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Thread: C-85 Oil pump loses prime experiences?

  1. #1

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    C-85 Oil pump loses prime experiences?

    I have a C-85 w ~1550 hrs ttsn (low TT) & "fresh o'haul" but never run from 25 years ago. It is not corroded in the cylinders and it was stored in a dry climate and area. I added a F & M full flow oil filter.

    I started it first time w 40 weight oil about May 25th & had a little trouble getting oil pressure. I flooded the line to the oil gage & then things seemed OK. I ran it about 30 minutes on the ground.

    Now 3 months later I'm almost ready to fly it in my J-4A, but I can't get any oil pressure again. I tried to back flush it thru the oil pressure gage restrictor w 40 weight oil from an oil can, and later from a small hydraulic pump, but so far no luck on the gage. My last run was ~ 30 seconds without any sign of pressure, so I tore off the cowl & reconnected the small pump to one of the oil galleries via the 1/2" npt port in the front of the engine.
    Now I get 20 psi gage indication with perhaps 1/2 gal/min leakage flow back thru the engine, pump etc of 40 weight oil - all at ~75 degF.

    Q - Have any one else experienced this? If so, how much oil did it take to prime the pump via the restrictor? How long between need for repriming? The restrictor is open.

    I'm thinking that I probably have it primed now, but for how long is questionable. If necessary I'm thinkiing of using a small weed sprayer to force oil thru the restrictor so that I get a known quantity of oil into the engine.

  2. #2
    JimRice85's Avatar
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    Occassionally, the C-85 on my Cub will lose its prime if everything is lined up just so and it sits for a long period. When that happens, I pick the tail up high...I use a rope around the fuselage handle and allow the nose to almost touch the ground...and hold it for a couple of minutes and pull it back down using the rope. Yes, it really has to go that tail high/nose low to work. Lower it back down and the oil pump will typically pick up its prime. Just be sure you have your prop turned horizontally before you do it. You don't want to hit the prop on the ground, even standing still.
    Jim Rice
    Wolf River Airport (54M)
    Collierville, TN
    1946 Globe GC-1B Swift N3368K
    1946 Piper J-3C Cub N7155H

  3. #3

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    Remove the oil filter adapter or figure which hole lines up with the upper oil hole on the adapter and pump oil into this port to flood the oil pump exit. turn the engine backwards as you get oil into the pump to back the oil through the pump into the inlet side of the system. You might want to add a little STP or Lucas oil treatment to make the oil a little "stickier".
    I am not certain about the C-85 since the O-200 is different and the above works on it.
    Either way the easiest way is to pump oil from the oil cooler bypass back to the pump and turn the engine backwards to pump the oil "backwards" into the engine oil path.
    From CPA....

    From CPA:To: Cliff The easiest way to prime the oil pump for your installation is to remove the oil filter and pumpoil into the non-threaded port of the oil filter adapter. A piece of clean hose the size of the hole is all youneed and several ounces put into the pump cavity should be all you need. With all the bottom spark plugsremoved spin the engine by hand and make sure you have an oil flow out the same port. Spin the filterback on and put the plugs back in and you should be ready to run.
    If there is no filter adapter installed, remove the oil bypass plate as has been done in this picture of the oilbypass pad with the gasket still installed; feed the priming oil in the top hole..the bottom hole feeds the
    left gallery and oil injected there would not get to the pump.

  4. #4

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    Quote Originally Posted by nrpetersen View Post
    I have a C-85...

    I started it first time w 40 weight oil about May 25th & had a little trouble getting oil pressure. I flooded the line to the oil gage & then things seemed OK.
    That always worked for me as well, C-85/C-120. Someone had installed a "T" fitting in the gauge presssure line at some point, I can only guess that perhaps that was the reason.

    Are you sure the issue isn't related to adding the filter?

  5. #5

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    Thanks guys! I'm going to fill the galleries & try again since they are exposed now.

    Next time it happens I'll try the nose-down method first, then try the lube thru the oil filter adapter, then try the prime thru the restrictor. I don't want to tear the cover off the engine if at all possible.

    Yeah - it just might be related to the oil filter - but that could also be considered part of the second solution w a vacuum pump.

    The Aeronca forum had an interesting comment from a very observant member. He noted that the side plate of the gear pump is bolted into blind tapped holes and that these holes show a slight pulling of the soft magnesium material. This spaces the side plate out a little bit unless it is relieved and is the possible source of a lot of oil pump back leakage etc. I have not seen the inside of one but I'm sure gonna look for that.

  6. #6

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    The oil filter adapter is intended to be used with the filter that has an anti drainback valve. Once the filter is filled ( engine pressure oil flow, running) it should not let the oil drain back to the sump via the pump. If the oil filter was not filled after installation then the oil would be able to drainback with little trouble.
    Follow the instructions from CPA:
    http://www.cessna120-140.org/forum/f...e_loss_all.pdf
    Best of luck,

    JDB.

  7. #7

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    JDB - That oil pump .pdf file is incredible! It should be part of every C-85 owners file. Thanks for pointing it out.
    NRP

  8. #8

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    I had exactly the same problem with a newly overhauled C-85, As some one rightly said you have to prime the pump and I found it was easy to uscrew the filter and prime into the port in the housing that goes back to the pump. I found it was useless trying to prime by pressurising one of the oil galleries because of the non return valve in the filter which stops the oil getting to the pump. I have never been successful lifting the tail.

    Ian

  9. #9
    Mike Berg's Avatar
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    Actually the easiest was is to removing the oil temperature sender at the screen housing and squirt (clean) oil into the housing which is just above the oil pump. Works every time (and saves your back).

    Mike
    If God had intended man to fly He would have given us more money!

  10. #10
    JimRice85's Avatar
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    Lifting the tail requires lifting it very high to work. Just lifting to head high isn't sufficient. The air filter/box needs to almost touch the ground to work. You'll need a rope to tie to the tailwheel or fuselage handle (Cub) to hold it from going to far and to pull it back down.

    I've seen this work on more than one occasion. Of course, YMMV.
    Jim Rice
    Wolf River Airport (54M)
    Collierville, TN
    1946 Globe GC-1B Swift N3368K
    1946 Piper J-3C Cub N7155H

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