Broken screw thread on GRX 800 crankset

Question

I made my gravel-dream bike few month ago by hand. I followed all the user-manual sheets from Shimano in order to properly mount the GRX 800 crankset and the pedals on it. I respected the tightening torque for everything.

Unfortunately after 2 months, I started to hear a crackling noise when pushing on the pedals. At first, I thought it was a lack of grease in the bottom bracket, but didn't solve the issue.

After few days of research on Youtube, forums, etc, I realized that it was coming from my pedals that were a bit loose.

But the evil was already here: the screw threads inside my left crank arm has been altered, and even if I firmly tight the pedal, the noise is coming back after a few kilometers.

Now I have 3 choices:

1. Buy another crankset, but to be honest, it's hard to find those day and it's very exepensive.
2. Find a way to "repair" the threads, but I don't know any technic to do that
3. Find a equivalent/compatible left crank arm.

Note that length is 172.5.

Also pedals are Shimano GR500. They are made of Chorome-Vanadium, and I don't think their threads have been altered. But maybe shall I change them as well?

Thanks for you advices!

Answer 1

You don't mention what you're putting on the threads if anything. Pedal threads are important to lubricate and then torque properly, which could be the entire problem if not done.

It sounds like the pedal is still threading in and able to be torqued down. If that's true then it's likely the threads are still intact enough to simply be chased with a pedal tap, which shops have. That only takes a few minutes and is simpler/cheaper than the alternatives, so it's a prudent thing to try first in many cases, even though it may not work.

If that doesn't work, have the crank helicoiled. The tools to do this are expensive so it's also a shop-level job only. You could also replace it but that will probably be more expensive and difficult in this case.