'30 under tank gas valve threads
- Thread starter duke36
- Start date
Y-Blockhead
Well-known member
The tank threads are ¼" pipe thread. Sorry I don't remember what the fuel line is off the top of my head.
Duke - one thing to be careful with is that the output side of the gas valve is a flare fitting, it's not a standard SAE straight thread. I've not had success finding a "hardware store" solution, rather just buy the right gas line from the suppliers.
Further to YB, technical names for the input side thread is 1/4"-18 MPT (male pipe thread) or 1/4"-18 NPT-M (National Pipe Thread - male) for the fitting, and 1/4"-18 FPT or 1/4"-NPT-F for the tank. If you are going to use a tap to clean up the threads in the tank be careful you don't overdo it, with a tapered thread the farther you go in the bigger the hole, and you may inadvertently make it too large for the valve to properly seat. DAHIK.
Don't forget to put a screen into the gas valve before reinserting it.
JayJay
Y-Blockhead
Well-known member
Haha, Have you ever seen a ¼" pipe thread that wasn't ¼-18 NPT? I don't need no stinky technical names...
No, I just wanted to emphasize the different thread standards. Wasn't trying to clarify for you. I've seen more than a couple of folks screw a 1/4"-20 SAE into a 1/4"-18 NPT without understanding the difference. It will start but then when it gets tough they just keep turning and totally screw up the fitting. Not something you want to do on the bottom of the fuel tank.Haha, Have you ever seen a ¼" pipe thread that wasn't ¼-18 NPT? I don't need no stinky technical names...
JayJay
Pipewrench
New member
Im trying to find out the same thing. Have a new tank in the back and Im using the stock Model-A 1930 shut off valve. Cant use the aftermarket pipe since its to short.
Pipewrench
New member
Its 5/8" - 18
johnbuckley
Well-known member
" Haha, Have you ever seen a ¼" pipe thread that wasn't ¼-18 NPT? ....Y-Blockhead"
Oh yes, in the wide world beyond the shores of the USA.
Oh yes, in the wide world beyond the shores of the USA.
Keith True
Well-known member
I think you need to back up a little bit.The tank thread size is 1/4 pipe.It is not fine.The outlet to the gas line is not pipe or compression,it is flare.
BRENT in 10-uh-C
Well-known member
This is kinda getting way skewed. The output is ⅝-18 U.S.F thread, so it is not anything special -however where the issue can be found is modern fittings are not always manufactured to the same thread diameter as Ford engineers specified.
Below is a PDF that shows a portion of the A-9190 print that gives exact specification of the threads. As shown in the print, Ford used special gages to verify fit for many pieces such as this in their QC process.
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Duke - Others have very ably preceded me, but:
1/4"-18 NPTF gas tank fitting, that's 1/4"-18 National Pipe Thread FEMALE, not fine. The NPT standard defines the taper and the pitch, and the F defines that it's a female (internal thread). The corresponding fitting on the valve is 1/4"-18 NPTM, with the "M" standing for "male" (external thread).
Output to the gas line is (as noted above) 5/8"-18. But as I stated above, it's a flare fitting. I believe that a 5/8"-18 UNF (Unified National Fine, which is 5/8"-18) die should chase the threads if that's what you're after.
And we don't even want to start a conversation about thread shapes...
JayJay
BRENT in 10-uh-C
Well-known member
I don't want to sound like we are ganging up on you as that is definitely not my intent, but look at the print above and I think you will see that it really is not smart to "chase" the tank threads unless you have the proper tap ...which Ford used a different thread pitch than what I think you will find in taps today. I have experienced many gas tanks that had the threads cut oversized due to an incorrect tap size.
Concur. I've found over the years in many pipe thread applications that "chasing" a female tapered fitting with a tap results in an oversize hole, and the male fitting threads in too far. Many folks equate "chasing" with "cutting new metal". If you cut new metal with a tapered tap you are increasing the diameter of the hole. If you do choose to "chase" a tapered thread hole, be sure to do it very delicately so that you are only cutting rust or paint, not enlarging the hole. Some time in the last 90 years someone(s) did that to the fuel valve seat in the tank of my pickup, and the valve bottoms out in the hole without sealing tight. Needs liberal doses of thread sealant, and frequent replacement (the sealant, not the valve).
BTW, same caution on "chasing" the GAV housing thread in a Zenith, that's a 1/8"-27 NPTF.
JayJay