Cessna 120-140 Association

I am recovering a 1946 140 and the gas tank filler necks are rusted pretty badly. I would like to replace the filler necks before they go back in the wings for the next 40 years. Is there a way to replace them relatively easily? It seems that there is no aluminum tank flange they thread into. It appears that aluminum weld filler has been used. I am thinking I can wire brush wheel the rust off as best as possible and paint, but I'd rather replace them with new filler necks if there is a minimally invasive way to do that. Any help appreciated!
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I'm pretty sure they just "welded" the aluminum right to the threaded steel filler neck.

Digging around more I'm starting to believe it is brazed on.

Ugh...don't have a good answer for the necks, that will depend on how deep the rust is into the metal. Fuel resistant paint is a must. The cap should be bead-blasted and powder coated or otherwise painted with fuel resistant paint. The cap grommets are easy to replace and obtainable from any hardware store.

8231 wrote: ↑Mon Dec 31, 2018 9:59 pm Digging around more I'm starting to believe it is brazed on.

Brazing would not involve melting either base material. I'm not sure what the name of the process is, but, the filler rod is aluminum and is welded to the tank but brazed to the neck.

One of the filler necks was rusted through in spots so it has to be replaced. I'm a little surprised this isn't a more common problem, apparently Cessna had never heard of galvanic corrosion when joining dissimilar metals.

I'm convinced it was brazed based on what little information I've been able to find and a welder at work also believes it to brazed.

Any ideas who might know what braze rod is usable or "approved" for this repair?

I'm pretty sure this was discussed in the old forum, and the conclusion was that aluminum welding is used (the filler rod is aluminum and it is melted into the tank material) but the base metal of the filler neck is not melted. Call it brazing if you will, but, if you cut it apart you will see that the fillet around the neck is continuous with the tank surface. I think the only way you will be able to replace the neck is to cut the old one out and repeat the process, or install a flange in its place.

Just got an answer back from a friend. He suggests that you "braze" a thin coating of aluminum to the steel neck then weld the tank to the aluminum coating without melting the steel. HE said the threads on the filler neck are necessary to provide mechanical strength.

David PM sent.

Rick