Morning all.

I need to replace a bottle cage boss on the downtube of my old carbon road bike as the bolt is corroded in place. I’ve already tried lubing/tapping/drilling out just the bolt but it’s proper stuck and I’ve made a right mess of it so plan now is to drill out the old rivnut and insert a new one, sounds easy! This looks like a pretty good guide:

So what epoxy to use? It’s an old frame (~14 years) and will probably be replaced in the next 2-3 years so am I overthinking it and can do without the epoxy? I figure if I’m doing it I might as well do it properly but since I’ll only need a tiny amount of resin I’m loath to spend £30 on a tube that will just dry out before I need it again.

Ta

Easy Composites epoxy repair compound – it’s black and blends in well, has carbon filler so is a lot stronger than just a resin. I made a computer mount for my racing kayak, glueing 2 pieces of carbon tube and it got clattered countless times by my paddle in racing and never broke

There does seem to be a massive variation in the strength of different expoxies. The projectfarm guy on youtube did a couple of tests, definitely worth a watch before deciding which one to get.

2 Part Araldite will do the job Araldite

Above sounds like a good tip.

I would suggest that any Epoxy will do the job – it’s runny so a paste is maybe a better option. A 2 part epoxy putty could do the job as well – very easy to work with – sands down easy – you can paint it. Comes in a stick so you just cut of a small piece and the rest stays good for latter use.

Note plumbers putty is not the same as 2 part epoxy putty.

Avoid Polyester based resin. Much more toxic and more likely to have an adverse reaction with other materials.

When I drilled out the rivnut on my carbon frame I just put some decent tape around the nut to be drilled, then drilled it so it was thin enough to tap out by putting a screwdriver or something on it and using it as a punch to smack a hammer against. Then collect the rivnut from the BB shell and install a new one without any epoxy – I don’t see what the epoxy brings to the job here.

Thanks all. Not too worried about strength as it’s just a bottle cage and the M5 rivnut should be able to manage the load.

Munrobiker – I don’t think the epoxy is a strict requirement but it is recommended to avoid galvanic corrosion brought on by having the carbon and aluminium in direct contact. Since my frame is old and will be replaced in a few years I’m less worried about that.

Side note, while I was explaining this weeks reason for spending too long in the garage, the wife commented that I’m probably due a new road bike. I almost fell over.

I’d just go for araldite or similar. I think when I’ve seen data, a UHU product had better adhesion between aluminium and a PU painted surface. Surface prep made the biggest difference. The riv but will be held in place mechanically as well. When I did this on an alu frame that alone was sufficient.

I wouldn’t be concerned about galvanic corrosion. Alu is bonded to carbon all the time. Be more worried if you used a steel bolt. I doubt you’d even get a galvanic cell on a bike? Isn’t the carbon acting as a conductor rather than cathode/anode. In which case you’d need a steel component elsewhere and a complete circuit – unless I’m missing something?

Araldite ordered. No idea on your question jonba, I was just going by what the bloke in the YouTube link said. I get the feeling he’s quite belt and braces though as he said himself that a lot of frame manufacturers just put the rivnuts in dry.

I’ll use some just to make sure that the contact between the rivnut and frame is smooth as there’s no telling what unseen damage might be caused by my hamfisted DIY

Araldite should fine, but if anyone comes across this it is also worth looking at the methacrylate adhesive that easy composites sell.

A dry rivnut into a carbon frame is a very bad idea for galvanic corrosion. An adhesive will help to form a small barrier and prevent moisture ingress. Wouldnt be a terrible idea to seal the bore of the hole with some adhesive and let it go off for a few hours before a fresh application and fitting the rivnut as this will help prevent it being displaced.