jyl

There is a decent bit of rust inside the BB shell of this old Motobecane I am rehabilitating. It is not terrible - doesn't seem structural, the BB threads are okay - but it is fugly and bugs me.

How would you treat that internal rust before putting the bike back together? Paint the inside with some sort of rust convertor? Or just coat with oil and call it good?

HillRider

"Navel Jelly" was the usual recommendation to remove surface rust and convert (phosphatize) the underlying metal. It does work pretty well but doesn't leave a long lasting protective surface. After the rust is removed, either phusically or chemically, coat the frame tube's interiors (including the stays and fork blades) with Weigel's Frame Saver or Amsoil HDMP as a good long term protector.

JTGraphics

Use what is known as a rust converter several companies make it you can get it someplace like Gimpers or the Rust Store comes in spray or liquid.
It uses a chemical reaction so you actually apply it directly on the rust so o need to try to remove it first.
Its fast and will stop rust from getting any worse, can use for any steel application I have used it for fencing as well as other applications.
Once it does its thing you can sand and paint also it makes soft flakey rust get hard you must stop the rust not just apply something to clean it and paint it.

Myosmith

Small steel brush (looks like a big toothbrush) to remove the loose stuff from inside the BB shell, then Naval Jelly or other rust remover. After the rust remover does its thing, clean with rags and mineral spirits then coat with a rust converting primer (just in case a few specks of rust remain inside pits or defects in the metal surface. Problem solved.

Ira B

A round wire brush attachment chucked in a corded drill should make pretty short work of it and will also do a great job of cleaning the threads at the same time. Then rinse it out with carb cleaner and when dry slather it with grease.

rtz549

Here is one potential option:


https://www.eastwood.com/internal-fra...ay-nozzle.html

Another option; read up on aviation literature about using hot linseed oil in metal tubing. Scroll down to where it says "Protection For Welded Steel Fuselages" as an example:

https://members.eaa.org/home/homebuil...rotection.html

3alarmer 

Get it at Home Depot, spray it inside through a small plastic
straw, like the ones that come with spray oils, swirl it around
inside the frame by turning it over and around a few times,
give it a couple of days to dry and drain the excess.

You can do a couple of coats if the rust is really bad.

Local framebuilder/repairer uses it and recommended it.

And knock out all the loose scale and stuff prior to using it.

gforeman 

Best stuff I have ever used is POR-15. This stuff encapsulates rust. I had a rusty old Datsun PU, and this stuff stopped the rust. But be aware it is not UV safe, but since it is inside the frame, that is not a problem. They do make a UV top coat if you use it exposed.