CH Oil return 45 fitting NPT sealant?

Discussion in 'Firewall Forward & Fuel System' started by cgzro, Apr 8, 2018.

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  1. Apr 8, 2018 #1

    cgzro

    cgzro

    cgzro

    Peter Ashwood-Smith P

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    Have an annoying minor leak at the 45 degree NPT to flair AN fitting that connects the oil return line to the cylinder head in my Lycoming. Not at all serious but annoying as otherwise my engine never drips.

    The 45 fitting wont take another turn without putting it in an NPT die for 1/2 turn or so which leaves sealant as an option, but if course it gets bloody hot there.

    What do folks recommend?
     
  2. Apr 8, 2018 #2

    Dennis Flamini

    Dennis Flamini

    Dennis Flamini

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  3. Apr 8, 2018 #3

    ndlakesdreamer

    ndlakesdreamer

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    About the only thing you can use is Hardening Permatex. I think that is Permatex #1, same stuff you use with silk thread to seal case halves at overhaul.
     
  4. Apr 8, 2018 #4

    bf92

    bf92

    bf92

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    I used Permatex 2B on a similar issue, and have had no problems since.

    Danny
     
  5. Apr 8, 2018 #5

    PittsDriver68

    PittsDriver68

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    The design contour of the female pipe thread is slightly different that the male contour of the fitting's threads. The engineers expect some type of sealer to be applied to the threads to prevent leaking. If you never expect to remove the fitting again, Permatex #1 works. Loctite also works and the fitting is easier to remove later.

    Best of luck,

    Wes
     
  6. Apr 8, 2018 #6

    Dana

    Dana

    Dana

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    That drawing Dennis posted is a 1-20 straight thread, not NPT... but a swiveling NPT to AN fitting like that would have solved the leak that put me down in a swamp. Is there such a thing?
     
  7. Apr 9, 2018 #7

    PittsDriver68

    PittsDriver68

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    The fitting in the drawing goes into the engine accessory case. The cylinder head oil return line takes a pipe thread AN fitting.

    There is something called a "banjo fitting", but it is a 90 degree fitting and is not used on any engines that I am aware of. Won't fit on a cylinder head. So the answer is no, there are no AN swiveling pipe thread fittings on general aviation aircraft. Have not looked at the entire MS catalog.

    Best of luck,

    Wes
     
  8. Apr 9, 2018 #8

    cgzro

    cgzro

    cgzro

    Peter Ashwood-Smith P

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    Im leaning towards adding a 1/2 turn with a NPT die, either that or try a few other fittings and hope for a different thread phase.
     
  9. Apr 9, 2018 #9

    dimcuesta

    dimcuesta

    dimcuesta

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    I got annoyed by this as well. ...and that set screw... I remember using very educative vocabulary with it. I had the engine mount/ firewall clearance on my airplane so I decided to switch to a straight fitting with a 60 deg hose end. Way simpler and no leak. See here.
     
    Last edited: Apr 9, 2018
  10. Apr 9, 2018 #10

    Dana

    Dana

    Dana

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    Where in the engine accessory case? Because on my O-290, the hole in the accessory for the oil cooler line case is a pipe thread, and my problem was caused by the incorrect use of a straight thread (not the one in the drawing above but still a straight thread) in the tapered hole.
     
  11. Apr 9, 2018 #11

    PittsDriver68

    PittsDriver68

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    For the inverted system, the lower oil screen fitting is removed and the fitting supplied with the inverted system replaces it. Straight threads.

    The port for the oil cooler is higher up on the accessory case, and is indeed a pipe thread.

    Best of luck,

    Wes
     
  12. Apr 9, 2018 #12

    PittsDriver68

    PittsDriver68

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    "and that set screw..."

    I have never tightened that set screw. No leak here. You can take that fitting apart and replace the O-rings.

    I tried a straight fitting and an angled hose end. In order to accommodate movement of the rear of the engine, I used a hose long enough to put an arch in it between the firewall valve and the oil screen fitting. Otherwise the movement of the engine repeatedly stretches the hose. Which leads to hose problems. Could never get the AN900 gasket to seal completely. Always got loose after some flights as the orientation of the hose allowed the hose to rotate the fitting slightly as the rear of the engine moved.

    Perhaps you used an aluminum crush gasket instead of the copper asbestos AN900?

    Best of luck,

    Wes
     
  13. Apr 10, 2018 #13

    dimcuesta

    dimcuesta

    dimcuesta

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    Used the copper gasket that comes with the Raven fitting but yes, my hose does quite a large loop to get to the oil valve. So far so good!
     

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