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Thread: O-320A2B oil pressure problem

  1. #1

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    O-320A2B oil pressure problem

    Caution, you must have a "cents" of humour or you'll cry.
    I hope I'm in the right place for this thread.
    I have asked Lycoming about this problem already but I'm no wiser, so I thought I'd ask "group intelligence".
    So here we go, I have foolishly bought another aircraft that was junk from a dead guy that I talk to a lot but get no answers yet. The aircraft was flown "apparently" with a bent crank for some time, it shook the gizzard out of it, there was a substantial amount of silicone within and without the engine and airframe (*** why did I buy this thing). Anyway what's done is done. So I have gone through the aircraft and patched and fixed things, removing silicone, mouse excrement and patching bear damage. I sent the engine case out to have it overhauled because it was fretted badly. I put another standard crank and bearings in it, new lifters, cam, rods, mags, ignition wires etc. overhauled or new. I did NOT have the accessory case inspected, the pump looked OK, in fact, after I put the engine together, I had the plugs out and flipped the prop over by hand and had oil pressure in about 15-20 flips. So after I felt that the oil was well through the engine and fiddled around with a few other things, I fired it up, it ran smoothly oil pressure came up to 65 at 650rpm. I let it idle for a while and shut it down to see what might be dripping or anything unusual. Everything was OK so I ran it again---
    rpm 1000, oil pres 85lb, oil temp 160, cht 110c;
    rpm 1700, mags checked OK, oil pres 75lb, oil temp 165, cht 150c;
    rpm 2000, oil pres 70lb, oil temp 165, cht 150c;
    rpm 2300, oil pres 65lb, oil temp 165, cht 180c;
    rpm 1000, oil pres 85lb, oil temp 175, cht 190c and cooling for shut down

    Emailed Lycoming asked them what's up but other than saying it could be a crack somewhere on the intake of the oil pump, a gap in a gasket ( they didn't say which gasket could be responsible for this outcome), or maybe I put the wrong oil or an additive in the oil and it's foaming (negative), they didn't have any other suggestions. I don't think any of that will actually explain what's going on. But foaming might explain it if I had put to much oil in it, I used 6qt. of Phillips66 av-oil.
    I took it up for about 10 minutes but the it never made any difference, 60-65lb is all I got.
    So I'll rest my case there, and think some more before I tear it down.
    My little brain just can't come up with a scenario that will explain this. Maybe someone out there may have experienced something like this.
    You have probable guessed this is not a certified aircraft, and I have a weakness for junk.
    Robert

  2. #2
    windy's Avatar
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    Did you try adjusting the pressure relief valve on the engine case, above cylinder #3?


    Sent from my iPhone using SuperCub.Org

  3. #3

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    Yes I did, the pressure relief valve had 1 washer in it originally, about 75lb at 1000rpm and at 2300rpm about 58lb, I put 2 more washers in to see what would happen, it went up to 85lb at idle and 65lb at 2300rpm. I would think it should be higher at 2300rpm.
    Also I should say I check the screens and they are clean.
    Last edited by piggy; 04-28-2021 at 07:49 PM.

  4. #4
    cubdrvr's Avatar
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    Had something that might be similar on a C90 PA-11. Weak oil pressure that nothing seemed to change. Turned out that the oil pump facing had to be milled to mount flush with the case.
    But, nothing wrong with 65# if temps are good.
    "Sometimes a Cigar is just a Cigar"

  5. #5

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    I'm not ready to take it apart just yet but when I do I'll take a closer look at it, maybe I missed something, I must have. Might be something else I haven't thought of.
    Robert

  6. #6

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    I had an oil pressure gauge do exactly what you are describing .
    not to say that’s your issue, but best to start by eliminating the cheapest and easiest potential problem.

  7. #7
    windy's Avatar
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    O-320A2B oil pressure problem

    ..
    Last edited by windy; 04-28-2021 at 10:34 PM.

  8. #8

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    That's worth looking into. Thanks Oliver.
    Robert

  9. #9

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    Yes it defies logic, I overlooked that as a cause. Thankfully, checked it before pulling accessory housing.
    Hopefully something as simple as that. please let us know what you come up with.

  10. #10

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    Yes, windy they are standard size. I think it's nothing like that, the oil pressure is 85 at 1000rpm and 60-65 at 2300.
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  11. #11
    Gordon Misch's Avatar
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    Sucking air somehow?? Or blocked pickup, so can't pull high flow??
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

  12. #12

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    Yes I think so. Time to take a look. I checked the gauge, its good. So I think this is the day to start taking it apart.

    Thanks everyone for your input. I'll tell you what I find.

    I should add that I pulled the plug on the oil pan, there was nothing there, it was clean. I tried to wiggle the pickup tube, it didn't move.

    Robert
    Last edited by piggy; 04-29-2021 at 10:28 AM.
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  13. #13
    BC12D-4-85's Avatar
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    Somewhere I read a leak in the pickup tube setup was the cause of lower oil pressure. As rpms rise the oil level in the sump dropped which made sucking it up less efficient. Not saying it's that here. Might have been on a small Continental that it happened.

    Gary
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  14. #14

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    I think its the gasket on the pickup tube, that's about the only thing that suits the criteria, maybe a crack thereabouts.
    Thanks Gary

  15. #15
    Gordon Misch's Avatar
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    Or oil pump clearances, meaning within spec both axially and radially.
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)
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  16. #16

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    Funny you should say that Gordon, I have ordered a new pump, mine was the old type, that had the two piece pump body, on close inspection I found some suspicious areas on the intake side were they mate up, the old pump has some ADs on it so I thought, what the heck the gov. says they need the taxes so I bought a new one. It won't be here for a couple of weeks but I have lots to do on the airframe. I'm not sure that will solve the problem. There was a blank cover with a junky gasket on it too, it might have been for a prop governor. I'll just keep fiddling with it until one us gives up.


    Robert
    Last edited by piggy; 04-30-2021 at 10:13 PM.

  17. #17

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    Try thicker oil
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  18. #18

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    Worn cam journal too, engine heats up, case expands more than cam, more oil bypassing therefore less pressure.

  19. #19

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    Thanks for your input. The case and cam were reworked, so that was good. I think it was sucking air at the pump or the prop governor accessory cover gasket. I replaced both and the pressure is good now.
    Thanks everyone, that was a puzzle.
    Thanks BC12D-4-85, marcusofcotton thanked for this post

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