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Thread: Oil pressure fluctuation after overhaul

  1. #1
    mmoyle's Avatar
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    Default Oil pressure fluctuation after overhaul

    Performed the engine break in flight today....that was after aligning the landing gear...now she tracks straight. First 30 minutes cylinder head temperature...spark plug bayonet type...on the bottom plug of number three cylinder. Temperature reached 450 on climb out. Varied the throttle between 2300 and 2500 temperature dropped to 430 at 2300 up to 450 at 2500.. oil temperature never got over 170. Added a quart of oil..flew some more..another 45 minutes with no detectable oil consumption.
    What was disconcerting was the fluctuation of the oil pressure. 82 or so and would drop to 60. Movement of the analog O.E.M. Gauge was quick...obvious something is opening and closing. Oil pressure would jump every 15 seconds or so, but steady at 80 psi on final or when I pulled the throttle. Is not equipped with a vernatherm....has a spin on filter. The oil pressure bypass valve....didnít disassemble it so I donít know if the case had a cage for the check ball. Marv doesnít recall one. The oil pressure regulator housing is NOT adjustable. It did not have the problem before overhaul. So is this the old style oil pressure regulator housing requiring the cage?
    Mark M.


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  2. #2
    gliderman's Avatar
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    Default Re: Oil pressure fluctuation after overhaul

    Seen this before- replace the ball and spring on the bypass valve. make sure the surface that the ball sits in is free from nicks and cooties( good aviation term). as you know- 3 washers max on the small housing and 7 on the big one for oil pressure adjustment

    hope this helps

    Shane-o

  3. #3
    mmoyle's Avatar
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    Default Re: Oil pressure fluctuation after overhaul

    Quote Originally Posted by gliderman View Post
    Seen this before- replace the ball and spring on the bypass valve. make sure the surface that the ball sits in is free from nicks and cooties( good aviation term). as you know- 3 washers max on the small housing and 7 on the big one for oil pressure adjustment

    hope this helps

    Shane-o
    Shane,
    This has a short housing with a few washers. Right now I donít recall a counterbore for the check ball cage... does the short housing require the cage? Iím thinking about replacing the whole thing with the adjustable oil pressure regulator... Glacier Aircraft in Palmer has or can get the cage..spring and check ball...
    Thanks
    Mark


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  4. #4
    rocket's Avatar
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    Default Re: Oil pressure fluctuation after overhaul

    Mark,
    Sounds like your over pressure poppet is unporting, the one that keeps your oil cooler from exploding... I think

  5. #5

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    Default Re: Oil pressure fluctuation after overhaul

    I was just chasing a similar issue. Oil pressure needle on the old analog style gauge bouncing from 80 or so to 60. On mine it was rock solid at idle and solid before the oil was warmed up. After the oil was warm it bounced a fair amount. Turned out I had an air bubble in the oil line from the restricted fitting on the engine to the gauge. Every time I bled it the bouncing improved. Of course, I am dense so I had to bleed it a few times until I got it right. I didn't realize that one could get air in that line that didn't bleed automatically but it turns out that you can. I bled mine at the gauge with the starter motor turning the prop to build oil pressure for what its worth.

  6. #6
    mmoyle's Avatar
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    Default Re: Oil pressure fluctuation after overhaul

    Quote Originally Posted by stretchedpacer View Post
    I was just chasing a similar issue. Oil pressure needle on the old analog style gauge bouncing from 80 or so to 60. On mine it was rock solid at idle and solid before the oil was warmed up. After the oil was warm it bounced a fair amount. Turned out I had an air bubble in the oil line from the restricted fitting on the engine to the gauge. Every time I bled it the bouncing improved. Of course, I am dense so I had to bleed it a few times until I got it right. I didn't realize that one could get air in that line that didn't bleed automatically but it turns out that you can. I bled mine at the gauge with the starter motor turning the prop to build oil pressure for what its worth.
    Thank you.... I will give that a go!!

  7. #7
    mmoyle's Avatar
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    Default Re: Oil pressure fluctuation after overhaul

    Adjustable oil pressure regulator installed...little to windy for my comfort.. looks like the old non adjustable pressure regulator requires the cage.... working on the lower cowl to improve differential pressure. Removed the 1Ē lip in favor or a 2-1/4Ē. Kept the shape of the lower cowl. Forming the radius pieces...will finish those tomorrow. Will also add baffle seals around the air filter to reduce the airflow around the filter..


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  8. #8
    51-pa22's Avatar
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    Default Re: Oil pressure fluctuation after overhaul

    Mark if I recall correctly, during case overhaul the original oil pressure relief valve was recut for the adjustable oil pressure relief valve. It’s one of the SIs the case overhauled is suppose to check during an “overhaul”. So check with the shop that did the case to confirm.

  9. #9
    Steve Pierce's Avatar
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    Default Re: Oil pressure fluctuation after overhaul

    Did you have the case overhauled? If you did and it had the old pressure relief valve cage it was probably modified to the new style which is not compatible with the old style pressure relief valve nut. Here is a thread with pictures.
    http://www.shortwingpipers.org/forum...f-valve-sleeve

  10. #10
    JPerkins's Avatar
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    Default Re: Oil pressure fluctuation after overhaul

    Anyone have the SI number on this? I ask because my case was not modified at overhaul and I'm wo deering what the reasoning behind it is.

    Sent from my SM-G930V using ShortWingPipers.Org mobile app
    Jason Perkins

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