New Fuel Pump Leaking

[68 Sport Satellite]

So I had recently replaced my water pump and since I had everything apart I decided to replace my fuel pump also on my 360 small block. So I ordered a Carter mechanical from Mancini to replace the original stock mechanical pump. Everything went fairly smooth. I replaced all of the rubber fuel lines and this time used fuel injection rubber hose lines to prevent kinking since it has a stiffer wall. I used the metal screw hose clamps and since the Carter pump doesn't ship with the mating brass hose fittings I picked those up at the local parts store.

When I fired it up for a test run, it was leaking like crazy from what appears to be either on the pump outlet side or from the rubber pump seals. There was so much fuel flowing I couldn't tell, but after I fired it up a 2nd time, I was able to rule out all of the rubber hose connections and it sure looks like it's coming from the pump outlet fitting.

Now after reading the Carter pump instructions that say not to use any teflon tape to seal the threads and after reading many posts on here that advise against using teflon tape, I didn't use teflon tape. I wonder if I overtightened the threads? I screwed in the brass fitting by hand with the pump out of the car and then tightened snug with a crescent wrench. I called Mancini and they said they've never heard of the Carter's leaking from the circumferential pump seals where the pieces fit together with the 8 or so screws around the pump body and they seemed almost certain it was the brass fitting and told me to use teflon thread sealant - not the tape, but the goopy stuff.

What do you guys think? I hate to have to pull the pump and I think I can get the thread sealant on without taking off the pump and the alternator all over again. Or is there a high chance I over-tightened the threads, in which case would I need to buy an all new pump because I've galled the internal pump threads?

 

[GTXKen]

You shouldn't need the tape because the threads are tapered so that when you tighten them adequately they seal. If you can seal them by tightening them I'd try the Teflon tape, just make sure you start after the first couple threads. If you get the tape in fuel line you could end up with it clogging a passage on the carb of stuck in the needle and seat, jet...etc

 

[68 Sport Satellite]

yeah, I really want to avoid using any tape. I talked to my regular mechanic and he even advised against using any of the permatex liquid thread sealant, saying that they should seal dry if tightened correctly. I tightened those threads fairly tight by hand and if anything, I was worried that I overtightened them. I will try to get a wrench on there tonight while the pump is still mounted and see if it will go any tighter. If not, I guess I'll have to take everything apart again, try a new brass fitting, put it all back together and see what happens.

 

[68 Sport Satellite]

You shouldn't need the tape because the threads are tapered so that when you tighten them adequately they seal. If you can seal them by tightening them I'd try the Teflon tape, just make sure you start after the first couple threads. If you get the tape in fuel line you could end up with it clogging a passage on the carb of stuck in the needle and seat, jet...etc

Are NPT threads really tapered? I did some other online searches about this and many people have problems with leaking pressurized NPT fuel fittings. Why didn't Carter just include the correct fittings with the pump? I have read that some people use AN fittings with flares or silicone O-rings, but that still doesn't tell me how to keep the pump's female NPT end from leaking because when you look inside that hole in the pump, it's a thru-hole with no seat, so I can see nothing that it would seal against.

Any others with advice? I don't want to use tape or sealant if I can avoid it. What fittings should I use?

 

[68 Sport Satellite]

Here is some good info off of Wikipedia on NPT pipe threads. It looks like if I can find an NPTF fitting it may help without using sealant:

The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other, as opposed to parallel/straight thread fittings or compression fittings in which the threads merely hold the pieces together and do not provide the seal. However, a clearance remains between the crests and roots of the threads, resulting in a leakage around this spiral. This means that NPT fittings must be made leak free with the aid of thread seal tape or a thread sealant compound. (The use of tape or sealant will also help to limit corrosion on the threads, which otherwise can make future disassembly nearly impossible.)

There is also a semi-compatible variant called National Pipe Taper Fuel (NPTF) also called Dryseal American National Standard Taper Pipe Thread, defined by ANSI B1.20.3, designed to provide a more leak-free seal without the use of teflon tape or other sealant compound. NPTF threads are the same basic shape but with crest and root heights adjusted for an interference fit, eliminating the spiral leakage path.

 

[72Satellite440]

I say take her off again -I dought you over tightened those fittings unless you really wrenched it Id take it apart and inspect the diaphram on the inside-
Other than that id definitly try another fitting

Or why not avoid this problem all together and return it and order a new one

 

[68 Sport Satellite]

I really think that the pump is fine and that the brass NPT fitting I installed is not installed correctly. I finally found online where it says this Carter pump has 1/4" NPT female inlet and outlet. If I remember correctly when I brought the pump to the auto parts store the counter guy test fitted both 1/4" NPT and 5/16" NPT and he sold me the 5/16 NPT fittings. Could it be that I installed a fitting that is too large and when I tightened it the threads became galled and are now leaking?

 

[Satellite65]

a 5/16" male NPT fitting would NEVER fit into a 1/4" female NPT fitting properly. You may have gotten a bad fitting, or it just didn't seal right. Just because they have tapered threads doesn't mean you don't need to use any kind of sealant, you just don't want it to get anywhere you don't want it, like inside your carburetor.

Use the teflon tape, just be careful to start it about a thread up from the bottom and wrap it neatly and fairly tight. Go about 3-4 wraps on 1/4" or 5/16".

If you really want to use some good stuff, go into the plumbing dep't of Home Desperate or Blowes and get the yellow teflon tape made for natural gas lines. It's softer and thicker, seals real well and you use less, about 1-2 wraps should do it.

Don't over-think this crap, it's not that technical.

 

[68 Sport Satellite]

PROBLEM SOLVED!

It turns out it was the fittings. When I bought the original fittings I brought the new carter fuel pump into the auto parts store. The guy test fitted some fittings and sent me on my way with what were 5/16" brass line fittings. The pump instructions didn't call out a size or thread type so I didn't know any better until I looked on a carter distributor website last night. The original fittings he gave me had threaded in all the way just fine.

Today I picked up some 1/4" brass NPT fittings and now the pump is leak free. I didn't use any tape to seal things.

The 5/16" line fittings have a straight thread and the first few threads of the 1/4" NPT happen to be the same size, which explains why both fittings were able to be threaded into the pump.

I took some photos prior to the re-install, but I forgot to change the photo resolution so they're too large to post here. I'm glad the fix was something easy!