Steel frame corroded water bottle boss

In terms of will it work, a rivnut will be fine, the hole will want cleaning up though and as to whether you'll then get a suitable rivnut into the hole or a different matter, not much use if it goes in but the hole means it's m12 or something.

Personally I'd be less concerned with how to reattach the bottle cage mind than what state the rest of the frame is in if - as it looks - it's corroded through. I'd be worried it's a sign the rest of the frame is about to follow in some much more facially critical place, like right the way round the down tube.

That being said the steel looks very thin indeed where the boss has been so the failure might be nothing sinister at all but it may also mean there's insufficient material for a rivnut to grab directly without spacing washers

For context it's an 8 year old Charge Plug road bike. It's in generally decent exterior nick (from a distance at least) but there are some surface rust spots at cable rub points and dropouts.

I live in the sunshine blessed South East, and when I commute to work it stays in a covered bike shed, so isn't excessively exposed to water. But it doesn't get much care or attention either. And crucially I've never treated the inside with anything.

The tubes are Tange Prestige which I think might be 0.4mm in the middle, hence the very thin appearance.

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A brazer could cover that up with a bit of tubing fine - you'd want to check the frame is good enough to justify it tho.

If the bottle boss has gone, check all the breather, blow or threaded holes on the frame below that point, especially round the back of the bottom bracket and ends of the chain/seat stays. Bottom bracket out as well...

I've seen many frames with a "minor bit of rust" round there turn out to actually mostly be made of rust with just the paint holding them together.

The tubes are Tange Prestige which I think might be 0.4mm in the middle, hence the very thin appearance.

Yep, that would look thin!

0.4mm might be below the grip range on rivnut i think m4 is 0.5mm+ in its smallest guise.

Best fix is a small patch and big headed boss, silver soldered in place. Here's one I did earlier on a home made frame where tiny bosses didn't like bumpy Alps descents with 1 litre bottles.

I could do for you if in NW, or make you the bits if you fancied DIY (a plumbing MAPP blowlamp works fine).

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What’s the best fix here?

Looking at the material pulled away to one side, I'd be tempted to just bin it, I know it's not and old frame but it's looking a bit too crumbly...

The little bit of material at the side is indicative of a fatigue failure due to the bottle cage flexing the boss around, especially in a very thin tube - I had exactly the same with my fracture (the tube broke a few mm around the boss and not the original silver soldered joint). There is nothing wrong with the frame and it is a cheap and simple repair, and with stress spreading patches will probably outlast the bike.

Here is the bike on top of an Alp. And it got ridden as a jagged hole for quite a while with no crack propagation.

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I think that last suggestion sounds about right. Probably not helped by using a fairly rigid metal cage, which doesn't flex anywhere near as much as the plastic ones I've got on other bikes. And thanks for the offer Mick, but I definitely don't fancy taking a torch to it myself (and I'm nowhere near the North West).

So does anyone have any recommendations for a frame repairer near South West London?

- Winston Vaz at Varonha sounds highly regarded, but he's on holiday til April and in any case is an hour and half each way, and only open Mon-Fri which would be a challenge
- Cogs Workshop in Dorking advertise frame repairs, but still aren't exactly close and have even more limited opening hours
- Bikefix in Central London seems to be the most convenient option I've come across so far

A competent sheet metal fabrication/engineering concern could make that repair

As above silver solder would do it and doesn't need anything more than a mapp torch. I am not a welder just a tinkerer.

Have you ever soldered a plumbing pipe joint? If I sorted you the bits it really isn't any harder than that. A plumber could even do it 🙂

We've done this before via the forum
https://singletrackmag.com/forum/topic/steel-frame-repair-gurus-help/

You can buy everything you need form here, a boss, a boss reinforcer plate, silver solder and flux. https://www.ceeway.com/Bosses.htm Rub paint of approx 1" around the hole.

Now go find a friendly old school plumber who still does soldering, or any workshop with oxy-acetylene. it's maybe a 5 mintue job.

RE- That Stooge thread linked above, that was my frame originally and recently got it back with the repair.
2 years on and I can vouch that it's still a solid repair. Running it single speed and cranking it up hills. No issues.