Crankarm coming loose

Macka

Well-Known Member
Hi,
My (non drive side) crank arm bolt occasionally (every 100miles or so) comes loose. It is a square taper BB so has the bolt screwing into it to hold the crank arm in place.
Is there anything I can do to stop this happening...threadlok etc.
I am aware of it so it is checked regularly.
Thanks in advance
 

GrumpyGregry

Here for rides.
This is one of those problems best avoided rather than fixed.

Once the crankarm becomes loose it can deform and become impossible to tighten up permanently again learned article about same here
 

Renard

Guest
I've seen it happen with nice Race Face cranks on a mtb and no matter what was done it kept recurring. If I was you I would try thread lock but start saving in the meantime for a new crankset.
 

kyuss

Veteran
Location
Edinburgh
Yep, sounds like it's goosed. Once it's ridden loose the taper on the crank arm 'rounds off' making it impossible to tighten back up properly. Time for a new crank unless you want to bodge it. I had a similar thing happen on an old MTB of mine that I fixed by shimming out the corners of the taper on the crank with bits of razor blade (coke cans might work). Worked a treat. Lasted about 2 years before the whole bike went in the bin.
 

swee'pea99

Legendary Member
Um, before you start doing anything major, perhaps you could try a couple of cheapo solutions that may or may not help. First off, it's possible that you've somehow got grease into the thread of the BB axle and/or fixing bolt - the first thing I think I'd do is use a cut down toothbrush and neat fairy liquid and boiling water to make sure both are as squeaky clean as it's possible to get them. If that didn't cure the problem, I might try to get a split-washer to see if that might stop the thing unscrewing itself. If neither of those worked, then I guess I'd start thinking about something a bit more radical. 
 

betty swollocks

large member
Is it newly put on?
They have a habit of loosening slightly for the first few rides after.
Keep on screwing it on with a nice long allen key for the leverage and eventually it'll stay.
You did grease the taper didn't you? You should.
 
OP
M

Macka

Well-Known Member
Hi,
Thanks all for the advice.
The actual crank arm isn't coming loose just the bolt.
I think (as mentioned before) is that the bolt had been greased so cleaned it all yesterday and will see how it goes.
May add a split washer as well.
Cheers All
 
Hi,
Thanks all for the advice.
The actual crank arm isn't coming loose just the bolt.
I think (as mentioned before) is that the bolt had been greased so cleaned it all yesterday and will see how it goes.
May add a split washer as well.
Cheers All
Use some Loctite Threadlock (on the bolt, not the square taper!)
 
Bolt coming loose but not the crank? How very queer. Without wanting to state the bleedin obvious it sounds like the bolt is not being re-tightened enough. Is the bike still under warranty? If so it aint your problem, take it back to the shop.
 

threebikesmcginty

Corn Fed Hick...
Location
...on the slake
When I was on holiday recently a local cycled past us and as he did the crank and pedal fell off his bike - he then bashed it back on with a piece of wood but he'd done so with the pedals now both in line. Nice little comedy cycling moment. :smile:


As you were...
 
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