SonexBuilders.net

About a year and a half ago I installed the Oops fittings in my fuel tank, and then I put some brass plugs in the fittings on the bottom side to seal everything up to do a leak test. After that, I installed the tank in the plane but left the brass plugs in the bottom, thinking I might as well leave them to keep dust and stuff out.

Fast forward to this week, and I decided I needed to rivet a few things to the upper firewall, so I removed the tank to get it out of the way. I noticed there were a bunch of little chunks of unidentified debris rattling around in the tank. I removed the brass plug in the large fuel supply fitting so I could rinse everything out.

Well, the brass and aluminum corroded each other, so the internal threads of the Oops fitting were pretty much gone! That explained the source of all the bits of crap in the tank.

As a bonus, I decided I should have applied some thread locking compound to the fittings after I did the leak test and initially installed the tank. I didn't want to loosen everything and redo the test, so I put a couple drops of Loctite 290 on each fitting. That is the Loctite that penetrates joints that are already tightened. That stuff is way stronger than I really intended, so I ended up having to cut the nut off the Oops fitting with a dremel tool to get the fitting out.

So, two lessons learned! 1) Don't leave brass plugs in the Oops fittings long term, and 2) Loctite 290 is probably stronger than you want for the tank fittings!

IMO, threadlockers should never be anywhere near oil or fuel lines.

I feel like I read somewhere that someone recommended using something just on the oops fittings to keep them from working loose, but I can't remember... It was like fall of 2018. Maybe that was overkill

I believe Loctite 567 is the one to be used here.

Have you been running 100LL Avgas or some Mogas, and if the later, did it have ethanol ? Problem sounds like what happens when ethanol sits long enough to deteriorate into acid. If you are using the Jabiru standard fuel pump and Bing Carb, might want to check those as well since both have bras and aluminum parts.

David A.

I'm still building so my tank has never had anything but air in it! I sealed it up in Arkansas though before I moved to West Texas so I guess it was pretty humid air!

I checked mine today. The only brass was the finger strainer. It has been sitting in 100LL for 1-1/2 yrs or so since I put in the Opps fittings with proseal.

There was not any corrosion on either the brass or aluminum threads. The soldered seam on the strainer was corroded with a whitish-greenish powder. I don't know what to do about that, other than eliminate the strainer. For now, I just wiped it off and blew it out with compressed air. Reinstalled with fuel lube as the thread sealant.

Rick Caldwell
Xenos 0057

racaldwell wrote:The soldered seam on the strainer was corroded with a whitish-greenish powder.

That's what mine looked like except it was bad enough that the plug took a bunch of the aluminum threads of the oops fitting with it when I unscrewed it. Maybe having everything submerged in fuel protects it since it keeps oxygen out. Perhaps when I'm done messing with the tank and lines I should put a couple gallons in!

Spaceman wrote:I feel like I read somewhere that someone recommended using something just on the oops fittings to keep them from working loose, but I can't remember... It was like fall of 2018. Maybe that was overkill

Hello all, well, that might have been me that said I used small, 4-40, or maybe 6-32 set screws in a 90 deg arraingment on the oops fitting retaining nuts, and might have used just a dab of loctite on those set screws. Only problem here is that I have to remember the set screws are there, and not try to undo or tighten the opps fittings nuts without removing the set screws.

from what I have read here, the whit-ish patina on the soldered portion of the screen may well be normal oxidation colored with the aroma of nearby 100 LL blue since that portion of the aircraft wont get massive ammounts of fresh moistureless air durring hanger time. If it can be wipped off easily, that sounds to me like that is what it is. maybe just rub a thin overall layer of fuel lube,or even medium weight grease, to 'protect' the solder? Just MHO, as always!

fly safe!