Technical Tanx fuel tank question

I have a Tanx fuel tank that I'm planning on running in my 31 Studebaker. It's designed for a 33 Plymouth, but it's close enough to fit well. I won't be using the pickup tube, as I've fabbed an adapter to use the original tube at the top of the tank, so I want to block it off. A 1/4npt plug fits, but goes in too far to be npt threads, so must be straight. What's the best way to seal this hole? I'm not familiar with this style fuel hookup.

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Why not contact Tanks and ask them what they recommend?.

 

Thats not an inverted flare fitting on the inside is it?

 

Will be doing that tomorrow. I figure this is a modern standard used in newer cars, and someone may have been though this before.

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That appears to be a fitting designed to take a 5/16" inverted flare fitting, which I believe was the stock Plymouth line size.

Inverted flare line, showing tube, and tube nut:


The threads on a 5/16" tube nut are 1/2"-20. You should be able to get an inverted flare plug at a decent auto parts store.

Inverted flare plug:


Same sealing surface, same basic shape, but the plug has no hole for a tube in it.

It is noting new. Inverted flare fittings were the de-facto standard by the 1930's, and are still used, in one form, or another, today.

 

Took a better look at this, and the bottom of the fitting is flat. If it was for a flared fitting, I would expect to see a beveled bottom that would seal against the flare. Maybe just an o-ring gasket and a short bolt would do. I'll call the manufacturer tomorrow and find out for sure what they recommend.

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If it is an inverted flare fitting, flare plugs are very easy to get. I strongly caution against using a substitute, as a failure here means a fuel leak.

Fuel leaks can leave you stranded, at minimum. At maximum, you can lose more than just your car.

 

Ok. - it's supposed to be an NPT fitting, but either the weld flange or my plug was cut wrong, allowing it to bottom out, instead of seal. I really hope it's the plug that's wrong.

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Shorten up the narrow end of your plug.