---------------------------------------------------------- Yak-List Digest Archive --- Total Messages Posted Wed 06/14/23: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 01:13 PM - Re: weepy fuel header tank fitting, CJ6A (Justin Drafts) 2. 04:15 PM - Re: Re: weepy fuel header tank fitting, CJ6A. Attn: Justin Drafts (W LANNON) 3. 05:32 PM - Re: Re: weepy fuel header tank fitting, CJ6A. Attn: Justin Drafts (Robert Graves) ________________________________ Message 1 _____________________________________ Time: 01:13:42 PM PST US From: Justin Drafts Subject: Yak-List: 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 @ Paine Field WA ________________________________ Message 2 _____________________________________ Time: 04:15:34 PM PST US From: W LANNON Subject: Re: Yak-List: 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" Sent: Wednesday, June 14, 2023 1:13:06 PM Subject: Yak-List: 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 @ Paine Field WA ________________________________ Message 3 _____________________________________ Time: 05:32:58 PM PST US From: Robert Graves Subject: Re: Yak-List: RE: weepy fuel header tank fitting, CJ6A. Attn: Justin Drafts Thanks for the explanation Walt. Haven=99t heard from you in a long ti me. Hope you=99re doing well. Sent from my iPhone > On Jun 14, 2023, at 7:17 PM, W LANNON wrote: > > =EF=BB > Hi Justin; > > Don't even think about re-tapping these threads. > > What you (and probably most CJ owners) need is at least a basic understand ing of Pipe Thread. Pipe thread was developed by the British in the early d ays of steam power. It is a British Standard unilaterally adopted by the re st of the world. The US of course made some minor changes and re-issued it a s a US Standard as well. > > There are two distinctly different versions of Pipe Thread both of which a re clearly shown in your photo. The size designation is based on the O.D. o f the pipe (or tubing) that the fittings enclose. In this case there is no s uch pipe or tubing but if there were it would probably be referred to as 5/1 6" or 3/8" (I am at home so do not have one to measure). In any case the Ch inese 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 corresponding ly tapered hole it is reliably self-sealing. If it were NPS to NPS the joi nt would require a sealing washer. > > What you have shown here is an NPS fitting installed in an NPT hole. Leak age is guaranteed! I am sure you are not alone. > > Best regards; > Walt > > > > > > > > From: "Justin Drafts" > To: yak-list@matronics.com > Sent: Wednesday, June 14, 2023 1:13:06 PM > Subject: Yak-List: 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 f or ref.) > Ie- what size tap to use? And where to find? > Advice? > > Thanks all, any advice much appreciated- > Justin Drafts > N280NC @ Paine Field WA > >
>
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