Partially Stripped Crank Thread - OK to Use?
 

I was swapping the pedals out on the Schwinn Super Le Tour I bought at the local bike swap a couple of weeks ago. The non-drive side pedal took a great deal of effort to extract, and a fair amount of the threads came out with it. It could have been cross-threaded in there. It’s hard to be sure. There really aren’t that many threads left in there, but my new pedal did thread into the space, and it seems tight, (though I certainly didn’t crank down on it once it was snug). Since the force on the pedal is not really horizontal, I would think it would be safe enough to use, but I thought I would check on the collective wisdom here. What do you think? The pedal is the original one I removed.
https://cimg4.ibsrv.net/gimg/bikefor...4343869385.jpg
https://cimg5.ibsrv.net/gimg/bikefor...7b91e0aaba.jpg

What is partially stripped there? That whole thing looks chewed up and spit out. I would not trust it. You could potentially put a helicoil in there and make it work but as it stands I wouldn't use the crank looking like that. I would just get a new crankset if I was dedicated to keeping this going.

Were you turning the pedal in a clockwise direction? :innocent:

Ditto.

I'm not sure those should even be called threads anymore. Unless you can put some serious shop work into them, they're done.

I say, install the pedals and go for a few rides. If it holds, it holds, if not you end up walking home, or calling for a ride home.

No way that holds for more than a ride or two, if that. Toast.

It's okay if you use it. For yourself.

How long it will keep you from having to get something else is a entirely different question. You might get to save some money for a while or you might have to spend it after the next ride.

It could be fixed somewhat with a insert. Such as a heli-coil. 9/16-20 left hand thread. I don't know how easy they are to find. Might need a left hand drill bit too! <grin>

If it works at all, it will only be if you can tighten it down to normal torque. Leaving it only snug will destroy the threads faster.

Thanks - I'll probably simply replace it. I have a few bikes in the shed that haven't been ridden in a long time. I'll see if any of them have a 170mm crank arm. That would be the cheapest route. (It's a lovely bike, a fully chrome 1977 Super Le Tour. It already has a hodge podge of parts, so there's no worry about keeping it in pristine vintage condition.) It's a question of do I spend the money for an approximately matching crank arm on Ebay or leave it looking funky with mismatched crank arms - which, admittedly, only I would ever notice.

I rode it around the neighborhood, and it doesn't seem any worse, but it's really not in my nature to trust something that really isn't right. I'm tempted to try to fit a helicoil in there, just for the experience, but I'm sure the helicoil kit to replace a pedal thread would amount to an expensive experiment, and since I've never done it before, it would probably be a failed experiment, and on top of that, I would have a helicoil kit I would never use again getting in the way of all my other tools.

I was mostly wondering if anyone out there had experience riding on a mostly stripped crank. Usually there's at least one person out there saying things like "it's not ideal, but I rode my bike with a crank like that for 87 years. If it screws in, it will stay there." Or, to the contrary, "I got two miles from home and the pedal came flying out of the crank right when I was on a twisty descent."

The photos show both a left side (non drive side for single bikes:)) crank arm and pedal. My first thought is that the pedal wasn't installed with grease on its threads, resulting in galvanic corrosion. I see what looks to be rust on the steel axle suggesting enough time exposed to water, add road salt and time and you have a stuck seatpost, I mean pedal.

My second thought is that the bike was ridden with the pedal not fully tightened in the arm and the loose pedal axle acted like an auger to the soft arm.

Either way a possible fix is to install a Helicoil into the arm and make sure the pedal threads are clean, undamaged, lubed before installing it. Is there a LBS near you? Some shops won't do this type of repair, it is a method with varying results and is dependent of the skills of the person doing the fix. Having a pedal fall off the crank arm when riding is not something a shop wants to deal with (and hopefully their liability insurance is paid and is large enough to cover the possible rider injuries. The far more "reliable" fix is to replace the arm. Andy.

It's possible a LBS near you might already have a kit for their own use when they get other customers bringing the same to them. So go visit a few and ask if they can put a insert in and how much they want.

It's a good opportunity to go out and socialize with bicycle related discussion. Unless your bike shops are big business model shops and very compartmentalized.

The drive side was also stubborn, but did unscrew correctly. It did not appear that the previous owner - or whoever installed the pedals - put any grease on the threads, so the corrosion theory may be correct. I also strongly suspect the non-drive side pedal was cross threaded, though I wonder if someone could screw it in all the way if it was cross threaded at the start. It was very, very, very difficult to get that pedal to budge at all. A voice in the back of my head kept telling me to give up and ride it with the pedals that it came with. (The toe-clips were a little short, and I had a pair of MKS city pedals with longer toe-clips I wanted to put on, but I knew I could just remove or replace the toe clips.) However, knowing that it just wasn't right made me want to see what wasn't right about it.

Looking at how much aluminum is missing a helicoil may not be a 100% guaranteed fix. Something like a threadsert, (see below), might be better but as you've seen this can get expensive for a proper reverse threaded part even when doing it yourself and drilling out the hole it has to be exactly perpendicular to the arm which can be a little tricky in this situation. Personally, would just look for a used replacement arm on ebay or from Co-Ops or you might find a new one for cheap somewhere.
https://static.grainger.com/rp/s/is/...ei=536&wid=536

It's dead, the pedal won't stay attached if you try to use it. It's not worth trying to fix, NDS cranks are cheap. I'd advise against trying to salvage a used crank from another bike, as you could end up needing two new cranks instead of one. Just be sure to grease the thread when you fit the pedal to the replacement crank.

They make inserts specifically for bicycles that are more akin to a "Timesert", which is an insert that has the same nominal thread pitch on two sides of a wall--it's the thinnest possible piece for a full-strength repair, which you don't get literally anywhere else. As was indicated elsewhere, removing more material than necessary may not be a good idea.

As Andy indicated, no fancy mechanical machinery necessary: the bicycle industry solved this particular problem many years ago with Eldi's reaming tool/insert set. It is a pair of oversized pedal taps, with a tapered reamer at the nose. Provided the arm in question is not completely knackered, no special tooling or experience (other than basic mechanical fabrication skills) are necessary. The tapered nose makes it almost impossible to tap into the arm off-center. Unior's current taps have a longer taper, which makes it easier to start in a "just barely stripped" hole.

That said, the OP's crank is, well, likely too knackered to use. If there is any unsupported part of the threaded axle between the end and the face, it will try to rock, and there is nothing you can do to stop it. If your repair cannot restore that part, you cannot fix it.

the arm is damaged to the point where re-tapping it for a helicoil or threadsert is not an option.. those cranks have a fairly marginal tip cross section anyway...

The pedal is also damaged, and in such a way that re-facing the Shoulder would be difficult, and simply not worth it.

40+ year old parts, damaged beyond reasonable repair...... get some fresh parts for the venerable Super LeTour... they're great bikes when working properly!
:thumb:

Toast.

Leave 'em behind.

Fitting those for re-use isn't a safe or wise proposition.

The crank threads are trashed, the pedal threads aren’t much better - just buy a new crank at least 🙄

The crank threads are trashed, the pedal threads aren’t much better - just buy a new crank at least 🙄

I just wrote up my experience using a helicoil-type crank pedal thread repair kit: https://www.bikeforums.net/bicycle-m...hel-icoil.html

A replacement left crank arm will be cheaper and more reliable than a repair in this case.

Eldi, Unior and others made threaded insert kits for exactly that purpose. Perhaps a local shop has one?
https://cimg2.ibsrv.net/gimg/bikefor...a8c4d597e7.jpg

With lack of most threads, the pedal axle will precess even more than with standard thread clearance (why pedals are L/R threaded to stay tight), very high likelihood of loosening, and not knowing about it until it comes off.

As mentioned above, there is a new thread on helicoiling pedal threads on crank. Do that, or replace the crank.

I don't know others' opinions, but I personally use aluminum (silver) anti-seize on all pedal threads, to prevent seizing, and galling.

Admitting I'm a fan of anti-seize as well. Any details on when the oft-mentioned 'grease on all bike threads' may instead benefit from using anti-seize?