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Thread: New Owner with some questions on Fuel tank leaks

  1. #1

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    Default New Owner with some questions on Fuel tank leaks

    Hey all, I just became the proud owner of a new to me KF IV Classic 1200, built in 2001 and currently with ~1100hrs TTAF and 140 on the engine, last flight was in 2019 before the owner unfortunately passed away. The previous owner had some fuel tank leaks and fabric repairs that were never addressed and I want to get everything fixed correctly.

    The header tank leaked (poly tank), and I am planning to replace it with a new aluminum one from KF. The wing tanks don't have any signs of de-lam and I was told the previous owner only ran 100LL. However, the fittings for each tank leaked and caused some fabric damage. On top of the that, the fittings look too close to the outer most wing rib to remove without either pulling the tanks or cutting the ribs.

    Maybe a stupid question but I think the 90 degree brass fitting goes into the female brass which I assume is threaded into the tank, not bonded?

    My thoughts are to pull the fabric off the tanks the entire circumfrence of the wing so that I can fix the leaking fuel fittings, and at the same time have a good sample to perform a pull test to determine fabric condition. I plan to repair all of the little nicks and squawks I have with the current fabric before repainting the entire plane (assuming it tests well) so I am not opposed to a bit of fabric work.

    In regards to fuel fittings and lines, what are the best practices, I've seen some run hard lines (aside from pivot points etc), others use rubber, and I want to use whatever the collective minds on here reccomend.

    Am I missing an obvious answer, or is there an easier way to fix these leaks than pulling all the fabric off the tanks area of the wings? Any insight and advice is greatly appreciated!


    IMG_3450.jpgIMG_3451.jpgIMG_3440.jpgIMG_3439.jpg

  2. #2
    Administrator DesertFox4's Avatar
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    Default Re: New Owner with some questions on Fuel tank leaks

    Steve, congrats on picking up a model 4. Good move on replacing the plastic header tank with an aluminum version.
    The brass fitting that the 90 screws into is not bonded (at least it’s not supposed to be) into the fuel tanks.
    Notching out a little of that rib to facilitate removal of the fitting is somewhat common.
    The fuel tanks of that vintage did not always hold up well for some while burning auto fuel. I had that exact issue with my model 4 fuel tanks when trying auto fuel for the first time. If you decide to unmask the fuel tank or tanks, consider installing new fuel tanks from Kitfox Aircraft which are now resistant to today’s auto fuel laced with who knows what kinds of additive packages and alcohol. I will assume your fabric is painted with Polyfiber Polytone paint not Aerothane. Polytone is much easier to repaint after fabric repairs. In one photo it looks like the leak damage is slightly away from the tank drain. Maybe it migrated there or maybe the leak is not the fuel drain fitting.
    What to use to seal the fittings on fuel tanks has been covered many times on this site with several viable recommendations. Do a search for that topic and enjoy the solutions offered by many with actual in the field experience. I used good old mil spec fuel lube to do mine with satisfactory results so far.🤞🤞
    Sorry for slow response Steve. Good luck with repairs. The model 4 is a great version and really sporty.


    DesertFox4
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  3. #3
    Senior Member bbs428's Avatar
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    Default Re: New Owner with some questions on Fuel tank leaks

    Congratulations Steve! The Classic 1200 is an awesome aircraft!

    Yes the fittings are threaded.
    Fuel line from the tanks is rubber hose to your NEW aluminum header tank. Gates 27003 fuel line comes to mind.
    Cannot comment on the fuel line from the header tank. Someone who owns a IV can chime in. All old rubber fuel line should be replaced.
    I know you said no delamination but I would send a camera inside just to make sure they are NOT delaminating, if all is good then replace the fittings, fill them up and see if they still leak.
    You should be able to remove some wood on the rib to get the fittings out without worry.

    I agree with Desertfox4 that the new tanks are your best bet for peace of mind.

    All the best to you and keep us informed on what you find!
    Somebody said that carrier pilots were the best in the world, and they must be or there wouldn't be any of them left alive. — Ernie Pyle

    Brett Butler
    Flying: 1998 Model 5 Outback, 912ul Zipper 110hp, G3x avionics, ss7 upgrades

  4. #4

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    Default Re: New Owner with some questions on Fuel tank leaks

    Thank you very much for the responses! I did a bit more searching as suggested and I have a pretty good idea on what the fuel fittings should look like etc. The plane had bubble doors by the way, which had contact pads that landed where the majority of the fabric damage is, so I believe the sump was not leaking, but rather that outlet to the wing root and then collecting on that contact pad.

    I think my plan of attack will be to scope the tanks as suggested and make a visual inspection. I wish the new tanks weren't quite as pricey as they are but for peace of mind it's probably worth it and the ability to run Mogas in the future if I wanted to, which I don't plan to atleast not with the Jab that is currently mounted but who knows. I will have to do some research to understand the best way to replace the tanks but I planned on pulling the wings anyways which I hopefully can get done this week.

    I saw a few posts on the Banjo fitting style fuel finger adapters and I like that idea, probably will be adding those to my order from KF as well.

    Thanks again!

  5. #5

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    Default Re: New Owner with some questions on Fuel tank leaks

    I had a bit of time before work today to run a scope in the tanks and below is what I found.

    IMG_3468.JPGIMG_3470.JPGIMG_3471.JPG

    Some definite cracks near the baffles where I would expect a solid bond and some evidence of debris in atleast one of the tanks. Not sure how these compare to everyone else's but as mentioned I plan to pull the fabric off the tank area anyways so I might as well drop in two new tanks for peace of mind anyways.

    The fabric is polyfiber with polytone according to the build logs so I plan to order the supplies for that along with the fuel system components from KF this week. Then strip back the entire tank bay, replace tanks, repair fabric there and in a few other places before painting the plane. I have some MEK on hand so I can do a pull test this week too, by and large the rest of the fabric other than where fuel damaged looks good, but might as well test the pieces coming off of both wings.

    Any reccomendations on additional maintence or tricks I should look into while the wings are off and the tank bays stripped?

  6. #6

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    Default Re: New Owner with some questions on Fuel tank leaks

    I found this a while back, I thought it might help.

    https://www.nvav.nl/images/stories/kitfoxresealingtanks.pdf

  7. #7
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    Default Re: New Owner with some questions on Fuel tank leaks

    Interesting write up on the tank repair. I've sealed tanks on two different airplanes, but didn't cut the tanks open to do it. The one had aluminum tanks, and they did seal up, but eventually they did start to leak again. I don't know what happened to the other one, as I sold the plane, and never heard anything negative from the new owner. It was good while I had it though. That being said, I would do it again if need be. I took the wings off, and used my wing rotators so I could roll the wings around to get everything coated inside the tanks. I used KBS coatings and would do it again. JImChuk

  8. #8

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    Default Re: New Owner with some questions on Fuel tank leaks

    Thank you all very much for the information and knowledge. This forum has been amazing. It's looking like the deeper I go the more projects I seem to find....as with anything but that's half the fun.

    I think I will start a build/rebuild thread this week to continue sharing the process and asking for input along the way. Today I found some bent tubing in the landing gear area, quick measurements indicate minor damage with only one affected tube (immediately over where the grove gear mounts. There was no mention of a rough landing in the logs just that the gear was replaced without reason ~350 hrs ago in 2012 so I am guessing that was the time it happened. In any case I don't want to stray too far away from the original thread here but wanted to say thank you again to everyone who commented!

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