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Thread: “New” C90-8F oil pressure issues

  1. #1

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    “New” C90-8F oil pressure issues

    Just test flew my L18-C with my Dons Dream Machines overhauled C90-8F and had some interesting oil pressure issues. Started out high after run up and takeoff (right at red line) and then kept on tending lower....to the point that break in cruise 2275 rpm was about 23 Psi in the yellow and when I came in to land and pulled over it would come all the way back to low red line around 10psi. It was a warm afternoon in AZ...90°ish. Was hoping to put in a whole hour flight but came back after 20 minutes to make sure
    I didn’t have a oil leak. Oil temp was steady at around 190°. No oil leaks noticed after landing. Anyone seen this before. Hopefully just a faulty gauge after sitting around for 15 years.
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  2. #2
    BC12D-4-85's Avatar
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    I'd call the rebuilder and exchange info so far. What oil is in the engine?

    Gary
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  3. #3

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    Check the oil pressure relief valve for a speck of dirt or something on the needle or seat. Very common with new engines.
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  4. #4
    Crash, Jr.'s Avatar
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    This might be better posted on the J3-cub.com forum as they have more people experienced with small Continentals on there. Don's Dream Machines is on that forum too so you might get some assistance from the builder of the engine.

  5. #5
    wireweinie's Avatar
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    Is it making metal?

    Web
    Life's tough . . . wear a cup.

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    gntw's Avatar
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    Quote Originally Posted by wireweinie View Post
    Is it making metal?

    Web
    I have built a lot of engine and that is usually because of to much bearing clearance. Have seen 10 under crank with std bearings have that problem

  7. #7
    wireweinie's Avatar
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    I was thinking more of something to tight, keeping pressure high. If it peeled some metal out of that location, the pressure would drop.

    Web
    Life's tough . . . wear a cup.

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    Quote Originally Posted by wireweinie View Post
    Is it making metal?

    Web
    They checked the screen and no metal. Talked to Lee at Don’s dream machines and he thinks it’s fine and possible just cooling on the hot day as they usually only see 180° on a C90 on a J3 with the exposed cylinders. Headed back out to fly it again tomorrow and will check the baffles (they are new) and see how it goes on a cooler day. Hope to get a few more hours on it if everything looks ok. I guess low redline is normal on a warmed up C90 at idle.

  9. #9
    cubdriver2's Avatar
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    Quote Originally Posted by gravytime View Post
    They checked the screen and no metal. Talked to Lee at Don’s dream machines and he thinks it’s fine and possible just cooling on the hot day as they usually only see 180° on a C90 on a J3 with the exposed cylinders. Headed back out to fly it again tomorrow and will check the baffles (they are new) and see how it goes on a cooler day. Hope to get a few more hours on it if everything looks ok. I guess low redline is normal on a warmed up C90 at idle.
    C90 is no different then C75- 0200. I have had C85, 2-C90 and a 0200 and never had pressure that low at cruise rpm even at 210f oil. Even on a C90 with over 2200 hrs. My C85 stroker at 210f on a 90f day still has over 40psi

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  10. #10

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    Quote Originally Posted by cubdriver2 View Post
    C90 is no different then C75- 0200. I have had C85, 2-C90 and a 0200 and never had pressure that low at cruise rpm even at 210f oil. Even on a C90 with over 2200 hrs. My C85 stroker at 210f on a 90f day still has over 40psi

    Glenn
    Interesting, will have to see what they say tomorrow and if they ended up changing anything.

  11. #11
    BC12D-4-85's Avatar
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    Here's the small engine Continental Ops Manual: https://www.manualslib.com/manual/19...-A-Series.html

    Note the recommended C90 oil pressure (30-60 p.s.i.) and oil temp range (75-225*F) and limits. At idle with hot oil 10 p.s.i. is the absolute minimum. That's when operating in above +40*F air and using 50W oil viscosity at normal operating temperature in cruise and after landing. Single and multigrade oils are accepted.

    I've had a C85-8, a C90-8F, and now a C85-12F Stroker (C90 equivalent). All had a new overhaul to new specs. In cruise on a Standard air temp day I'd see 35-40 pressure at 190-210F and never below 20-25 later at idle.

    What oil's in the engine? Is the oil temp and pressure gauge accurate? Test both.

    Gary
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  12. #12
    cubdriver2's Avatar
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    Quote Originally Posted by gravytime View Post
    Interesting, will have to see what they say tomorrow and if they ended up changing anything.
    But.......I also know of high time engines that flew forever and never saw 30 psi even when cold

    Glenn
    Last edited by cubdriver2; 04-21-2021 at 08:28 PM.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  13. #13
    BC12D-4-85's Avatar
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    It should be possible to adapt a cylinder leak-down tester so it feeds the oil pressure gauge (?) calibrated air. Oil temp accuracy can generally be noted from placing the temp probe in boiling water. I'd make sure of that soon B4 blaming the engine or overhauler.

    I'm just an owner that keeps dollar bills rolled up like toilet paper when it comes to these matters.

    Gary

  14. #14
    Hardtailjohn's Avatar
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    I'd quickly rig a second gauge/line. Check the fitting where it leaves the engine, maybe flush the galley out and try that. It's cheap and easy. Then I'd go from there. Did they run the engine after build up?
    You could check your gauge with a good regulator on an airline...not very scientific, but it'll probably tell you if it's obviously that gauge.
    John
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