Snapped crank.

[Yellow Saddle]

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)

No, we use it for all evidence of fretting. In aluminium it happens to be black, but it is still rouged.
It is also evident in stainless steel, where the rouge has not turned brown, yet it is still referred to as rouge.

It certainly isn't only used in wire rope either, that's just the first example I found on the web.

Also look up jeweller's rouge. I use it to finish off sharpened knives and blades on a leather strop. Here the outcome is black because the iron had not yet rusted.

 

[KneesUp]

As for the cleaning regime, i’ve given up cleaning anything that isn’t a mating surface..

One for you here @Fnaar

 

[12boy]

I've probably ridden at least 70 k miles in the last 60 years and never have broken a crank like that. I use pretty much Sugino and Shimano cranks, some of which are at least 25 years old. Having read your previous posts I gather road grime and grit and hard climb rides are every day for you but I still think there was a flaw in the crank to begin with. Salt is used here in the winter and that will trash components fairly quickly, so I do remove that after riding, I do protect the inside of my frames, and I do wax chains since the wax doesnt pick up grit like oil and grease do. Other than that, not a lot of maintenance other than rebuilding bearings when needed.

 

[Kell]

I've probably ridden at least 70 k miles in the last 60 years and never have broken a crank like that.

Well, according to Strava I’ve done 8,278 miles on the Brompton in 4 years.

Like other things that have happened with this bike, it’s proving to have a lot of firsts.

It might be that everything is just that little bit lower to the ground which is causing more problems with ingrained dirt etc. But my previous commuter bikes never had these problems.

Other problem, yes.

 

[cyberknight]

found mine

 

[berlinonaut]

Well, according to Strava I’ve done 8,278 miles on the Brompton in 4 years.

From the Brompton manual, page 11:

• Aluminium components: As on other lightweight machines, aluminium alloy is used in the construction of the Brompton, and this material has a finite design life before failure. In normal use, the risk of aluminium fatigue failure is remote, even after many thousands of miles. However, the risk of failure increases with use, especially with hard riding or other severe loading.As such a failure could cause injury, the hinge clamp plates, handlebar, chain set, seat pillar and pedals should be replaced every 5,000 miles (more frequently if they are subjected to hard use), and we recommend that these items are checked regularly.
  

 

[Kell]

From the Brompton manual, page 11:

• Aluminium components: As on other lightweight machines, aluminium alloy is used in the construction of the Brompton, and this material has a finite design life before failure. In normal use, the risk of aluminium fatigue failure is remote, even after many thousands of miles. However, the risk of failure increases with use, especially with hard riding or other severe loading.As such a failure could cause injury, the hinge clamp plates, handlebar, chain set, seat pillar and pedals should be replaced every 5,000 miles (more frequently if they are subjected to hard use), and we recommend that these items are checked regularly.

Pretty sure that it would be cheaper to buy a new bike at that rate.

 

[Kell]

However.

On that advice, I’m going to order a new set of clamps.

 

[Kell]

Also, also...

Lightweight machines?

 

[rogerzilla]

Pedal washers don't help much. They're the same size as the pedal axle and they chew against the crank in just the same way. My TA cranks came with them, I use them but the crank's little recess for the washer still deepens with time.

If these were the original Brompton cranks (made by Stronglight) with the permanently-fixed chainring, they're just not up to the job. I replaced mine with Sugino cranks. The usual failure mode is that the ring shears from the crank when you're giving it some.

 

[berlinonaut]

If these were the original Brompton cranks (made by Stronglight) with the permanently-fixed chainring, they're just not up to the job. I replaced mine with Sugino cranks. The usual failure mode is that the ring shears from the crank when you're giving it some.

As one can see from the picture these were the newer style cranks with the spider, not the ones with the fixed chainwheel. Also clear with the bike being four years old - this makes ist date from 2015 while the newer style cranks were invented in 2013. With the old ones the ring shearing off the crank did happen but in my eyes by far not often enough that I would call them "not fit for the job" or the incident "the usual failure".
I second the analysis of @Yellow Saddle in https://www.cyclechat.net/threads/snapped-crank.253599/post-5749025 - this thing has been developing over a longer period of time and probably has a root cause that we do not know. There's a good chance that it would have been recognized early with the part being inspected regularly as Brompton even recommend in their manual. The cranks were well beyond their exchange interval, which, I assume, not too many Brompton riders stick to - still this kind of incident seem not to happen very often, given the amount of reports compared to the amount of Bromptons made. So basically, though not nice, for the most part a user created incident.

 

[Banjo]

In the marine industry a red die is painted on critical parts which shows up cracks invisible to the naked eye.

Get it on paintwork and it's there for good so maybe not ideal for bikes but could be carefully used on cranks.

 

[rogerzilla]

Does anyone know if the new cranks are forged or cast? A forged crank can still break, but it's a lot stronger than a cast one and less likely to have flaws in the metal. Brompton don't fit particularly high quality parts, so I'd be suspicious.

 

[Kell]

All points taken on board.

I’ve never opened the manual, so didn’t know about the 5,000 mile limit.

That would have been about a year and a half ago, so if I’d stuck to that then this wouldn’t have happened.

I think even I could tell that this wasn’t a sudden failure, the darker patches clearly indicate ingrained dirt. Though now i’ve Taken the old crank off, I think you’d have been hard pressed to see any evidence of the crack developing from behind.

It would have been totally hidden.

Once it moved around the sides, however, a little more vigilance may have spotted it.

But then I probably wouldn’t as I wasn’t looking for it.

Who knows?

All I know now, is that it was a lucky escape. And i’ll Make a note of installation mileage of the new part.

 

[Yellow Saddle]

In the marine industry a red die is painted on critical parts which shows up cracks invisible to the naked eye.

Get it on paintwork and it's there for good so maybe not ideal for bikes but could be carefully used on cranks.

All industries use that die. Yes, it is lethal stuff and can even ruin white paint. However, on bicycles it isn't necessary. The aluminium rouges black and cracks are very evident.