NPT fuel fittings weeping

[scottiec]

Hi Guys!

I FIRED THE MOTOR YESTERDAY! But only very briefly since I still need to get some stuff done before letting it idle for a while and really run. This junkyard motor I rescued came back to life. No hard cranking, no sputtering. Once fuel made into the bowls, this thing exploded to life. Timing sounded good too even though I did it quickly and just kind of eyeballed it.

Here is where I would like some advice. The inlet and outlet on my mechanical fuel pump are weeping fuel. I can tell because the liquid thread sealer I used on is becoming runny and diluted with fuel. So its not leaking leaking, but weeping. I am nervous about cranking down even more on the brass hose fittings that go into the pump. What do you guys suggest?

Scottie

[phileas_fogg]

I got nothing to solve your problem, but WAY TO GO! Surely there's a video somewhere...


John

[scottiec]

I got nothing to solve your problem, but WAY TO GO! Surely there's a video somewhere...


John

LOL! Will be taking video with my father today.

[edwardb]

Hi Guys!

I FIRED THE MOTOR YESTERDAY! But only very briefly since I still need to get some stuff done before letting it idle for a while and really run. This junkyard motor I rescued came back to life. No hard cranking, no sputtering. Once fuel made into the bowls, this thing exploded to life. Timing sounded good too even though I did it quickly and just kind of eyeballed it.

Here is where I would like some advice. The inlet and outlet on my mechanical fuel pump are weeping fuel. I can tell because the liquid thread sealer I used on is becoming runny and diluted with fuel. So its not leaking leaking, but weeping. I am nervous about cranking down even more on the brass hose fittings that go into the pump. What do you guys suggest?

Scottie

Congrats on your first start! A big milestone.

For the fuel pump fittings, assuming they really are NPT (ones I've used were) then the seal is made by tapered threads. They do need to be tight and sealant is mandatory. Make sure they're not bottoming out. But also the right number of threads going in. Thread engagement should be 4 to 6 turns. Another hint: Some instructions I've seen for NPT's say to screw it in and tighten several times without sealant to burnish the threads. Then apply sealant and final tighten.

If the sealant is running out, maybe you used the wrong kind or didn't allow it to set long enough? Most I've used (like Loctite 565) say to wait 24 hours. Although at the relatively low pressure of a mechanical fuel pump, they should seal pretty much immediately.

[GoDadGo]

Pull the fittings and replace them.
Use teflon tape and tighten the new fittings down.
This should do the trick.

NOTE: Remember that when you disconnect the fittings fuel will siphon from the tank so be careful any time you are dealing with any fuel.

[scottiec]

Congrats on your first start! A big milestone.

For the fuel pump fittings, assuming they really are NPT (ones I've used were) then the seal is made by tapered threads. They do need to be tight and sealant is mandatory. Make sure they're not bottoming out. But also the right number of threads going in. Thread engagement should be 4 to 6 turns. Another hint: Some instructions I've seen for NPT's say to screw it in and tighten several times without sealant to burnish the threads. Then apply sealant and final tighten.

If the sealant is running out, maybe you used the wrong kind or didn't allow it to set long enough? Most I've used (like Loctite 565) say to wait 24 hours. Although at the relatively low pressure of a mechanical fuel pump, they should seal pretty much immediately.

Edward - It is a sealant that doesn't dry I believe. It is PTFE rated. I will check to make sure it is not bottoming out.

[scottiec]

Pull the fittings and replace them.
Use teflon tape and tighten the new fittings down.
This should do the trick.

NOTE: Remember that when you disconnect the fittings fuel will siphon from the tank so be careful any time you are dealing with any fuel.

Is there a reason I should replace the fittings? Can't I just clean them up and use teflon tape? I recall reading not to use tape and to go with the liquid sealer, but not sure of the reasoning behind that.

[DaveS53]

There is no need to replace the fittings, just clean off the sealant apply at least 4 turns of tape. Wrap the tape clockwise and don't let the tape lap past the end of the fitting. I always hold a fitting or pipe in my left hand and the roll of tape in my right, with the running clock wise over the top of the roll. That makes the tape come off the roll easily as it's applied to the fitting.

I get far more experience wrapping lawn sprinkler fittings than anything. PVC threads can be under-size and require at least 6 turns to create a seal without a lot of torque.

[scottiec]

There is no need to replace the fittings, just clean off the sealant apply at least 4 turns of tape. Wrap the tape clockwise and don' let the tape lap past the end of the fitting. I always hold a fitting or pipe in my left hand and the roll of tape in my right, with the running clock wise over the top of the roll. That makes the tape come off the roll easily as it's applied to the fitting.

I get far more experience wrapping lawn sprinkler fittings than anything. PVC threads can be under-size and require at least 6 turns to create a seal without a lot of torque.

Dave,

Thanks for the info. I will make sure I have enough turns on the threads, if it still weeps, then I will pull out and tape.

[CVOBill]

Congrats on the first start and it sounds like you have a plan for the weeping.

[scottiec]

Congrats on the first start and it sounds like you have a plan for the weeping.

Thanks Bill. Can't wait to get home from work and get back at it.

[RoadRacer]

FWIW, I always use this stuff, and make sure it's only on the threads, not the sealing part of the fitting.

https://www.summitracing.com/parts/arp-100-9904

[edwardb]

Edward - It is a sealant that doesn't dry I believe. It is PTFE rated. I will check to make sure it is not bottoming out.

Right. Most don't get hard. But they still have a cure time. Check the instructions. I see multiple recommendations for Teflon tape. FWIW, many don't recommend tape for fuel lines. Don't flame me. Just reporting what I've read and heard multiple times. I've not had any trouble getting a good seal with any of the mainline sealants from Loctite, Permatex, or the ARP product mentioned.

[scottiec]

Right. Most don't get hard. But they still have a cure time. Check the instructions. I see multiple recommendations for Teflon tape. FWIW, many don't recommend tape for fuel lines. Don't flame me. Just reporting what I've read and heard multiple times. I've not had any trouble getting a good seal with any of the mainline sealants from Loctite, Permatex, or the ARP product mentioned.

Edward - Thanks for the response. Trust me, just like you, I have heard to not to use tape. But I can't find a good reason. I'll let you guys know if I am still having trouble after I run it tonight.

[jrcuz]

Way to go Scott, mostly good news. You'll get the weeping stopped quickly. BTW I 'm planning to do my eng/trans install Fri 8/11. I've asked John but he is not sure he will make it. Craig will be coming thankfully. A local to me builder will be here also. You're invited if you don't have to work. Waiting on the video.
JR

[NAZ]

Save the teflon tape for the plumber -- it has no place in automotive. Using teflon tape will result in pieces of the tape being sheared off and contaminating whatever system you're working with. For a water system in your house there's not much it will plug but a hydraulic or fuel system on a vehicle is not as tolerant. I use Loctite PST like edwardb suggested and it works great. Make sure you really do have NPT threads on both parts not just that the thread count looks close. NPT (National Pipe Thread) has approximately 1-degree of taper so one end of the thread will be noticeably larger than the other. Inspect the threads on both the ID & OD for damage -- as was mentioned above, the threads make the seal so they must be damage free.

[DaveS53]

You can get tape sheared off if you're dumb and let the tape extend past the end of the fitting. Otherwise, no problem. I have also used Earl's thread sealant with no problems.

[Gromit]

Maybe a stupid question. If its a mechanical "stock" pump perhaps the fitting should be a flared tubing like a brake line? In that case the problem is the tubing flare you don't need to put sealant on the threaded nut the tube goes through.

Chris AKA Gromit

[Connedale]

I can tell you that teflon tape used on high strength steel NPT connections can hold past 13,000psi in a test chamber!

[Connedale]

Also, be careful. Once NPTs are galled, you are much more likely to get a leak. Normally the male galls, so easy to replace.

[initiator]

In my experience, once NPTs are galled (only happened in stainless), they've become one with each other and destined to never part again.

[DaveS53]

The pipe fitters that I've worked with hated installing SS pipe due to the chances of galling. They used both teflon tape and anti-seize to seal the pipe and avoid galling.

The same goes for using SS bolts and nuts. If you forget to use ant-seize, you may never get the two apart. If only one part is SS and the other aluminum or steel, it not likely to be a problem. I still use ant-seize when I put SS bolts into aluminum.

I used stainless steel bolts and nylock nuts for just about everything bolted onto my car. All of the bolts screwed into threads that I tapped into the frame are also stainless.

[NAZ]

Teflon tape vs anaerobic pipe sealant is a battle of opinions about like the age-old question of which is better, Ford or Chevy. I've formed my opinion based on my professional experience spanning close to half-century now in maintenance roles where I used these products and as an engineer, specified these products for maintenance personnel to use. Others may have different experiences. I've used both with success but from my experience, the anaerobic sealants are superior and need no special application technique to successfully make a seal. Follow the link to see what a maintenance industry organization Plant Engineering has to say about sealants. http://www.plantengineering.com/single-article/guidelines-for-choosing-a-pipe-thread-sealant/5103ee62235def2053cec5d46dd34156.html

[scottiec]

This is all incredible info guys. Thanks so much.

Jcruz I will let you know man!

[rich grsc]

Save the teflon tape for the plumber -- it has no place in automotive. Using teflon tape will result in pieces of the tape being sheared off and contaminating whatever system you're working with. For a water system in your house there's not much it will plug but a hydraulic or fuel system on a vehicle is not as tolerant. I use Loctite PST like edwardb suggested and it works great. Make sure you really do have NPT threads on both parts not just that the thread count looks close. NPT (National Pipe Thread) has approximately 1-degree of taper so one end of the thread will be noticeably larger than the other. Inspect the threads on both the ID & OD for damage -- as was mentioned above, the threads make the seal so they must be damage free.

My thoughts exactly. Although I have used it when I had nothing else available. Its far too easy to get a piece inside of the fuel line.