Why did my crank snap?

Discussion in 'UK and Europe' started by spindrift, Mar 31, 2006.

  1. spindrift

    spindrift Guest

    Never seen this before.

    Doing about 15 mph outside Liverpool St Station and the whole pedal
    crank sheared off near the base.

    Could have been really nasty is it had happened earlier- imagine
    approaching a hill and hammering down on the pedal when it snaps, you'd
    be tipped sideways.

    The bike shop pointed out that where the pedal snapped off the metal
    was shiny at the broken bit but only halfway across, the other half was
    covered with grease and mud so there must have been a hairline fracture
    that I never noticed.

    £55 for new crank and pedals, bugger.
     
    Tags:


  2. Ian Blake

    Ian Blake Guest

    On 31 Mar 2006 04:52:32 -0800, "spindrift" <[email protected]>
    wrote:

    >Never seen this before.


    I have twice
    First time Miche Primato Pista
    Second time TA Alize.
    Both good cranks. Hard work cycling with one leg. (There is a one
    legged audax rider who is very impressive).

    >
    >Doing about 15 mph outside Liverpool St Station and the whole pedal
    >crank sheared off near the base.


    My cranks broke near the pedal.

    >
    >Could have been really nasty is it had happened earlier- imagine
    >approaching a hill and hammering down on the pedal when it snaps, you'd
    >be tipped sideways.


    It's just like inadvertantly unclipping. On the my first failure I
    tried several times to reclip before I looked and realised that's
    funny, I am clipped in.

    The second time I was climbing a little hill but no problem.

    >
    >The bike shop pointed out that where the pedal snapped off the metal
    >was shiny at the broken bit but only halfway across, the other half was
    >covered with grease and mud so there must have been a hairline fracture
    >that I never noticed.
    >
    >£55 for new crank and pedals, bugger.


    Why do you need new pedals? Remove and refit.

    Oh and the reason "Why did my crank snap?" You pay £55 for pedals and
    crank what do you expect?
     
  3. Phil Cook

    Phil Cook Guest

    spindrift wrote:

    >Never seen this before.
    >
    >Doing about 15 mph outside Liverpool St Station and the whole pedal
    >crank sheared off near the base.
    >
    >Could have been really nasty is it had happened earlier- imagine
    >approaching a hill and hammering down on the pedal when it snaps, you'd
    >be tipped sideways.
    >
    >The bike shop pointed out that where the pedal snapped off the metal
    >was shiny at the broken bit but only halfway across, the other half was
    >covered with grease and mud so there must have been a hairline fracture
    >that I never noticed.


    Crack growth until catastophic failure. This happened to me once as I
    was riding to work. I got out of the saddle to mash it up the slope of
    Vauxhall Bridge and landed in a heap. I had the presence of mind to
    wave a hand in the air and one of my colleages in their red van stoped
    behind me to stop the traffic whilst I picked myself up. They gave me
    a lift in the rest of the way and I later cycled home on one pedal.

    More crank failures here
    http://pardo.net/pardo/bike/pic/fail/FAIL-001.html
    --
    Phil Cook looking north over the park to the "Westminster Gasworks"
     
  4. spindrift

    spindrift Guest

    "Oh and the reason "Why did my crank snap?" You pay £55 for pedals and

    crank what do you expect? "

    Cranky, rather.

    You mean my crank snapped in anticipation of my being over charged for
    a new crank and pedals?

    My snap was like the last photos on your link, Phil, right at the
    widest possible part.
     
  5. spindrift wrote:
    > Doing about 15 mph outside Liverpool St Station and the whole pedal
    > crank sheared off near the base.
    >
    > Could have been really nasty is it had happened earlier- imagine
    > approaching a hill and hammering down on the pedal when it snaps, you'd
    > be tipped sideways.
    >
    > The bike shop pointed out that where the pedal snapped off the metal
    > was shiny at the broken bit but only halfway across, the other half was
    > covered with grease and mud so there must have been a hairline fracture
    > that I never noticed.


    http://www.sheldonbrown.com/brandt/breaking-cranks.html

    Plenty more information on that kind of thing if you search
    rec.bicycles.tech.

    Anthony
     
  6. spindrift

    spindrift Guest

    Thanks guys.
     
  7. Simon Brooke

    Simon Brooke Guest

    in message <[email protected]>, Ian Blake
    ('[email protected]') wrote:

    > On 31 Mar 2006 04:52:32 -0800, "spindrift" <[email protected]>
    > wrote:
    >
    >>Could have been really nasty is it had happened earlier- imagine
    >>approaching a hill and hammering down on the pedal when it snaps, you'd
    >>be tipped sideways.

    >
    > It's just like inadvertantly unclipping. On the my first failure I
    > tried several times to reclip before I looked and realised that's
    > funny, I am clipped in.


    Yup. Been there, done that...

    --
    [email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/
    ;;Drivers in the UK kill more people every single year than
    ;; Al Qaeda have ever killed in any single year.
     
  8. spindrift wrote:
    > Never seen this before.
    >
    > Doing about 15 mph outside Liverpool St Station and the whole pedal
    > crank sheared off near the base.
    >
    > Could have been really nasty is it had happened earlier- imagine
    > approaching a hill and hammering down on the pedal when it snaps, you'd
    > be tipped sideways.
    >
    > The bike shop pointed out that where the pedal snapped off the metal
    > was shiny at the broken bit but only halfway across, the other half was
    > covered with grease and mud so there must have been a hairline fracture
    > that I never noticed.
    >
    > £55 for new crank and pedals, bugger.


    I had the top of the crank crack above the bolt hole, causing the pedal
    to drop out and not stay in. Wedged a stick in the hole and it got me
    home!

    peter
     
  9. the.Mark

    the.Mark Guest

    Simon Brooke wrote:
    > in message <[email protected]>, Ian
    > Blake ('[email protected]') wrote:
    >
    >> On 31 Mar 2006 04:52:32 -0800, "spindrift"
    >> <[email protected]> wrote:
    >>
    >>> Could have been really nasty is it had happened earlier-
    >>> imagine approaching a hill and hammering down on the pedal
    >>> when it snaps, you'd be tipped sideways.

    >>
    >> It's just like inadvertantly unclipping. On the my first
    >> failure I tried several times to reclip before I looked and
    >> realised that's funny, I am clipped in.

    >
    > Yup. Been there, done that...


    Me too. Odly enough I was in your part of the world Simon, I was in
    Southerness at the time.
    --
    Cheers
    the.Mark
     
  10. spindrift wrote:

    > Never seen this before.
    >
    > Doing about 15 mph outside Liverpool St Station and the whole pedal
    > crank sheared off near the base.
    >
    > Could have been really nasty is it had happened earlier- imagine
    > approaching a hill and hammering down on the pedal when it snaps, you'd
    > be tipped sideways.
    >
    > The bike shop pointed out that where the pedal snapped off the metal
    > was shiny at the broken bit but only halfway across, the other half was
    > covered with grease and mud so there must have been a hairline fracture
    > that I never noticed.
    >
    > £55 for new crank and pedals, bugger.
    >

    They usually snap because they're old and because the pedal has gouged
    the face of the crank. As for only half the crack face being shiny,
    once a fatigue crack reaches what's called the "Griffith critical
    length" (which may take months or years) it goes bang in an instant.
    This length varies according to the thickness and toughness of the material.
     
  11. Sue White

    Sue White Guest

    Zog The Undeniable <[email protected]> whizzed past me shouting
    >spindrift wrote:
    >
    >> was shiny at the broken bit but only halfway across, the other half was
    >> covered with grease and mud so there must have been a hairline fracture
    >> that I never noticed.


    >They usually snap because they're old and because the pedal has gouged
    >the face of the crank. As for only half the crack face being shiny,
    >once a fatigue crack reaches what's called the "Griffith critical
    >length" (which may take months or years) it goes bang in an instant.
    >This length varies according to the thickness and toughness of the
    >material.


    An engineer of our aquaintance found that a crack round an alloy
    handlebar where it meets the stem goes critical after only about 5mm.
    I'm sure of this, I saw the two pieces afterwards.

    --
    Sue ]8:))

    Just off to check my cranks for cracks...
     
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