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R-1 Compression numbers

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  • Engine: R-1 Compression numbers

    I had the valve covers off the Avanti doing a swap with Jerry Forrester. I decided to take out the plugs and run a compression test. With the throttle blocked wide open, all the cylinders hit 120 to 125 on the first turn and all pumped up to 165 with five or six turns. Avanti Shop Manual calls for 180-190 (or there abouts- already can't remember what I read 30 minutes ago).
    I'm kind of in a quandary- don't know whether to believe my 35-year old compression tester or not, but I'm impressed with how even the readings are. The car has just under 80,000 miles, carries good oil pressure. If the compression had been low or very uneven, I'd pull the heads and have them rebuilt. At the very least I will replace the valve guide seals as the car shows every symptom of needing them.
    Any recommendations?
    Paul Johnson, Wild and Wonderful West Virginia.
    '64 Daytona Wagonaire, '64 Avanti R-1, Museum R-4 engine, '72 Gravely Model 430 with Onan engine

  • #2
    Paul...

    It's been a long time since I've done any serious engine tuning, but I've always understood that even readings were more important than actual numerical readings when it come to the health of an engine (within reason). Since Studebaker engines have mechanical lifters, it's quite possible you may need to readjust the valves...they may all be adjusted equally, but at the wrong clearances, and that could lead to somewhat lower compression numbers than the book calls for.

    Also...was the engine at temperature or cold? That could make a difference.

    If you want, you're more than welcome to use my compression tester...but it's about the same age as yours.
    Poet...Mystic...Soldier of Fortune. As always...self-absorbed, adversarial, cocky and in general a malcontent.

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    • #3
      I would be happy with 165 on a cold engine. Hot engine perhaps a little more. But as long as you have it down it probably needs it. Can't hurt.

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      • #4
        Engine was cold- hadn't been run for a couple months.
        Paul Johnson, Wild and Wonderful West Virginia.
        '64 Daytona Wagonaire, '64 Avanti R-1, Museum R-4 engine, '72 Gravely Model 430 with Onan engine

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        • #5
          Nice even readings is a very good thing. I wouldn't be concerned at all. Check it again hot, you'll probably be up 10-15 psi. Pressure on the first turn is meaningless. Crank it until the numbers stabilize, usually 6 or more revs.

          A perfect engine, 10:1 compression ratio will pump 195 psi or a bit less depending on cam.

          If all else fails, you can get a new, decent, compression tester for $20.
          Last edited by jnormanh; 03-08-2012, 01:35 PM.

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          • #6
            The numbers sound good to me. My Avanti shows around 180 psi with the engine hot. A 5 pound variation is good. If the engine has good oil pressure and doesn't use a bunch of oil, I wouldn't worry about it. Bud

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            • #7
              Originally posted by jnormanh View Post
              Nice even readings is a very good thing. I wouldn't be concerned at all. Check it again hot, you'll probably be up 10-15 psi. Pressure on the first turn is meaningless. Crank it until the numbers stabilize, usually 6 or more revs.

              A perfect engine, 10:1 compression ratio will pump 195 psi or a bit less depending on cam.

              If all else fails, you can get a new, decent, compression tester for $20.
              What made me nervous about my tester was that after the first cylinder the needle wouldn't return to zero, stuck at 10 psi then 60 psi. I haven't looked at new ones. Mine has the flexible hose that makes it easy to screw in to the spark plug holes.
              Paul Johnson, Wild and Wonderful West Virginia.
              '64 Daytona Wagonaire, '64 Avanti R-1, Museum R-4 engine, '72 Gravely Model 430 with Onan engine

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              • #8
                Yes, near to the same readings on all cylinders is a good thing.

                No, 165 PSI on an R1 is not good.

                Maybe, it's because the engine sat all winter. Run the engine, drive it around til it's hot, then let it cool, pull the plugs and check it again. My experience is the compression will probably be higher because the rings have loosened up and there will be some oil on the cylinder walls.

                jack vines
                PackardV8

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                • #9
                  By all means. Fix it cause it ain't broke. cheers jimmijim
                  Originally posted by Alan View Post
                  I would be happy with 165 on a cold engine. Hot engine perhaps a little more. But as long as you have it down it probably needs it. Can't hurt.
                  sigpicAnything worth doing deserves your best shot. Do it right the first time. When you're done you will know it. { I'm just the guy who thinks he knows everything, my buddy is the guy who knows everything.} cheers jimmijim*****SDC***** member

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                  • #10
                    To: 53k,---- In this world of crummy gasoline, take the 165 and run!!

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                    • #11
                      Originally posted by jnormanh View Post
                      Pressure on the first turn is meaningless. .
                      Not so sure about that. Compression on the first turn or the first "puff" of the gauge is an indicator of ring condition. You want the first puff to be at least or near 100lbs. psi.

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                      • #12
                        Originally posted by Paul K. View Post
                        Not so sure about that. Compression on the first turn or the first "puff" of the gauge is an indicator of ring condition. You want the first puff to be at least or near 100lbs. psi.
                        Thanks. I knew there was a reason for recording the first "puff", but I couldn't remember why.
                        Paul Johnson, Wild and Wonderful West Virginia.
                        '64 Daytona Wagonaire, '64 Avanti R-1, Museum R-4 engine, '72 Gravely Model 430 with Onan engine

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