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So, I broke a Shimano Sora rear derailleur last night... Ouch, there goes a load of cash...

What had happened was the hanger was bent slightly inwards, yet was functioning fine, so I rode it home. Came to a slight bump in the road whilst in first gear, and then the rear wheel spokes decided the derailleur looked tasty, caught the mech and bent it all the way up, over, in front of and then below the chain-stay. Long story short, it broke. Just in case you hadn't gathered. :P

I've repaired bikes for years, but I've never come up to this part; Can I use HeliCoils to place into the bolt holes for where the hanger itself is meant to meet? I cannot bring myself to part with this frame as it was my best friend's, and he had died after riding this bike in a small criterium near me, I brought it up to scratch, offered it to the family to help pay for funeral costs and they decided I should be the one entrusted to look after and care for it. I screwed up big time.

Theoretically, HeliCoils should ('should') work in this application; If it works holding brake calipers on cars, it should work for this. But, would there be any other way to fix the threads (which are warped and stretched, not even a thread chaser would work on it!) so I can still use the same bolt size? I don't want to have to bodge it together with a bigger bolt size in a larger, re-tapped hole. In fact, I'm not even sure THAT would work, either.

Could I put a big tack weld in where the hole is and then drill the weld out to tap a thread into? (After rubbing the paint back and all, though Aluminium is a pain to weld) I've never tried anything to do with frame/fork work directly, I'm used to fixing bikes, not frames, if you know what I mean by that.

Any help would be great, and I'm curious if HeliCoils would actually work. Cheers.

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    Can you take a picture of the damage?
    – Batman
    Sep 10, 2017 at 18:04
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    Whatever you do, please take decent photos and post them in your own answer.
    – Criggie ♦
    Sep 10, 2017 at 20:05
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    You've found out why spoke protectors are a good idea.
    – Daniel R Hicks
    Sep 10, 2017 at 22:42
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    Are you sure that the holes were threaded to begin with? Some hangers fit on both sides of the dropout, with screws running through, and the threading is in the "back" side of the hanger.
    – Daniel R Hicks
    Sep 10, 2017 at 22:49
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    BTW, based on a quick Google, the Carrera Virtuoso eating its derailer appears to be a common occurrence. If you look around (at other sites) you will find several threads on this topic.
    – Daniel R Hicks
    Sep 10, 2017 at 22:50

1 Answer 1

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It's a little unclear, but I'm gathering that you've got a hanger that secures with two little screws, probably M3x0.5, that thread into the frame, and those frame threads are toast with some distortion/warping of the holes also present. If so it depends on how enlarged the holes are - the oversize tap that would come in the M3 helicoil kit has to have enough material to cut into to do its thing. Beyond that, there should be no issue.

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