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Stripped pedal threads

Old 07-05-20, 12:44 PM
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IceNine
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Stripped pedal threads

I'm working on two bikes, my own 1984 Raleigh Portage, and a 1986 Trek Elance 300 for my daughter. The Trek came with a slightly cross-threaded left crank. We cannot get the pedal to thread correctly. We tried going in from the back to see if that would help, but the pedal didn't go far enough to get to the section where the threads are damaged, right at the front. It feels like it is cross-threading when we attempted to attach the pedal normally. It gets started and then gets difficult to turn.:

I also managed to really bugger the right pedal thread on my Portage. Really a shame because this bike is in nice condition, is a unique and valuable vintage bike, and has original cranks on it, and I'd love to salvage them. It is stripped so bad that when I was turning the pedal wrench, it was just spinning around without coming out. I had to apply some pressure between the crank and the pedal to get it to start backing out.





I have some bike wrenching experience, although obviously I screwed things up stupidly on the Portage. I do have crank pullers and other assorted tools. I don't however, have any taps. It looks like the most recommended option is something like the unior tap + bushing. I also see some 9/16" taps on Amazon for $20. Would that work for the less stripped crank? Could a person put some jb weld on the inside of the really buggered crank, and then just use a 9/16" tap?

Edit to add: there used to be a bike coop in Madison where I took a couple of classes in days gone by, and they were open to people coming in to use the tools to work on their bikes, in exchange for some parts or whatnot. I don't know if they are still doing that these days, but I could check out if they are still doing that these days.

Last edited by IceNine; 07-05-20 at 12:55 PM.
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Old 07-05-20, 01:25 PM
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Juan Foote
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On that upper one would probably just chase the threads with a tap and see what's left. Unless there is a value there beyond what I am thinking, would probably choose a decent popular pedal and loctite it in place after the chase if there is enough good meat left.

As to the other one....that is pretty damaged. I have no idea what the metal strength as to the size of the hole on the crank arm...in relation to a helicoil or bushing. I see no other reversible way to deal with that though. Is that crank something you can find?
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Old 07-05-20, 01:56 PM
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Both of those cranks could be repaired by Heicoil or Unior inserts.
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Old 07-05-20, 02:14 PM
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Originally Posted by dsbrantjr View Post
Both of those cranks could be repaired by Heicoil or Unior inserts.
I get that. My question was could the less severely damaged one be fixed with just a 9/16" tap, and could the more severely damaged one be fixed with jb weld plus 9/16" tap. I'm trying to be as frugal as possible until the pandemic subsides.
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Old 07-05-20, 02:32 PM
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Originally Posted by IceNine View Post
My question was could the less severely damaged one be fixed with just a 9/16" tap, and could the more severely damaged one be fixed with jb weld plus 9/16" tap. I'm trying to be as frugal as possible until the pandemic subsides.
It depends on how much good thread is left. Taps can't restore missing material, but they can clean up a damaged area enough to allow engagement with undamaged threads. I wouldn't count on JB Weld to be strong enough to be a long term solution. And be aware that for the non-drive side arm, you'll need a 9/16" x 20tpi left hand tap.

The best long term solution is either a helicoil or bushing, or replacement of the damaged arm.
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Old 07-05-20, 03:01 PM
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Tooling for helicoils is a little more money than I'd spend on those cranks. The actual insert itself is cheap and if you have some experience you can fabricate your own tooling to install it. But if you want to salvage them, that's the way to go.

If you don't feel comfortable with DIY, you might can find a local machine shop that will do it. I'd want the crank arm held securely and drilled with a drill press or vertical mill so there wouldn't be any slop from wobbling around with a handheld drill and so the hole drilled will be more accurately perpendicular to the crank arm.

Don't forget one is likely to be left threaded. And no, you can't just put the helicoil in upside down. <grin>
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Old 07-05-20, 03:21 PM
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https://www.ebay.com/itm/Vintage-Tag...wAAOSw3blfAhke
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Old 07-05-20, 07:52 PM
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Thank you. This probably makes the most sense for my buggered crank.
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Old 07-05-20, 07:58 PM
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I'm sure Yellow Jersey in Arlington would also be able to helicoil/tap those out.
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