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Old 03-26-2018, 11:00 AM   #1
hazelhoff
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Default Shut off thread

I had to rebuild the lower part of my gas tank. Thougt I welded the right nut in to accomodate a new shut off valve. Since Murphy is living living upstairs, obviously a repo fuel valve does not fit.

I somehow retreived the right thread size in the past, but lost the little yellow paper on the way. murphy will find it when the job is closed I guess ...

For once and for all, what in earth is the CORRECT thread for a 28/29 to connect to the tank ? Remember, from what I remember from welding in this 'nut', I found it at a Caterpillar dealer, out of the old stock, being served by an elderly gentleman who took some two hours to fnd it. Proud he was succeding !

Please help me out here ....

Henk
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Old 03-26-2018, 11:26 AM   #2
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Default Re: Shut off thread

1/4"- pipe thread. Use a 1/4"-18 NPT Pipe Tap
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Old 03-26-2018, 12:15 PM   #3
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Default Re: Shut off thread

Quote:
Originally Posted by Y-Blockhead View Post
1/4"- pipe thread. Use a 1/4"-18 NPT Pipe Tap
Ok,

Do you know why the repos are 5/8 straight thread ? Even with bert's ?

Thx,

Henk
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Old 03-26-2018, 12:41 PM   #4
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Default Re: Shut off thread

I am sorry, I mean the repos are 1/2 " npt aren't they ?
1/4 " is quite small ....
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Old 03-26-2018, 12:47 PM   #5
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Default Re: Shut off thread

Pipe thread size is NOT the actual size. Google this or you will be even more confused.
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Old 03-26-2018, 02:00 PM   #6
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Default Re: Shut off thread

Quote:
Originally Posted by 1930-Pickup View Post
Pipe thread size is NOT the actual size. Google this or you will be even more confused.
Boy isn't that the truth.

Quote:
Originally Posted by hazelhoff View Post
I am sorry, I mean the repos are 1/2 " npt aren't they ?
1/4 " is quite small ....
Just for a backup I re-checked. This direct from Bratton's...

Solid BRASS with original style stamped handle. This is a quality U.S. made valve. Gas valve threads in tank are 1/4" pipe thread. When the handle is vertical the gas is flowing. For 1928 to May 1931 with valve under tank. Won't leak; 3 year warranty.
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Old 03-26-2018, 02:11 PM   #7
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Default Re: Shut off thread

Quote:
Originally Posted by hazelhoff View Post
I am sorry, I mean the repos are 1/2 " npt aren't they ?
1/4 " is quite small ....
I just went out to the garage. The threads on a NPT tap is ~.845", almost ⅞" in diameter.
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Last edited by Y-Blockhead; 03-26-2018 at 11:21 PM.
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Old 03-26-2018, 07:58 PM   #8
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Default Re: Shut off thread

Years Ago I Had A Gas Tank With A Lot Of Crud In The Tank. After Washing The Tank Out Several Times. I Ran A 1/4 x 18 ? Short Pipe In The Tank Approximately 1/4 Inch Above The Inside Bottom Of The Tank. I Then Put A Fitting On The Bottom Of Tank For Shut Of Valve. That Worked Great. Please Dry Fit This My Memory Maybe Off A Little lol
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Old 03-26-2018, 10:50 PM   #9
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Default Re: Shut off thread

Have not read the catalogs from Snyders, Brattons or Berts as to what the gas tank threads are, but I just measured a 1928 CCPU gas tank and a 1930 Coupe gas tank shut off valve thread.. i measure1/4" pipe thread and a 1/4" pipe fitting screw into the shut Off boss in the bottom of the tanks.
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Old 03-27-2018, 07:24 AM   #10
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Default Re: Shut off thread
Have not read the catalogs from Snyders, Brattons or Berts as to what the gas tank threads are, but I just measured a 1928 CCPU gas tank and a 1930 Coupe gas tank shut off valve thread.. i measure1/4" pipe thread and a 1/4" pipe fitting screw into the shut Off boss in the bottom of the tanks.

Agree....I'm working on a 29 tank right now. It's 1/4" pipe thread. Pipe threads are a different animal from bolt and nut threads. Do not confuse the two types of threads.
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Old 03-27-2018, 03:32 PM   #11
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Default Re: Shut off thread

And remember, there are MALE & FEMALE threads! Common sense will tell you which is which---LOL---Do you have KIDS?---When sumbody ask my Single Son that, he'd say, "NOT THAT I KNOW ABOUT"--LOL
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Old 03-27-2018, 05:31 PM   #12
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Default Re: Shut off thread

NPT (Model A shut-off valve-male end) vs. NPTF Taper Pipe Threads

The two most common taper pipe threads used in the United States are NPT (Model A shutoff male end) and NPTF. Applications range from electrical conduits and hand railings to high-pressure pipe lines that carry gas or caustic fluids.

NPT threads are for mechanical or low-pressure air or fluid applications and require the use of sealing compounds like Teflon tape, to provide the seal. When the application is more critical, and the sealing compound may fail due to high heat or pressure, NPTF Dryseal threads are used.

Visually, both threads appear to be identical. Both have a taper over one foot of length. Both have the same pitch diameter at the top of the hole of internal threads or end of the pipe on external threads, and both have the same thread lengths or depths. However, there is a subtle difference in the thread form that differentiates the two. The major and minor diameters of both threads differ slightly.

With NPT threads, after a wrench is applied, slight spaces at the major and minor diameters may exist that would allow the assembly to leak and therefore a sealing compound is used to fill any gaps.

On the other hand, NPTF threads are designed to ensure that sufficient crushing of the entire thread form will take place to produce a mechanical seal.
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Old 03-27-2018, 06:05 PM   #13
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Default Re: Shut off thread

The OD of 1/4" pipe is .540"

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Old 03-27-2018, 08:38 PM   #14
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Default Re: Shut off thread

I hope the OP got his answer now, from the 2nd post on. LOL
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Old 01-03-2020, 10:28 PM   #15
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Default Re: Shut off thread

What method did you use to flush out the tank?
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Old 01-03-2020, 10:45 PM   #16
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Default Re: Shut off thread

Suggest starting your own thread or google "Fordbarn; Model A gas tank cleaning"
I see you joined in 2012 and this is your first post, welcome to the forum.
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Old 01-04-2020, 12:42 PM   #17
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Default Re: Shut off thread

The national pipe thread standards are based on the inside diameter of the pipe since that is how pipe is used. It's all about flow characteristics of the pipe. The size and pitch of the tapered thread is always going to be much larger than the inside diameter since it affects the outside diameter of the pipe only. The most common three standards are straight thread NPS, tapered thread NPT, and tapered thread for fuel NPTF or dryseal type. There are others too but they are not common and the NPTF is also not all that common either.

The thread size and pitch are the same between NPT and NPTF but the root and crest of the threads is cut differently so the taps & dies are not interchangeable. You can get away with using NPTF tooling for an NPT fit but it won't work the other way around since NPT taps & dies will not create a dry seal.

This link illustrates it better: https://content.cpcworldwide.com/Por...20Products.pdf
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Old 01-04-2020, 11:12 PM   #18
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Default Re: Shut off thread

Good info, but this string is from March of 2018.
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Old 01-05-2020, 09:53 AM   #19
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Default Re: Shut off thread

A 1/4-18 NPT (National Pipe Thread) is used to thread a 1/4" inside diameter pipe. A 1/4" NPT tap will produce a 1/4" tapered thread with 18 threads per inch. US pipe tap sizes are sized by the inside diameter of pipe, not the the OD (outside diameter).
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Old 01-05-2020, 10:19 AM   #20
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Default Re: Shut off thread

Somebody likely linked it to a thread and it came back up. I don't always look at the dates very carefully. New guys do this stuff all the time instead of just making a new thread.
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