Sonex Fuel Tank & Oops Fittings

[Bryan Cotton]

Thanks John. Sounds like I should get one of each if I understand.

For the tank straps, should I pre-bend them to the tank?

[fastj22]

Thanks John. Sounds like I should get one of each if I understand.

For the tank straps, should I pre-bend them to the tank?

Yes two, and prebending is not required. Your cussing when pulling the ends together will be sufficent to get them to yield to your will.

[kevinh]

Bryan,

I'm considering doing the same thing when I reach the same point in my build. One question: Why are you leaning towards installing the oops fittings rather than instead putting in a 1/4" thick tapped plate and proseal? Someone recently posted that solution and I thought it was great.

Kevin

[WaiexN143NM]

Hi all,
We recently had the side plug weap/ leak on our waiex . U could smell it, was a couple drops overnite. We originally thought it was the threads in he plug. After draining the tank a couple times and putting seal and tape to no avail on the plug threads we realized it was the molded fitting in the tank. Our fix holding up for a week now was to go to ace hardware, we got a nylon 1/8 pipe thread piece w a hex head , 2 alum washers and some locktite plastic repair glue (looks like super glue gel) made for poly-e (sonex tanks) or poly-p. we had some left over orange baffling material and cut a round piece to match the washers. We slid the sandwich of washer/orange rubber/ washer over the nylon threads , smeared on the glue. The plastic we ruff up w sandpaper . Threaded in hole and snugged up . So far so good :) :) keeping fingers crossed.

WaiexN143NM
Michael RADTKE

[wlarson861]

I did the proseal and plate method. I resorted to that when i ovaled the main fuel line fitting, hole in the tank while trying to reduce the thickness on the inside. If the tank was not in the airplane I think I would have been more successful with the Oops fitting. I would have rather had the Oops fitting as I think that once installed it is more fail proof than the method I used.
P.S. the plate I used was 1/8" 6061-T6.
I have used the LocTite plastic glue to repair a refrigerator and to stick a cable tie to the Sonex tank. Both have held for a year now. This stuff has an activator in a felt tip pen and a tube of glue. I wish it was available when I needed to repair my tank as I think it may be the only adhesive that will stick to the poly tanks.

[Waiex 49]

I recently installed the oops fittings in my fuel tank.

I replaced the three fittings in the fuel sump (2 ea. of the smaller 1/8" NPT fittings and the single larger 3/8" NPT fitting). The larger fitting was not leaking, nor had it spun out. I replaced it so that I would have a 1" diameter hole to work thru to make the install of the smaller oops fittings easier.

I saw no need to replace the other two 1/8" NPT fittings (one is for the fuel vent, the other on the back of the tank for the fuel quantity sight gauge). They were not leaking and they are located at the very top of the tank and only submerged in fuel when the tank is very full. Both of these fittings are located close to the tank walls and I had doubts that the "shoulder" of the oops fittings would fit. I left well enough alone.

Even though it was a pain in the tail section, I am glad I removed the tank. Drilling out these three holes left a ton on junk in the tank (and I was being careful about this). With the tank out I was able to aggressively flush out the tank.

With the fittings installed and plugged, I poured in a few gallons of gas to check for leaks. So far so good with no leaks.

Having been through all of this, if I had to replace one of the smaller fittings in the sump I would carefully drill it out and screw into the tank a 3/8" NPT reducer fitting (bushing). Much easier than the oops fittings.

The stock Sonex fuel tank fittings suck. Making matters worse is that Sonex is in total denial about this problem. We have been lucky that the reported leaks have all been slow leaks. Could you imagine a fitting breaking loose and 16 gallons of fuel draining into the cockpit. Doing a dead stick landing with gallons of fuel sloshing around in the cockpit would be a real thrill.

[DCASonex]

I am going to pre-emptively add the oops fittings. Do you replace all 4 small ones and the large one?

Replace the ones that will be immersed and you may want to remove later. If you are just going to plug them and not use the sight gauge, that one can stay stock. The big one and the fuel probe one are the ones that fail.

The way in which one of mine failed that was never over torqued, and did not spin, but developed a leak where plastic should have boned to fitting, I would replace all that are on bottom of tank. You will still have to screw in a plug and risk disturbing the fitting's bond even for those you will not be using. Replacing the large one makes access to the smaller ones much easier.

David A.

[radfordc]

Having been through all of this, if I had to replace one of the smaller fittings in the sump I would carefully drill it out and screw into the tank a 3/8" NPT reducer fitting (bushing). Much easier than the oops fittings.

That method works for the large fitting, too. When you screw a brass reducer into the tank you have essentially done the same thing that the molded in fitting are supposed to do, only in a way that won't leak and can be easily accomplished.

[WaiexN143NM]

Hi all ,
I think that the thing to do is to install the oops fittings during the build when the tank is out. It is not a matter of if , but when it will develop a leak. Our rt side fitting that we never used ( its for the fuel tube sight guage, we have a Princeton fuel probe on the bottom fitting) started leaking not at the threads, but the bond between the insert and molded plastic. To the good folks at Sonex, consider a design change to the molded tank and sell the oops fittings as standard with the kit! We will regret the day we develop a leak in one of the other fittings.

Waiex N143NM
Michael Radtke

[Bryan Cotton]

My tank seems like it is as forward as I can push it, but the straps don't line up with the molded in strap lines. Seems like the tank is up against the firewall stiffener though. Is this common?