I have managed to break a crank.... advice?

jay clock

Massive member
Location
Hampshire UK
I am a solid build but slow and steady pace (two hours at 24kmh yesterday). About a mile from home we cycled along a tarmac path, flat and gentle, then across a gravel car park. As I went on to the road I heard a noise and noticed that it felt like my pedal on the right was flexing down/rightwards as I was on the down stroke.

Got home, and today tried different shoes and pedals (both Look Keo) and problem still there. Felt like a possible bent crank (although somewhat unlikely). On close examination I found this https://www.dropbox.com/s/pa6eekjluhb6xi4/File 13-05-2019, 12 26 53.jpeg?dl=0

Ouch. I am not some monster sprinter and I tend to spin rather than grind. First time for me. Googling it, it sounds uncommon. Am I just unlucky?

New chainset time!
 
Last edited:

MichaelW2

Veteran
From the surveys and investigations I have seen, this is something that can happen to any brand/model but esp to high end ultralight premium grade cranks, where material thickness is reduced.
It could originate from a manufacturing defect or later damage.
If the crank has separated, a photo of the fractured surfaces can inform educated engineers.
 

Salty seadog

Space Cadet...(3rd Class...)
I am a solid build but slow and steady pace (two hours at 24kmh yesterday). About a mile from home we cycled along a tarmac path, flat and gentle, then across a gravel car park. As I went on to the road I heard a noise and noticed that it felt like my pedal on the right was flexing down/rightwards as I was on the down stroke.

Got home, and today tried different shoes and pedals (both Look Keo) and problem still there. Felt like a possible bent crank (although somewhat unlikely). On close examination I found this https://www.dropbox.com/s/pa6eekjluhb6xi4/File 13-05-2019, 12 26 53.jpeg?dl=0

Ouch. I am not some monster sprinter and I tend to spin rather than grind. First time for me. Googling it, it sounds uncommon. Am I just unlucky?

New chainset time!
How old and how used are
 

Jody

Veteran
Ha ha!! Reflection of a stripy rug!! No accidents either
Above that. The bit that looks like an impression of someones finger print which ends near to where the crack looks like it originates.
 

ColinJ

Puzzle game developer
Yikes - that could have been very nasty if you had stood on the pedals and sprinted***!

If you haven't crashed the bike or otherwise damaged the crank, then it must be a manufacturing defect. It is highly unlikely that anybody would be strong enough to cause that.

I think Shimano should replace it, even if it is outside the warranty period because it isn't the kind of component that wears out.





*** I know from painful personal experience what can happen when the transmission fails in such circumstances...
 

ColinJ

Puzzle game developer
Ha - I took a young bodybuilder colleague out on a hilly ride once and he DID manage to damage his transmission. He insisted on using the big ring everywhere, including a 25% climb! I told him to use lower gears and spin his legs but he stuck to using masses of brute force. After a couple of hills he ripped the chain apart ... :whistle:
 

Milkfloat

An Peanut
Location
Midlands
Shimano warranty is past from what I can see. Looks like a new one needed
Certainly a new one is needed, but even though it is out of warranty Shimano may send you a new one. They did for a friend you snapped a 3 year old crank on condition they had the old crank to inspect. It took a month to sort out though, so he purchased his own and now has a spare.
 
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