Aux tank cover

Burt · #1 06-14-23, 08:09 PM

When I put more than 12 gallons of fuel in my right aux tank it leaks. I have removed all the screws in the aux tank cover but still cannot remove the cover. This is a 1966 A model 337. There is a boom fairing that covers the outboard rear corner of the cover. The fairing is riveted in place so is not easy to remove. I am wondering if there is another screw under the fairing holding the rear outboard corner of the cover? Anyone have experience with this issue?

Burt

wslade2 · #2 06-15-23, 02:37 AM

I did CiES probes and took all upper panels over the tanks off last year. Out of those hundreds of screws, I think one of everything that could complicate it happened.

Did a screw head break off? Is there a retained screw shaft? There are 4 screws in the fairing you are talking about with 4 countersunk washers. Be sure all 4 screws are out. If less than 4 screws are removed, it is possible a head came off and the screw shaft is hanging you up. Hopefully nobody cheated and put a blind rivet in any of the holes (you mentioned it is riveted down but not if any rivets look like they pass through the panel). If either, it will have to be drilled out. Be careful about drilling out and use drill bit smaller than 10-32 screw. Preferably a reverse bit. If you can see a shaft, get an ease out in it if possible and plenty of oil soaking. The screws screw into wing rib with either nut plate you can't access or a tap into the aluminum itself. You will need to preserve the diameter of the hole so you can go back in with a tap or helicoil depending on the situation if things are buggered up.

It takes some wiggling, lifting and slight bowing of the panel to get the cover off. Also, it can get hung up on some burs, recesses/flush head dimples, imperfections. I found some aluminum flashing and wide putty knives/scrapers from hardware store useful to slip the panels in and out so they wouldn't get hung up on these and to lift away overlapping aluminum. The space the panels slip into are tight. You will see in my photo I had a screwdriver lifting up the boom fairing you are talking about at one point, upper left hand of photo.

To make my future life easier, i put a dab of fuel lube on the screws when they went back in. This also saved stripping out the screw holes. Start them all by hand. Don't get over zealous with a power driver and strip anything out. If using a power driver, preferably one with a clutch.

BTW-while there check your tank vent. For the aux tanks, in the connector fitting, they placed a small diaphragm with 3 pinholes in it. These pinholes easily get clogged blocking off the vent.

Burt · #3 06-15-23, 10:46 AM

Thanks for the very thorough response. I too experienced several different issues getting all those screws out. And yes, I do have all of them out that I can see, including the four that go through the edge of the boom fairing and have countersunk washers.

I especially appreciate seeing the picture that you included. From the picture it seems obvious that there is no screw in the corner of the cover that is under the fairing. So I guess that I just need to keep working at it.

On another note, I did not know that CiES had probes for the 337.

wslade2 · #4 06-15-23, 08:15 PM

One other thing: I built a cradle for the boom (you can barely see it in the background of my photo) to support the boom and reduce twisting motion of the wing since the panel is part of the structural for the aircraft. Also. Supported the outer portion of the wing with large cushion (like a couch cushion), a piece of plywood under that, all held up by a jack like used to lift the aircraft for a gear swing. There are stringers in the underside of the panel that can bind and hold it down with slight twisting/bending of the structure. I found dropping the outer support jack an inch or two relived some compression jamming the stringers in their recess. After insertion, raising it back up to get things lined up. A little movement is all that’s necessary. Not using the boom support allows twisting complicating the removal and insertion process and it was my observation that just fractions of twisting or bending made things tough coming out or going back in.

Burt · #5 06-16-23, 12:12 AM

Excellent! I already have the wing and tail boom supported. I will try your suggestion about varying the amount of support to relieve pressure on the tank cover.

Burt · #6 06-18-23, 12:36 PM

Got the cover off. Thanks for the help.