Bent cranks?

Hi,

Not sure if anyone will be able to help but bought a bike off here and have been finding that on longer rides the right hand crank works itself loose from the BB - only gradually, say over 3-5 miles or so, but eventually it's completely loose. To date I've been tightening it up after each ride but obviously this isn't the best way to go about things. I guess that the crank arm is slightly bent, meaning that in pedalling I'm forcing it off the BB, but would appreciate any thoughts...

Thanks for looking.

My thoughts would be: it could've been damaged or it could have been incorrectly installed and now it is damaged. No way of proving either way now since you've probably repeatedly under-torque it and the tapers are probably fucked.

Thanks - so it's off to the classifieds...

Was it sent in a box?

Fruit sent me a bike in a box and they clearly dropped it at some point and slightly bent one of the cranks, was ok in the end just needed a little heating up and bending back.. Good as new.

Sounds like you've fucked the tapers on yours though - I take it that you've tightened the shit out of it? You need to put some serious torque into that - it could also be that the bottom bracket is the wrong width and so you're just tightening onto the cups—are the cranks really really stiff to start with before they get loose?

Assuming it's square taper, it sounds like it was under tightened, and has rounded off over time. Solution is to replace the crank arm.

Take it to your local bike shop to be sure.

All - thanks for the tips. Wasn't sent in a box and from the above and sheldon etc. think it's the tapers. I've tightened it with a bog-standard allen key as much as I can - will see if I can put any more on it this evening. It's not on the cups BTW.

Thanks all

If it's already worn, there's no saving it. time to replace.

i suffered a wall collision, now something is bent.

i want to know how to sus whether it is the pedal spindle (best option) crank (worst option) or bb spindle (alright option). it was a flint wall and i kind of side swiped it, and now you have the weird feeling of something being bent (not me, but for the right cash...). so, for the pedals i can just swap it for a another one right? any ideas how to check the crank and bb bentness or not?

remove pedal, hold the pedal in your fingers and spin the axle, you'll feel if its bent as it spins in a weird way.

bike upside down and spin the cranks. look directly at the crank bolt on one side then the other and see if it simply rotates like it should or if it moves in an exaggerated circle. if it does look weird then it'll be the bb axle. not sure how youd check the cranks other than eyeing them very carefully along their length for twists or deformations and comparing one side to the other (very unlikely to bend both in one go). nice one for spotting there was somethng amis though. people can go for ages without noticing anything like that. maybe go to drinks and let a select few (pre drink) ride it and see what they think. i reckon id be able to rule out one or two things simply by riding/looking. sometimes its best to let mates have a look too and see what they think.

by the way, do you use clips and straps? if so, check that its not the cage of your pedal thats bent cos that could give you a funny feeling while riding too.

sorry its not better advice.

nah that was good thanks. i have swapped the pedal for another one i had lying around, and it seems to be better, maybe still a little bit but i cannot remember the history of this pedal so it may be duffed up a bit. i am using platform pedals and restraps. i compared the distance between the end of crank and chainstay on both sides, and it was the same, will check the bb spindle and eye the cranks closer tomorrow.