broken crank arm

Discussion in 'Cycling Equipment' started by cliff, Oct 25, 2004.

  1. cliff

    cliff New Member

    Joined:
    Apr 19, 2003
    Messages:
    21
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    0
    I sheared off my right crank arm near the pedal tonight while riding home. I was thankfully making a left turn, so my weight was on the left. The arm sheared as I was applying torque and it made me fall to the right. My backpack saved me from serious injury as I landed on my right side back. That crank is a 20+ years old Stronglight 105 (anyone remember this one?). The crank had seen heavy usage for about 5 years in the early 80's when it was on my only bike. Since then it's use has been relatively light. Maybe a total of 15k-20k miles. I've weighed the same all these years: 150#.

    I know this has been discussed before, but can this be attributed strictly to fatigue, or age, or poor design. This is a grooved, forged "alloy" crank arm. Should I take any precautions to my other cranks such as replacement at a certain point? (for example a Ritchey non-grooved arm from the late 80's/early 90's that is on my primary CX bike, which I use to race CX)
    Thanks for any input.

    BTW, I was going to replace the broken crank with a NOS Stonglight 93...
     
    Tags:


  2. jim beam

    jim beam Guest

    cliff wrote:
    > I sheared off my right crank arm near the pedal tonight while riding
    > home. I was thankfully making a left turn, so my weight was on the
    > left. The arm sheared as I was applying torque and it made me fall to
    > the right. My backpack saved me from serious injury as I landed on my
    > right side back. That crank is a 20+ years old Stronglight 105 (anyone
    > remember this one?). The crank had seen heavy usage for about 5 years
    > in the early 80's when it was on my only bike. Since then it's use has
    > been relatively light. Maybe a total of 15k-20k miles. I've weighed the
    > same all these years: 150#.
    >
    > I know this has been discussed before, but can this be attributed
    > strictly to fatigue, or age, or poor design.


    it probably failed because of fatigue [although lack of photos make this
    a guess!] fatigue in this situation is typically a function of
    design/manufacture execution, any damage & material. age can come into
    it with some alloy systems also.

    > This is a grooved, forged
    > "alloy" crank arm.


    consider that neither campy nor shimano, the largest manufacturers with
    the largest r&d budgets, use grooved cranks these days. a smooth oval
    design helps mitigate fatigue.

    > Should I take any precautions to my other cranks
    > such as replacement at a certain point? (for example a Ritchey
    > non-grooved arm from the late 80's/early 90's that is on my primary CX
    > bike, which I use to -race - CX)


    unless you have access to crack testing equipment, periodic replacement
    is the the only safe way to go. consider the maufacturer's warranty as
    an indicator! you can also undertake regular visual inspection, but
    it's no guarantee, especially if you don't have much experience of what
    you're looking for.

    > Thanks for any input.
    >
    > BTW, I was going to replace the broken crank with a NOS Stonglight
    > 93...
    >


    i'd use campy or shimano. search on this group for the link to a
    gallery of broken cranks. there's no new campy represented, and only
    one freak shimano. unfortunately, stronglight is there more than once.
     
  3. cliff wrote:

    > I sheared off my right crank arm near the pedal tonight while riding
    > home.


    Ah yes - they usually go at that end.

    <snip>

    > I know this has been discussed before, but can this be attributed
    > strictly to fatigue, or age, or poor design.


    The pedal gnawing away at the face of the crank, and some fatigue.

    This is a grooved, forged
    > "alloy" crank arm. Should I take any precautions to my other cranks
    > such as replacement at a certain point? (for example a Ritchey
    > non-grooved arm from the late 80's/early 90's that is on my primary CX
    > bike, which I use to -race - CX)


    I would consider changing those if they have been riddden every week.
    There are no hard and fast rules - it depends on your weight, road
    surfaces, mileage, riding style etc etc.
     
  4. On Tue, 26 Oct 2004 06:43:18 -0700, jim beam wrote:

    > consider that neither campy nor shimano, the largest manufacturers with
    > the largest r&d budgets,


    and the largest marketing departments. I don't think there is anything
    magic about their cranks.

    > unless you have access to crack testing equipment, periodic replacement is
    > the the only safe way to go. consider the maufacturer's warranty as an
    > indicator!


    Oh, boy. Do you get a commission on this? Sure, things break.
    Eventually. But it it ludicrous to replace every part based on the
    manufacturer's warranty. Most spokes have no warranty at all, but in
    properly-built wheels they can last for decades. I don't have any cranks
    that old, but I have hubs and seatposts that are nearly 40 and going
    strong.

    Most parts, including cranks, don't go from pristine to failure without
    some signs. Look at the cracks on that gallery of broken cranks; most
    have a large area that is corroded, indicating the crack was there for a
    long time before it completely failed. A simple visual inspection,
    replacing parts that show cracks, is a better idea than replacing every
    part when its warranty runs out.

    > i'd use campy or shimano. search on this group for the link to a gallery
    > of broken cranks. there's no new campy represented, and only one freak
    > shimano. unfortunately, stronglight is there more than once.


    And Campy has many, many representatives, mostly from the same time period
    as the stronglight that broke in this story. Maybe a good idea to avoid
    cranks of that era, and to avoid those with grooves cut into them, but not
    a particular endorsement of shimano or Campagnolo.

    --

    David L. Johnson

    __o | You will say Christ saith this and the apostles say this; but
    _`\(,_ | what canst thou say? -- George Fox.
    (_)/ (_) |
     
  5. cliff <[email protected]> writes:

    >I know this has been discussed before, but can this be attributed
    >strictly to fatigue, or age, or poor design.


    It's not poor design, there are still many stronglight 93/105 cranks
    on the road (105 is just a 93 with rings that are missing a spider,
    105bis is drilled as well.)

    All cranks are aluminum. Aluminum has no lower fatigue limit. After
    XYZ fatigue cycles, aluminum will fail. There is no way around this
    problem.

    About the only thing you can do is inspect the cranks for hairline
    cracks regularly, possibly with a non-permanent magic marker which
    will infiltrate the cracks and make them visible. For failures at the
    pedal eye, you can use pedal washers and/or adopt jobst brandt's 45
    degree chamfering (beveling?) technique on the pedal spindle, if you
    have access to machine tools. search the usenet archives
    (www.google.com, "Groups" link) for details

    - Don Gillies
    San Diego, CA
     
  6. On Tue, 26 Oct 2004 15:23:50 -0400, "David L. Johnson"
    <[email protected]> wrote:

    >Most parts, including cranks, don't go from pristine to failure without
    >some signs. Look at the cracks on that gallery of broken cranks; most
    >have a large area that is corroded, indicating the crack was there for a
    >long time before it completely failed. A simple visual inspection,
    >replacing parts that show cracks, is a better idea than replacing every
    >part when its warranty runs out.


    [jim beam wrote:]

    >> i'd use campy or shimano. search on this group for the link to a gallery
    >> of broken cranks. there's no new campy represented, and only one freak
    >> shimano. unfortunately, stronglight is there more than once.

    >
    >And Campy has many, many representatives, mostly from the same time period
    >as the stronglight that broke in this story. Maybe a good idea to avoid
    >cranks of that era, and to avoid those with grooves cut into them, but not
    >a particular endorsement of shimano or Campagnolo.


    Dear Cliff, Jim, and David,

    This is probably the gallery of broken parts that Jim and
    David have in mind:

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

    Carl Fogel
     
  7. On 26 Oct 2004 12:48:48 -0700, [email protected] (Donald
    Gillies) wrote:

    >cliff <[email protected]> writes:
    >
    >>I know this has been discussed before, but can this be attributed
    >>strictly to fatigue, or age, or poor design.

    >
    >It's not poor design, there are still many stronglight 93/105 cranks
    >on the road (105 is just a 93 with rings that are missing a spider,
    >105bis is drilled as well.)
    >
    >All cranks are aluminum. Aluminum has no lower fatigue limit. After
    >XYZ fatigue cycles, aluminum will fail. There is no way around this
    >problem.
    >
    >About the only thing you can do is inspect the cranks for hairline
    >cracks regularly, possibly with a non-permanent magic marker which
    >will infiltrate the cracks and make them visible. For failures at the
    >pedal eye, you can use pedal washers and/or adopt jobst brandt's 45
    >degree chamfering (beveling?) technique on the pedal spindle, if you
    >have access to machine tools. search the usenet archives
    >(www.google.com, "Groups" link) for details
    >
    >- Don Gillies
    >San Diego, CA


    Dear Cliff and Don,

    To search, go here:

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

    select "search only in rec.bicycles.tech," and search for
    "jobst damerell pedal eye," which will lead you to:

    http://groups.google.com/[email protected]&rnum=1

    or http://tinyurl.com/6ymve

    which in turn mentions where David Damerell has very nicely
    hosted a detailed picture for us of Jobst's conical washers
    and chamfered pedal eyes.

    All of which leads up to my question: has anyone else on
    rec.bicycles.tech actually modified their pedal eyes like
    this?

    Carl Fogel
     
  8. cliff

    cliff New Member

    Joined:
    Apr 19, 2003
    Messages:
    21
    Likes Received:
    0
    Thank you everyone for your input on this. I only wish that I had inspected the crank more closely and with regularity as I'm not sure if I would have seen the crack. I certainly would like to know what to look out for in the future...

    Cliff
     
  9. jim beam

    jim beam Guest

    David L. Johnson wrote:
    > On Tue, 26 Oct 2004 06:43:18 -0700, jim beam wrote:
    >
    >
    >>consider that neither campy nor shimano, the largest manufacturers with
    >>the largest r&d budgets,

    >
    >
    > and the largest marketing departments.


    that's not mutually exclusive to research or q.c.

    >I don't think there is anything
    > magic about their cranks.


    "magic", no. "quality", yes.

    >
    >
    >>unless you have access to crack testing equipment, periodic replacement is
    >>the the only safe way to go. consider the maufacturer's warranty as an
    >>indicator!

    >
    >
    > Oh, boy. Do you get a commission on this? Sure, things break.
    > Eventually. But it it ludicrous to replace every part based on the
    > manufacturer's warranty. Most spokes have no warranty at all, but in
    > properly-built wheels they can last for decades. I don't have any cranks
    > that old, but I have hubs and seatposts that are nearly 40 and going
    > strong.


    one broken spoke in a wheel of many is not a catastrophe. a broken
    crank is. the op has concerns about failure, and also has concerns
    about not being able to see something similar in the future. short of
    recommending they spend money on a dye penetrant kit & leaning how to
    use it properly, the /safe/ advice is replacement. new cranks are
    cheap, particularly if you have uncertain mileage, weight, strength &
    habits of leaning up against nice scratchy stone walls.

    >
    > Most parts, including cranks, don't go from pristine to failure without
    > some signs. Look at the cracks on that gallery of broken cranks; most
    > have a large area that is corroded, indicating the crack was there for a
    > long time before it completely failed. A simple visual inspection,
    > replacing parts that show cracks, is a better idea than replacing every
    > part when its warranty runs out.
    >
    >
    >>i'd use campy or shimano. search on this group for the link to a gallery
    >>of broken cranks. there's no new campy represented, and only one freak
    >>shimano. unfortunately, stronglight is there more than once.

    >
    >
    > And Campy has many, many representatives, mostly from the same time period
    > as the stronglight that broke in this story. Maybe a good idea to avoid
    > cranks of that era


    agreed - maybe i should qualify - i'd use /new/ campy or shimano.

    >, and to avoid those with grooves cut into them, but not
    > a particular endorsement of shimano or Campagnolo.
    >
     
  10. On Tue, 26 Oct 2004 21:32:30 -0700, jim beam wrote:

    > one broken spoke in a wheel of many is not a catastrophe. a broken crank
    > is. the op has concerns about failure, and also has concerns about not
    > being able to see something similar in the future. short of recommending
    > they spend money on a dye penetrant kit & leaning how to use it properly,
    > the /safe/ advice is replacement. new cranks are cheap, particularly if
    > you have uncertain mileage, weight, strength & habits of leaning up
    > against nice scratchy stone walls.


    Replacement how often? Based on what criteria? By that logic, it would
    be "prudent" to regularly replace brakes, seatposts, forks, frames,
    stems, as well as bars and --- well, every single part, as a preventative
    measure. The failure of a brake could be disastrous; the potential
    risk of impalement due to failure of a seatpost is too awful to
    contemplate. Bars and stems _do_ fail.

    This all seems too scary to be "safe", and yet millions of cyclists manage
    not to impale themselves on broken seatpost shards year after year.

    Occasionally, some part may fail. For most riders, that is a very rare
    event, and usually one that is not unpredictable. You should periodically
    inspect every part for cracks as well as wear. Cranks, stems, bars, and
    brakes should get a close examination, since they are known to fail --
    depending on design. Most failures do not result in a catastrophe.

    But if you consider it prudent to replace parts that show no signs of
    failure on a regular basis, what you should be doing is replacing your
    entire bike every two years, and that is neither cheap nor reasonable.

    The amount of risk-aversion you are displaying suggests that you consider
    cycling too dangerous to engage in.

    --

    David L. Johnson

    __o | The lottery is a tax on those who fail to understand
    _`\(,_ | mathematics.
    (_)/ (_) |
     
  11. H

    H Guest

    [email protected] (Donald Gillies) wrote in message news:<[email protected]>...
    > [...]
    > About the only thing you can do is inspect the cranks for hairline
    > cracks regularly, possibly with a non-permanent magic marker which
    > will infiltrate the cracks and make them visible. For failures at the
    > pedal eye, you can use pedal washers and/or adopt jobst brandt's 45
    > degree chamfering (beveling?) technique on the pedal spindle, if you
    > have access to machine tools. search the usenet archives
    > (www.google.com, "Groups" link) for details
    >
    > - Don Gillies
    > San Diego, CA
    >



    I get concerned everytime this subject comes up. I have a bike with
    old nuovo record cranks. I know that these have been used a lot before
    I got them, and I am now using them.

    I try to inspect the cranks regularly (once a month or so), with
    careful attention to the pedal holes. However, there are so many scuff
    marks all over the cranks and especially near the pedal holes-- it
    makes me wonder if I am missing any cracks which may be in progress.

    So my question:
    Is it adviseable to "polish out" scuffs and scratches? I think if I
    had a nice surface finish, I would be able see any cracks better.

    -H.
     
  12. Jay Beattie

    Jay Beattie Guest

    <[email protected]> wrote in message
    news:[email protected]
    > On 26 Oct 2004 12:48:48 -0700, [email protected] (Donald
    > Gillies) wrote:
    >
    > >cliff <[email protected]> writes:
    > >
    > >>I know this has been discussed before, but can this be

    attributed
    > >>strictly to fatigue, or age, or poor design.

    > >
    > >It's not poor design, there are still many stronglight 93/105

    cranks
    > >on the road (105 is just a 93 with rings that are missing a

    spider,
    > >105bis is drilled as well.)
    > >
    > >All cranks are aluminum. Aluminum has no lower fatigue limit.

    After
    > >XYZ fatigue cycles, aluminum will fail. There is no way

    around this
    > >problem.
    > >
    > >About the only thing you can do is inspect the cranks for

    hairline
    > >cracks regularly, possibly with a non-permanent magic marker

    which
    > >will infiltrate the cracks and make them visible. For

    failures at the
    > >pedal eye, you can use pedal washers and/or adopt jobst

    brandt's 45
    > >degree chamfering (beveling?) technique on the pedal spindle,

    if you
    > >have access to machine tools. search the usenet archives
    > >(www.google.com, "Groups" link) for details
    > >
    > >- Don Gillies
    > >San Diego, CA

    >
    > Dear Cliff and Don,
    >
    > To search, go here:
    >
    >

    http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&group=rec.bicycles.tech
    >
    > select "search only in rec.bicycles.tech," and search for
    > "jobst damerell pedal eye," which will lead you to:
    >
    >

    http://groups.google.com/[email protected]&rnum=1
    >
    > or http://tinyurl.com/6ymve
    >
    > which in turn mentions where David Damerell has very nicely
    > hosted a detailed picture for us of Jobst's conical washers
    > and chamfered pedal eyes.
    >
    > All of which leads up to my question: has anyone else on
    > rec.bicycles.tech actually modified their pedal eyes like
    > this?


    The OP had a failure near the pedal, but apparently not at the
    pedal eye. Pedal eye failure was not uncommon on the old
    Campagnolo NR cranks, and Jobst made the same modification to an
    80s vintage Dura Ace -- the same crank I raced/rode for 20+ years
    and many miles with no problems (at various weights around
    200lbs). I see no reason to worry about crank failure absent
    signs of cracking, crash abuse or known defects. Periodic
    replacement certainly is not necessary, and that pedal eye
    modification is expensive unless you own machining equipment and
    can DIY. -- Jay Beattie.
     
  13. jim beam

    jim beam Guest

    David L. Johnson wrote:
    > On Tue, 26 Oct 2004 21:32:30 -0700, jim beam wrote:
    >
    >
    >>one broken spoke in a wheel of many is not a catastrophe. a broken crank
    >>is. the op has concerns about failure, and also has concerns about not
    >>being able to see something similar in the future. short of recommending
    >>they spend money on a dye penetrant kit & leaning how to use it properly,
    >>the /safe/ advice is replacement. new cranks are cheap, particularly if
    >>you have uncertain mileage, weight, strength & habits of leaning up
    >>against nice scratchy stone walls.

    >
    >
    > Replacement how often? Based on what criteria? By that logic, it would
    > be "prudent" to regularly replace brakes, seatposts, forks, frames,
    > stems, as well as bars and --- well, every single part, as a preventative
    > measure. The failure of a brake could be disastrous; the potential
    > risk of impalement due to failure of a seatpost is too awful to
    > contemplate. Bars and stems _do_ fail.


    actually, replacement of those items /is/ prudent. ttt for example are
    kind enough to give mileage & use replacement recommendations on their
    handlebars & stems. others rely on the old catch-all "inspect after
    every ride". there are only 2 options: inspect or replace. inspection
    requires experience and/or expensive equipment. i doubt anyone here
    would consider it viable to spend a few hundred dollars doing ultrasound
    or x-ray on a crank that can be replaced for less.

    >
    > This all seems too scary to be "safe", and yet millions of cyclists manage
    > not to impale themselves on broken seatpost shards year after year.


    yes, and millions of bicycles never wear out even /one/ set of tires.

    >
    > Occasionally, some part may fail. For most riders, that is a very rare
    > event, and usually one that is not unpredictable. You should periodically
    > inspect every part for cracks as well as wear. Cranks, stems, bars, and
    > brakes should get a close examination, since they are known to fail --
    > depending on design. Most failures do not result in a catastrophe.
    >
    > But if you consider it prudent to replace parts that show no signs of
    > failure on a regular basis, what you should be doing is replacing your
    > entire bike every two years, and that is neither cheap nor reasonable.
    >
    > The amount of risk-aversion you are displaying suggests that you consider
    > cycling too dangerous to engage in.
    >


    no, you're trying to make it sound that way to sensationalize the issue.
    unless you have experience in non-destructive testing, can you
    /safely/ say a component will not fail? judging from the number of
    fatigue-initiated vintage campy cranks i've seen at bike swaps, i'd say
    either the whole planet is populated by unscrupulous crooks, or, much
    more likely, most people simply have no clue what they're looking for
    when they inspect. again, the _cheap safe_ option is to replace.
     
  14. jim beam

    jim beam Guest

    Jay Beattie wrote:
    > <[email protected]> wrote in message
    > news:[email protected]
    >
    >>On 26 Oct 2004 12:48:48 -0700, [email protected] (Donald
    >>Gillies) wrote:
    >>
    >>
    >>>cliff <[email protected]> writes:
    >>>
    >>>
    >>>>I know this has been discussed before, but can this be

    >
    > attributed
    >
    >>>>strictly to fatigue, or age, or poor design.
    >>>
    >>>It's not poor design, there are still many stronglight 93/105

    >
    > cranks
    >
    >>>on the road (105 is just a 93 with rings that are missing a

    >
    > spider,
    >
    >>>105bis is drilled as well.)
    >>>
    >>>All cranks are aluminum. Aluminum has no lower fatigue limit.

    >
    > After
    >
    >>>XYZ fatigue cycles, aluminum will fail. There is no way

    >
    > around this
    >
    >>>problem.
    >>>
    >>>About the only thing you can do is inspect the cranks for

    >
    > hairline
    >
    >>>cracks regularly, possibly with a non-permanent magic marker

    >
    > which
    >
    >>>will infiltrate the cracks and make them visible. For

    >
    > failures at the
    >
    >>>pedal eye, you can use pedal washers and/or adopt jobst

    >
    > brandt's 45
    >
    >>>degree chamfering (beveling?) technique on the pedal spindle,

    >
    > if you
    >
    >>>have access to machine tools. search the usenet archives
    >>>(www.google.com, "Groups" link) for details
    >>>
    >>>- Don Gillies
    >>>San Diego, CA

    >>
    >>Dear Cliff and Don,
    >>
    >>To search, go here:
    >>
    >>

    >
    > http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&group=rec.bicycles.tech
    >
    >>select "search only in rec.bicycles.tech," and search for
    >>"jobst damerell pedal eye," which will lead you to:
    >>
    >>

    >
    > http://groups.google.com/[email protected]&rnum=1
    >
    >>or http://tinyurl.com/6ymve
    >>
    >>which in turn mentions where David Damerell has very nicely
    >>hosted a detailed picture for us of Jobst's conical washers
    >>and chamfered pedal eyes.
    >>
    >>All of which leads up to my question: has anyone else on
    >>rec.bicycles.tech actually modified their pedal eyes like
    >>this?

    >
    >
    > The OP had a failure near the pedal, but apparently not at the
    > pedal eye. Pedal eye failure was not uncommon on the old
    > Campagnolo NR cranks, and Jobst made the same modification to an
    > 80s vintage Dura Ace -- the same crank I raced/rode for 20+ years
    > and many miles with no problems (at various weights around
    > 200lbs). I see no reason to worry about crank failure absent
    > signs of cracking, crash abuse or known defects. Periodic
    > replacement certainly is not necessary, and that pedal eye
    > modification is expensive unless you own machining equipment and
    > can DIY. -- Jay Beattie.
    >
    >


    rhetorical: if the crank did not fail at the pedal eye, how would this
    modification have mitigated the failure?
     
  15. jim beam

    jim beam Guest

    H wrote:
    > [email protected] (Donald Gillies) wrote in message news:<[email protected]>...
    >
    >>[...]
    >>About the only thing you can do is inspect the cranks for hairline
    >>cracks regularly, possibly with a non-permanent magic marker which
    >>will infiltrate the cracks and make them visible. For failures at the
    >>pedal eye, you can use pedal washers and/or adopt jobst brandt's 45
    >>degree chamfering (beveling?) technique on the pedal spindle, if you
    >>have access to machine tools. search the usenet archives
    >>(www.google.com, "Groups" link) for details
    >>
    >>- Don Gillies
    >>San Diego, CA
    >>

    >
    >
    >
    > I get concerned everytime this subject comes up. I have a bike with
    > old nuovo record cranks. I know that these have been used a lot before
    > I got them, and I am now using them.
    >
    > I try to inspect the cranks regularly (once a month or so), with
    > careful attention to the pedal holes. However, there are so many scuff
    > marks all over the cranks and especially near the pedal holes-- it
    > makes me wonder if I am missing any cracks which may be in progress.
    >
    > So my question:
    > Is it adviseable to "polish out" scuffs and scratches? I think if I
    > had a nice surface finish, I would be able see any cracks better.
    >
    > -H.


    i wouldn't. i'd just inspect, but much more regularly than once a
    month. this http://pardo.net/pardo/bike/pic/fail/Dscn2410_640.jpg
    is where i most often see cracking in cranks at swap meets.

    reference pages:
    http://pardo.net/pardo/bike/pic/fail/FAIL-008.html
    http://pardo.net/pardo/bike/pic/fail/000.html
     
  16. Jay Beattie writes:

    > The OP had a failure near the pedal, but apparently not at the pedal
    > eye. Pedal eye failure was not uncommon on the old Campagnolo NR
    > cranks, and Jobst made the same modification to an 80s vintage Dura
    > Ace -- the same crank I raced/rode for 20+ years and many miles with
    > no problems (at various weights around 200lbs). I see no reason to
    > worry about crank failure absent signs of cracking, crash abuse or
    > known defects. Periodic replacement certainly is not necessary, and
    > that pedal eye modification is expensive unless you own machining
    > equipment and can DIY.


    Just because you had no failures does not mean others won't. As I
    outlined in the articles describing the modification I would like to
    see become common on cranks, I also mentioned that I regularly broke a
    crank per year, Campagnolo and Shimano and that since modifying the
    cranks have had none.

    My Campagnolo Nuovo Record cranks broke through the pedal eye in a
    record distance of less than 2500 miles of use. They were the all
    time worst.

    As another item, my friend who weighs 165 lbs had a Shimano DuraAce
    crank fail at the pedal eye and took a serious dive to the pavement.
    The absence of failure on your bicycle does not prove that they do not
    occur and often.

    Jobst Brandt
    [email protected]
     
  17. Jay Beattie

    Jay Beattie Guest

    <[email protected]> wrote in message
    news:[email protected]
    > Jay Beattie writes:
    >
    > > The OP had a failure near the pedal, but apparently not at

    the pedal
    > > eye. Pedal eye failure was not uncommon on the old

    Campagnolo NR
    > > cranks, and Jobst made the same modification to an 80s

    vintage Dura
    > > Ace -- the same crank I raced/rode for 20+ years and many

    miles with
    > > no problems (at various weights around 200lbs). I see no

    reason to
    > > worry about crank failure absent signs of cracking, crash

    abuse or
    > > known defects. Periodic replacement certainly is not

    necessary, and
    > > that pedal eye modification is expensive unless you own

    machining
    > > equipment and can DIY.

    >
    > Just because you had no failures does not mean others won't.

    As I
    > outlined in the articles describing the modification I would

    like to
    > see become common on cranks, I also mentioned that I regularly

    broke a
    > crank per year, Campagnolo and Shimano and that since modifying

    the
    > cranks have had none.
    >
    > My Campagnolo Nuovo Record cranks broke through the pedal eye

    in a
    > record distance of less than 2500 miles of use. They were the

    all
    > time worst.
    >
    > As another item, my friend who weighs 165 lbs had a Shimano

    DuraAce
    > crank fail at the pedal eye and took a serious dive to the

    pavement.
    > The absence of failure on your bicycle does not prove that they

    do not
    > occur and often.


    I am not against a beneficial design change, but absent evidence
    that modern aluminum cranks are breaking regularly at the pedal
    eye, I just do not see the need for us all to go out and get
    expensive custom machine work. Also, custom machining carries its
    own risks; it probably voids any warranty, and it is expensive. I
    will let the manufacturer make that change rather than relying on
    an unknown local machinist. -- Jay Beattie.
     
  18. jim beam <[email protected]> writes:

    >i wouldn't. i'd just inspect, but much more regularly than once a
    >month. this http://pardo.net/pardo/bike/pic/fail/Dscn2410_640.jpg
    >is where i most often see cracking in cranks at swap meets.


    Bad advice. Some materials, such as glasses, gain significant,
    significant tensile strength if their surfaces have no imperfections
    (e.g. scratches). For example, some glasses can have higher strength
    that steel if they are formed as "float glass" on a mercury bed with
    absolutely no surface imperfections.

    It is common knowledge that this applies to aluminum cranks as well.
    Campagnolo cranks often get hairline cracks that begin developing on
    both sides of the crank arm where it joins the spider. If you gently
    sand and polish the crank in this area, you can virtually eliminate
    all failures in this area using this very same principle. You can
    effect this repair even after the cracks start forming, if you catch
    them early and polish out the hairline cracks.

    - Don Gillies
    San Diego, CA
     
  19. Jay Beattie <[email protected]> writes:

    > I am not against a beneficial design change, but absent evidence
    > that modern aluminum cranks are breaking regularly at the pedal eye,
    > I just do not see the need for us all to go out and get expensive
    > custom machine work. Also, custom machining carries its own risks;
    > it probably voids any warranty, and it is expensive. I will let the
    > manufacturer make that change rather than relying on an unknown
    > local machinist.


    I'm not suggesting that, only that it can be done and those who
    experience such failures have a way out, expensive as it may be. My
    interest is that manufacturers look at this with as much interest as
    went into the threadless steertube. I had enough fretting stems,
    frozen (oxidized) un-removable stems and stupid head bearing
    adjustments. As you see on Sheldon's web page, I modified the old
    Shimano DuraAce head bearing to work with a new threadless fork and
    stem. That is what needs to be done by manufacturers. I am not sad
    to see the quill stem go away nor will I mind when conical faces are
    the standard for pedal shafts.

    Jobst Brandt
    [email protected]
     
  20. jim beam

    jim beam Guest

    Donald Gillies wrote:
    > jim beam <[email protected]> writes:
    >
    >
    >>i wouldn't. i'd just inspect, but much more regularly than once a
    >>month. this http://pardo.net/pardo/bike/pic/fail/Dscn2410_640.jpg
    >>is where i most often see cracking in cranks at swap meets.

    >
    >
    > Bad advice. Some materials, such as glasses, gain significant,
    > significant tensile strength if their surfaces have no imperfections
    > (e.g. scratches). For example, some glasses can have higher strength
    > that steel if they are formed as "float glass" on a mercury bed with
    > absolutely no surface imperfections.


    float glass is a quick cheap [but highly capital intensive] way to make
    glass flat - and it happens that the natural "blob" thickness of molten
    glass on molten tin [NOT mercury] is about 1", the maximum thickness
    typically used in sheet. it's got nothing to do with strength. you are
    correct that glass failure is due to [surface] defects, but glass with
    what appears to be a perfectly smooth surface is still massively flawed
    on a scale that seriously impacts strength. the way to address this is
    tempering which puts the surface in compression thus not allowing the
    inherent surface flaws to propagate. float is not tempering.

    >
    > It is common knowledge that this applies to aluminum cranks as well.
    > Campagnolo cranks often get hairline cracks that begin developing on
    > both sides of the crank arm where it joins the spider. If you gently
    > sand and polish the crank in this area, you can virtually eliminate
    > all failures in this area using this very same principle. You can
    > effect this repair even after the cracks start forming, if you catch
    > them early and polish out the hairline cracks.
    >
    > - Don Gillies
    > San Diego, CA


    well, you're right about cracks being dangerous, but what is a scratch
    and what is a crack? and at what point does removal of protective
    anodizing expose a 2000 series aluminum alloy to stress corrosion from
    chlorides or other agents? just removing material in the hope that
    because you can no longer see it, you've removed the crack is a
    dangerous way to approach this problem.
     
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