I have a '77 Skyhawk with a significant fuel leak. It isn't enough to ground the plane, but i need to fix it ASAP as it is making a mess of my new paint. The rubber connection tubes were replaced this year and were just checked for tightness a couple months ago. Any help will be greatly appreciated.
Any fuel leak of any significance should be cause to ground the airplane... I suspect that the leak is showing up close to the sample drain. (Inboard aft area) A few scenerios here, Is the sample valve leaking? If not I would suspect the rear tank outlet nipple that attaches the aft fuel line to the tank. It could also be the tank neck, this is dependent on how the airplane is fueled. Tank neck leakage is primarily caused by letting the fuel hose "hang" in the tank unsupported. The tank nech is a weak point and cracking is common and usually only shows up with full fuel. Could also be the fuel tank sending unit gasket. To verify all of these with the exception of the sender require removal of the fuel tank. The most common cause of fuel tanks leaking in Cessna's is the retaining straps either coming loose or breaking, causing the tank to move around thus cracking the rear tank outlet nipple. This repair is a simple welding job if you can find a welder that will do it. The tank must be purged with nitrogen during the welding process, a lot of welders will not touch fuel tanks due to the possibility of explosions. Good luck hope the info helps...
Andy,
My 72 Skyhawk developed a small leak a few years ago. It really never leaked enough to stain the paint, but if she was closed up for several days I could faintly smell avgas upon entering the cockpit.. After several times looking for the source I finally noticed a slight dicoloration or tiny greenish streaks on top of the rear of the right door (inside). Upon removing the post cover (plastic) the discoloration was much more obvious in the skin. It was not leaking enough to run all the way down the rear door post before evaporation. There was a rubber hose coulping right above the stains that appeared to be the source. I was sure that simply tightning the clamp would stop the problem. From what I remember (several years ago) , I believe that the line was comming off the tank cross feed line just before the "y" type junction located at the top of the door rear post. Anyway, I topped it off with fuel and to my surprise there was just enough fuel present to dampen your finger tip when ran across the forward end of the rubber coupling. Tightened it some more,, no luck,, replaced it,, no luck.. So I got in the cockpit one dark night with a flashlight a was able to locate it by the "wet" reflection from my light. There was a slight pinhole in the aluminum tubing about 1/8" of an inch in front of the rubber coulping. There was no sigh of chaffing or any other sort of contact marking on the tubing what so ever.... I believe it was just defective from the getgo.. Note: Noting unusual was found upon re-inspecting the interrior of the tubing.
Larry R Standifer Wrote:
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> Andy,
> My 72 Skyhawk developed a small leak a few years
> ago. It really never leaked enough to stain the
> paint, but if she was closed up for several days I
> could faintly smell avgas upon entering the
> cockpit.. After several times looking for the
> source I finally noticed a slight dicoloration or
> tiny greenish streaks on top of the rear of the
> right door (inside). Upon removing the post cover
> (plastic) the discoloration was much more obvious
> in the skin. It was not leaking enough to run all
> the way down the rear door post before
> evaporation. There was a rubber hose coulping
> right above the stains that appeared to be the
> source. I was sure that simply tightning the clamp
> would stop the problem. From what I remember
> (several years ago) , I believe that the line was
> comming off the tank cross feed line just before
> the "y" type junction located at the top of the
> door rear post. Anyway, I topped it off with fuel
> and to my surprise there was just enough fuel
> present to dampen your finger tip when ran across
> the forward end of the rubber coupling. Tightened
> it some more,, no luck,, replaced it,, no luck..
> So I got in the cockpit one dark night with a
> flashlight a was able to locate it by the "wet"
> reflection from my light. There was a slight
> pinhole in the aluminum tubing about 1/8" of an
> inch in front of the rubber coulping. There was no
> sigh of chaffing or any other sort of contact
> marking on the tubing what so ever.... I believe
> it was just defective from the getgo.. Note:
> Noting unusual was found upon re-inspecting the
> interrior of the tubing.
