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Old 10-21-09, 09:41 AM   #1
Metaluna
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Stripped bottle cage boss on CF frame. What repair options?

I've got a Motobecane CF frame which appears to have a stripped thread on the upper seat tube bottle cage boss. I've read about various repair methods (Riv-nuts, helicoils, etc.) but all the information I've found seems to be for metal frames, where the procedure is usually to drill out the old boss and put in a riv-nut. Is it pretty much the same for CF, and if so is it something a good LBS should have experience with? The bosses in my frame look like they could be Riv-nuts but I've never seen one except in pictures so I can't say for sure, and I don't know if those are commonly used in CF.

I'm pretty sure the damage is to the thread itself, not a loose boss. I think I cross threaded it at some point and it finally gave out. The bolt just sort of spins and won't take more than a finger-tight torque. I have it held in with the some blue loctite at the moment but it's loose enough that I can move the cage around a little with my fingers.
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Old 10-21-09, 09:57 AM   #2
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I ran-in a license plte screw into a boss once, a metal bike. The thread was more coarse and the tip was somewhat self threading, not pointy, just relief tapered.
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Old 10-23-09, 08:40 AM   #3
Metaluna
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As a follow up, I think I'm going to give this product a try. I also ordered a helicoil M5x0.8 repair kit but I'm not sure if the walls of the boss are thick enough to withstand drilling and tapping.
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Old 10-23-09, 09:58 AM   #4
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You won't be able to use a helicoil insert because the walls are almost certainly too thin to accommodate the larger thread diameter. The Permatex stuff will work if you don't over torque the screw, and don't plan of removing the cage often. I'd feel better about the Permatex repair if it were the lower mounting bolt, since the upper gets more strain and is being pulled away from the frame. If you ride on bad roads you might want something stronger.

Replacing the riv-nut is the best long term solution, and rather than buying the tool, you might ask a shop that sells lots of carbon bikes what they'd charge for the job.
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