Fuel tank fittings distortion after welding

[Shay King]

Hi again guys,
I just finished welding up one of my wing tanks today. Unfortunately when I tried to screw in the filler neck it wouldn’t go further than about half a turn. Before welding it would screw in all the way by hand. The bung is aluminium and the neck is steel, both from Aircraft spruce. Any suggestions on how to fix this welcome.
Happy New Year everyone.

[Kamcoman77]

Did you try leaving the steel neck in the freezer for a few hours? That might shrink it enough to screw into the bung. You might want to heat up the bung before trying reassembly.

[Shay King]

Thanks for your reply Keith. I did try heating up the bung but not freezing the filler neck. I may try that. A gyro builder friend with a lot of engineering skill has offered to make a thread chaser for me as a possible solution.
With hindsight, I think I shouldn’t have welded around the threaded portion. I should have kept the weld on the outer flange.