drafters65

The first time it fell off I thought It was because I forgot to screw or tighten the nut on the crank after taking it off for polishing but this time I'm positive that I tightened it to or exceeding the recommended torque spec. I've done a search and I might have idea of what it could be but I just want to make sure so I've posted some pics of the BB and the crank.



I couldn't get the point and shooter to focus on the taper





It got chewed up after a taxi ran over it after it fell off the first time....=T

Well what do you guys think? Let me know if you need pics in a different angle.

operator

Pics don't load.

If you're positive it was up to torque spec 30+NM, then most likely your crank is shot. Left, square taper arms are readily available in differeing lengths 165mm-175mm. Also note that there's different rotations of the square on the spindle itself. e.g diamond/square Keep that in mind when purchasing a replacement arm.

JohnDThompson 

No pictures visible, but if it got "chewed up" you'll probably need to bite the bullet and replace the arm, especially since it has already fallen off on its own more than once.

DannoXYZ 

Here's the link to Park Tool's recommended torque-values for most bike-components:
https://www.parktool.com/repair/readhowto.asp?id=88

Notice that crankarms are in the range of 25-35 lb*ft (34-47 Nm). The manufacturer will usually give you the torque-specs for any particular model in the manual. Typically you only have one chance to install the crankarm to its proper torque; the very first time only. If it loosens just once, the taper in the crankarm can get mangled and it'll NEVER EVER fit properly again, even IF you tighten it to proper specs. There are rare cases where the rider's sensitive enough to detect a loose-crankarm and stops immediately to tighten it up and manages to save the crankarm. But you gotta do this within the 1st 1/4-mile or so or else it'll wobbled too much and gotten damaged.

It sounds like the arm got pretty messed up the 1st time, it's not surprising that it didn't hold upon re-installation. What torque did you tighten it to if you knew you exceeded the recommended spec? You'll need a new crankarm now anyway.

drafters65

weird because I can see the pictures myself....hmm lets try this link
https://mail.google.com/mail/?ui=2&ik...3f13&disp=imgs

drafters65

thanks operator, JDT and Danno. Its too bad the pics aren't loading to confirm but from your answers and reading some similar threads I kinda knew that the crank arm is shot. Brightside is now I'm justified to get a ss/fs crankset.

DannoXYZ 

Pics don't load because BikeForums needs to log onto Gmail in order to retrieve the picture. Better to upload to a picture-hosting site like PhotoBucket.com.

drafters65

thanks...alrights lets try this again.

DannoXYZ 

Looks like there's some slight gouging of the taper in that 1st picture. I would clean up both the taper in the crankarm and the spindle with acetone and remove all traces of dirt & grease. Then apply a drop of oil to each side of the spindle and install the crankarm. Use a new bolt with blue Loctite and a star lockwasher. Tighten it to 35 lb*ft (47 Nm) with a torque-wrench and see if it'll hold. At this point, you've got nothing to lose really.

BTW - hold onto the other crankarm when using the torque-wrench...

DOS

+1. Might be worth replacing the bolt (or nut depending on the spindle) before giving up on the crank arm. Problem could be a defective bolt/nut that keeps working itself loose rather than damage to arm itself. That said, the problem may have started as one with the bolt/nut but that problem could very well have resulted in irreparable damage to the arm itself. Still, replacing the nut to see if a new one oholds seems like the way to go.

drafters65

I replaced the nut the first time it fell off since i didn't know when it fell but i will definitely try the methods mentioned. I'll let you know guys know how it turns out. Thank for all the help guys.