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Thread: Fuel tank sump thread repair

  1. #1
    cozzmo81's Avatar
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    Default Fuel tank sump thread repair

    Does anyone have a good source or method for repair of the NPT fitting on the bottom of the PA-20 fuel tank. I have developed a slow leak on the sump drain and when I went to install the new valve I noticed it threads almost all the way into the fitting before getting snug. It seems that the taper of the NPT bung in the tank has been damaged over the years and the valve bottoms out on the bung before its tight enough to seal the leak.


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    Adam Rhoads

  2. #2
    Administrator Steve Pierce's Avatar
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    Default Re: Fuel tank sump thread repair

    I am not sure about a Heli-coil sealing in a fuel sump. I think I would remove the tank, drill the bung out and weld in a new one.

  3. #3
    Frank Green's Avatar
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    Default Re: Fuel tank sump thread repair

    That's what I did, cut off the old one down to the flange, made a new one out of 6061 and had it welded on. Made a brass plug to hold the new one in position and aligned threads in old to new. With the cap and sender removed you can water wash it good and clean first.
    Yea PITA to remove tank for all of this but you don't want it to come loose in flight.
    -Super Stub-

  4. #4
    cozzmo81's Avatar
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    Default Re: Fuel tank sump thread repair

    Thanks for the suggestions. It looks like Iíve got some work to do.


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    Adam Rhoads

  5. #5
    Jim's Avatar
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    Default Re: Fuel tank sump thread repair

    Hi,

    My first though would be silver solder over the threads on the quick drain and run a pipe thread die over it. It probably doesn't need much more than a little more diameter to snug up earlier. If it didn't tighten enough to make you comfortable you wouldn't be losing much to throw it away.

  6. #6
    MWflyer's Avatar
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    Default Re: Fuel tank sump thread repair

    I acquired a brass bushing of the same size as the original drain valve and put the next size down drain valve into the bushing,it all tightened up and has been holding for a couple years.

  7. #7
    Gilbert Pierce's Avatar
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    Default Re: Fuel tank sump thread repair

    I had the same problem. I screwed a brass 1/4 to 1/8 mpt reducer into the tank with permatex on the threads and then a 1/8” Safe-air quick drain valve. The pipe threads and taper on the reducer were slightly larger than those on the valve.
    I measured a number of those valves and found all of them to be at the small end of diameter spec.

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