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8.1MPI FCC Fuel Seep

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richie

Regular Contributor
I had to replace the elbow that attaches to the FCC (fuel control cell) on my gas crusader engine. This line returns fuel to the tank and was leaking at the joint as shown in pic1.

I replaced it with an elbow that uses a hose barb. After I replaced it and coated the threads with Permatex High Temperture Thread Sealant it began "seeping" fuel at the thread connection, see pic2, arrow shows where it was seeping. I then removed it and put Permatex Aviation Form A Gasket #3 sealant. It's still seeping fuel even with this fuel resistant sealant. I really cant tighten it any more because the elbow shape will cause the fuel line to kink. So now I'm thinking of using the connector shown in pic3. Does anyone know what kind of sealant Crusader initially used, it obviously works. I'm at a total loss as to where to proceed from here.

Thanks, richie​
 

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I would start with a new 90 deg elbow, and use PST by locktite. But first, look for cracks in the housing at the threads.
 
I'll bet you lunch there's a hidden, sneaky crack there that opens as the fitting(s) are tightened.

No way it should leak after all you've done--no way!

Jeff
 
I tend to agree with Jeff. I sounds like as that fitting is driven deeper into the threads and tightened, it is spreading a mini crack in the housing causing the weeping. If you have a magnifying glass or opti-visor, take a really good look. Maybe swap it with a cotton swap to see if it creeps out as you mop up the current fluid. It seems as though you hit it with everything and it's still wet, gotta be a thin weeping crack
 
knuckle47 said:
I tend to agree with Jeff. I sounds like as that fitting is driven deeper into the threads and tightened, it is spreading a mini crack in the housing causing the weeping. If you have a magnifying glass or opti-visor, take a really good look. Maybe swap it with a cotton swap to see if it creeps out as you mop up the current fluid. It seems as though you hit it with everything and it's still wet, gotta be a thin weeping crack
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I've inspected closely and I don't see anything obvious. I really think it was the replacement fitting. I have since learned that not all male NPT brass fittings are exactly the same. They can be slightly different depending upon where they are manufactured, i.e. US,Japan,China. So I went online and found a place where I was able to order the actual fitting made for Crusader using a Crusader part number from the Crusader parts manual for my engine. Hopefully, once it arrives It will fix the problem, especially now that I have the correct sealant.
 
Richie: I tend to agree with you about the quality of commonly available fittings. I've had more issues in the past couple years than in the same number of decades before - all due to poor quality control. I found there are two paths: 1) buy hiqh quality fittings from a domestic source or 2) buy the imports junk and use loctite 270 during assembly.
 
diver_dave said:
Yes; notice it takes a 24 hour cure. It is fuel tolerant.
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OK I have the Loctite PST 565 thread sealant. I did a practice seal on some threads two days ago. Some of the sealant oozed out from the end of the threads and formed a nice bead of sealant. Problem is, the sealant is still gooey and wet. How long does it take to harden ?

richie
 
richie said:
OK I have the Loctite PST 565 thread sealant. I did a practice seal on some threads two days ago. Some of the sealant oozed out from the end of the threads and formed a nice bead of sealant. Problem is, the sealant is still gooey and wet. How long does it take to harden ?

richie
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Give it a day; but it won't get hard.
 
565 is anaerobic - that means it cures in an environment with limited oxygen. The stuff that ozzed out (contact with the air) will stay soft. The stuff between the threads should have cured a day ago.
 
makomark said:
565 is anaerobic - that means it cures in an environment with limited oxygen. The stuff that ozzed out (contact with the air) will stay soft. The stuff between the threads should have cured a day ago.
Click to expand...

Do you just leave it there or wipe it off ?

Also, when I screw the elbow into the FCC, do I put the force of a gorilla to it or just get it good and snug ? Remember, it's an elbow, so I have to be able to stop with the opening facing down as in the picture I posted.
 
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either way doesn't matter.

small size pipe threads don't need much torque applied to seal them, especially with PST. Usually finger tight + one turn is more than enough. two is a maximum limit.
 
One more question. When pushing/connecting the fuel line onto the barb is it ok to put some oil on the barb so the hose will slide on more easily ?
 
BTW If this fix doesn't work I'm going to bring out the big guns for my backup plan. I will use "Marine J-B Weld" if necessary.
 
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