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Old 07-24-2021, 06:48 PM   #1
Barry in St.Paul
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Default gastank shutoff valve leak at threads- options?

hi,
just installed a new shut-off valve on dad's 29 roadster. Have always used Permatex high-tack on these, and never had one leak (or similar threads).

Was disappointed a week later to come up to farm and wipe my fingers over the new valve and have slight weep, just enough to leave trace of gas on fingers. What to do differently? No way I'd get a full additional 360deg rotation to further tighten without snapping the thing off (or stripping threads). Different type of sealant? Teflon tape? (which I know is discouraged in gas systems but WAS on the valve I removed and no leaks for 15 years). Don't have a NPT pipe tap/die set or i'd just touch it a bit for that additional turn. Suggestions? Hate any gas fumes floating around with six cars in the shop. Thanks.

PS: just re-registered after a few years off the site (Studebaker project now). The thing re-set my standard username to something I'll NEVER remember; anyway to SELECT my own username like every other system??
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Old 07-24-2021, 07:42 PM   #2
LeonardS
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Default Re: gastank shutoff valve leak at threads- options?

How about Harvey Seal, gas pipe sealant? It’s non hardening. I’m sure there are similar products. Are you sure it’s the threads and not the valve?
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Old 07-24-2021, 07:44 PM   #3
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Default Re: gastank shutoff valve leak at threads- options?

Well you could use yellow teflon tape which is used for chemicals and gas lines. Are you sure it is coming from the threads?
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Old 07-24-2021, 07:49 PM   #4
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Default Re: gastank shutoff valve leak at threads- options?

I use Loc-tite thread sealer. It is made for automotive fuel fittings. Works great. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Last edited by Ruth; 07-24-2021 at 08:15 PM.
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Old 07-24-2021, 08:28 PM   #5
J Franklin
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Default Re: gastank shutoff valve leak at threads- options?

Are you sure the leak is from the threads? or maybe the shut-off body. A bit of bar hand soap on the threads will stop gas leaks.

Last edited by J Franklin; 07-24-2021 at 11:38 PM.
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Old 07-24-2021, 10:07 PM   #6
Barry in St.Paul
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Default Re: gastank shutoff valve leak at threads- options?

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thanks.
Yes, re: threads. Or, at least I wiped it off several times, and then later felt ONLY along gas tank/threaded area. And always damp. Brand new valve (not that they can't be bad). Would it wick UP the valve to the tank? Rest of valve not really anything much, sure seems to be the threads... I guess next time I'm up will have to wrap it tightly with a shop towel, and check it after a bit and see where it STARTS. (and IF the valve, be very PO'd yet another new valve failed; last one only 10 years old and leaking THROUGH the valve so weeping at carb instead).

The one silver lining would be i waited 3 months for the little screen/filter to stick in the valve & tank, back-order after back order, three different companies, and finally made my own using a .22 shell (lathed off the firing rim) and poorly soldered an old Ford 8N screen rolled up. 3 days later Dad called and the back-ordered screen showed up from Mac's :-) Sigh...
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Old 07-24-2021, 10:18 PM   #7
CWPASADENA
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Default Re: gastank shutoff valve leak at threads- options?

If you use Teflon Tape, do not wrap it around the first thread or two. That will prevent it from sheading and have the stuff get loose and get caught in the valve or in the filter.

I try to stay away from Teflon Tape but sometimes you have to use it as a last resort.

My opinion,

Chris W.
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Old 07-25-2021, 07:23 AM   #8
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Default Re: gastank shutoff valve leak at threads- options?

Are you sure it is gas or just the valve sweating from high humidity? Buy a rebuild kit for the old one and re-install.
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Old 07-25-2021, 08:19 AM   #9
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Default Re: gastank shutoff valve leak at threads- options?

Something solid other than teflon that forms into place. This works for me. Smash it into the second and third male thread.
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Old 07-25-2021, 11:06 AM   #10
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Default Re: gastank shutoff valve leak at threads- options?

I use teflon pipe dope that plumbers use. Has chunks of teflon in it and have never had a leak, plumbing or otherwise.
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Old 07-25-2021, 01:35 PM   #11
Ernie Vitucci
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Default Re: gastank shutoff valve leak at threads- options?

Good Morning...I am like ronn...the pipe dope works...one other caution...when you screw the valve into the tank, do NOT stop turning in the rotation and 'back up' as this almost always creates a leak...I've done a number of these valves and learned to give it a dry fit, count the turns, and see how it alligns with the pipe that goes to the fire wall...then remove the valve, coat with dope, and put in slowly turning, counting the turns, and not stopping until I arrive at the final position from the dry fit...Ernie in Arizona
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Old 07-25-2021, 02:59 PM   #12
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Default Re: gastank shutoff valve leak at threads- options?

Permatex #2 This is a tried and true product that is often overlooked.
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Old 07-25-2021, 04:08 PM   #13
john in illinois
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Default Re: gastank shutoff valve leak at threads- options?

I use loctite pipe sealant as mentioned. It has been proven in industry for years.

Another trick is to flow solder in the pipe threads to make it fit tighter on the right position. I have done this on model T fuel bowls.
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Last edited by john in illinois; 07-25-2021 at 04:19 PM.
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