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On a climb I started to notice something feeling similar to a slipping chain. A couple minutes later while pedaling standing up, my left crank arm got completely misaligned as you can see in the picture:

misaligned crank arms

With my multitool I managed to take off the crank arm, realign it and tighten it as much as possible. This was enough to ride the last 3 kilometres to my accommodation without any further problems (no uphills on this stretch though and I pedaled very softly).

I'm currently on a bike tour and there is no bike shop nearby. Is this something that will keep happening and I need to head to a bike shop immediately or could it be possible to ride the last couple days (300km) of my tour without any major problems?

For extra context: The crank arm has a sticker on it saying "tighten to 14-15nm using a torque wrench". Also it is likely that my chain is quite stretched and worn and I might need a new cassette as well.

Crank: crank

Spindle: spindle

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  • As an aside, the sticker really says 14-15 Nm now? It's been 12-14 for a very long time. I wonder if Shimano revised the torque spec due to reports of these cranks failing exactly like yours did.
    – MaplePanda
    Commented Jul 19 at 21:59
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    I would be highly interested in how this turned out on the end, i.e. what was the damage in the end and if there is some idea what was the root cause of the failure. So if you would give some feedback about it, at least I would be glad to read it.
    – Benedikt Bauer
    Commented Jul 20 at 8:56
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    @BenediktBauer I carefully limped to a bike store and got a new crank installed there. It has held up well since then. Sadly they were not too talkative and there was a language barrier, so I don't know much more than what I learnt in this post, but I guess the main reason was me never tightening the pincher bolts of the crank... I still plan to do a more thorough bike service once I'm back home, but I hope I don't have to replace any more parts
    – nikostra
    Commented Jul 21 at 14:01

5 Answers 5

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Summarise: You're on-tour and have 300 km to get home, with no bike service nearby. Your crank/spindle interface is badly worn and will loosen again.

I'd say the BB and the crank arm are dead and need replacement.

To get you home, cut a piece of aluminium off a soft-drink can and wedge it between crank and spindle. Perhaps 10mm by 40mm, and wrap it around the axle then put the crank arm on top. You may need to gently lever the pinch bolt area apart, or reduce the amount of aluminium strip, or even lightly hammer the crank in place with a rock.

Where to get a softdrink can? Roadside litter is your best candidate. Otherwise consider cutting the tail off a shifter cable where it exits the derailleur and using that short stub of wire. May need to untwist some of the strands to get a useful thickness. Aiming for function, not pretty.

Regardless of what you put in the crank/BB interface, the goal is to reduce/eliminate the rotational play that allows each crank arm to move slightly with respect to each other.

Stay seated on any climbs and spin, just in case it does let-go suddenly.

Every time you stop for a break or for the night, check the crank arm and tighten if it has play. I assume you have a hex driver.

Good luck with getting home and remember, this is type-2 fun - the sort you can look back on with fondness but not at the time.

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    The suggestion of an aluminum shim is masterful.
    – ichabod
    Commented Jul 18 at 16:44
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    The ability jerry rig some trash together in order to keep your bike moving is part of why I love bicycle touring.
    – TheLoneMilkMan
    Commented Jul 19 at 18:08
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    "Zen and the Art of (Motor)cycle Maintenance".
    – Mark Morgan Lloyd
    Commented Jul 20 at 14:39
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    The 3004 aluminium in a soft drink can is work hardened - you really want something softer or to aneal the 3004 - it's not that easy to heat to 340 C and then air cool on the side of the road.
    – D Duck
    Commented Jul 21 at 2:39
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    +1 Criticism: spindle is steel so might still be perfect. It's inexpensive but a drag to replace. Idea: ask if anyone has any type of glue.
    – Vorac
    Commented Jul 23 at 16:48
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First of all: get that checked as soon as possible. Not only can it permanently damage your crankset (if it has not happened already) but if the thing goes loose again in the wrong moment, it might result in a crash.

Edit, after you added some more photos: this looks permanently damaged.

The longer answer: this should normally not happen since the interface between crank and spindle is held by form closure. That means that either the teeth, that hold the crank in place with respect to the spindle all ripped off or the crankset was assembled in a way that the teeth did not engage with the spindle and the whole thing was only held by friction.

In the former case, this would be some serious case of manufacturing defect and the manufacturer (both of the bike and the crankset) should be informed about it.

In the latter case (incorrect assembly) this can either mean that the interface between crank and spindle might have survived without damage - then just reassembling the whole thing correctly should solve the thing - or that they have been damaged by your "incident" - in this case you would need a new crankset. (Edit: Again, from your photos I would guess that this will result in a makeshift on-trailfix and a new crankset after your tour).

I would highly recommend to go to the nearest bike shop to get that checked and repaired. If that means you have to cycle there, I would advise you to do that very cautiously since the type of incident that caused this failure might happen again if your on-trail repair did not properly fix the problem but just made it kind of work to limp home the last couple kilometers.

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    Thanks a lot for your comment! I'm trying to find someway to see a bike mechanic but it is not easy since I'm in a remote area right now. I also added some more pictures for clarification. The crank arm comes off pretty easily if I loosen the pincher bolts and it almost looks to me like the "grooves" on the arm are worn...
    – nikostra
    Commented Jul 18 at 9:12
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    @nikostra yes its been run loose for so long that the ridges are all worn down by fretting. Did you not notice rotational play while pedalling over the last few months ?
    – Criggie ♦
    Commented Jul 18 at 10:13
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    @Criggie I don't think there was much rotational play, but in the last couple days I could notice a clicking sounds appearing sometimes while pedaling, that might well be related...
    – nikostra
    Commented Jul 18 at 10:21
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    @Criggie To be fair, that kind of damage can also happen instantaneously. The interface (albeit loose) will hold up until you apply a little bit more torque than it can bear, at which point the hardened steel spindle just shears off all the softer aluminum splines.
    – MaplePanda
    Commented Jul 18 at 10:43
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    Wow, that's not much...
    – Benedikt Bauer
    Commented Jul 18 at 11:41
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Yikes, that crank arm has seen better days. Given your situation and your comment that your drivetrain is entirely worn, I would suggest that you clean the joint as best you can (so that dirt and grease aren’t getting in the way of what remains of the splines), tighten the crap out of the pinch bolts (with the knowledge that the crank arm is scrap anyways, but don’t strip the threads!!!), and finish the ride. Definitely avoid massive sprints. When you get home you’re pretty much replacing the entire drivetrain anyways, so even if you damage the right crank arm by overtightening it’s not really a big deal.

300km isn’t crazy far—that’s what, another 2-3 days at most? I think you’ll be okay. It’s not like you’ve got another 3000km to go. You can figure out what went wrong after you get home. Who last installed the crankset? Regardless, this is also a good reminder to check the torque on all fasteners before heading out on a long journey.

Edit: I wonder if you should intentionally get the interface dirty. Definitely remove as much grease you can to maximize friction, but I’m thinking about whether dirt (ideally fine sand) could act as an impromptu friction enhancer. Might be worth trying.

Edit 2, another possibly dumb idea: if you pass by any convenience stores or whatever, see if they have any superglue or epoxy or anything like that.

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    Thanks for your comment! I'm not 100% certain but I don't think anyone touched the crankset since I got the bike 3 years ago. In that case it would be either on the bike manufacturer (Cube) or on the bike shop that built the bike up for me, right?
    – nikostra
    Commented Jul 18 at 10:25
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    @nikostra To be honest, after three years the onus is on you. Things can loosen up over time, and as I mentioned in the answer you should be checking these critical fasteners somewhat regularly (in particular, also your stem bolts). Yeah, maybe the actual fault lies with the bike shop or whatever, but really at some point during those three years you should have checked that the cranks are tight. It would be a little different if you just got the bike serviced last week before you left or something. For now though, just get home first and you can deal with the rest later.
    – MaplePanda
    Commented Jul 18 at 10:49
  • that's fair! The bike has been to various bike shops for check ups and services and I definitely wasn't aware that this is something I need to be checking but I will make sure to do that from now on. Thanks for the help
    – nikostra
    Commented Jul 18 at 10:57
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    Superglue has essentially no gap-filling capability and is brittle. Epoxy, on the other hand might do something. You'd have to degrease the interface thoroughly, apply Epoxy all over, the mating faces then tighten. Ideally allow to cure overnight, and avoid the fastest setting types of Epoxy. This might mean further destruction on removal; you'll probably lose the spindle.
    – Chris H
    Commented Jul 18 at 11:24
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Whatever you do, walk up steep hills and spin up gentle ones until you get this fixed. No hard sprints on the flat either, and don't stand up on the pedals for a stretch

This is partly to avoid injury if it fails suddenly with your weight on it, but also to reduce stress on the interface. Every time it goes it will get worse and even once more might total it.

Looking on a big screen I maybe have some good news for your trip - only half the length of the splines in the crank arm looks stripped. You can see on the axle as well that the outer half of the splines has aluminium on there. That almost certainly means it was loose for some time, and went when only about 50% engaged. If you're really gentle, the remaining 50% should get you home. You might not even need a new BB.

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What might get you down the road is some JB Quikweld and a bit of prepall. Clean it good with prepall before using the JB Make sure you allow 6 to 8 hours of cure time Expect to have to cut the parts off to replace them when you fix it properly.

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    Good idea - a 2 part epoxy is so versatile it might be worth including a small amount in the travel repair tool kit, along with some fasteners, cable ties, spare inner cables, brake pads, chain, etc.
    – Criggie ♦
    Commented Jul 19 at 0:57
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    @Criggie sturdy cable ties will do for mixing and spreading the glue, using something like an empty snack packet as a surface to mix. But I'd like smaller tubes and medium setting speed. The best I can do is 2x15g (no room for anything else that long in my tool case), either 5 minute or overnight cure. OTOH high temperature JB weld comes as a solid stick that's mixed by kneading. Maybe a slice cut off that would be a good addition (carry disposable gloves), or maybe it doesn't cost surfaces as well as more liquid types.
    – Chris H
    Commented Jul 19 at 6:54
  • You can get smaller, light weight "double bubble" packs of epoxy.
    – D Duck
    Commented Jul 21 at 2:37

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