Rounded Crank Arm Bolt

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  • Rounded Crank Arm Bolt
  • Premier Icon wwaswas

    hammering a torx tool into the hole is the next choice as the sharper edges help create their own grooves to bite into.

    Make sure the other crank arm bolt is well done up (nor rounded!) so that the bolt you are trying to undo is not under tension from the two bits of crank arm it holds together.

    also, if there was threadlock on the bolt when you did it up then heat the area it’s in up with a paint stripper gun so that the threadlock breaks down a bit.

    I’ll have a go with the Torx tool.

    Any advice on size? i.e. next size up from the allen key i’ve been using?

    Does the hammering wreck the tool?

    No threadlock fortunately, mainly since I don’t have any of that.

    Premier Icon wwaswas

    Does the hammering wreck the tool

    ‘it depends’ really.

    I think you should be prepared for it to as the splines aren’t that strong but you may get away with it.

    as for size – pick one that doesn’t quite fit in whatever rounded mess you currently have 🙂

    Premier Icon Northwind

    Best bet is a seperate torx bit from a screwdriver set, rather than a bigger handled tool- easier to hammer in, and more disposable.

    Are you absolutely sure you need to get the cranks off? Best option is to do so obviously but it’s often possible to thread a middle ring over the arms.

    Premier Icon wwaswas

    Something like this is ok, and disposable;

    Definitely have some of those little fellers hanging around. I’ll try and knock one in tonight.

    It did cross my mind to try and get the ring off the other side but the cranks feel a bit stiff when they spin. I put a spot of grease on the spindle when I put them in last time, not sure whether I shouldn’t have, or whether I should’ve put a lot more in. Hence thinking that it might be best to get the crank arm off and have a proper look at what’s going on.

    Hooray for amateur mechanics :/

    Edric 64

    Stiff cranks may be too much pretension before you bolted the cranks up ?

    Thread title says it all really.

    For reference this is a Shimano Deore XT Hollowtech crank.

    Looks like a combination of cheap/slightly wrong sized allen key in the hex bolt and also a little over-tightening. Needless to say the hole is well and truly rounded. Lesson learnt for next time…

    So i spent most of last night trying to find out the easiest and cheapest way of fixing the issue – I need to get the crank arm off to replace the middle ring on the other side. The cranks are also stiff to turn making me think that I did something wrong last time i put them back together.

    I’ve seen 3 possible options for fixing:

    – Buy one of those tools that screw into the knackered bolt and allow you to back the bolt out. This sounds a bit fiddly and from what I can see from googling, the bolt is liable to break if not done right leaving you with a hardened steel bolt in the middle of whats already knackered.

    – Make a groove in the bolt so that a flathead screwdriver can be used to undo the bolt. I’d be up for giving this a go but the bolt head sits inside the crank arm and I don’t think I have the necessary tools (dremel?) to make the groove unless someone can suggest an alternative?

    – Epoxy an Allen Key into the hole, leave to set for a number of hours and undo. Seems to me like it could be the least hassle route, although I’ve not done anything with epoxy before. Does this generally work or am I likely to be left with an even bigger mess than when I started?

    I’ve also tried to hammer the next size allen key in but the keys I have are way too big.

    I’d prefer to keep it out of the bike shop unless it’s going to be significantly less hassle than me doing the work but at the same time, I’d prefer not to shag the cranks.

    Anyone have any experience of doing this? Can you point me in the right direction please?!

    While we’re at it, I’d really appreciate it if someone can suggest a reasonably priced torque wrench/tool – I’ve not bought one before but think I’d be looking for 5nm to 20nm to handle most of the things on the bike (seems like the only thing above 20nm is the BB which needs 40nm but that’s bike shop territory for me atm).


    EDIT: Appreciate this has been covered on the forum beforehand. Just need a pointer on the easiest way to fix which other threads seem to differ on, depending on crank type.

    Is the Pretension adjusted on the BB or something to do with the crank?

    I tightened the BB using a special spanner as I presumed tighter is better. Can’t see anything on the crank which would allow me pretension anything

    Premier Icon wwaswas

    have a read of this;

    It’s the little plastic ‘hat’ in the end that we’re talking about – it shouldn;t be too tight.

    Thanks. Yup – That plastic thing was really tight when I went to undo it last night.

    I don’t remember doing it up that tightly as the guide I read said finger tight but will be extra gentle next time round.

    Fingers crossed I can slide the middle ring off the other side and ignore the rounded bolt issue for a bit longer!

    Premier Icon wwaswas

    That plastic thing was really tight when I went to undo it last night.

    you might find that having the crank arm bolts done up tight puts pressure on the plastic bit and makes it appear tighter than when you put it on.

    I wouldn’t leave that bolt too long – it’s not going to get any easier to take off 😉

    Haven’t been successful removing the bolt, despite trying the torx tool and epoxy.

    Looks like I need a T35 tool and only have T40 or T30 and epoxy wouldn’t set (one of those cheapish unibond syringes).

    Going to have another go tonight banging a flat head screwdriver into the hole which seemed to be the only thing with any purchase.

    On the bright side, I managed to get the middle ring off the drive side crank meaning I could still go out for a ride on Sunday.

    I’ve also got so many replacement bolts I’ll never have to worry about them rounding off again because I’ll be able to replace immediately. If anyone needs a couple of replacement bolts let me know, I’ve got 50!



    Happened to me, the bolts are crap so now I always replace them just to make sure.

    I had to drill mine out. good luck



    Happened to me, the bolts are crap so now I always replace them just to make sure.

    I had to drill mine out. good luck

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