# Stripped pedal threads on crankarm. Any fix?



## TMR (Sep 24, 2004)

Hello wizards,

My buddy just had the misfortune of having his pedal fall off due to some stripped threads. Crank is a Truvativ Elita. Was wondering if anyone has had success with re-tapping the threads with a male die, and if so, what size. Any help would be great. 

Thanks,

Jon


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## Akirasho (Jan 27, 2004)

Helicoil inserts...

http://www.helicoil.com/products/helicoil.html

Check with your local shops.


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## ianhale (Sep 3, 2005)

*Look out for stress/fatigue cracks*

Retapping with a Helicoil tap and inserting a Helicoil is a good suggestion with one cautionary note, and that is the oversize tap involved removes metal in a highly stressed area and so weakens the end of the crank arm. You can get a red die crack detection kit at a welding supply store for probably less than $20 that would detect a stress/fatigue crack forming long before the end of your crank arm splits and susequently hurts you big time. Checking for stress/fatugue cracks every few months with the red die after the Helicoil repair would be advised.

Helicoiled threads are advertised as stronger in tension than the original threads simply because of the oversize tap creates bigger threads in the parent material and the space between the pedal threads and the new threads in the crank arm are filled with this high strength helical insert. This is fine but it assumes infinite parent material which a crank arm obviously does not have and does not take into account the stress induced in the limited material of the crank arm from the bending moment created by the force at the end of your pedal.

There are lots of bicycle parts on Ebay if you want to buy a new crank arm.


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## Anti-gravity (Jul 16, 2004)

TMR said:


> Hello wizards,
> 
> My buddy just had the misfortune of having his pedal fall off due to some stripped threads. Crank is a Truvativ Elita. Was wondering if anyone has had success with re-tapping the threads with a male die, and if so, what size. Any help would be great.
> 
> ...


If it's the non-drive crank arm, you might want to forgo heli-coiling it. You'll need a left-hand heli-coil, which might be hard to find in that size (I've never seen one). I'd try and tap it first, then if that doesn't work (and it's the non-drive) then I would just look into replacing. If it's the drive-side crank, then finding the right heli-coil might be easier, but as mentioned above, you risk weakening the crank arm. Try and repair the threads first, then use the heli-coil if you desire. We have a set of pedal taps at work, but I can't remember the size (9/16"x20 I think). I don't believe that size is available through a hardware store, so it's probably best to just take it to a shop.


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## Kerry Irons (Feb 25, 2002)

*Hopeless?*

For a situation as you describe it, tapping out the crank is pretty much hopeless. There are no pedals in "the next larger size" and the steel pedal threads pulling out of the crank arm pretty much removed all of the thread metal in the crank arm. Running a tap in there will still not give you enough thread for the pedal to grab. The only hope is that the pedal had nearly completely unthreaded from the crank before coming out, leaving adequate threads for the majority of the thickness of the crank arm. The helicoil suggestion is your only hope, with all the concerns raised about stressing the metal to be considered.


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## Dave Hickey (Jan 27, 2002)

TMR said:


> Hello wizards,
> 
> My buddy just had the misfortune of having his pedal fall off due to some stripped threads. Crank is a Truvativ Elita. Was wondering if anyone has had success with re-tapping the threads with a male die, and if so, what size. Any help would be great.
> 
> ...


The old Dura Ace AX cranks had an oversize pedal spindle. There was a company that sold an adaptor that converted the cranks to accept a standard spindle. I can't remember their name but I see the adaptors on eBay all the time...You'd have to drill out the crank and tap it for the oversize Dura Ace AX pedals and install the adaptor.

It is a lot of work but it would work....


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## ianhale (Sep 3, 2005)

*Alternative to Helicoils ?????*

9/16"-18 (threads per inch) right hand seems to be the common Helicoil size and not 9/16-20. 

An alternative I have seen is a thread restorer kit made by Loctite that has a two part adhesive for the crank arm and a mould release coating for the pedal threads. Loctite claims to be able to repair internal treads to hold grade 5 (125,000 psi tensil stress) steel bolts. A good auto store shoud have the Loctite stripped thread repair kit for less than $10. The advantage of this approach (beside the fact that it actually exists) is that you are not weakining the end of the aluminum crank arm. It might not work because of the high bending moment placed on the new plastic threads from the end load on the pedal. Check to see if the repaired crank arm threads are holding pedal thread torque before and during each ride.

The reason that plastic threads stand half a chance is because it is flexible and distributes the tensil force of the pedal threads over the entire lenght of the threads. In the original aluminum the tensil force of the steel pedal shaft is taken up in just the first 2 or three threads.


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## Mel Erickson (Feb 3, 2004)

Good replys, all, but I'm amazed no one suggested simply replacing the crankset. Looks like Nashbar has a Truvativ Elita road double for $75. By the time you monkey around with some of the suggested solutions you've probably got just as much invested and what do you have? A used crankset that may or may not stand up to the fix and may or may not have a short lifespan. If it were me I'd buy peace of mind by buying a new crankset.


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