The Stovebolt Site Forums The Shop Area General Truck Talk How tight for a brass nipple?

I'm installing a 1" long brass nipple, 1/8" pipe thread, 27 TPI. One end goes into a female fitting on the gas tank for fuel output, the other end goes into a 90 degree fitting that connects to the fuel line and is also a fuel shutoff valve.
I don't want this to leak and I don't want to do the job more than once and I don't want to break anything---especially the female fitting in the tank!
When I screw the nipple into the tank fitting it starts to get tight after just a little turning. How much can I tighten it? A 1/2 turn, 1 turn? What is the best tool to use to get it tight without damage?
Would it be better to install the nipple into the 90* fuel line/shutoff fitting first? I'm trying to line it up and use the existing fuel line so it has to be tight enough not to leak.
Finally, what kind of thread sealer, if any, would be best?
Thanks in advance for answering such basic questions! I know what I know but there is lots I don't know! Jim

I would obtain a steel nipple of the same size and thread as your brass nipple. You can cut longitudinal grooves in the steel nipple to help the rust find a way out as you use this nipple as a thread cleaner.
The brass nipple will then go in much easier and you will have a better feel for how tight is tight enough. I would not use any sealer if you can clean up the threads.
Carl

Or you could use a 1/8" pipe tap, don't go more than 3/4 of it's depth.
Yes, put the ell on first, but not tightly. Then turn the fitting to tighten both in. That will give you the best chance to get the alignment correct, because both ends will share the torque.

Way too much worry. There is low pressure. Just tighten tight, it's an interference fit. Put a brass nipple into the tank, then put on the valve and let it sit over night with a pan under it to leak test all those joints. No leak? Continue. Leak? determine where and tighten a bit. Leak test again. The most critical part is the gas tank female. If you bust that off, it's a bad day. You can use a paste type sealant for gas if you want to. Just don't have it near the starting end of threads. A little space of dry threads first. That way it won't migrate into the system.
If you have other places that you fear a leak, use a valve to temporarily close off to test. Of course you need gas in the tank for these tests. Don't use any long wrenches and keep your hand near the fitting, not on the end of the wrench, at first. Tighten real tight from there. Then slide out to end for a small snug turn. Never jerk any fastener when tightening. This is a no no in the engineering world. You have no idea or feel of the pressure at that point.

For small size threads, with your hand close to the fastener you can't over tighten and your natural instincts will tell your brain when to stop....or You can do what I do, turn til my elbow clicks.

If you tighten it real tight and it still leaks, you will have to take it loose and retighten it or get another Chinese fitting out of the same bin. The law of probabilities says the next one will work. Six Sigma. If it still leaks, park it over some weeds you want to die.

Here's my take on the subject from someone who's been a mechanic of one sort or another for 50 years the last 32 before retirement as an industrial maintenance guy. The rule of thumb I go by is, the threads need to be clean on all parts, and should thread on close to 2 turns before starting to bind up. I would never try to put a pipe threaded joint together without some kind of pipe dope or tape, if for no other reason than it serves as a lubricant. In this case I'd go with something advertised as being fuel safe. As far as how much to tighten goes I agree that you need to use the shortest tool possible and keep your hand close to the fitting tightening the whole assembly at once. Once it starts feeling tight bring it around the last part of a turn to where the fitting needs to be pointing. It is a matter of feel as to if its tight enough but if it leaks although its a pain you can always tighten more or take it apart and do it again if need be.

What Dave ^ said about using pipe dope. Without it the threads can gall and leak even though they feel tight.

A product called Gasoilia would be ideal, but I would not be afraid to use teflon tape on the nipple threads. Just wrap it so that it doesn't lap over the end of the threads. As far as tight, use a small wrench and grab it around where you've put the wrench on the fitting and turn it like you would a screwdriver (arm aligned with the nipple). You probably won't be in danger of overtightening it or breaking something unless you're a competitor in the World's Strongest Man contest.

Thanks everyone. I'm going to use a 1-1/2" nipple instead of the shorter length as it's easier to grasp and turn.
I've got Permatex thread sealant which is rated for fuel fittings or I also could use teflon tape. I'm leaning towards trying the Permatex.
I dry fitted the connections and think I'll be able to get things to line up like I need. Wish me luck!

No Teflon tape should be used. It does nasty things to the tiny holes in the carburetor.

If applied correctly, (not lapped over the end of the male threads), nothing will wind up in the system. If you do a sloppy job of wrapping, then you'll get bits of teflon tape where they don't belong.

Agree with Carl. Teflon tape is not recommended. Definitely the white and the yellow is not. It will shred and possibly turn to goo. The best thing is nothing unless it is made for gasoline.
If there is a leak and the white or the yellow seals it, it means there was a gap, which means the tape filled the gap, which means the gas will come in contact with it, which means there is a reverse leak path back into the line.

It may work, but the risk for me, doesn't work.

I'm hopeful that the teflon tape isn't a death sentence for my carb. I just went through this yesterday on my 51. The petcock was leaking and my research indicated that replacing it with a brass valve from the hardware store was the way to go. When I went to install it-- one of my kids had obsconded with it. So, I pulled apart the old valve, chased the threads and wrapped them with teflon tape. Reinstalled and added a gallon of no ethanol fuel to the tank. Gave my fuel filler a kiss and blew in- gas flowed to the pump so no blockage. No leaking from the valve after an hour or two yesterday.
Now I'm fighting the next battle but hope the tape doesn't come back to bite me.

Don't lose any sleep over it, your old valve will probably start leaking before your threads do. It is just another way that these old trucks mark their territory.

Eureka jim This is 4 years late but it might help others brass fittings often get tight too soon. Use the 1/8 th tap to free them up,if using teflon (I do) pull off about 1 foot and stick it on a board flat. Use a sharp knife to split it lengthwise into 3/16 th strips,then like it says stay away from the end so it wont shed in there. Since you freed-up the threads with your tap you'll get enough depth to seal the joint. If you dont want teflon get paste pipe dope rated for gasoline,probably a teflon type. With teflon shoot for 3.5 rounds,narrow tape= neat job !!Good Luck ! My 43rd year of fighting leaks in water oil gas propane natural gasoline diesel ammonia !

Ground up Teflon works well for me, lasts so long in the can, it starts to dry out. A shot of @cetone revives it.

Ed

While working in the Nuclear Power Generation field for 41 years (machinist for 27 of those years), when teflon tape first came out, it was the “cure all” for any pipe thread job. After several pneumatic valve operator failures, they banned the use of teflon tape and substituted it with teflon paste. The issue was not that the teflon was incompatible with the medium being used, but due to improper installation. The tape must be installed so when tightening the joint, it would tend to tighten on the pipe threads and not unravel. In addition, you must start the tape on the second or third thread so it doesn’t wrap over the end.

All that being stated, I use teflon paste as it is much easier to apply and does IMHO, a superior job.

As for the amount of thread, I shoot for two to three threads tightened by hand, then tighten snug, not gorilla tight. Use a pipe tap to clean and deepen the thread if you don’t get at least two threads. You can always tighten a bit more if you encounter a leak ,but if you over tighten brass, you will more than likely snap it off in the fitting, then you got a bigger problem.

Hey Fixite-7, thanks for the reply to my 4 year old question! It has been so long that I don't even remember what I did to stop my leak---I think I used a Permatex gas proof thread sealer and installed the valve into the tank fitting. The next day there was a very minor seepage from the connection but before I could get back to try the repair again it stopped and has no seepage now!

klhansen Split the teflon with a sharp knife,then wrap on neat go clockwise so it doesn't wad up .