While using a tap seems like a good idea, if it doesn't start correctly you have very good chance of really screwing it up by cross cutting threads.  Cutting the end of a tap off if not straight can cause a misthread.


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

If I was to grind the tapered part of the tap off, is there a way to know if it is done right? Like if you saw a bolt the start threads may not be cleaned out properly to screw a nut on and need filing. What should the starter thread cutters look like on the tap after grinding?

Brad
Sierra Vista Arizona
1954 Lincoln Capri

If your line is 5/16 diameter (likely), the thread is 1/2-20.  If it is 3/8 diameter line, (unlikely), the thread is 5/8-18.  These are machine threads, not pipe threads.  You might be able to use a fine thread bolt with notches sawed or filed in the threads as a thread chaser if you don't have a tap available..

John - "The Hoosier Hurricane"

Excellent idea, bottom tap. I didn't know those existed. Thx
Isn't the threads a special type of threads? Straight threads vs pipe threads.

Brad
Sierra Vista Arizona
1954 Lincoln Capri

You may be able to use a thread file on the line side of the fitting. The bottoming tap is also a great idea for the tank side. . 
Hope this helps. 

Located in Harford County Maryland 

A "bottom tap" might clean up the first threads of the tank fitting.  A bottom tap has no lead-in taper, full thread starts right at the end of the tap.  They are used to cut the threads all the way to the bottom of a blind hole.  If you can't find a bottom tap, you could grind the tapered part of a regular tap off.

John - "The Hoosier Hurricane"

It was suggested to me by a friend of mine that it would behoove me to change out the original fuel line for new. That way I could cut the fitting off the old lune and use that to try and fix the threads on the tank. I'm sure it would be difficult to completely clean all the crap in the old one so it would be worth it to put on a new line.

Brad
Sierra Vista Arizona
1954 Lincoln Capri

Another option is to use the same size inverted flair nut without the tube and use that to thread into the hole.  Using the correct nut will ensure that the threads are good all the way down to the raised bevel at the bottom of the hole.  As Paul mentions, the existing nut with the tube within it must be at the correct angle before being able to start within the hole.  It’s very easy to cross-thread those inverted flair nuts if not being careful with the angle when starting them into their respective threaded holes.

Lorena, Texas (South of Waco)

Is the fitting in the tank and inverted flare?  If so, it has a straight thread (not pipe).  Try threading a bolt of the correct pitch and size in the hole (don't thread it in too far and hurt the flare inside).  If it goes in ok, then it's the fitting on the line.  Sometimes its difficult getting something like that to start if the line is bent a little  so the threaded part is on a slight angle so it won't thread in.  Just a trial and error thing.  I've had this problem in the past if the angle is just a little bit off.


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

The tank hasn't seen gas since 1965 and I cleaned it out. So I think it's safe. Seeing if there's a way to fix the first little bit of threads

Brad
Sierra Vista Arizona
1954 Lincoln Capri