Crank pedal-eye fretting question

Discussion in 'Cycling Equipment' started by Mr Pook, Apr 15, 2004.

  1. Mr Pook

    Mr Pook Guest

    On Wenndesday, June 05 [email protected] wrote:
    >For bicycles the proper modification would be to a tapered shoulder

    on
    >the pedal spindle instead of a flat one, and of course a matching
    >taper in the face of the crank. I have by installing a split conical
    >faced washer between the pedal shoulder and the crank in such a way
    >that it securely clamps the spindle on the inside as it is tightened
    >into the taper faced crank bore. This reduces the probability of
    >crank failure at the pedal eye as well as getting rid of left hand
    >threads on left pedals.


    >This is not something that can be done at home. It takes a lathe and
    >milling machine. I chose stainless steel for the washers because it
    >is not a high stress application where currently aluminum is the
    >contact and I didn't want these to rust.
    >
    >Jobst Brandt <[email protected]> Palo Alto CA


    As Mr. Brandt has pointed out, this is not something that is easy to
    do at home.

    So my question is: would a soft aluminium sump-plug washer of correct
    size also circumvent the problem, acting as a sacrificial face, on
    which this fretting damage could occur?
    Whether such a 'soft' washer would wear instead of the crank face I
    haven't a clue.
    Obviously this would not get around the left-handed thread issue, but
    is this really a problem at all?

    Anyone?

    Thanks,

    Thomas Hood
     
    Tags:


  2. Thomas Hood writes:

    >> For bicycles the proper modification would be to a tapered shoulder
    >> on the pedal spindle instead of a flat one, and of course a
    >> matching taper in the face of the crank. I have by installing a
    >> split conical faced washer between the pedal shoulder and the crank
    >> in such a way that it securely clamps the spindle on the inside as
    >> it is tightened into the taper faced crank bore. This reduces the
    >> probability of crank failure at the pedal eye as well as getting
    >> rid of left hand threads on left pedals.


    >> This is not something that can be done at home. It takes a lathe
    >> and milling machine. I chose stainless steel for the washers
    >> because it is not a high stress application where currently
    >> aluminum is the contact and I didn't want these to rust.


    > As pointed out, this is not something that is easy to do at home.


    > So my question is: would a soft aluminium sump-plug washer of
    > correct size also circumvent the problem, acting as a sacrificial
    > face, on which this fretting damage could occur? Whether such a
    > 'soft' washer would wear instead of the crank face I haven't a clue.
    > Obviously this would not get around the left-handed thread issue,
    > but is this really a problem at all?


    I predict that such a washer would soon extrude from the interface and
    leave a loose pedal. Offering no better hold than the flat face that
    is already there, it adds nothing to the attachment but an additional
    failure point.

    This is another one of those design problems that bore the industry
    to death and get the response James Annan got about disc brake
    location, something that is equally simple to remedy.

    Jobst Brandt
    [email protected]
     
  3. Werehatrack

    Werehatrack Guest

    On 15 Apr 2004 10:40:08 -0700, [email protected] (Mr Pook) may
    have said:

    >So my question is: would a soft aluminium sump-plug washer of correct
    >size also circumvent the problem, acting as a sacrificial face, on
    >which this fretting damage could occur?


    No. You need to either distribute the load across a more durable and
    rigid interface, or lock the shaft against motion. The soft aluminum
    washer would, in my experience, have the opposite effect, likely
    making the problem worse. It would be more effective to substitute a
    machined, hardened washer with a slightly concave contact face which
    would increase the steel/aluminum contact patch, in my opinion...and
    such a washer would probably be thick enough that it would hazardously
    reduce the dept of the threaded stub's penetration into the crank eye,
    so it would still need a pedal shaft mod before it would be workable.
    Jobst's split conical collar is a better fix for the same amount of
    work.

    On the other hand, in my collection of cobbled-together bits and
    bikes, there's a unit with an old set of Deore LX cranks that I
    obtained gratis because the threads in the left crank were wallowed
    and torn out. I drilled and tapped the eye for a bushing, and
    loctited a right-hand-thread pedal in there. It's been working
    acceptably for quite a while, but this is not a solution I'd apply on
    a bike that was going to see heavy use.

    I will note that an inexpensive (in mass production) better design for
    the pedal mounting method would not be difficult to implement at the
    component manufacturing level, but there are two big problems with
    trying to introduce any such change..

    First, the existing design has incredible marketplace inertia, as it
    has literally been in use for a century and has become regarded as a
    truly standardized part of bike design with just one change in that
    time; an increase in the threaded stub's diameter for the three-piece
    cranks. As a result, any attempt to introduce a new design would have
    to be embraced by both the crank makers and the multitude of specialty
    pedal manufacturers before it would have a chance of becoming popular.

    Second, the failures, though hardly unusual, are not so common that
    they constitute a major source of ire for the buying public. It is
    difficult to get people excited about a product that solves a problem
    that they never have had themselves. This factor is also a big part
    of the reason that the disc brake wheel ejection issue doesn't get
    more attention; until it happens to enough people (or exactly the
    right single individual), it's obscured by a "not my problem" field.

    I will also note that the inclusion of a suitable steel bushing in the
    end of the crank could essentially eliminate the problem you're
    addressing, but this adds both cost and weight to an item whose buyers
    are typically sensitive to at least one of those factors. (And yes,
    there are some cranks with this feature in my experience, but they're
    not top-of-the-line gear.)

    --
    My email address is antispammed; pull WEEDS if replying via e-mail.
    Typoes are not a bug, they're a feature.
    Words processed in a facility that contains nuts.
     
  4. Mr Pook

    Mr Pook Guest

    [email protected] wrote in message news:<[email protected]>...
    > Thomas Hood writes:
    >
    > >> For bicycles the proper modification would be to a tapered shoulder
    > >> on the pedal spindle instead of a flat one, and of course a
    > >> matching taper in the face of the crank. I have by installing a
    > >> split conical faced washer between the pedal shoulder and the crank
    > >> in such a way that it securely clamps the spindle on the inside as
    > >> it is tightened into the taper faced crank bore. This reduces the
    > >> probability of crank failure at the pedal eye as well as getting
    > >> rid of left hand threads on left pedals.

    >
    > >> This is not something that can be done at home. It takes a lathe
    > >> and milling machine. I chose stainless steel for the washers
    > >> because it is not a high stress application where currently
    > >> aluminum is the contact and I didn't want these to rust.

    >
    > > As pointed out, this is not something that is easy to do at home.

    >
    > > So my question is: would a soft aluminium sump-plug washer of
    > > correct size also circumvent the problem, acting as a sacrificial
    > > face, on which this fretting damage could occur? Whether such a
    > > 'soft' washer would wear instead of the crank face I haven't a clue.
    > > Obviously this would not get around the left-handed thread issue,
    > > but is this really a problem at all?

    >
    > I predict that such a washer would soon extrude from the interface and
    > leave a loose pedal. Offering no better hold than the flat face that
    > is already there, it adds nothing to the attachment but an additional
    > failure point.
    >
    > This is another one of those design problems that bore the industry
    > to death and get the response James Annan got about disc brake
    > location, something that is equally simple to remedy.
    >
    > Jobst Brandt
    > [email protected]



    Oh well. Just out of curiousity, was the supposition that the 'soft'
    washer would wear instead of the crank face correct?

    On a slightly different topic, have you seen the New Dura Ace cranks
    up close. I was looking at a pair in a shop the other day (not that
    I've the means, nor inclination to spend $400 on a pair of cranks) and
    the 'web' where the two arms meet the crank appears to be very
    substantial. I'd estimate it to be 3-4mm thick. Is this still a likely
    point of failure. Any other impressions of the design (BB inclusive)
    as a whole?

    Thanks,

    Thomas Hood
     
  5. Me

    Me Guest

    Not sure if this has anything to do with this topic, but my new Felt TK2
    track bike came with a thin metal washer (unknown composition to me) for
    each arm/pedal. First time I've ever scene that. The cranks are made by
    Truvativ.

    Randy Hermann

    "Werehatrack" <[email protected]> wrote in message
    news:[email protected]
    > On 15 Apr 2004 10:40:08 -0700, [email protected] (Mr Pook) may
    > have said:
    >
    > >So my question is: would a soft aluminium sump-plug washer of correct
    > >size also circumvent the problem, acting as a sacrificial face, on
    > >which this fretting damage could occur?

    >
    > No. You need to either distribute the load across a more durable and
    > rigid interface, or lock the shaft against motion. The soft aluminum
    > washer would, in my experience, have the opposite effect, likely
    > making the problem worse. It would be more effective to substitute a
    > machined, hardened washer with a slightly concave contact face which
    > would increase the steel/aluminum contact patch, in my opinion...and
    > such a washer would probably be thick enough that it would hazardously
    > reduce the dept of the threaded stub's penetration into the crank eye,
    > so it would still need a pedal shaft mod before it would be workable.
    > Jobst's split conical collar is a better fix for the same amount of
    > work.
    >
    > On the other hand, in my collection of cobbled-together bits and
    > bikes, there's a unit with an old set of Deore LX cranks that I
    > obtained gratis because the threads in the left crank were wallowed
    > and torn out. I drilled and tapped the eye for a bushing, and
    > loctited a right-hand-thread pedal in there. It's been working
    > acceptably for quite a while, but this is not a solution I'd apply on
    > a bike that was going to see heavy use.
    >
    > I will note that an inexpensive (in mass production) better design for
    > the pedal mounting method would not be difficult to implement at the
    > component manufacturing level, but there are two big problems with
    > trying to introduce any such change..
    >
    > First, the existing design has incredible marketplace inertia, as it
    > has literally been in use for a century and has become regarded as a
    > truly standardized part of bike design with just one change in that
    > time; an increase in the threaded stub's diameter for the three-piece
    > cranks. As a result, any attempt to introduce a new design would have
    > to be embraced by both the crank makers and the multitude of specialty
    > pedal manufacturers before it would have a chance of becoming popular.
    >
    > Second, the failures, though hardly unusual, are not so common that
    > they constitute a major source of ire for the buying public. It is
    > difficult to get people excited about a product that solves a problem
    > that they never have had themselves. This factor is also a big part
    > of the reason that the disc brake wheel ejection issue doesn't get
    > more attention; until it happens to enough people (or exactly the
    > right single individual), it's obscured by a "not my problem" field.
    >
    > I will also note that the inclusion of a suitable steel bushing in the
    > end of the crank could essentially eliminate the problem you're
    > addressing, but this adds both cost and weight to an item whose buyers
    > are typically sensitive to at least one of those factors. (And yes,
    > there are some cranks with this feature in my experience, but they're
    > not top-of-the-line gear.)
    >
    > --
    > My email address is antispammed; pull WEEDS if replying via e-mail.
    > Typoes are not a bug, they're a feature.
    > Words processed in a facility that contains nuts.
     
  6. Werehatrack

    Werehatrack Guest

    On Sat, 17 Apr 2004 00:02:18 GMT, "Me"
    <[email protected]> may have said:

    >Not sure if this has anything to do with this topic, but my new Felt TK2
    >track bike came with a thin metal washer (unknown composition to me) for
    >each arm/pedal. First time I've ever scene that. The cranks are made by
    >Truvativ.


    Truvativ's manual shows that they supply those with the cranks. I
    suspect it's a recognition of the fact that if you're buying a
    Truvativ crank set, you're probably going to ride it hard.

    --
    My email address is antispammed; pull WEEDS if replying via e-mail.
    Typoes are not a bug, they're a feature.
    Words processed in a facility that contains nuts.
     
  7. Thomas Hood writes:

    >>> So my question is: would a soft aluminium sump-plug washer of
    >>> correct size also circumvent the problem, acting as a sacrificial
    >>> face, on which this fretting damage could occur? Whether such a
    >>> 'soft' washer would wear instead of the crank face I haven't a
    >>> clue. Obviously this would not get around the left-handed thread
    >>> issue, but is this really a problem at all?


    >> I predict that such a washer would soon extrude from the interface
    >> and leave a loose pedal. Offering no better hold than the flat
    >> face that is already there, it adds nothing to the attachment but
    >> an additional failure point.


    >> This is another one of those design problems that bore the industry
    >> to death and get the response James Annan got about disc brake
    >> location, something that is equally simple to remedy.


    > Oh well. Just out of curiosity, was the supposition that the 'soft'
    > washer would wear instead of the crank face correct?


    If it is softer than the crank, it would extrude out of the interface
    to cause a loose pedal in the crank. I have seen that happen years
    ago when that was the NEW idea.

    > On a slightly different topic, have you seen the New Dura Ace cranks
    > up close. I was looking at a pair in a shop the other day (not that
    > I've the means, nor inclination to spend $400 on a pair of cranks)
    > and the 'web' where the two arms meet the crank appears to be very
    > substantial. I'd estimate it to be 3-4mm thick. Is this still a
    > likely point of failure. Any other impressions of the design (BB
    > inclusive) as a whole?


    I see it as a response to the failure of the previous design, that as
    I said in this thread, I predicted years ago. These are difficult
    interfaces, especially with such high torque that is uncommon in most
    machines.

    I'm not thrilled with the embedded spindle in the right crank, but it
    gets rid of that interface (possibly) while the attachment of the left
    crank is well done. Other than that, I haven't had one of these in
    hand and have not ridden one so I don't know where the next weakest
    spot is. The square taper was a great leap forward when it was
    introduced to replace steel cotter attached steel cranks. Just the
    same it has some major weaknesses.

    Jobst Brandt
    [email protected]
     
  8. > Thomas Hood writes:

    >>> So my question is: would a soft aluminium sump-plug washer of
    >>> correct size also circumvent the problem, acting as a sacrificial
    >>> face, on which this fretting damage could occur? Whether such a
    >>> 'soft' washer would wear instead of the crank face I haven't a
    >>> clue. Obviously this would not get around the left-handed thread
    >>> issue, but is this really a problem at all?


    >> I predict that such a washer would soon extrude from the interface
    >> and leave a loose pedal. Offering no better hold than the flat
    >> face that is already there, it adds nothing to the attachment but
    >> an additional failure point.


    >> This is another one of those design problems that bore the industry
    >> to death and get the response James Annan got about disc brake
    >> location, something that is equally simple to remedy.


    > Oh well. Just out of curiosity, was the supposition that the 'soft'
    > washer would wear instead of the crank face correct?


    > If it is softer than the crank, it would extrude out of the interface
    > to cause a loose pedal in the crank. I have seen that happen years
    > ago when that was the NEW idea.


    > On a slightly different topic, have you seen the New Dura Ace cranks
    > up close. I was looking at a pair in a shop the other day (not that
    > I've the means, nor inclination to spend $400 on a pair of cranks)
    > and the 'web' where the two arms meet the crank appears to be very
    > substantial. I'd estimate it to be 3-4mm thick. Is this still a
    > likely point of failure. Any other impressions of the design (BB
    > inclusive) as a whole?


    I see it as a response to the failure of the previous design, that as
    I said in this thread, I predicted years ago. These are difficult
    interfaces, especially with such high torque that is uncommon in most
    machines.

    I'm not thrilled with the embedded spindle in the right crank, but it
    gets rid of that interface (possibly) while the attachment of the left
    crank is well done. Other than that, I haven't had one of these in
    hand and have not ridden one so I don't know where the next weakest
    spot is. The square taper was a great leap forward when it was
    introduced to replace steel cotter attached steel cranks. Just the
    same it has some major weaknesses.

    Also, the outboard spindle bearings solve one problem, that of too
    small a BB inside diameter for a good bearing, but now these are
    overhung on thin shells, something I would not readily do without a
    lot of high stress test riding. It looks bad from the outset. Maybe
    they tested the design but I can't see how these bearing cups can
    survive, especially the right cup that alternately has huge chain
    loads in addition to vertical ones. I'll wait and see. I am not
    ready to try them from what I see.

    Jobst Brandt
    [email protected]
     
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