Bicycle Mechanics - stripped crank

i was riding uphill and somehow my pedal came off and stripped the inside of my crank....it came off with threads. That is the pedal had its own threads as well as the cranks threads, which fell off as soon as I took the pedal out. So now the inside of the crank arm is threadless and there is no way for me to screw in the pedal. I was wondering if there was something I can put in there without changing the entire thing. Other then welding I mean...maybe there is some paste or something I can put in there that can bind the two metals to each other. But it has to hold good enough for me to do some mountain biking once a week or so.

A threaded insert like a Heli Coil may be able to do the job. Which side is it? It will be tough to find a left-hand thread Heli Coil, maybe if you have a bike shop in the area with a really good service dept they have heli coils in stock.

There are thread repair epoxies available but I would not trust them for any application where there is a load like a pedal or where you want to take the part off again.

If it was me, I would be shopping for a new crank and making sure the threads are properly greased and properly tightened.

if you know some one in the tool maker or something along those lines business, they could probably re-thread the thing for you.

but if you re-thread it, will the pedal still fit?

i checked out heli coils...looks very promising, but prolly wont be strong enough to keep the pedal in...is there something to keep the pedal permanently in place there? i dont care if it comes off or not.

What makes you think the helicoil insert isn't up to the job? Is it a steel helicoil in an alloy crank?

If the threads pulled out that easily, something tells me that there was already a helicoil on that crank. Threads wouldn't pull out neatly. They would shred, leaving shrapnel inside the crank. Is this a bike that you bought used?

If installed properly the Heli coil will be stronger than the original aluminum threads. Many many times stronger than any magic epoxy fix.

Consider that the aluminum part of the joint is now a larger diameter and therefore has more surface area to support the threads. Also, the threads that the pedal holds against are now steel and are far less likely to wear or break.

If installed properly the Heli coil will be stronger than the original aluminum threads. Many many times stronger than any magic epoxy fix.

Consider that the aluminum part of the joint is now a larger diameter and therefore has more surface area to support the threads. Also, the threads that the pedal holds against are now steel and are far less likely to wear or break.

Absolutely. We actually use heli-coils in the cylinder heads of our race motorcycles; we have the heads on and off so often that it prevents the cylinders from having their threads weakened/ruined. If they can survive combustion chamber pressures...

There is another brand (or two) of this type of thread repair. The one that comes to mind is Thread-Sert. (I think that's what it is... Or is it Time-Sert?)

In any case, to go this route, you will need a kit. It will have the proper drill bit, a tap, the insertion tool, and a few coils. While not super expensive, they're not exactly cheap, either. I would call around to different machinists and also any real race shops (motorsports). If they have the size you need, they may be able to just do the job for you for less than the kit cost.

The size you are looking for is 14-1.25 (14mm diameter with a 1.25mm thread pitch). I gots the measurin' tools, so ah reckoned ah'd yank a pedal off ma bike fer ya' ;). When you call around, be sure sure to specify whether it's a left-hand or right-hand thread... Luckily, this also correlates to the right and left-hand sides of the bike.

You also might want to consider ebay... For a similar price of a repair, you might score a good crankset, and get spare chainrings as a bonus. Maybe even a better crankset!

As for the cause of your malady, it sounds like someone in the bike's past either over-torqued the pedal or tried really really hard to loosen it in the wrong direction.

Epoxies? I won't say that they wouldn't work, but I personally would not trust them for a pedal. Besides, you could risk injury if the epoxy let go at the wrong time.

FWIW,
-Erik

If the threads pulled out that easily, something tells me that there was already a helicoil on that crank. Threads wouldn't pull out neatly. They would shred, leaving shrapnel inside the crank. Is this a bike that you bought used?

I have had, on more than one occasion, that very thing happen. The screw comes out of the hole with a very neat spiral of aluminum in the threads and the hole is left surprisingly clean and smooth. I have never had a Heli Coil fail... yet.

yeah i bought the bike used and brought it up to par, but i ride hard..you know...so things like this happen. + i keep my bike outdoors so components tend to wear out more easily.

i will try helicoils, but i was looking more in terms of a cheeper solution that will just take care of the problem for now, and in about a month or so i will find a permanent solution.

thank you for all your help.

Is it the drive or non drive side. Many LBS will or may have some non drive arms laying around they will let go for pennies.

i'm a weight weenie, but i agree with him ^^^^^^^^