Rehabilitating a rusty BB shell?

[alexnharvey]

Just forcefully extracted a BB and found a rusty shell lurking. Would drilling a drain hole, wire brushing the interior and installing the new BB with plenty of anti seize be a good strategy?

[alexnharvey]

One other thing I'm considering is kurust type rust converter gel. Is that worthwhile?

[Mick F]

What I've done, is when the seatpost and BB are out, injecting Waxoyl into the frame whilst hanging it up in the warm to allow it to run and spread. It's a brilliant rust eater and rust protector and stays soft.

Waxoyl is waxy and also Kurust-y too.
https://en.wikipedia.org/wiki/Waxoyl

I have a big can of it from the days I was working on Minis in the 70s 80s and 90s.

[alexnharvey]

Ok, nearly all the drain holes in the other tubes show some evidence of rusty water drainage so I'd been thinking of waxoyl. Is the aerosol easiest for bike frames?

In previous threads I've just read I noted you're not a fan of drain holes Mick. I might give it a try without.

The shell is now covered in grease to remove the rust because I don't have any waxoyl on hand.

[Mick F]

Not that I'm no fan. but my Mercian has none at all.
Built for me in October 1986.
No drain holes at all, but that's the way they built it.

There's tiny hole in the front end of the top tube into the head tube but none at the rear. The down tube, seat tube and chainstays are hollow into the BB shell but no other holes whatsoever.

I've put Waxoyl in down the seat tube with the BB out whilst hanging the bare frame to let it spread and tried to get in into the down tube and chainstays. How far it's gone in, I don't know, but by hanging the frame this way and that, I'm sort of happy that's it has done its job. Absolutely no way into the top tube to inject anything.

[Brucey]

....There's tiny hole in the front end of the top tube into the head tube but none at the rear............ Absolutely no way into the top tube to inject anything.

eh?

cheers

Brucey

[Gattonero]

I've seen some manufactures sealing their frames by brazing a piece of rod in the venting holes, the theory is to have the tubing completely sealed on the inside so as long as there is no residual humidity inside it -and note that tubing should be thoroughly cleaned prior welding- it will stay mint forever.

[Gattonero]

Just forcefully extracted a BB and found a rusty shell lurking. Would drilling a drain hole, wire brushing the interior and installing the new BB with plenty of anti seize be a good strategy?

If you're worried about the conditions of the shell, it all depends how badly rusted it was. After brushing, cleaning and chasing the thread you will have an idea by screwing a new BB cup.
There is no substitute for regular cleaning of the bike, removing the BB every few years is a good habit. Unless you have a BB shell that is completely sealed (the Brompton frame is one of the very few I know) there will be water leaking in/dripping down the BB shell. Using a thick waterproof grease will mitigate the rust, but the resulting "gunge" formed is all but good for the BB unit/bearings, so it's best to remove it whenever possible. A drain hole can help by removing excess of moisture/water, you can drill an M6 hole in the lowest position and close it with a short screw.

[Mick F]

....There's tiny hole in the front end of the top tube into the head tube but none at the rear............ Absolutely no way into the top tube to inject anything.

eh?

cheers

Brucey

Fact.

The top tube is blank where it abuts the seat tube.
There's a tiny hole where it abuts the head tube. You can see it when the forks are out by looking inside the top of the head tube.