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compression test date needed

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  • compression test date needed

    I'm gonna do a C-test on my president next week and was wondering what numbers I should be shooting for. IF the mileage is correct it has 75K on it. I'm hoping the rings should be ok. I am burning a bit of oil (smoke) but I think thats from the valve seals, it stopped smoking for the most part when I used 20w50 oil, but still a bit of smoke on start-up after sitting some time, so I'm leaning on valve stem seals. I also have good oil pressure, so a complete rebuilt isn't needed. I'm hoping I'll just replace seals and gaskets when pulling the engine, and freeze plugs. Should I do rings since I have the motor out? What else do you guys think????

    (2) 1955 Presidents

  • #2
    I'd be looking for compression readings in the 100 to 130 range. Just so long as there's not more than 15% variation between any of the cylinders. Since you've obviously driven it some, the readings shouldn't be too much apart. Now, if this was a test wherein the engine had been sitting for years just prior, I might expect to see even some wild variance in readings because of rings being sticky and valve faces having aquired some light rust (or being a bit sticky themselves)[8D]
    I think you ought to do the valve stem seals without tearing the engine down or removing the heads and then see how it does. A good-running engine doesn't need to come apart just for valve seals. And even freeze plugs can be done IN the car.
    Of course, if the engine's coming out primarily to afford freshening and detailing of the engine and it's home - that's a differnt approach.

    Miscreant at large.
    No deceptive flags to prove I'm patriotic - no biblical BS to impress - just ME and Studebakers - as it should be.

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    • #3
      The "book" calls for 140 to 160 @ cranking rpm, (apx 150 rpm). Now, we all know that an engine with a few miles is gonna be lower. I'd go with no less than somewhere around 115, with even pressures across the board, before I'd start thinking rebuild, ('cause if I'm doing rings, no sense not to do the bearings, heads, etc.). Although real low pressures do effect engine performance, if it's a road car, I'm with Bob, it's more important that there's not more than 15% difference between cylinders.

      How about this, if you get even, but acceptable low pressures across the board with your "dry" test, then do a "wet" test too. That's what I do and although it's not necessary, you should expect to see higher readings on an engine with low pressures across the board, AND the WET readings should be within 15% of each other. You might get a big surprise, I have. After a dry AND wet test you'll have a MUCH better idea about which, if any, cylinders really are weak(er) and where. Of course, if you get individual cylinders reading low with the dry test, a wet test is mandatory.

      Oh, here's a common mistake, don't forget to make sure that the throttle is held WIDE open for your compression tests! (That means the fuel line needs to be disconnected and plugged. ) Actually I pull the carb. because it's just easier than trying to make sure that the screwdriver that I jammed down there is keeping the throttle wide open and no matter what you do, (unless you open it the day before), when you open the throttle all the way just before you test the first cylinder, that first cylinder is ALWAYS a wet test! That and the carb tends to dribble while the throttle is wide open too.

      As for the valve stem seals, I'm tight with Bob on doing them with the heads on.

      Good luck!


      Sonny
      http://RacingStudebakers.com
      Sonny
      http://RacingStudebakers.com

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      • #4
        Alright guys thanks for the replys. I'll be looking for some of those numbers. I'll report back later this week (i hope so). One last question, I have always done C-testing with a warm engine, does this hold true? About the throttle wide open, I have known about this too, but should I remove the fuel line??? I don't think enough vacuum will be made to draw fuel into the cylinder, BTW, I'll have all plugs removed when doing the test.

        Thanks

        (2) 1955 Presidents

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        • #5
          From personal experience.
          You might want to disconnect the coil/distributer wire. Enough vaccuum is formed to put fumes out the spark plug holes, and if a sparking plug is nearby, it goes Whoosh!

          Tom Bredehoft
          '53 Commander Coupe
          '60 Lark VI

          Comment


          • #6
            quote:Originally posted by 55pres

            Alright guys thanks for the replys. I'll be looking for some of those numbers. I'll report back later this week (i hope so). One last question, I have always done C-testing with a warm engine, does this hold true? About the throttle wide open, I have known about this too, but should I remove the fuel line??? I don't think enough vacuum will be made to draw fuel into the cylinder, BTW, I'll have all plugs removed when doing the test.

            Thanks

            (2) 1955 Presidents
            http://RacingStudebakers.com
            Sonny
            http://RacingStudebakers.com

            Comment

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