Bicycle Mechanics - Stripped Crank Arm Threads, now what?

Hey,

As of today, I'm a proud owner of a new (to me) Paramount from the '90s. When I got the bike back home, I switched out the pedals (from cleated to platform) and was disappointed to see that the right crank arm's threads are stripped pretty badly on this newly acquired bike. Once out, the other pedals will not go back in even, and would not stay in at all. At this point, I'm concerned that I'll have to replace the whole arm, which seems silly given it's just some stripped threads.

At this point, would you try to unbuy this bike? I would hate to do this, as I'm really ready to love this bike -- my first road bike. Or do you think this kind of thing can be fixed easily enough? If so, should I take it to a standard bike shop or would you take this to some kind of a metal/drill shop? I'd run it over myself to have them take a look, but the closest good bike store is about an hour from where I live, so I wanted to run this by you all first. I appreciate your help with this.

Best,
Andy

Are you sure that removal didn't strip the threads? How hard were the old pedals to remove?

The right side crank is right threaded (i.e. not reverse) so it should be possible to find a threaded insert for the crank arm (e.g. a Helicoil). The threading is 9/16" x 20.

There are both Helicoils and threaded inserts available to solve this problem for either crank arm.

Regardless of causative factors - if they are stripped: New crank-arms. Assuming you want mint - on a Paramount, I would. End game.

I'm not sure I'd rely on a helicoil for pedal threads. Something relatively stationary, like a derailleur bolt, no problem, but I'd replace the cranks.

I'm not sure I'd rely on a helicoil for pedal threads. Something relatively stationary, like a derailleur bolt, no problem, but I'd replace the cranks.


Done right, a helicoil is just as strong as original.

-R

Done right, a helicoil is just as strong as original.
Absolutely. And nobody but you and your mechanic need know (until if/when you decide to sell it, anyway -- then full disclosure should be done).

Done right, a helicoil is stronger than original.

-R

Fixed. Some alu cranks come stock with steel inserts for this very reason.

Absolutely. And nobody but you and your mechanic need know (until if/when you decide to sell it, anyway -- then full disclosure should be done).

I think I'm at least partially at fault here, as the threading flaked off as I was unscrewing the pedal. However, I spoke with the guy I bought the bike from, and he had said he had run into this same problem previously and just had it re-thread. So I guess the full disclosure was lacking.

Either way, I wouldn't mind replacing the crank arm since it appears this has been a recurring problem and similar arms are pretty cheap on e-bay. The only thing is it's a discontinued line and I'm having a hard time finding an exact copy. Do you guys have any suggestions for this? It's a Shimano 600 fc-8400.

I really appreciate all your thoughts. On an off chance -- I'll be getting this repair done in Greensboro, NC. Does anyone know a good mechanic there?

Thanks much.

You must mean FC-6400. I've got that crank on my late 90's roadie. There are a few available on eBay

I would still go with the helicoil.

You must mean FC-6400. I've got that crank on my late 90's roadie. There are a few available on eBay

Yup! I need my eyes checked. Thanks. I'll try to have someone re-thread using the helicoil, and if that doesn't work I've got a backup. Thanks for all of your help.

Yup! I need my eyes checked. Thanks. I'll try to have someone re-thread using the helicoil, and if that doesn't work I've got a backup. Thanks for all of your help.

Good! Solutions and discussions like this show the REAL value of BF.

It would be a shame to chuck out an otherwise fine crankarm. If you don't want to go the helicoil route, there used to be small parts available called cranksavers made especially for stripped pedal threads. The cranksavers were akin to larger chainring nuts (smooth on the OD, threaded on the ID); you drilled the pedal holes to the correct diameter, then inserted the cranksavers through the backside of the crankarms. The pedal would then go on as normal. I'm not sure these are still being made, but if they are, it is another option for you. Luck.

Done right, a helicoil is just as strong as original.

-R

+1.

I have a close personal friend to whom I sold an S&S equipped tandem for foreign vacation trips. He's unusually tall so he wanted 180mm cranks which, at least at that time, weren't available in Ultegra. The solution was DA but, since this was on the front of a tandem, they had to be swapped side-for-side. Santana converted them via helicoil or something similar. I'm not sure if he removes the pedals or the whole crank arm when he packs it into the big suitcase but that was 10 years ago and the couple is still riding that bike with no problems. I'll probably do a 35 miler with them this Friday.

Here is one source for the helicoils: http://www.biketoolsetc.com/index.cgi?id=92531081272&d=single&c=Shop-Aids&sc=Thread-Repair&tc=Complete-Kits&item_id=BI-916K

Here is a second version: http://www.biketoolsetc.com/index.cgi?id=92531081272&d=single&c=Shop-Aids&sc=Thread-Repair&tc=Complete-Kit&item_id=EL-2299