Snapped crank.

[Kell]

By the looks of it, this has had a crack in it for a bit.

Luckily, it went when I was sat down going uphill rather than when I was stood on the pedals.

Using it as an opportunity to switch to a black crankset.

 

[fossyant]

Get a lottery ticket ASAP.

 

[presta]

Got the T-Shirt:

Had the bruises too.

 

[SkipdiverJohn]

@Yellow Saddle will appear shortly to give a technical analysis on the cause of the failure.....

 

[Kell]

Probably because I don’t clean my wheels often enough.

 

[Yellow Saddle]

Probably because I don’t clean my wheels often enough.

Yup.

 

[Yellow Saddle]

@Yellow Saddle will appear shortly to give a technical analysis on the cause of the failure.....

Here's my best guess.

1) It is a right crank. Not right as in wrong, but right as in not left.
2) A chain "incident" or FD that moved over too far, scored the crank on the inside at two spots equidistant from the crank spindle.
3) A crack developed from a stress riser at that point and traveled inwards towards the junction of the two legs of the "U" A different photo may reveal this initial gouge.
4) The failure has three distinguishable areas. The large rouged section on the left of the cross-section photo. The silver section in the centre and the smaller rouged section on the right. The two dull, rouged areas are the initial crack and the silver section represents the last straw that broke the camel's back. That held on until the last minute and broke suddenly and completely. The two darker areas indicate an area of the crack that has been there for months or more, gradually increasing in size and all the time, fretting, creaking and oozing black discharge. All of this would have been noticed had the bike been cleaned and inspected regularly.
5) A crank works in three ways: in torsion, flexion and extension. Torsion because of the pedal that's offset, not central like a piston on a connecting rod. Flexion because of the in-plane component of pedal torque and, extension (stretch) when you stand on the pedals when the crank is at the bottom of its stroke.
6) It was mostly torsion that killed the crank. That can be seen from the shape of the crack.

Before cranks became hollow, through some very clever engineering by Shimano, the U-shape or channel was one preferred way of making cranks lighter. However, a channel like that is a very poor structure for resisting torsion. You just have to handle a plastic rain roof gutter to demonstrate how weak it is in torsion. Nowadays Shimano cranks are hollow, essentially tubes, and they are stiffer under twisting.

As for Presta's photo of the pedal eye on a crank that broke off: it was probably not his fault. The stupid way pedals attach to cranks causes gouging at the eye which leaves stress risers which quickly crack and break off. One way to alleviate it is to install steel pedal washers and most cranks today come with pedal washers which users promptly lose and ignore.

 

[Kell]

I don’t recall the chain ever coming off and getting stuck, but I may just not remember an incident.

What’s FD?

As for the cleaning regime, i’ve given up cleaning anything that isn’t a mating surface. Doesn’t matter how much I attempt to clean the tubing of the bike, the grime it picks up will not come off.

Once a month the chain, chain ring, chain tensioner, rear cogs and chain pusher all come off to be properly cleaned down.

Every weekend, I run the chain through one of those park tools chain cleaners, but it really doesn’t do enough, hence the full overhaul once a month. I also do the wheels on a regular basis.

I’d normally give the cranks nothing more than a cursory wipe down but certainly not inspected them.

I will keep an eye on them in the future however.

 

[Yellow Saddle]

What’s FD?

Front Derailer.

 

[raleighnut]

Here's my best guess.

1) It is a right crank. Not right as in wrong, but right as in not left.
2) A chain "incident" or FD that moved over too far, scored the crank on the inside at two spots equidistant from the crank spindle.
3) A crack developed from a stress riser at that point and traveled inwards towards the junction of the two legs of the "U" A different photo may reveal this initial gouge.
4) The failure has three distinguishable areas. The large rouged section on the left of the cross-section photo. The silver section in the centre and the smaller rouged section on the right. The two dull, rouged areas are the initial crack and the silver section represents the last straw that broke the camel's back. That held on until the last minute and broke suddenly and completely. The two darker areas indicate an area of the crack that has been there for months or more, gradually increasing in size and all the time, fretting, creaking and oozing black discharge. All of this would have been noticed had the bike been cleaned and inspected regularly.
5) A crank works in three ways: in torsion, flexion and extension. Torsion because of the pedal that's offset, not central like a piston on a connecting rod. Flexion because of the in-plane component of pedal torque and, extension (stretch) when you stand on the pedals when the crank is at the bottom of its stroke.
6) It was mostly torsion that killed the crank. That can be seen from the shape of the crack.

Before cranks became hollow, through some very clever engineering by Shimano, the U-shape or channel was one preferred way of making cranks lighter. However, a channel like that is a very poor structure for resisting torsion. You just have to handle a plastic rain roof gutter to demonstrate how weak it is in torsion. Nowadays Shimano cranks are hollow, essentially tubes, and they are stiffer under twisting.

As for Presta's photo of the pedal eye on a crank that broke off: it was probably not his fault. The stupid way pedals attach to cranks causes gouging at the eye which leaves stress risers which quickly crack and break off. One way to alleviate it is to install steel pedal washers and most cranks today come with pedal washers which users promptly lose and ignore.

I take it you mean 'roughed' as opposed to wearing makeup,



These pair are rouged.

 

[presta]

As for Presta's photo of the pedal eye on a crank that broke off: it was probably not his fault. The stupid way pedals attach to cranks causes gouging at the eye which leaves stress risers which quickly crack and break off. One way to alleviate it is to install steel pedal washers and most cranks today come with pedal washers which users promptly lose and ignore.

It was my fault, I'd grounded the pedal on a corner. The pedal spindle had already gone a few months earlier, but the penny didn't drop until the crank went the same way.

 

[Kell]

Front Derailer.

I figured that’s what you might be referring to, but this is a Brompton.

 

[Grant Fondo]

Here's my best guess.

1) It is a right crank. Not right as in wrong, but right as in not left.
2) A chain "incident" or FD that moved over too far, scored the crank on the inside at two spots equidistant from the crank spindle.
3) A crack developed from a stress riser at that point and traveled inwards towards the junction of the two legs of the "U" A different photo may reveal this initial gouge.
4) The failure has three distinguishable areas. The large rouged section on the left of the cross-section photo. The silver section in the centre and the smaller rouged section on the right. The two dull, rouged areas are the initial crack and the silver section represents the last straw that broke the camel's back. That held on until the last minute and broke suddenly and completely. The two darker areas indicate an area of the crack that has been there for months or more, gradually increasing in size and all the time, fretting, creaking and oozing black discharge. All of this would have been noticed had the bike been cleaned and inspected regularly.
5) A crank works in three ways: in torsion, flexion and extension. Torsion because of the pedal that's offset, not central like a piston on a connecting rod. Flexion because of the in-plane component of pedal torque and, extension (stretch) when you stand on the pedals when the crank is at the bottom of its stroke.
6) It was mostly torsion that killed the crank. That can be seen from the shape of the crack.

Before cranks became hollow, through some very clever engineering by Shimano, the U-shape or channel was one preferred way of making cranks lighter. However, a channel like that is a very poor structure for resisting torsion. You just have to handle a plastic rain roof gutter to demonstrate how weak it is in torsion. Nowadays Shimano cranks are hollow, essentially tubes, and they are stiffer under twisting.

As for Presta's photo of the pedal eye on a crank that broke off: it was probably not his fault. The stupid way pedals attach to cranks causes gouging at the eye which leaves stress risers which quickly crack and break off. One way to alleviate it is to install steel pedal washers and most cranks today come with pedal washers which users promptly lose and ignore.

You ought to do a Sheldon Brown type blog....epic.

 

[Yellow Saddle]

I take it you mean 'roughed' as opposed to wearing makeup,

View attachment 486673

These pair are rouged.

No I don't. Rouged is an engineering term you won't find in everyday dictionaries.

But look here, for instance.

http://www.wwwrope.com/pdf/EL_TB_03.pdf

Fretting causes rouging.

 

[raleighnut]

No I don't. Rouged is an engineering term you won't find in everyday dictionaries.

But look here, for instance.

http://www.wwwrope.com/pdf/EL_TB_03.pdf

Fretting causes rouging.

Nice try but that refers to Iron oxidation in a wire rope and is related to the red colouration achieved by the oxide (pretty similar to the red in make-up)