Crank arm replacement for an idiot

[acbenson]

Hi,

I would if anyone could help?
sometime ago, I clipped a kerb with my nearside (to kerb) pedal, resulting in this crank arm falling off.

Since then I have been unable to get the arm to stay on the bike, as I pedal the nut holding the arm in place loosens, the arm begins to wobble and the pedal/arm falls off :-(

I have 3 parts, in the pics attached, crank arm, nut and the hub. what I am missing?

Thanks
Tony
[attachment=1480][attachment=1481][attachment=1482]

[JonB]

If you fit the crank arm (without the nut), can you wiggle it off the spindle with your hands?

If so there's your problem:
you've killed the crank arm.

[acbenson]

i wouldnt say wobble with my hands at all, fits quite nicely really...

in fact this is a new crank arm, I figured the original must be shot after its unexpected meeting with the kerb

Tony

[DaveM]

If you're tightening the nut down at all firmly and the arm still falls off like that, the crank arm itself is probably damaged. It could be the BB spindle, but since those are steel, they're much harder to damage than the aluminum crank arm. You might try putting your old one back on just for comparison. A curb strike might not have actually done anything beyond cosmetic damage to it. But riding a loose crank arm very far will damage it very quickly.

[trevgbb]

look at the square on the crank arm from the back, if this looks at all bell-mouthed it will need replacing as it will never stay tight again.
It needs to be nutted up very tight the first time it is fitted and never ride with it loose, as this will keep happening.

[Ro-Ro]

i have the same problem with the second and third picture....i think they're stripped because when i ride it wobbles n falls off.....ive tried wrenching the nut back onto it as tightly as i can but when i ride it goes back to wobbling.....my brother in law[[i think]]said that it was stripped. Im wondering like how to fix it? any answers

[trevgbb]

(10-03-2010, 04:03 AM)Ro-Ro Wrote:  i have the same problem with the second and third picture....i think they're stripped because when i ride it wobbles n falls off.....ive tried wrenching the nut back onto it as tightly as i can but when i ride it goes back to wobbling.....my brother in law[[i think]]said that it was stripped. Im wondering like how to fix it? any answers

See my previous answer, it is rare for the axle itself to be the problem as this is heat treated steel and you can easily see if the axle thread is stripped, but I would always replace the nut as well as the crank arm, note if you buy a new crank arm, make sure the length of the arm and the orientation of the the square is the same as there are 2 types.