fuel tank restoration

[clipquito]

Does anyone know how to refurbish a PA-16 wing fuel tank? Mine are in pretty good shape, but I don't want any leaks after they go back into my rebuilt wings. Thanks.

[JohnW]

You pressure test them. I use a Cessna UNVENTED tank cap for the filler neck, and plug the outlets with brass "reducing bushings". On one of the outlets, I install a tee with an inlet for the air pressure along with a low pressure 1/4" gauge. On the other, I use a 1/4" brass stop cock (open to atmosphere, one end) so I can "bleed down" rather than "slam off" the horrendous test pressure, thus avoiding mechanical shock. Oh, about that horrendous test pressure...TWO PSIG is the MAXIMUM pressure to put to a fuel tank and what they were required to show for original certification. Anything above an absolute red line of three pounds and you risk deforming -possibly SEVERELY- and/or tearing the tank. These "antique tanks" are VERY UGLY when you turn them inside out! Two pounds of pressure is equal to 56 inches of Mercury, a factor of about 100:1 of what the head pressure is inside a full fuel tank!!! This is WAY more than enough to "soap" all the weldments and seams and score bubbles if anything leaks. You can have the tank gauge installed if you are so inclined (I don't, but you COULD probably finagle around and use all the actual tank fittings that will be there when the tank is in the wing, but I don't feel that is necessary if you use Parker Thread Lube on installation-and I recommend nothing else for the screwed fittings! Besides, they don't "install well into the wing" with the outlet fittings already in them, so why bother to soap fitting installations that you will have to remove?).

Should you "blow bubbles", any decent automotive-oriented Welder (note the capital "W") can TIG the threaded wells. They would know doubt be well versed in argon purging the tank (so they don't blow the roof off their shop!), and unless you have a New York City Burner's License I would recommend having you airplane tanks welded by a Pro that does this stuff every day. You want "perfect" if you need it welded, not merely "good enough". I'm "pretty good" with a TIG torch, and I send tanks out for welding.

FYI, I find acetone does an EXCELLENT job of removing old fuel stains on the outside of Piper tanks (which are great indicators of possible leak locations, so note every stain before you remove it). Even the ugly purplish fifty year old 80 octane stains that most old tanks have, come right off. If you are overly "weight concious", you probably don't want to epoxy prime your tanks, but it is a real good idea; if you want, "polish up" the tanks with nothing but ALUMINUM WOOL, never use steel wool! Then, clear Alodine them and the next restorer will probably be impressed. Two part epoxy and white Ranthane sure looks good, though!

[edit] Okay...I WAY overstated the "conversion factor" for inches of Mercury...still. two pounds is all you ever want to put to an aluminum tank (a 55 gallon steel barrel will turn open the folded seams around the ends at around forty psig...don't ask me how I know that...)

[clipquito]

THANKS SO MUCH FOR THE INFO. THIS IS VERY HELPFUL.

[clipquito]

Suppose I would just want to replace the fuel tanks. Where do you find tanks for a Clipper? Thanks.