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Fuel Drain Flange - Cracks?

bill.hutchison

Well Known Member
Did a little searching but didn't see this anywhere.

Both of the flanges (VA-112) on my RV6A are cracked - my mechanic found this during my CI. One is worse than the other. No evident fuel leaks. Probably wouldn't have even found it but we're replacing the sumps (the old ones were kinda gross and corroded) and found this.

Do any of you know *why* this would happen? They're cracked in the vertical plane, in line with the axis of the sump.

We're debating whether or not to pull the tanks and replace them, or if a weld could be a solution. Not sure yet. Never seen this anywhere else and wondering if anyone else had run into it.
 
MPT quick drain installed too tight? Would be fairly easy to overtighten in that application.
 
fuel drain flange crack

I've been working on a friends -8A that he purchased last summer. One of the things I found while crawling through it was a cracked drain flange, exactly as you described.

IMG_0448.jpg
As found

IMG_0449.jpg
paint removed

The tank drain valve was torqued in WAY to hard.....so I'm guessing somebody in the past torqued the cr*p out of the drain fitting when installing it, and cracked the flange.

The drain valve has been re-installed with the drain flange crack as is. It does not leak fuel. But, it is on the squawk list, to have the drain flange replaced some day.
 
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Cracks

Cracks in line with the axis of the threads can be caused by over tightening the fitting. Those fittings are NPT and they are tapered. Turn them in too far and the sump side (female) will split.

NPT fittings should be sealed with thread sealant like loctite 567 and installed until snug. If no sealant is used, the fittings will leak no matter how tight you make them…
 
Now for the repair. You have to change the fittings, and are either going to have to get into the back of the rear baffle in order to buck the new rivets or possibly use a countersunk pulled rivet twirled in tank sealant… either way not very fun!

I don’t know if the fittings are 6061 or not (I would think they are) but if you weld on them, you will for sure cook out the sealant and still have to get into the back to reseal. I would not weld them..
 
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If you access to a lathe, turn up an Alum cap with an ID about 1/16” oversize of the cracked hub, clean up the area and pro seal it on.
 

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I replaced that fitting on one of my RV6 tanks that was not pro sealed properly by the original builder of my used kit, and leaking very slowly. When you take the tank off the wing, the fitting is easily (?) accessed from the large cover plate on the inboard tank rib that houses the fuel level sender. No need to remove the sender from that round plate. Biggest part of the job is removing the old proseal. Drill out the original rivets and cracked fitting, remove the proseal in the affected area, re-proseal and rivet in the new fitting, fay-seal on the inside - being careful not to load up the quick drain threads with proseal, and let it cure.

I agree that the crack was probably caused from over torque, but I wonder what that torque should be. I worry about that when installing the quick drains, which I’ve done too many times on my “new” RV6. Anybody know what approximate torque should be used here? My plane will come out of the paint shop soon, and I’ll drain what little fuel is in the tanks before weighing it again. Quick drains will have to be reinstalled. I don’t want to crack a fitting.
 
torque value?

I seem to remember going about 1 turn past finger tight on mine. No idea what torque that comes out to. It is more than enough to keep the drain valve in.
 
Now for the repair. You have to change the fittings, and are either going to have to get into the back of the rear baffle in order to buck the new rivets or possibly use a countersunk pulled rivet twirled in tank sealant… either way not very fun!

I don’t know if the fittings are 6061 or not (I would think they are) but if you weld on them, you will for sure cook out the sealant and still have to get into the back to reseal. I would not weld them..

Why not use close-end blind rivets and fuel seal to reinstall the VA-112? Trying to figure out the correct size. Anyone know the original rivet size used? Not finding it (yet) in the plans.
 
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If they don't leak, don't fix them..... My Warrior had a cracked flange for the 20 years that I owned that aircraft. It never leaked. And had no problem passing annuals.

The only way they crack is (as stated many times) they were over tightened.
 
I replaced that fitting on one of my RV6 tanks that was not pro sealed properly by the original builder of my used kit, and leaking very slowly. When you take the tank off the wing, the fitting is easily (?) accessed from the large cover plate on the inboard tank rib that houses the fuel level sender. No need to remove the sender from that round plate. Biggest part of the job is removing the old proseal. Drill out the original rivets and cracked fitting, remove the proseal in the affected area, re-proseal and rivet in the new fitting, fay-seal on the inside - being careful not to load up the quick drain threads with proseal, and let it cure.

I agree that the crack was probably caused from over torque, but I wonder what that torque should be. I worry about that when installing the quick drains, which I’ve done too many times on my “new” RV6. Anybody know what approximate torque should be used here? My plane will come out of the paint shop soon, and I’ll drain what little fuel is in the tanks before weighing it again. Quick drains will have to be reinstalled. I don’t want to crack a fitting.

16 in-lbs for 1/4" pipe thread.
 
Did a little searching but didn't see this anywhere.

Both of the flanges (VA-112) on my RV6A are cracked - my mechanic found this during my CI. One is worse than the other. No evident fuel leaks. Probably wouldn't have even found it but we're replacing the sumps (the old ones were kinda gross and corroded) and found this.

Do any of you know *why* this would happen? They're cracked in the vertical plane, in line with the axis of the sump.

We're debating whether or not to pull the tanks and replace them, or if a weld could be a solution. Not sure yet. Never seen this anywhere else and wondering if anyone else had run into it.

Never a good idea to weld on a fuel tank...... only as a last resort.
 
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