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Flibob
Joined: 25 Jun 2014
Posts: 28
Location: Indiana
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 Posted: Wed Jun 14, 2023 4:32 pm Post subject: weepy fuel header tank fitting, CJ6A. Attn: Justin Draft |
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Thanks for the explanation Walt. Haven’t heard from you in a long time. Hope you’re doing well.
Sent from my iPhone
| Quote: | On Jun 14, 2023, at 7:17 PM, W LANNON <wlannon(at)shaw.ca> wrote:
Hi Justin;
Don't even think about re-tapping these threads.
What you (and probably most CJ owners) need is at least a basic understanding of Pipe Thread. Pipe thread was developed by the British in the early days of steam power. It is a British Standard unilaterally adopted by the rest of the world. The US of course made some minor changes and re-issued it as a US Standard as well.
There are two distinctly different versions of Pipe Thread both of which are clearly shown in your photo. The size designation is based on the O.D. of the pipe (or tubing) that the fittings enclose. In this case there is no such pipe or tubing but if there were it would probably be referred to as 5/16" or 3/8" (I am at home so do not have one to measure). In any case the Chinese designation system is probably quite different.
If you take a close look at the two fittings you will notice the thread on the upper one is tapered and the lower one is straight!
Let's call these 3/8" fittings. The upper one would then be a 3/8" NPT (National Pipe Taper) and the lower one a 3/8" NPS (National Pipe Straight). They are not interchangeable.
NPT is probably the most common since, when installed in the correspondingly tapered hole it is reliably self-sealing. If it were NPS to NPS the joint would require a sealing washer.
What you have shown here is an NPS fitting installed in an NPT hole. Leakage is guaranteed! I am sure you are not alone.
Best regards;
Walt
From: "Justin Drafts" <draftsjust417(at)gmail.com>
To: yak-list(at)matronics.com
Sent: Wednesday, June 14, 2023 1:13:06 PM
Subject: RE: weepy fuel header tank fitting, CJ6A
Ok CJ6 maintenance experts, I please need some advice.
It's time to resolve my fuel header tank's weep from its forward fitting. (A chronic CJ6 problem, I understand?)
Removing the original Chinese fitting, I see the threads in tank & fitting have been scored. I'll try to tap new threads in the tank, but... what size threads are these? (Pls see the 2 pix, the new fitting next to the old one for ref.)
Ie- what size tap to use? And where to find?
Advice?
Thanks all, any advice much appreciated-
Justin Drafts
N280NC (at) Paine Field WA
<header tank fitting 2 (N280NC).jpg>
<header tank fitting 3 (N280NC).jpg>
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richard.goode(at)russiana
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| Posted: Thu Jun 15, 2023 7:23 am Post subject: weepy fuel header tank fitting, CJ6A. Attn: Justin Draft |
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An amusing tale comes from when I was in Moscow specifying a Sukhoi 26 in 1987 – the first one that was being sold directly to a private owner. I told the engineers that I wanted a smoke system, and this was a concept that the Sukhoi engineers were simply not aware of, as I explained how I needed an additional tank – which they cleverly put into the wings behind the spar – fuel was in front – and then I said one needed an electric pump to pump the diesel or oil into the exhaust pipes. Apparently there was no appropriate Russian pump, and in those days we were using a marine bilge pump which we had found was very tough and didn't mind impurities in the oil. So, on my next visit to Moscow I brought one of these pumps and give it to them, but saying that the threads on the female in and out fittings was BSP (British standard pipe) so that they would need to machine up an adapter to go to their metric fittings. The engineers came back about five minutes later saying that there was no problem whatsoever since every single domestic and industrial water pipe in Russia had exactly this British thread on the fittings! Richard.
[img]cid:image001.png(at)01D99FA5.552B1F90[/img]
RICHARD GOODE AEROBATICS
Rhodds Farm, Lyonshall, Hereford, HR5 3LW, UK
Tel: +44 (0)1544 340120
e-mail: richard.goode(at)russianaeros.com (richard.goode(at)russianaeros.com)
www.russianaeros.com
WORLD LEADERS IN SOVIET & CHINESE RADIAL AIRCRAFT ENGINES
In partnership with Aerometal Kft, Hungary.
[img]cid:image002.png(at)01D99FA5.552B1F90[/img]
From: owner-yak-list-server(at)matronics.com <owner-yak-list-server(at)matronics.com> On Behalf Of W LANNON
Sent: 15 June 2023 00:15
To: yak-list(at)matronics.com
Subject: Re: RE: weepy fuel header tank fitting, CJ6A. Attn: Justin Drafts
Hi Justin;
Don't even think about re-tapping these threads.
What you (and probably most CJ owners) need is at least a basic understanding of Pipe Thread. Pipe thread was developed by the British in the early days of steam power. It is a British Standard unilaterally adopted by the rest of the world. The US of course made some minor changes and re-issued it as a US Standard as well.
There are two distinctly different versions of Pipe Thread both of which are clearly shown in your photo. The size designation is based on the O.D. of the pipe (or tubing) that the fittings enclose. In this case there is no such pipe or tubing but if there were it would probably be referred to as 5/16" or 3/8" (I am at home so do not have one to measure). In any case the Chinese designation system is probably quite different.
If you take a close look at the two fittings you will notice the thread on the upper one is tapered and the lower one is straight!
Let's call these 3/8" fittings. The upper one would then be a 3/8" NPT (National Pipe Taper) and the lower one a 3/8" NPS (National Pipe Straight). They are not interchangeable.
NPT is probably the most common since, when installed in the correspondingly tapered hole it is reliably self-sealing. If it were NPS to NPS the joint would require a sealing washer.
What you have shown here is an NPS fitting installed in an NPT hole. Leakage is guaranteed! I am sure you are not alone.
Best regards;
Walt
From: "Justin Drafts" <draftsjust417(at)gmail.com (draftsjust417(at)gmail.com)>
To: yak-list(at)matronics.com (yak-list(at)matronics.com)
Sent: Wednesday, June 14, 2023 1:13:06 PM
Subject: RE: weepy fuel header tank fitting, CJ6A
Ok CJ6 maintenance experts, I please need some advice.
It's time to resolve my fuel header tank's weep from its forward fitting. (A chronic CJ6 problem, I understand?)
Removing the original Chinese fitting, I see the threads in tank & fitting have been scored. I'll try to tap new threads in the tank, but... what size threads are these? (Pls see the 2 pix, the new fitting next to the old one for ref.)
Ie- what size tap to use? And where to find?
Advice?
Thanks all, any advice much appreciated-
Justin Drafts
N280NC (at) Paine Field WA
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
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