Crank arm keeps becoming loose!

Alanstrainor

Hey guys, i'm having some trouble with the crank arm on my Giant FCR4. It's gotten to the stage where i have to tighten it every 10kms or so or else it becomes loose. It seems no matter how tight i tighten it, it still manages to become loose.
Does anyone know what's causing this, and what part/parts im going to need to buy to sort it?

lescol

That'll be the left crank arm? Does your bike have a square taper fitting? Have a read of this:- http://www.sheldonbrown.com/brandt/installing-cranks.html

Probably the easiest solution is to replace the crank.

kenmc

it sounds like the fit has deteriorated over time cos it was loose - the play in it would cause a bit of wear and tear and hence it doesn't fit properly onto the bottom bracket axle. I'm presuming a square taper like my fcr2 - the bolt is really just to force it onto the spline and hold it in position - if this bolt becomes loose as it did, then you'd get some play in that interface, which would cause it to become worn, thus self-propogating the problem. You could try to use plenty of threadlock on the bolt and see if that helps at all - though I suspect it won't do too much good.
If this is the case then you'll likely need a new bottom bracket and crank(s).

Alanstrainor

lescol wrote: »

That'll be the left crank arm? Does your bike have a square taper fitting? Have a read of this:- http://www.sheldonbrown.com/brandt/installing-cranks.html

Probably the easiest solution is to replace the crank.

Cheers for the quick response.

That sounds handy enough, you are correct it's the left crank arm that's in trouble. And yes it's a square taper fitting.
It's new crank time i think, does anyone know anywhere in Dublin city centre that would sell one? And roughly how much?

EDIT: Here's hoping i don't need to replace the BB and the right crank arm!

lescol

It's unlikely that the square axle will be damaged. Keep trying bike shops you may find one with just what you need lying around. Try asking on here, I know I have an old square taper chainset around...somewhere, I think it's 170mm, you'd be welcome to the left crank if it is suitable, but I'm in Kerry. You can buy a left crank online from St John St Cycles:- http://www.sjscycles.co.uk/cranks-left-dept895_pg1/#page=1 if all else fails.

doozerie

For info, when fitting the new crank, grease the square taper on the axle and also grease where the washer on the bolt rests against the crank and bolt head. Press fit parts strictly require grease on mating parts to allow them to be tightened sufficiently (without damage). You may well get away with them ungreased (and I have done for years myself through ignorance rather than any good reason), but it'll increase the risk of damage. You need to apply a lot of torque to crank bolts too.

tomasrojo

If you've whacked the pedal off anything lately, that can lead to the crank constantly coming loose.

Happened to me a few years ago. I had to replace the crank. I can't remember whether I replaced the bottom bracket spindle as well (it was an old-style three-piece bottom bracket), but I think I did.