Why did my crank snap?

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

Quoted message said:

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).

Quoted message said:

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

My cranks broke near the pedal.

Quoted message said:

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.

Quoted message said:

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?

spindrift said:

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"

"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.

spindrift said:

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

Thanks guys.

in message <[email hidden]>, Ian Blake

('NoNotMe@NotAnywhere') said:

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

Quoted message said:

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 hidden] (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.

spindrift said:

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

Simon Brooke said:

in message <[email hidden]>, Ian

Blake ('NoNotMe@NotAnywhere') said:

spindrift said:

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

spindrift said:

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.

Zog The Undeniable <[email hidden]> whizzed past me shouting

Quoted message said:

spindrift said:

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.

Quoted message said:

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...