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Thread: Lycoming O-360 Oil Leak

  1. #1
    N15642's Avatar
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    Lycoming O-360 Oil Leak

    Hi Folks,

    My A&P and especially I have a perplexing oil leak in the O-360 engine for my Cherokee. I am hoping that somebody out there has experienced this and found a remedy short of rebuilding the engine. Anyway, this leak appears to be coming from the left side of the engine case at the thread and bolt of the forward engine through-stud. In the Lycoming parts manual it is part # 76220.

    What is happening is that when the engine is run hot, especially on the ground in the summer, oil will start weeping out the threaded end of that bolt. My A&P and I degreased the engine and determined that is the source. What he has tried so far is to remove the stud, clean it and replace it using an additional amount of sealant to try to stop the weeping. This worked for about 2 hours and then it came back again yesterday. Has anybody heard of this before and if so I would sure appreciate any help in getting this eliminated. It does not appear to be a serious leak but is quite annoying as it shows up on the engine baffle and I had a passenger tell me a couple of months ago "is that normal?" I had to tell him in an embarrassing tone that it was not. Thanks so much for listening and your anticipated response.

    George
    Last edited by N15642; 09-09-2012 at 10:57 AM. Reason: typo

  2. #2

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    I am not an A&P but had a similar thing in a Cont TSIO520 and it turned out to be a crack in the case. Another time we had a leak, similar thing , in that it occurred when hot. The A&P said he suspected a cylinder crack. It did not leak under a compression test, and when you looked at the exhaust port with the cylinder off it didn't look big enough to even leak. I was doubtful all the while he replaced the cylinder and the leak seemed to go away.

    If this leak is annoying but not unsafe, consider what oil you are using. I was using Shell 15w50 and that stuff will find its way into every nook and cranny. I had leaks most everywhere except the glove box. Seriously, when I swithced to mineral 100 to break in new cylinder the small prop seal leak stopped.
    Last edited by Bill Greenwood; 09-09-2012 at 12:32 PM.

  3. #3
    N15642's Avatar
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    Thanks Bill. I appreciate your input. My A&P is busy with other projects this week and said he can try to track it down again next week. So the mystery continues. I will mention to him about the oil trick and see what we can do that way as well.

    Thanks again!
    George

  4. #4
    When the case halves are mated together, there is an O-ring that goes between the two case halves where those studs pass through. It's really easy to snag one of those O rings when installing the stud (yup, I've done it), then you end up with a leak along the threads of the stud. However, if the oil is weeping out through the threads, I have seen this addressed by removing the nut and degreasing the stud and nut, then use some of the easy to remove lock-tite on the threads and torque back to spec. The lock-tite fills the void in the threads between the nut and stud to prevent oil seepage through the threads.

    -CubBuilder

  5. #5
    N15642's Avatar
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    Thanks for the lock-tite tip. That makes sense and I will let my A&P know.

    Thanks!
    George

  6. #6

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    Lock-tite makes a hydraulic sealant, which is similar to their better known thread locking compound, and would be a better product for sealing an oil leak. It is designed for hydraulic fittings. Good luck.

  7. #7
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    Thanks to all, especially the Lock-tite trick. That appears to have fixed it for now. I really appreciate all the input and help!
    George

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