be uniformly colored. If it broke
gradually from a crack initiation it will show waves from the clean
(last failure) to the initiation point.

> Actually, it was on my first racing bike. Today it snapped. My
> foot hit the ground on a bumpy dirt road uphill, with the pedal
> still clipped to it. No crash. Man, that was a first. I suppose
> it's something you don't want to happen too often. I wonder if this
> kind of thing is going to start happening with all this 20-year-old
> alloy stuff I'm using right now... Oh well! I must have another
> crank in a box around here somewhere...

As I have related often, failures at the pedal eye occurred on my
bicycle about every 10,000 miles on the average for more than 25
years. That's a lot of cranks and they were mostly Campagnolo and
later Shimano. Since then I modified the pedal end of the cranks so
they no longer fret, cause crack initiation, and break off through the
pedal eye.

So where did your crank break?

Jobst Brandt

[Jeff Potter]

wrote in message >...
> Jeff Potter writes:
>
> > I've been riding an Exel crank on my commuter for 20 years now.
>
> Was it standing in your garage that long or did it get any mileage?
> How much? Where did it break and how does the break look? If it was
> bad material, the fracture will be uniformly colored. If it broke
> gradually from a crack initiation it will show waves from the clean
> (last failure) to the initiation point.

Thanks, Jobst, yer the man! : ) The break is 2" above the pedal eye.
It is half white, half black and all rough with 1/8" roughnesses. I
rode it about twice a week half the year. But that crank might have
been idle a few years over those 20 yrs. My riding is irregular and I
swapo among bikes so I can't estimate it well.

[ ]
> As I have related often, failures at the pedal eye occurred on my
> bicycle about every 10,000 miles on the average for more than 25
> years. That's a lot of cranks and they were mostly Campagnolo and
> later Shimano. Since then I modified the pedal end of the cranks so
> they no longer fret, cause crack initiation, and break off through the
> pedal eye.

Sounds cool.

Ya know, this is about my first bike part failure. I ride with what
many call "crap." Old parts, lots of nice old Campy, tho; duct tape
here and there; it all works but some folks laugh. It's not in as bad
of tune as some racers' stuff I've seen (bent, hardly functioning
levers, bars, etc.). But I haven't had failures. Not that often
anyway. Maybe once a decade. More often due to simple accident---and
even then only once a decade as well (like bungie falling into spokes:
once). I have had a few rear axles break over the years---but never on
my racing bike for some reason. Bikes sure seem robust and tolerant by
and large. Perfect machines for me! : ) Especially when you branch
out to HPVs---I've had cargo bays last and work hard for years made
out of coroplast and zipties. I've gotten good speed gains from
ducttape and pieces of lycra. This is the scale of materials I like to
work with. : )

> So where did your crank break?
>
> Jobst Brandt

[Shawn Amir]

> wrote
>... Since then I modified the pedal end of the cranks so
> they no longer fret, cause crack initiation, and break off through the
> pedal eye.

Can you kindly point to where you have described the modifications. I
recall you writing about similar design issues with lug nuts on auto wheels,
but I must have missed your description of the actual mods.

Cheers, Shawn

[[email protected]]

On Tue, 25 May 2004 22:17:17 GMT, "Shawn Amir"
> wrote:

> wrote
>>... Since then I modified the pedal end of the cranks so
>> they no longer fret, cause crack initiation, and break off through the
>> pedal eye.
>
>Can you kindly point to where you have described the modifications. I
>recall you writing about similar design issues with lug nuts on auto wheels,
>but I must have missed your description of the actual mods.
>
>Cheers, Shawn
>

Dear Shawn,

Here's one of Jobst's posts on his lug-nut pedal
modification:

http://groups.google.com/groups?selm=lYsL8.8723%243w2.39832%40typhoon.sonic .net&output=gplain

David Damerell has done us all a favor by taking the time
and trouble to host a 700kb picture of Jobst's modified
pedal and crank:

http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg

At full size, the picture clearly shows the split in the
conical washer around the threaded pedal shaft and
corresponding conical depression in the pedal eye.

You can find more details by searching for "jobst lug" at:

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&group=rec.bicycles.tech

While google groups is slow to include new posts (up to a
day's delay), it's easily accessible (no newsreader needed),
offers a simple search, and goes back to the crack of doom
for rec.bicycles.tech.

Carl Fogel

[David Reuteler]

wrote:
> As I have related often, failures at the pedal eye occurred on my
> bicycle about every 10,000 miles on the average for more than 25
> years. That's a lot of cranks and they were mostly Campagnolo and
> later Shimano.

good lord, that scares the crap out of me. would you venture a guess at
the standard deviation of those failures? (not that i'm worried with
16,000 miles on my current crank and memories of a catastrophic failure
behind me).
--
david reuteler

[[email protected]]

David Reuteler > writes:

>> As I have related often, failures at the pedal eye occurred on my
>> bicycle about every 10,000 miles on the average for more than 25
>> years. That's a lot of cranks and they were mostly Campagnolo and
>> later Shimano.

> Good lord, that scares the crap out of me. Would you venture a
> guess at the standard deviation of those failures? (Not that I'm
> worried with 16,000 miles on my current crank and memories of a
> catastrophic failure behind me).

I don't know but that was more than one per year and the last
Campagnolo Cranks were C-Record that failed in less than 3000 miles.
That's when I switched to Dura Ace and finally modified these to put
an end to crank inspections before every ride. Although others had
failures, I had more than average occurrences. These my be affected
by the gears I ride and the terrain. I weight 180 lbs.

http://tinyurl.com/adls

As you can see, there are a lot of tours in between 1960 and 1990
whose reports were lost but they were much like the ones described.

Anyone who is good at searching the web for old postings and can find
those reports (that appeared on REC.BICYCLE) would be greatly
appreciated. I have not been able to find them and the people I rode
with and are mentioned in them would love to have copies.

Jobst Brandt

[Konstantin Shemyak]

wrote:
> How much? Where did it break and how does the break look? If it was
> bad material, the fracture will be uniformly colored. If it broke
> gradually from a crack initiation it will show waves from the clean
> (last failure) to the initiation point.

Please could you post a (link to a) picture showing these waves.

Also, you mention "crank inspection before every ride". What should
one look for?

Thank you,
Konstantin.

[Sergio SERVADIO]

On 26 May 2004, Evan Evans wrote:
> Old bikes are nice to look at but you are taking your chances riding
> them. Even the best components ore subject to fatigue. If you ride
> much a new bike every once & awile is cheep insurance. One trip to the
> emergancy room will go along way on that new bike.

You are taking your chances every time you ride what you know
nothing about. Better be well acquainted with your equipment,
whether old or new.

Sergio
Pisa

[Evan Evans]

Old bikes are nice to look at but you are taking your chances riding
them. Even the best components ore subject to fatigue. If you ride
much a new bike every once & awile is cheep insurance. One trip to the
emergancy room will go along way on that new bike.

[[email protected]]

On Wed, 26 May 2004 09:17:21 GMT, Konstantin Shemyak
> wrote:

wrote:
>> How much? Where did it break and how does the break look? If it was
>> bad material, the fracture will be uniformly colored. If it broke
>> gradually from a crack initiation it will show waves from the clean
>> (last failure) to the initiation point.
>
>Please could you post a (link to a) picture showing these waves.
>
>Also, you mention "crank inspection before every ride". What should
>one look for?
>
>Thank you,
>Konstantin.

Dear Konstantin,

Here's a gallery of some broken cranks:

http://pardo.net/pardo/bike/pic/fail/000.html

This one shows the waves:

http://pardo.net/pardo/bike/pic/fail/crank-fail-015.jpg

This non-bicycle link has some arrows and descriptions,
showing the fatigue origin zone, the "beach waves" spreading
out, and the instantaneous zone:

http://avsafety.nps.navy.mil/gouge/structures/sld007.htm

Carl Fogel

[[email protected]]

Konstantin Shemyak writes:

>> How much? Where did it break and how does the break look? If it
>> was bad material, the fracture will be uniformly colored. If it
>> broke gradually from a crack initiation it will show waves from the
>> clean (last failure) to the initiation point.

> Please could you post a (link to a) picture showing these waves.

Crank-fail-011 shows many waves, but these are only visible after
separation, something that should be avoided.

http://pardo.net/pardo/bike/pic/fail/FAIL-001.html

> Also, you mention "crank inspection before every ride". What should
> one look for?

Crank-fail-005 is a typical one that I caught by inspection. Red dye
makes the crack more visible. Note how great the fretting damage to
the pedal eye is. This is what generates the cracks that ultimately
cause failure.

This web sight has a collection of failures that might interest you.
Also check the home page for more.

Jobst Brandt

[Shawn Amir]

Many thanks Carl. It was very enlightning. I couldn't figure out whether
the "lug nut" effect was due to changing the interface angle or to
increasing the contact area. From Jobst's message, it appears to be both.

Now I wonder why Shimano doesn't use it on their cranks and pedals? Just
think, Shimano Bio-Lug cranks, which are off course compatible only with
SPD-BL pedals!

Cheers, Shawn

[Jay Beattie]

"David Reuteler" > wrote in message
. ..
> wrote:
> > As I have related often, failures at the pedal eye occurred
on my
> > bicycle about every 10,000 miles on the average for more than
25
> > years. That's a lot of cranks and they were mostly
Campagnolo and
> > later Shimano.
>
> good lord, that scares the crap out of me. would you venture a
guess at
> the standard deviation of those failures? (not that i'm
worried with
> 16,000 miles on my current crank and memories of a catastrophic
failure
> behind me).

The Campy NR cranks broke with some frequency. I broke at least
four in the 70s and 80s (and a few other brands, too). Jobst's
experience, IMO, represents the extreme end of the spectrum. I
have never broken a Shimano crank, and I raced at about 200lbs
for many years on them. I still ride an older Dura Ace crank
(1983) with probably 100K on it. There is not a whole lot to
fear for the average cyclist. Another interesting thing about
breaking a crank is that it usually does not result in a serious
crash. The OP's experience is the common one -- your foot hits
the ground and you wobble to a stop. Much like when you break a
pedal spindle. I would be more concerned with a broken bar,
which seems to be the popular thing to break these days (based on
the NG posts). -- Jay Beattie.

[Ted Bennett]

Shawn Amir wrote:

> Many thanks Carl. It was very enlightning. I couldn't figure out whether
> the "lug nut" effect was due to changing the interface angle or to
> increasing the contact area. From Jobst's message, it appears to be both.
>
> Now I wonder why Shimano doesn't use it on their cranks and pedals? Just
> think, Shimano Bio-Lug cranks, which are off course compatible only with
> SPD-BL pedals!


Because Shimano's opinion is that failures are so rare that there is no
reason to change the joint.

They are right about the rarity. Almost all cranks never get the amount
of use that leads to cracking and breaking. If it were otherwise,
Shimono's legal team would have something to say to management. Still,
jobst's point about a simple and effective fix is valid.

--
Ted Bennett
Portland OR

[[email protected]]

Jay Beattie writes:

>>> As I have related often, failures at the pedal eye occurred on my
>>> bicycle about every 10,000 miles on the average for more than 25
>>> years. That's a lot of cranks and they were mostly Campagnolo and
>>> later Shimano.

>> good lord, that scares the crap out of me. would you venture a
>> guess at the standard deviation of those failures? (not that I'm
>> worried with 16,000 miles on my current crank and memories of a
>> catastrophic failure behind me).

> The Campy NR cranks broke with some frequency. I broke at least
> four in the 70s and 80s (and a few other brands, too). Jobst's
> experience, IMO, represents the extreme end of the spectrum. I
> have never broken a Shimano crank, and I raced at about 200lbs
> for many years on them. I still ride an older Dura Ace crank
> (1983) with probably 100K on it.

> There is not a whole lot to fear for the average cyclist. Another
> interesting thing about breaking a crank is that it usually does not
> result in a serious crash. The OP's experience is the common one --
> your foot hits the ground and you wobble to a stop. Much like when
> you break a pedal spindle. I would be more concerned with a broken
> bar, which seems to be the popular thing to break these days (based
> on the NG posts).

I disagree. If you have broken a crank while standing, you fall to
the side of the failure, there is no recovery if you are traveling at
any reasonable speed. The effect is like trying to run with one leg
with a bicycle between your legs. If you are sprinting across the
intersection when the light turns green the readymix truck next to you
will make a pancake out of you and your bicycle.

You only imagine that a crank will break while sitting but the active
rider puts his peak force into the pedals while standing and therefore
the fracture generally occurs in that mode, the sitting mode being too
low a force to cause failure. Most of my cranks were discovered by
inspection but some were not. Some of the pictures in the Hjertberg
collection are mine as are two crank spindles. When a crank spindle
breaks there is no warning and no way to check for it because it
breaks inside the press fit of the crank.

These failures are probable fatalities for those who ride adjacent to
auto traffic... or a cliff.





Jobst Brandt

[jim beam]

Shawn Amir wrote:
> Many thanks Carl. It was very enlightning. I couldn't figure out whether
> the "lug nut" effect was due to changing the interface angle or to
> increasing the contact area. From Jobst's message, it appears to be both.
>
> Now I wonder why Shimano doesn't use it on their cranks and pedals?

because it's not necessary. has anyone ever noticed how few crank
failures there are these days? do a google search for post-70's broken
campy or dura-ace cranks. i'll bet the only failures you find are where
there surface damage is evident. all the other failures will be in
vintage stuff.

reality is, the failure cited by the o.p. has /nothing/ to do with this
proposed pedal redesign. and the reason we don't see many failures
these days is because material production practice is much better &
material cleanliness is much better - tiny fatigue initiators are
pretty much eliminated, in the quality components at least. fatigue
therefore never gets a hold unless the component is damaged and
initiates the crack growth process.

> Just
> think, Shimano Bio-Lug cranks, which are off course compatible only with
> SPD-BL pedals!
>
> Cheers, Shawn
>
>

[jim beam]

wrote:
> Jay Beattie writes:
>
>
>>>>As I have related often, failures at the pedal eye occurred on my
>>>>bicycle about every 10,000 miles on the average for more than 25
>>>>years. That's a lot of cranks and they were mostly Campagnolo and
>>>>later Shimano.
>
>
>>>good lord, that scares the crap out of me. would you venture a
>>>guess at the standard deviation of those failures? (not that I'm
>>>worried with 16,000 miles on my current crank and memories of a
>>>catastrophic failure behind me).
>
>
>>The Campy NR cranks broke with some frequency. I broke at least
>>four in the 70s and 80s (and a few other brands, too). Jobst's
>>experience, IMO, represents the extreme end of the spectrum. I
>>have never broken a Shimano crank, and I raced at about 200lbs
>>for many years on them. I still ride an older Dura Ace crank
>>(1983) with probably 100K on it.
>
>
>>There is not a whole lot to fear for the average cyclist. Another
>>interesting thing about breaking a crank is that it usually does not
>>result in a serious crash. The OP's experience is the common one --
>>your foot hits the ground and you wobble to a stop. Much like when
>>you break a pedal spindle. I would be more concerned with a broken
>>bar, which seems to be the popular thing to break these days (based
>>on the NG posts).
>
>
> I disagree. If you have broken a crank while standing, you fall to
> the side of the failure, there is no recovery if you are traveling at
> any reasonable speed. The effect is like trying to run with one leg
> with a bicycle between your legs. If you are sprinting across the
> intersection when the light turns green the readymix truck next to you
> will make a pancake out of you and your bicycle.
>
> You only imagine that a crank will break while sitting but the active
> rider puts his peak force into the pedals while standing and therefore
> the fracture generally occurs in that mode, the sitting mode being too
> low a force to cause failure. Most of my cranks were discovered by
> inspection but some were not. Some of the pictures in the Hjertberg
> collection are mine as are two crank spindles. When a crank spindle
> breaks there is no warning and no way to check for it because it
> breaks inside the press fit of the crank.
>
> These failures are probable fatalities for those who ride adjacent to
> auto traffic... or a cliff.
>
no one disputes the effect of a failure. what jay's saying, and i agree
with him, is that failures are very rare these days. your assertion
that a modern campy or dura-ace crank will fail in only 10,000 miles is
irresponsible scare-mongering. show us the beef. show us a single
undamaged campy or dura-ace crank that has failed within even 200% of
this figure.

[Richard Brockie]

jim beam wrote:
>> These failures are probable fatalities for those who ride adjacent to
>> auto traffic... or a cliff.
>>
> no one disputes the effect of a failure. what jay's saying, and i agree
> with him, is that failures are very rare these days. your assertion
> that a modern campy or dura-ace crank will fail in only 10,000 miles is
> irresponsible scare-mongering. show us the beef. show us a single
> undamaged campy or dura-ace crank that has failed within even 200% of
> this figure.

This photo does just that:

http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg

This is a side-by-side comparison of two used cranks, one with and
one without Jobst's modification. The lack of wear on the modified
crank is remarkable and is a clear indication of a superior design in
that the motion of the joint has been eliminated.

--
R.

<> Richard Brockie "Categorical statements
<> The tall blond one. always cause trouble."
<>

[jim beam]

Richard Brockie wrote:
> jim beam wrote:
>
>>> These failures are probable fatalities for those who ride adjacent to
>>> auto traffic... or a cliff.
>>>
>> no one disputes the effect of a failure. what jay's saying, and i
>> agree with him, is that failures are very rare these days. your
>> assertion that a modern campy or dura-ace crank will fail in only
>> 10,000 miles is irresponsible scare-mongering. show us the beef.
>> show us a single undamaged campy or dura-ace crank that has failed
>> within even 200% of this figure.
>
>
> This photo does just that:
>
> http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg
>
> This is a side-by-side comparison of two used cranks, one with and one
> without Jobst's modification. The lack of wear on the modified crank is
> remarkable and is a clear indication of a superior design in that the
> motion of the joint has been eliminated.

so which one has broken with fatigue? i can't see it.

[David Reuteler]

jim beam > wrote:
> no one disputes the effect of a failure.

to nitpick, but that's exactly what he was saying:

Jay Beattie writes:
> Another interesting thing about breaking a crank is that it usually does
> not result in a serious crash.
--
david reuteler

[bfd]

"jim beam" > wrote in message
om...
> wrote:
> > Jay Beattie writes:
>> no one disputes the effect of a failure. what jay's saying, and i agree
> with him, is that failures are very rare these days. your assertion
> that a modern campy or dura-ace crank will fail in only 10,000 miles is
> irresponsible scare-mongering. show us the beef. show us a single
> undamaged campy or dura-ace crank that has failed within even 200% of
> this figure.
>
What about this Dura Ace 9 crank:

http://pardo.net/pardo/bike/pic/fail/FAIL-010.html

or this Colnago Carbon crank:
http://pardo.net/pardo/bike/pic/fail/FAIL-007.html

here's a modern looking Campy crank:
http://pardo.net/pardo/bike/pic/fail/FAIL-005.html

Cranks can break....

[[email protected]]

On Wed, 26 May 2004 18:03:26 GMT,
wrote:

>Konstantin Shemyak writes:
>
>>> How much? Where did it break and how does the break look? If it
>>> was bad material, the fracture will be uniformly colored. If it
>>> broke gradually from a crack initiation it will show waves from the
>>> clean (last failure) to the initiation point.
>
>> Please could you post a (link to a) picture showing these waves.
>
>Crank-fail-011 shows many waves, but these are only visible after
>separation, something that should be avoided.
>
>http://pardo.net/pardo/bike/pic/fail/FAIL-001.html
>
>> Also, you mention "crank inspection before every ride". What should
>> one look for?
>
>Crank-fail-005 is a typical one that I caught by inspection. Red dye
>makes the crack more visible. Note how great the fretting damage to
>the pedal eye is. This is what generates the cracks that ultimately
>cause failure.
>
>This web sight has a collection of failures that might interest you.
>Also check the home page for more.
>
>Jobst Brandt


Dear Jobst,

How does the long-term fretting damage differ from the
deliberate conical boring-out?

That is, the fretting damage looks like a fairly smooth
indentation in the same area where much more metal is
removed to accept a conical washer:

http://pardo.net/pardo/bike/pic/fail/crank-fail-005.jpg

Is it the sharpness of the fretted area's internal shoulder
that you expect to initiate cracks that would be avoided by
the sloping conical shoulder?

|____| vs. \ ___/

Or is it something to do with the pedal shaft loosening and
rocking as it frets the pedal eye?

Does it matter that the original flat surface compresses
but does not expand the pedal eye, while the conical washer
is a wedge that presumably adds an expanding force that
would actually increase the likelihood of cracking?

Car wheels don't seem to crack much around their lug nuts,
but they're rather different than a pedal eye, so I'm
wondering exactly how all this works. I'm not even sure that
I understand why a lug nut works better than a flat-faced
nut, so any explanation will be helpful.

Carl Fogel

[[email protected]]

On Thu, 27 May 2004 05:58:39 GMT, "bfd" >
wrote:

>
>"jim beam" > wrote in message
om...
>> wrote:
>> > Jay Beattie writes:
>>> no one disputes the effect of a failure. what jay's saying, and i agree
>> with him, is that failures are very rare these days. your assertion
>> that a modern campy or dura-ace crank will fail in only 10,000 miles is
>> irresponsible scare-mongering. show us the beef. show us a single
>> undamaged campy or dura-ace crank that has failed within even 200% of
>> this figure.
>>
>What about this Dura Ace 9 crank:
>
>http://pardo.net/pardo/bike/pic/fail/FAIL-010.html
>
>or this Colnago Carbon crank:
>http://pardo.net/pardo/bike/pic/fail/FAIL-007.html
>
>here's a modern looking Campy crank:
>http://pardo.net/pardo/bike/pic/fail/FAIL-005.html
>
>Cranks can break....
>
>
>

Dear Bfd,

I was browsing that failure gallery and noticed those
pictures, along with others.

Note that the red Dura Ace pedal arm is half-broken and bent
inward, toward the frame, not downward as if from any normal
pedal force:

http://pardo.net/pardo/bike/pic/fail/FAIL-010.ht

I can't help wondering if the no-longer attached pedal
banged into the pavement sideways, putting a lot of sideways
force on the pedal arm in a direction that it wasn't
designed to take. Whatever happened, it doesn't look related
to the pedal eye.

The Colnago Carbon crank also seems to have remained intact
around the metal pedal eyer:

http://pardo.net/pardo/bike/pic/fail/FAIL-007.html

In any case, this carbon design is so utterly different from
a normal metal pedal arm that it's hard to imagine a normal
crank failing that way. (Look at that weird piece!)

At first, the last picture that you mention, the blue Campy
crank, looks like the kind of pedal-eye crack that Jobst
tries to avoid with his conical-washer and pedal-eye boring.

But then I remembered (d'oh!) that the pedal eye is at the
other end of the arm. That's the bottom-bracket eye. I don't
think that Jobst is proposing a conical washer modification
at that end.

Is that a modern Campy pedal arm? I know nothing about
Campy, so I have no idea how old this one is. Most of the
other pictures are dated 2001. There's a triple chain-ring,
there's a bottom-bracket with indents for removal, and
there's some lettering on the crank-retaining allen-nut and
on the bottom-bracket. (The pedal-arm, of course, might be
newer than the bottom-bracket.)

I'm not sure if that small hump that the crack runs out
through is the metal bulging at the crack, or the crack
running through a hump.

(I know so little about cracks that I'm not sure where it
started. Did it start at the outside and run smoothly for a
bit and then become jagged as it approached the frame side,
or the other way around?)

Can anyone tell by looking at the pictures how old that
cracked pedal arm is on the blue Campy?

And is there any way to tell whether the numerous cranks
failed from normal use alone, or from normal use after
banging the pedals into the pavement?

Carl Fogel

[[email protected]]

Carl Fogel writes:

>>>> How much? Where did it break and how does the break look? If it
>>>> was bad material, the fracture will be uniformly colored. If it
>>>> broke gradually from a crack initiation it will show waves from
>>>> the clean (last failure) to the initiation point.

>>> Please could you post a (link to a) picture showing these waves.

>> Crank-fail-011 shows many waves, but these are only visible after
>> separation, something that should be avoided.

http://pardo.net/pardo/bike/pic/fail/FAIL-001.html

>>> Also, you mention "crank inspection before every ride". What
>>> should one look for?

>> Crank-fail-005 is a typical one that I caught by inspection. Red
>> dye makes the crack more visible. Note how great the fretting
>> damage to the pedal eye is. This is what generates the cracks that
>> ultimately cause failure.

>> This web sight has a collection of failures that might interest
>> you. Also check the home page for more.

> How does the long-term fretting damage differ from the deliberate
> conical boring-out?

It's not the material removal that's the problem but the cracks that
are generated from welding and unwelding at the interface. Besides
that the stresses are higher in the asymptotic motion of a flat face
of the pedal shaft being worked laterally.

> That is, the fretting damage looks like a fairly smooth indentation
> in the same area where much more metal is removed to accept a
> conical washer:

http://pardo.net/pardo/bike/pic/fail/crank-fail-005.jpg

> Is it the sharpness of the fretted area's internal shoulder that you
> expect to initiate cracks that would be avoided by the sloping
> conical shoulder?

> |____| vs. \ ___/

> Or is it something to do with the pedal shaft loosening and rocking
> as it frets the pedal eye?

Removing metal by rubbing is the problem. It causes welding and
tear-out that makes a ragged surface with local cracks.

> Does it matter that the original flat surface compresses but does
> not expand the pedal eye, while the conical washer is a wedge that
> presumably adds an expanding force that would actually increase the
> likelihood of cracking?

The conical fit causes a compression contact that cannot slide, the
forces being normal to the surface of the conical contact. Think of
the middle of the pedal thread to be a ball joint.

> Car wheels don't seem to crack much around their lug nuts, but
> they're rather different than a pedal eye, so I'm wondering exactly
> how all this works. I'm not even sure that I understand why a lug
> nut works better than a flat-faced nut, so any explanation will be
> helpful.

They don't have a problem because they do not move at the contact
between nut and wheel.

Jobst Brandt

[[email protected]]

Carl Fogel writes:

> I was browsing that failure gallery and noticed those pictures,
> along with others.

> Note that the red Dura Ace pedal arm is half-broken and bent inward,
> toward the frame, not downward as if from any normal pedal force:

> http://pardo.net/pardo/bike/pic/fail/FAIL-010.ht

> I can't help wondering if the no-longer attached pedal banged into
> the pavement sideways, putting a lot of sideways force on the pedal
> arm in a direction that it wasn't designed to take. Whatever
> happened, it doesn't look related to the pedal eye.

If the crank is bent then it wasn't a fatigue failure but rather a
forced rupture. These are just failure pictures with no special trend.

Jobst Brandt

[Jay Beattie]

> wrote in message
...
> On Thu, 27 May 2004 05:58:39 GMT, "bfd" >
> wrote:
>
> >
> >"jim beam" > wrote in message
> om...
> >> wrote:
> >> > Jay Beattie writes:
> >>> no one disputes the effect of a failure. what jay's
saying, and i agree
> >> with him, is that failures are very rare these days. your
assertion
> >> that a modern campy or dura-ace crank will fail in only
10,000 miles is
> >> irresponsible scare-mongering. show us the beef. show us a
single
> >> undamaged campy or dura-ace crank that has failed within
even 200% of
> >> this figure.
> >>
> >What about this Dura Ace 9 crank:
> >
> >http://pardo.net/pardo/bike/pic/fail/FAIL-010.html
> >
> >or this Colnago Carbon crank:
> >http://pardo.net/pardo/bike/pic/fail/FAIL-007.html
> >
> >here's a modern looking Campy crank:
> >http://pardo.net/pardo/bike/pic/fail/FAIL-005.html
> >
> >Cranks can break....
> >
> >
> >
>
> Dear Bfd,
>
> I was browsing that failure gallery and noticed those
> pictures, along with others.
>
> Note that the red Dura Ace pedal arm is half-broken and bent
> inward, toward the frame, not downward as if from any normal
> pedal force:
>
> http://pardo.net/pardo/bike/pic/fail/FAIL-010.ht
>
> I can't help wondering if the no-longer attached pedal
> banged into the pavement sideways, putting a lot of sideways
> force on the pedal arm in a direction that it wasn't
> designed to take. Whatever happened, it doesn't look related
> to the pedal eye.
>
> The Colnago Carbon crank also seems to have remained intact
> around the metal pedal eyer:
>
> http://pardo.net/pardo/bike/pic/fail/FAIL-007.html
>
> In any case, this carbon design is so utterly different from
> a normal metal pedal arm that it's hard to imagine a normal
> crank failing that way. (Look at that weird piece!)
>
> At first, the last picture that you mention, the blue Campy
> crank, looks like the kind of pedal-eye crack that Jobst
> tries to avoid with his conical-washer and pedal-eye boring.
>
> But then I remembered (d'oh!) that the pedal eye is at the
> other end of the arm. That's the bottom-bracket eye. I don't
> think that Jobst is proposing a conical washer modification
> at that end.

Jobst's pedal eye fix addressed a reoccurring problem with the
old Campy NR/SR cranks. He must have had the same problem with
Shimano cranks because the picture of the fix is on an old Dura
Ace, the same model I have owned since 1983 without problems.
Maybe it will break tomorrow, but if it does, I figure 21 years
of service and 100K miles or more is not too bad. It has
outlived my fleet of Campy NR cranks as well as a Stronglight
and an Ofmega track crank (which was a PAB sale-table item which
I did not expect to last). I have one Campy NR crank left on a
track bike used mostly for rollering, so a failure there will
mean that I roll onto some carpet. I suppose I could collide
with the Hi-Fi or table fan. If I go back to track racing, I
will keep an eye on it -- assuming I do not buy a new track bike
to replace my dented, 70s Raleigh Pro.

I agree with Jobst that the magnitude of injury resulting from a
broken crank depends on a number of variables and that a rider
could be seriously injured under certain circumstances. However,
it has been my experience (and I have broken a crank while
sprinting) that injury is rare. IIRC, most of the people who
have posted to wreck.bike over the last five or so years
complaining about broken cranks have not reported serious
injury -- or any injury. There are exceptions, I am sure. There
are always exceptions. I would watch for cracks, but I would not
trot out the mill (don't you have one?) and chamfer my pedal eyes
and then manufacture some conical washers. But that is just me.
I am lazy. I rarely oil my chain let alone fabricate
components. -- Jay Beattie.

[[email protected]]

On Thu, 27 May 2004 00:32:55 -0600,
wrote:

>On Thu, 27 May 2004 05:58:39 GMT, "bfd" >
>wrote:
>
>>
>>"jim beam" > wrote in message
om...
>>> wrote:
>>> > Jay Beattie writes:
>>>> no one disputes the effect of a failure. what jay's saying, and i agree
>>> with him, is that failures are very rare these days. your assertion
>>> that a modern campy or dura-ace crank will fail in only 10,000 miles is
>>> irresponsible scare-mongering. show us the beef. show us a single
>>> undamaged campy or dura-ace crank that has failed within even 200% of
>>> this figure.
>>>
>>What about this Dura Ace 9 crank:
>>
>>http://pardo.net/pardo/bike/pic/fail/FAIL-010.html
>>
>>or this Colnago Carbon crank:
>>http://pardo.net/pardo/bike/pic/fail/FAIL-007.html
>>
>>here's a modern looking Campy crank:
>>http://pardo.net/pardo/bike/pic/fail/FAIL-005.html
>>
>>Cranks can break....
>>
>>
>>
>
>Dear Bfd,
>
>I was browsing that failure gallery and noticed those
>pictures, along with others.
>
>Note that the red Dura Ace pedal arm is half-broken and bent
>inward, toward the frame, not downward as if from any normal
>pedal force:
>
>http://pardo.net/pardo/bike/pic/fail/FAIL-010.ht
>
>I can't help wondering if the no-longer attached pedal
>banged into the pavement sideways, putting a lot of sideways
>force on the pedal arm in a direction that it wasn't
>designed to take. Whatever happened, it doesn't look related
>to the pedal eye.
>
>The Colnago Carbon crank also seems to have remained intact
>around the metal pedal eyer:
>
>http://pardo.net/pardo/bike/pic/fail/FAIL-007.html
>
>In any case, this carbon design is so utterly different from
>a normal metal pedal arm that it's hard to imagine a normal
>crank failing that way. (Look at that weird piece!)
>
>At first, the last picture that you mention, the blue Campy
>crank, looks like the kind of pedal-eye crack that Jobst
>tries to avoid with his conical-washer and pedal-eye boring.
>
>But then I remembered (d'oh!) that the pedal eye is at the
>other end of the arm. That's the bottom-bracket eye. I don't
>think that Jobst is proposing a conical washer modification
>at that end.
>
>Is that a modern Campy pedal arm? I know nothing about
>Campy, so I have no idea how old this one is. Most of the
>other pictures are dated 2001. There's a triple chain-ring,
>there's a bottom-bracket with indents for removal, and
>there's some lettering on the crank-retaining allen-nut and
>on the bottom-bracket. (The pedal-arm, of course, might be
>newer than the bottom-bracket.)
>
>I'm not sure if that small hump that the crack runs out
>through is the metal bulging at the crack, or the crack
>running through a hump.
>
>(I know so little about cracks that I'm not sure where it
>started. Did it start at the outside and run smoothly for a
>bit and then become jagged as it approached the frame side,
>or the other way around?)
>
>Can anyone tell by looking at the pictures how old that
>cracked pedal arm is on the blue Campy?
>
>And is there any way to tell whether the numerous cranks
>failed from normal use alone, or from normal use after
>banging the pedals into the pavement?
>
>Carl Fogel

It turns out that the red Dura Ace crank failure pictures
were posted here about a year ago and discussed by the usual
suspects.

When Amit Ghosh stood up to pedal, his pedal arm folded
inward. Here's the link to the beginning of the thread in
Google Groups:

<http://tinyurl.com/24vyd>

or

<http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&threadm=df5bdaa0.0305291607.1d188f18%40posting.goo gle.com&rnum=1&prev=/groups%3Fq%3D%2522pop%2Bcan%2522%2Bamit%2Bgroup:re c.bicycles.tech%26hl%3Den%26lr%3D%26ie%3DUTF-8%26group%3Drec.bicycles.tech%26selm%3Ddf5bdaa0.03 05291607.1d188f18%2540posting.google.com%26rnum%3D 1>

A likely possibility is that this odd failure was due to a
manufacturing defect, perhaps made worse by a few bumps and
bangs that normally would have had no effect, followed by
several years of pedalling.

Being trusting, innocent, and lucky, I forget that someone
else has to buy the one piece out of a thousand that's
defective.

Carl Fogel

[[email protected]]

Jay Beattie writes:

> Jobst's pedal eye fix addressed a recurring problem with the old
> Campy NR/SR cranks. He must have had the same problem with Shimano
> cranks because the picture of the fix is on an old Dura Ace, the
> same model I have owned since 1983 without problems. Maybe it will
> break tomorrow, but if it does, I figure 21 years of service and
> 100K miles or more is not too bad.

It won't break tomorrow if it doesn't have a crack today. These
cracks take time (miles) to grow and inspecting for cracks on a clean
crank is reasonable protection... except when nothing is found for a
long time and inspections are skipped. As I said, I discovered most
of them before separation. I have retired a pair of Shimano Dura Ace
cranks because they were developing cracks in the corners of the
square taper after about seven years of riding including a tour in the
Alps every summer. As you can see in rec.bicycles.rides currently,
there are plenty of steep roads around here as well.

> It has outlived my fleet of Campy NR cranks as well as a Stronglight
> and an Ofmega track crank (which was a PAB sale-table item which I
> did not expect to last). I have one Campy NR crank left on a track
> bike used mostly for rollering, so a failure there will mean that I
> roll onto some carpet. I suppose I could collide with the Hi-Fi or
> table fan. If I go back to track racing, I will keep an eye on it
> -- assuming I do not buy a new track bike to replace my dented, 70s
> Raleigh Pro.

I don't think you can crack a crank on rollers. The failure mode is
bending off at the bottom (or just before) of the crank in bending
inwards... while standing usually but certainly generated while riding
standing.

> I agree with Jobst that the magnitude of injury resulting from a
> broken crank depends on a number of variables and that a rider could
> be seriously injured under certain circumstances. However, it has
> been my experience (and I have broken a crank while sprinting) that
> injury is rare. IIRC, most of the people who have posted to
> wreck.bike over the last five or so years complaining about broken
> cranks have not reported serious injury -- or any injury. There are
> exceptions, I am sure. There are always exceptions. I would watch
> for cracks, but I would not trot out the mill (don't you have one?)
> and chamfer my pedal eyes and then manufacture some conical washers.
> But that is just me. I am lazy. I rarely oil my chain let alone
> fabricate components.

You have enough miles to make a reasonable assessment of imminent
failures, some people do not and I wouldn't like them to discover
their susceptibility to breaking a crank the hard way.

Jobst Brandt

[g.daniels]

the difference,
as analogy off course,
between
a chisel
and a punch?

[g.daniels]

are the cranks spoken of aluminum?
do steel cranks suffer the same?

[John McGraw]

Richard Brockie > wrote in message >...
> jim beam wrote:
> >> These failures are probable fatalities for those who ride adjacent to
> >> auto traffic... or a cliff.
> >>
> > no one disputes the effect of a failure. what jay's saying, and i agree
> > with him, is that failures are very rare these days. your assertion
> > that a modern campy or dura-ace crank will fail in only 10,000 miles is
> > irresponsible scare-mongering. show us the beef. show us a single
> > undamaged campy or dura-ace crank that has failed within even 200% of
> > this figure.
>
> This photo does just that:
>
> http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg
>
> This is a side-by-side comparison of two used cranks, one with and
> one without Jobst's modification. The lack of wear on the modified
> crank is remarkable and is a clear indication of a superior design in
> that the motion of the joint has been eliminated.

Wow! Just clicked on the above link. It looked as if Salvador Dali has
arisen & is painting again? I know I haven't taken any recreational
drugs since the '60s. Is the problem on my end or the host end?

[Tom Sherman]

John McGraw wrote:

> ...
>>http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg
>>
> Wow! Just clicked on the above link. It looked as if Salvador Dali has
> arisen & is painting again? I know I haven't taken any recreational
> drugs since the '60s. Is the problem on my end or the host end?

It looks like the pedal ends of two cranks (one Dura-Ace and one with
numerous surficial scratches), a two-sided SPuD pedal (made in Japan,
probably Shimano), and a Bic ballpoint pen to me.

--
Tom Sherman – Quad City Area

[remove the polite word to reply]

this all makes sense, but where do you get (and what is it called)
the conical nut to put onto the pedal threads?
thx.

[[email protected]]

On 1 Jun 2004 01:24:53 -0700,
(remove the polite word to reply) wrote:

>this all makes sense, but where do you get (and what is it called)
>the conical nut to put onto the pedal threads?
>thx.

Dear RTPWTR,

The trick is that there is no conical nut.

If you look closely at the picture, you'll see that Jobst
uses a split conical washer.

Of course, I have no idea where to find conical washers, but
they're probably in the same aisle as the conical nuts.

Helpfully,

Carl Fogel