Thread stripping in crank arm?
10-30-23, 07:18 AM
#26
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Hope it holds but if not an old established bike shop likely would repair it. If not here is a tool that may cost more than the bike.
https://uniorusa.com/collections/ped...ts/crank-saver
A ratty parts bike with a mismatched arm may be most cost friendly.
It's worth fixing; good luck.
https://uniorusa.com/collections/ped...ts/crank-saver
A ratty parts bike with a mismatched arm may be most cost friendly.
It's worth fixing; good luck.
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10-30-23, 08:06 AM
#27
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Because glue isn't strong enough and having your pedal break out of the crank arm while standing can cause a really bad crash.
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10-30-23, 10:08 AM
#28
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...we actually have the stuff at the co-op here, in Sacramento, to do a theadsert repair, if it were really needed. We used to do them for the cost of the threadsert, which is about five or six bucks. But I have to agree the threads look like they will still work OK in his photo. Given the length of time that has elapsed, I'm guessing those MKS pedals worked out fine. So except for the bickering, another mechanics thread with a happy ending.
...we actually have the stuff at the co-op here, in Sacramento, to do a theadsert repair, if it were really needed. We used to do them for the cost of the threadsert, which is about five or six bucks. But I have to agree the threads look like they will still work OK in his photo. Given the length of time that has elapsed, I'm guessing those MKS pedals worked out fine. So except for the bickering, another mechanics thread with a happy ending.
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10-30-23, 12:13 PM
#29
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I love legal stuff. Please provide pointers to any such cases. I realize asking is like trying to squeeze blood from a turnip, so, not holding my breath.
10-30-23, 12:24 PM
#30
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Says who? There are few situations in which glue is stronger, than on threads. I would properly clean the metal parts and use JB Weld if I wanted the cheapest solution.
Glue cannot cause that to happen.
Glue cannot cause that to happen.
10-30-23, 12:24 PM
#31
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Not since the invention of the injury lawyer.
I will admit, I don't have a link to any legal precedent here. Then again, I don't know of anyone foolish enough to actually take your repair advice yet, either.
I will admit, I don't have a link to any legal precedent here. Then again, I don't know of anyone foolish enough to actually take your repair advice yet, either.
10-30-23, 12:29 PM
#32
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If the threads are damaged enough to never get tight, the crush strength of the epoxy will not survive the down force on the pedal and it will shatter, allowing the pedal spindle to wallow out the crank.
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10-30-23, 01:19 PM
#34
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10-30-23, 01:36 PM
#35
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10-30-23, 01:48 PM
#36
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Can confirm. New pedals operating well after about 200 miles of mixed city riding, including a big hop when I saw rattlesnake in the path! The rims and hubs were shot, so I would up getting some new wheels, but no problems with the cranks or pedals since then!
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10-30-23, 06:14 PM
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When the pedal threads fail and you are pedaling standing up, there is every possibility that the side load of rocking the bike is going to force the pedal right out the side of the crank arm once it is loose enough. Or pop the end of the crank off.
I know it is fun to have an opinion, but why don't you insert it someplace that doesn't involve the safety of people going up to 50mph? Isn't there a Star Trek forum or something?
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10-30-23, 08:52 PM
#38
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i've crossed paths with a rattler once, while hiking through salal brush, on an undeveloped trail, of sorts.. Whychus creek area, below the overlook on Peterson's Ridge...1977... i jumped straight up about two feet... the snake made the mistake of not leaving the trail quickly... sadly, my survival instincts kicked in.... the snake didn't feel a thing... they taste great.... we needed the protein.... 2.5 feet of sheer terror... and a tasty dinner.
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10-30-23, 09:17 PM
#39
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Check threads (& pedal type) then helicoil OS
I just picked up a 1977 Super LeTour for tooling around town on a weekly Taco Tuesday ride of about 10 miles. It was priced right, seems pretty bulletproof, and it's the full-chrome version, so it's nice and shiny. Perfect for days I don't want to be the guy in lycra. I'm swapping out the brake pads for something made in this century, and I'll probably recable it, but otherwise, it's in great shape.
First check pedals for matching threads. You or a good shop with a good mechanic
I took it for a test spin at lunch today, about a mile in each direction. I wasn't pedaling particularly hard (it was in a spinny gear), and I'm 165 pounds, but the non-drive side pedal popped off. I went back, piced it up, and saw what looked like a teeny bit of silver metal in the threads. I was only 500 yards from home, so I cleaned off the threads on the spindle and in the crankarm with my finger, screwed it back by hand (seemed to move freely--no crossthreading), and started pedaling home slowly in my second-lowest gear. 200 yards later, the pedal popped out again, and this time, there was an obvious semicricular piece of crank in the spindle thread:
The crank arm looks like there's some stripping, but not a TON:
Any thoughts?
Options I've considered:
First check pedals for matching threads. You or a good shop with a good mechanic
I took it for a test spin at lunch today, about a mile in each direction. I wasn't pedaling particularly hard (it was in a spinny gear), and I'm 165 pounds, but the non-drive side pedal popped off. I went back, piced it up, and saw what looked like a teeny bit of silver metal in the threads. I was only 500 yards from home, so I cleaned off the threads on the spindle and in the crankarm with my finger, screwed it back by hand (seemed to move freely--no crossthreading), and started pedaling home slowly in my second-lowest gear. 200 yards later, the pedal popped out again, and this time, there was an obvious semicricular piece of crank in the spindle thread:
The crank arm looks like there's some stripping, but not a TON:
Any thoughts?
Options I've considered:
- Clean everything, grease everything, reinstall, and just torque the absolute crap out of it.
- New pedals?
- New crank arm (probably a whole new crankset -- there's a NOS-ish pulloff on eBay for $58 with shipping)
11-02-23, 06:48 PM
#40
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The problem I've experienced with this sort of failure is that although the crank thread looks mostly good it's no longer circular or parallel-sided and will not stay tight without some assistance.
11-02-23, 07:49 PM
#41
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Every time I get on my bike and put all my weight on my pedal I wonder how my crank continues to hold up. There are incredible forces at stake and really we are looking at just a short piece of tempered aluminum. Its a wonder for sure. Because of this I do not take any chances of having a weak, abused, or partially stripped crank arm. For me its just too dangerous. A Helicoil is probably your best repair. And I would have it installed at a machine shop. I would not rely on any kind of adhesive. I have only had a pedal/crank juncture fail on me once. Never again...
Anybody up for determining force at point "A"?
Chegg.com
Anybody up for determining force at point "A"?
Chegg.com
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11-03-23, 12:55 AM
#42
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Every time I get on my bike and put all my weight on my pedal I wonder how my crank continues to hold up. There are incredible forces at stake and really we are looking at just a short piece of tempered aluminum. Its a wonder for sure. Because of this I do not take any chances of having a weak, abused, or partially stripped crank arm. For me its just too dangerous. A Helicoil is probably your best repair. And I would have it installed at a machine shop. I would not rely on any kind of adhesive. I have only had a pedal/crank juncture fail on me once. Never again...
Anybody up for determining force at point "A"?
Chegg.com
Anybody up for determining force at point "A"?
Chegg.com
torque is about 55Nm when the crank arm is parallel to the ground, given that a mm is 1/1000 of a m
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01-03-24, 10:19 PM
#43
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Coincidentally... Yesterday, my ultralight and beautiful candy red bottom of the line racing bike pedal was loose. Naturally thinking about this thread, I unscrewed the thing and watched metal filings fall down. Vacuumed both the pedal end and the crank arm, saturated both with superglue, and screwed it back in there. Was able to tighten it down pretty hard, superglue oozing onto the floor. If it ever comes loose again, I'll just replace the cranks, and update this post. Could have used JB Weld, but probably not worth the effort since there was still some useful threading.
