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My pedal cannot get attached to the crank because the crank threads are worn/stripped. Based on this link, the solution appears to be to drill out the threads and insert a helicoil. I approached a repair person and proposed this solution, but he immediately said that I would have to actually replace the crank itself, his reasoning being that helicoils tend to fall out while riding. On top of this, he stated that I would have to replace the pedal too. (As a side note, he mentioned that I'd have to pay for a crank set and pedal set because these products are sold in pairs.) I am substantially skeptical that this amount of repair is needed. I frankly think he is attempting to get as many parts used in the repair as possible. Perhaps he receives a commission from his supplier(s) based on parts sold.

Is this degree of repair actually appropriate, or am I simply being ripped off? I have attached a one-minute clip and a few photos describing the issue at the following Google drive link. Note that the video is useless after the 30-second mark as it starts to blur. (Also, there is a piece of aluminum foil that is in the spindle hole in the video. Please ignore that — I was naively trying some things out!)

Any and all help would be appreciated!

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    Helicoils won't loosen if the pedal is fully tightened. No need to replace the pedal if its threads are undamaged.
    – MaplePanda
    Commented Jul 31, 2021 at 23:12
  • That google link says "You need access" Instead, try including the relevant images in your post with the edit function.
    – Criggie
    Commented Aug 1, 2021 at 0:41
  • There are respectable bike shops that will do a helicoil repair. Commented Aug 1, 2021 at 1:38
  • Thank you for the help all. I've corrected the Google link permissions, so it should be accessible if anyone would like to see the damage. Commented Aug 1, 2021 at 4:34

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Crankarms and pedals are sold in pairs. Once in a while you can get lucky finding a person selling a single, but don't count on it. We can't currently see how much damage has been done.

A shop would be more reluctant to warranty their work inserting helicoils (if they do it at all) than installing new, known-good parts. I suspect this is at least as much about ensuring you get a good repair as it is about making money off you. People don't go into the bike-shop business to get rich.

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  • Thank you for your answer, Adam. Makes sense. Based on your response, seems like the repair proposed was appropriate. Commented Aug 1, 2021 at 4:34
  • Cranks are usually sold as a pair. But right now, I’m Googling for Shimano left crank arm, and you do see a few shop listings for left arms alone at a few price points, usually performance level MTB and road stuff. I seem to have less luck for right arms. Basically, it may be possible for a shop to order a single arm. I know they can now order single shift levers. Not sure about SRAM or Campagnolo. If you try to verify this, do note that I am excluding listings that have power meters mounted.
    – Weiwen Ng
    Commented Aug 4, 2021 at 17:32
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Presumably the repair person was a bike shop, not a machinist. They'd rather sell you new parts and fit them - it would take less time.

Installing a "helicoil" or thread insert is not hard, but your chances are improved with better tools. A hand drill will not be enough, you'd need a pillar drill at a minimum.

A thread repair kit itself for pedals is surprisingly expensive, because 9/16" left and right hand threads at 20 TPI is an oddball size. The common industrial number is 18TPI and those will not fit your pedal's axles. Expect to pay hundreds of eurodollarpounds for an 8~10 piece kit, for each handed thread.

The axis of the hole you drill must be absolutely parallel to the bottom bracket. Otherwise any misalignment will be felt through the foot on that side.


Depending on the damage, you might get away with simply re-tapping the hole in the crank, though if you're talking inserts then the damage has gone further.

It might be worth exploring for a replacement crank from a donor bike too, rather than buying new.

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    Sounds good — thank you Criggie. The helicoil option appears to be more inconvenient. Seems like the bike repair person's proposed repair is a good course of action (i.e., not outlandish). Commented Aug 1, 2021 at 4:40
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    @AnshulPattoo In terms of risk - selling/fitting some new parts is 99% likely to fix the problem. Repair has a lower success rate, while similar or greater cost. Personally I'd try the repair if I had access to the tools, but the 20tpi inserts are stupid-expensive, hence why I'd probably end up with a good used part.
    – Criggie
    Commented Aug 2, 2021 at 1:20
  • Excellent, thanks! I will go with the fitting new parts option. Commented Aug 2, 2021 at 16:22
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Pedal thread helicoils do not fall out while riding. It is a very safe repair. The one thing that can keep it from being safe would be if too much material has been lost, such that the new threads cannot be fully formed. The crank is done if that's true, but that's not usually the situation and does not appear to be true of your crank.

The whole procedure to install a pedal thread helicoil takes maybe 30 minutes for an experienced mechanic including all the cleanup and getting the crank on and off. Getting the alignment square when you're starting to cut the new threads and trimming down the insert to look neat are both steps that take some time and care. The part costs something as well. For a right crank, even a basic one, it is still usually cheaper than a new crankset plus installation labor, and that's if a new crank can necessarily be had that can use the existing bottom bracket. For left cranks from basic low-end cranksets, just putting on a new left crank is almost always cheaper if one is available, but even there is the fact that a good match might not always be available.

If a crank has significantly worn chainrings, it's easy for it to be the case that a whole new crank is a better value. The catch there can be that even if it's a better value in the overall sense, dropping in a new crank in a worn out drivetrain is problematic, i.e. a customer who needs a new drivetrain but wasn't planning on being confronted with the fact.

Not every shop really does crank helicoils but many do a lot of them. Some people basically just don't get the physics of how they work and why they're safe, unfortunately including some mechanics. The tool to install them is also fairly expensive.

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  • I go double belt and braces with thread repair inserts - I apply 2 part epoxy to the outside of the insert before final insertion. Though that's been M5 and M6 repairs, not pedal/crankarm. Probably overkill but as they say, there's no such thing as overkill....
    – Criggie
    Commented Aug 4, 2021 at 0:32

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