Fuel fitting nut torque?

[Dan L]

I’m in the middle of my 2018 Condition Inspection and discovered that there is some fuel seepage at a couple of my plastic fittings. I found this after opening the panel behind the fuel valve and with a flashlight seeing some blue fuel dye on the connections.

Thinking the nut had backed off a bit, despite the Superglue applied originally, I gently tightened the nut a very small amount. By very small I mean maybe one or two degrees of rotation. Almost nothing. Much to my surprise the nut cracked and a stream of 100 LL spewed out. I quickly threw some rags around it all. Some black electrical tape wrapped around things soon had the flow staunched.

These fittings are upstream from the valve. I turned the valve to the side causing the problem and drained 10 gallons out into empty jugs. That was a short term fix.

For a a permanent fix I called the CC parts department and ordered some new fittings after Laceigh told me the replacements are made from a different material. Crack-proof I hope.

So, all of this is leading up to my question; how much tightening torque are builders putting on these nuts? The Nyloseal instructions say two to two and a half turns. I suspect I had these over tightened and that was the source of the seeps. But maybe not. Any advice?

E7981CEE-0674-4A37-9B8B-BF73F24439E4.jpg

[TroyBranch]

I followed the instructions and it did seam like a lot. I had other builders tell me that it needed that or it will leak in our climate with huge temp changes that we fly in. I wonder if they become brittle from the extreme cold? I always found that white plastic becomes brittle over time but I would not think that would be the case with these. I sure hope not. You are one of the first kits, is the fitting dry and brittle?


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[N867SP]

I’m in the middle of my 2018 Condition Inspection and discovered that there is some fuel seepage at a couple of my plastic fittings. I found this after opening the panel behind the fuel valve and with a flashlight seeing some blue fuel dye on the connections.

Thinking the nut had backed off a bit, despite the Superglue applied originally, I gently tightened the nut a very small amount. By very small I mean maybe one or two degrees of rotation. Almost nothing. Much to my surprise the nut cracked and a stream of 100 LL spewed out. I quickly threw some rags around it all. Some black electrical tape wrapped around things soon had the flow staunched.

These fittings are upstream from the valve. I turned the valve to the side causing the problem and drained 10 gallons out into empty jugs. That was a short term fix.

For a a permanent fix I called the CC parts department and ordered some new fittings after Haleigh told me the replacements are made from a different material. Crack-proof I hope.

So, all of this is leading up to my question; how much tightening torque are builders putting on these nuts? The Nyloseal instructions say two to two and a half turns. I suspect I had these over tightened and that was the source of the seeps. But maybe not. Any advice?

E7981CEE-0674-4A37-9B8B-BF73F24439E4.jpg

Dan,

I remember those nuts being very delicate from day one. I think I cracked a few during initial torque. If I recall it was finger tight then 1 1/2 - 2 turns.



Looking at your photo it appears that you have not completed SB00029

http://legacy.cubcrafters.com/techni...ations/34/view

This gives you the reroute to forward drain valve.

I, as I am sure with the other builders, appreciate these posts as the information is invaluable to us in maintaining/inspecting our aircraft.





Pete Meyer
Severna Park, MD
CCK-1865-0078
✈️N9PW

[Dan L]

Pete, I’m planning to take care of that SB now while it is alll opened up. I can’t see how water could collect anywhere as it was originally designed though. It seems like a solution looking for a problem to me.

I found three different torque specs. My manual says 2 turns in one place and 1.5 turns in another. The SB you referenced says 2.25 turns. And the Nyloseal folks say 2-2.5 turns. I wonder what the CC guys putting these together everyday are using? I’m sure I would have been either 1.5 or 2 turns according to the manual. I’d have no reason to think it was wrong and over torque the nuts. When I take the old fittings off I’ll look for the Sharpie dots and can probably tell from that. Unless the fuel seep has removed them?

Troy, the plastic didn’t seem brittle to me.

[Dan L]

I received the new fittings from the parts department today. The Tee is part number SP60003-001 and the Elbow is SP60004-001. They are different parts than the ones that were furnished with my kit. The plastic is whiter and the flats are concave, for easier finger tightening I'd guess. I think the originals were Nyloseals and these are probably from a different manufacturer.

[Dan L]

I’ve now changed out my fittings to the new style plastic and complied with the fuel drain SB. Thinking all was well I put a couple of gallons of gas in each tank. It didn’t take long to find a leak. And it wasn’t where I’d changed any fittings, it was coming right out of the valve. Fuel was seeping out of the detent holes in the valve with OFF being the worst position.

I will call Monday and see if there is a rebuild kit.

I think the the reason the first fitting cracked when I tried to tighten it is because of the Superglue applied to the threads during assembly. I had a couple more do that.

The puzzle for for me is why did I have 4-5 leaks at all? All the nuts were dotted and torqued up. All the line ends had ferrules. Everything seemed as it should be. Except they leaked. And the valve has been leaking for an unknown length of time. I don’t often put in the OFF position. In any of the other positions it leaked but not much faster than the little seep evaporated.

[ceslaw]

Had the same issue with the selector valve leak. Mitch sent me a new one. It leaked too. Next he sent a set of replacement O rings. When I swapped them out noticed something odd. The new factory valves had slightly thinner O rings. Put the thicker replacement ones in and that leak stopped.

I often wondered if anyone else would have the same problem, since it seemed like there must have been a batch sent out with the wrong O rings. You have answered that question.

the leak was slight and the fuel typically evaporated but enough found its way down to cause a slight thin blue tint on the fabric near the forward gear fastening point, barely visible

The good news is that changing the O rings is an easy task. The bad news is you have to remove the valve to do it.

Chuck

[EVRoosevelt]

Dan I didn't use any of the plastic fittings on any of the CCubs I built if you want all the fittings I have I will box them up and ship them to you for what ever the shipping is?
EV

[40m]

"Had the same issue with the selector valve leak. Mitch sent me a new one. It leaked too. Next he sent a set of replacement O rings. When I swapped them out noticed something odd. The new factory valves had slightly thinner O rings. Put the thicker replacement ones in and that leak stopped."

Every gram counts.

[Dan L]

Dan I didn't use any of the plastic fittings on any of the CCubs I built if you want all the fittings I have I will box them up and ship them to you for what ever the shipping is?
EV

Thanks for the offer EV but I’m ok on these. I got some new fittings that are a better looking part than the Nyloseal originals. More robust I’d call them.

I also have have some new O-rings coming from Jon for the fuel selector.