Bicycle Mechanics - Is this crank toast?

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Ganesha
09-11-05, 08:54 PM
Or more specifically, are the threads on this crank usable?

I was riding along toady and all of a sudden my pedal bends and get stuck at about 10-20 degrees above its normal position.

Anyway, I get home and undo the pedal with a pedal wrench. With effort I can still thread the pedal into the crank and it seems to seat, but I'm skeptical if they will stay together under load.

The threads on the pedal look fine.

http://homepage.mac.com/william_wu/.Pictures/crank.jpg

AndrewP
09-11-05, 09:03 PM
I dont think they will take a load. Go to a well equiped bike shop and ask about helicoil inserts. If they have the tools to do this it would be a trustworthy solution.
gmason
09-12-05, 01:51 AM
It looks as though the pedal was only half inserted (or less) when it failed. True?

Retro Grouch
09-12-05, 03:58 AM
Well, you can always replace the crank later if you need to. If it was my bike I think that I'd try the cheapest solution first. I'd run a pedal tap through from the back side to clean up whatever thread is left and see how it goes.
Ganesha
09-12-05, 03:14 PM
Well I first felt the pedal start to go, to pedal was 1/2 inserted, couldn't have been like that for more then a week, since I have pictures from last week that clearly show the pedal was fully inserted.

Anyway started with the cheap (free) solution and had the the LBS and had the LBS run a tap though it.

I'll see how it holds together for the next few rides.
crgowo
09-13-05, 01:10 PM
Well, you can always replace the crank later if you need to. If it was my bike I think that I'd try the cheapest solution first. I'd run a pedal tap through from the back side to clean up whatever thread is left and see how it goes.
Pretty much what I did when the exact same thing happened on a friends bike. But I instead of a tap I just used the pedal. Screwed it in on the back inside of the crank all the way in to clean out the outer threads then put the pedal in the correct side. Never had a problem since.
poopncow
09-13-05, 10:03 PM
Some old machinists used to tell me that 7 turns (of thread) is all you ever need. Not sure how true.

College story: A hand me down bike had the pedal striped completely off and brazed back on ! (b4 being handed down to me) . 2 years of service and then the pedal came off on the climb at the very northern tip of Central park. It took a while to limp back to the lower east side :)