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Project in my work stand at the moment is a Colnago C40 of the B-stay variety. Whomever built it up before I got it must have used something on the threads when they mounted the cages, because they're all gummed up. I've tried chasing the threads, but the mounts just spin in the frame. Does anyone here have any ideas? I could pop rivet the cages on, but that's really a last resort.
 

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I'd try to bond the insert into place (super glue between the insert and the frame).
 

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You should be able to find those mounts somewhere. If you can, just change them. If not, I couldn't find any way to fix them. I had the same problem with my old bike, Scott S40, and nothing I tried could fix it.
 

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Project in my work stand at the moment is a Colnago C40 of the B-stay variety. Whomever built it up before I got it must have used something on the threads when they mounted the cages, because they're all gummed up. I've tried chasing the threads, but the mounts just spin in the frame. Does anyone here have any ideas? I could pop rivet the cages on, but that's really a last resort.
This happens with any frame that has "rivnut" style bottle cage mounts. A good bike shop will have replacement rivnuts and the tool to install them. It is likely that they can apply the tool to the existing rivnut and fix the problem.
 

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As a rivnutter in one of my first jobs, I'd say listen to Mike. If you cannot fix it, then you've got a mess on your hands. Its' a blind fastener. You know what that means?
 

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To add to my previous answer, it helps to understand what a rivnut is (if you didn't already know).

It is most useful as a fastener when one only has access to one side of the work (ie blind), like a bike tube.

The rivnut is threaded onto the installation tool which then pulls up on the threaded portion and deforms the section above that to form a rivet-like fastening.

View attachment 280713

The only way to remove one, is to drill or grind the front, visible bit, and then the rest falls into the tube. If you can disassemble the bike and there is an opening through to the tube, you are OK. Otherwise it's going to rattle around.

If you find someone with the proper tool, they can try tightening it. Failing that, epoxy, and failing that, removal.
 

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The only way to remove one, is to drill or grind the front, visible bit, and then the rest falls into the tube. If you can disassemble the bike and there is an opening through to the tube, you are OK. Otherwise it's going to rattle around.
Let me add, while you are trying to drill or grind off the head, the whole assembly will be spinning (unless you can lift an edge and hold it), while it is spinning in the frame they will wallow out the hole (especially on a material like carbon fiber/resin) making it harder to install a new one well (best to install wet with some epoxy and rivet).
 

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I have a C-50 frame that had that same problem. Drilled it out and installed a new one. Added some epoxy to it, with the hopes of keeping it from happening again. There was enough of the rivet sticking out of the frame that I could get a set of vice grips locked on to it, kept it from spinning in the frame. Only one of the 4 bottle mounts had this problem.
 
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