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

[rogerzilla]

Never seen one go there before. Cranks usually crack at the pedal eye after a massive mileage - the pedal chews away at the crank in use (washers don't really help) as well as fatigue.

Must have been Friday afternoon at the Shimano foundry.

 

[jay clock]

I contacted Madison who said Shimano Warranty Manager wants to see it. I have to go via CRC who I bought the bike from. Let's see

New one on order in the meantime

 

[andrew_s]

Never seen one go there before.

I have (though not personally).
The crack starts at the thin web between the spider arm and the crank arm, and propagates.

 

[jay clock]

OK. after FOUR months of very slow ding dong emails between me to CRC>Madison>Shimano>Madison>CRC>me and back and forth, I now have a brand new boxed chainset to sell as I had replaced it of course. On Ebay but contact me if interested https://www.ebay.co.uk/itm/133177803850?ul_noapp=true

 

[Levo-Lon]

Id think its a metal fatigue flaw issue.
Maybe from day one.

Shimano may replace it and I'd think quality control may like to have a closer look..

 

[jay clock]

Id think its a metal fatigue flaw issue.
Maybe from day one.

Shimano may replace it and I'd think quality control may like to have a closer look..

If you read the post they have looked at it and they have replaced it!

 

[fossyant]

If you read the post they have looked at it and they have replaced it!

Glasses for meta ion

 

[silva]

Yesterday evening I suffered the same. Never had before. Left crank broke off around its pedal mount hole. Stronglight Track 2000 chainset. It has been mounted 2 years. And I've certainly no strong legs, I also wasn't pushing hard on the moment - it occurred near a bridge up but not on its steeper slope.
Stuck luckily on the return not that far from home, so I went on foot the bridge up then put my left foot on the unused front luggage rack then pushed with the right further at twice walking speed.
I never replaced a crank/crankset but since too much time to reach a nearby dealer with no / unsure direct solving, stuck.
But I had an older crankset of this bike, replaced due to a need for a different chainring mount (bcd).
The allen bolt came out easy, but the crank itself not. I don't have a crank removal tool. I spent hours trying to hammer (carefully - it puts stress on the bearings etc) it off the square taper along two punches 180 degrees against and slipping next to eachother as to decrease the chance on tilting, the hammered punch at the side of the broken crank as to minimalize damage to the bike side. I tried defixing sprays but it all didn't help. In the end, the only option I had left, was saw diagonally through the cranks mount, to close to the square taper, then a punch to split it. Aluminium is quite easy to saw in so after about 15 min and a final hammer blow it split and freed the taper. There were some burrs on it. Then I cleaned it all thoroughly and oiled it. The old one seemed (one can never be sure due to chance on slight differences in mechanical specs) a fit.
Then I turnt the small broken part off the pedal, and mounted that on the crank.

It's not clear what the cause of the breaking was. I noticed quite some burrs on the square tapered end, and also within the old crank arm, a burr in the middle of every of the four sides. Also, the Stronglight cranks inner thread was heavily damaged. Screwing a crank removal tool in it would very likely have been quite hard / and the force under tension may have ruined the thread before the crank shifted off the square taper. No idea what could have damaged the thread like that.

So it looks now like I can ride the bike again, but I'm unsure whether or not my noob-replacement may result in some failure in a (near) future. Maybe I should visit a dealer first in order to get a check of it, and maybe a clue on what may have caused the crank to break there. Metal fatigue? But how? My axle is longer (7mm more on each side) than first, to get the chainline straighter. Does this put some unusual load/stress around the pedal mount? One rather expects higher forces near its bottom bracket mount, due to the bigger leverage due to the longer distance.
Could a pedal strike (fixed gear - sometimes happens in a turn) cause a start of a break? I did have some, but none worth speaking off. At least I think.
I've have had some much more serious pedal strikes with an older bike. One that threw up the bike (and me) including a spin before hitting the ground, with quite some damage as result (spokes, handlebars, rack). This crank arm breakage is a first one for me, and it could have put me in much more trouble than it has now. Luck is something to not count on.

I just found this here: https://www.cyclechat.net/threads/snapped-crank.253599/post-5749025
Those washers I will place as soon as I found some, taking into account the minimum thread engagement length (11 mm according to some video)
Will make a test ride now.

 

[silva]

6 km test ride result: stopped 5 times to check the bolt of the crank (took an allen key for it with me), everytime it had loosened a bit (a quarter turn to retension).
So looks like something wrong.

Then another test ride. Same story, only that I waited a longer time to retension the bold, for what the usage duration difference is worth: the bolt doesn't seem to loosen more than in the shorter time, alike the bolt ceases loosening at some point.

Still, a losening bolt means some force, or at least a direction vector of it, pushes or pulls it away. The only thing I can think of is different slopes of the tapering, which in case could be explained by an ISO versus JIS standard.
The broken crank arm is from the Stronglight Track 2000 set which is specified on the sellers site as "Requires 107mm bottom bracket with JIS (Shimano type) taper"
The old replacing crank arm is from the original crankset that the dealer of the bike specified as "Crankset Sugino XD 170mm" which is specified as "4-TAPER(JIS)".
So it doesn't look like a JIS/ISO difference cause.

My focus now is the cause of this crank breaking at the pedal "eye" (as it is named here).
I cleaned the parts and took some pictures:










First 2 pictures are from my nonprofessional (lack of crank puller and last resort in order to cause no further damage) crank removal
Last 3 hopefully contain some clues about the cause.
Remember: the pics show cleaned parts. Right after the breakage, a part of the break section was black, the other silverish, indicating an existing partly breakage before the total come off. I inspect (putting it upside down) the bike every morning upon arrival at work, and I whip off dirt but I didn't notice it. I should have taken pics before cleaning too, just realize it now, but too late.

Some notes:
- The thread inside the broken Stronglight crank got somehow quite damaged - there were 3-4 loose or partly loose thread strip offs, thin and narrow burrs. I remember when it was installed to replace the Sugino that the dealer afterwards had to replace the axle with a longer one due to chainline got changed to a chainring-frame colliding position. Apparently the crank puller or whatever it was seriously damaged the thread. Worser: the old Sugino, now mounted as replacement, also had serious thread damage. Meaning that a future crank puller usage may ruin the thread remainders instead of pulling the crank off the tapered end, leaving a bottom bracket replacement as sole solution to remove the crank.
- A difference between Sugino and Stronglight: the latter had around the hexagon bolt a threaded (outside) ring with two small tool holes (aside of the big centered crank bolt hole of course) in it, near its circumference, 180 degrees apart, which may have served as a dust cap or so, since the Sugino had some plastic nonthreaded thick ring instead.
I just started to think that this may (also?) serve as a bolt locker (the bolt has a washer end in once piece) so I decided to remove the bolt and replace the plastic nonthreaded ring with the threaded alu ring from the Stronglight crank.
Then I tightened that ring using two small screwdrivers.
Next is to test if that threaded ring indeed prevents the crank bolts loosening.

 

[silva]

As later proved, the square tapers of both sides of the connection must have been different somehow (different brands).
Now past, because since weeks I don't need to tension the bolt further. They must have deformed to match eachother.

 

[fossyant]

JIS vs ISO probably.

 

[Ajax Bay]

I don't have a crank removal tool. . . . . In the end, the only option I had left, was [to] saw diagonally through the cranks

Buy a crank removal tool - I know you are concerned that the threads in the crank was damaged but the tool is steel and the crank is Al alloy: it would have done the business. But you surely need this tool in your box. How else will you remove the crankset you currently have fitted?

 

[silva]

JIS vs ISO probably.

That's what I also thought first - it's the most logical explanation, a next one would be a quite big tolerance difference between both brands.
But, according to the specifications of both parts, they both should be JIS.
One crank (the broken thus replaced one) was market with the brandname (StrongLight).
The other (as originally mounted - Shimano) wasn't marked at all. Though, the right side (chainring/drivetrain side) crankarm was.

An uncommon explanation could then be that the bike was delivered with a crankset of which the left crank had been replaced by some other brand that uses the ISO standard for the square taper dimensions.
For an unknown reason then, maybe something went wrong during mounting and damaged the original Shimano left crank.

Fact is that the Stronglight (the newer crankset that replaced the original Sugino) right side crank, the allen bolt head there, is seriously damaged, which must have been caused by the dealer when he replaced the crankset (and also had to mount a longer axle, so the replacing crankset had to be unmounted/remounted that same time).
I found the inner thread of the Stronglight left crankarm (so the broken one) also seriously damaged, well possible that if I had have a crank removal tool that it would have stripped the thread before releasing the arm.

I was present during the work but didn't notice. I also didn't know what I know now - at the time I knew nothing about cranksets.
If this would really be the explanation, then the current (the original) left crank arm's ISO mount and the axles JIS mount must have been forged to some inbetween both standards slope (if required forces possible at all, any idea?), meaning that it can also be a problem in the future.

 

[SkipdiverJohn]

As a matter of interest, has anyone ever broken, or heard of someone breaking, a cottered steel crank? I've seen a couple of bent ones resulting from crash damage, but never one actually break.

 

[silva]

Buy a crank removal tool - I know you are concerned that the threads in the crank was damaged but the tool is steel and the crank is Al alloy: it would have done the business. But you surely need this tool in your box. How else will you remove the crankset you currently have fitted?

I've planned to buy such tool (a Park tool CWP-7), only that I decided to wait until I have to order other parts, otherwise the shipping cost doubles the price, and that the dealers I so far used don't have it in their shop.
About my concern, I know the tool is steel and the crank is Al alloy (if it had been steel I'd have had alot more work to saw it through in order to get it off haha), so the concern wasn't the tools survival but the thread survival, since thread damaged the remainder of the thread may well strip before the crankarm looses, leaving me with no other option than again sawing it through.

I'm now unsure what to do next. I also suffer an out of center somewhere around the bottom bracket, first I thought it was a Stronglight lack of accurate production but it now starts to look alike the dealer messed up things my chain tension variation may be caused by a deformed square taper axle end on the driveside, precisely something that another dealer gave me a couple weeks ago as explanation.

One thing got certain by now: this bike, despite its big price tag, was delivered with a long list of problems.
I'm currently in the process of replacing the hydraulic brakes (Magura) with common V brakes - I'm done with the crap to have to empty/reflate the tyre everytime I want to remove/place back a wheel. I started to suspect it and asked but the answer was ofcourse not that would be crazy, to then finally be forced to admitting it when he had to do it himself during aboves replacement of the crankset.
Since I never mounted brakes, and probably lack tools, I thought / planned a job for the dealer. But now I start to doubt, it could turn out as yet another mess. The current hydraulic ones already have had a problem - the oil line between rear brake and its handle was mounted with a too short turn under the handlebars - and it broke there after some months. It had to be replaced and I asked to let it pass along the lower instead of upper tube since that appeared as the necessity for that too short turn and yet again an additional cost.

It's just a neverending story, this bike, everytime I think all problems solved, new ones pop up. I thought I'd seen all in the past, and that this bike would finally be a what I wanted out from the box. NOT.
The crankset in particular - first one that had a chainring that hadn't the 1/8" width I had demanded.
In order to find a 1/8" wide ring, the bcd 110 mount had to be changed to 144, so a crankset replacement.
Then the replacing crankset made the chainring void the frame, causing the need to place a longer axle.
Then left crankarm breaks, and the original that I used to replace can now have been a different square taper, with possibly axle damage (deformation JIS > ISO) as result. Sigh.