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Measuring crankcase pressure

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  • Measuring crankcase pressure

    how to use an airspeed indicator to measure your engines crankcase pressure
    Attached Files
    N29787
    '41 BC12-65

  • #2
    More on this...
    Attached Files
    N29787
    '41 BC12-65

    Comment


    • #3
      Is there a correlation between leak down cylinder tests and elevated crankcase pressure? How about exhaust valve guide leakage into the valve covers and onward to the breather? The pressure can come from some source(s) including the front crankshaft oil seal mentioned.

      I know for some air cooled motorcycle engines that fail to break-in properly and have a good piston ring seal it's common to have excessive crankcase oil and fumes directed into the intake where they are plumbed.

      Correlation isn't necessarily causation as some scientists like to say.

      Gary
      N36007 1941 BF12-65 STC'd as BC12D-4-85

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      • #4
        Originally posted by PA1195 View Post
        Is there a correlation between leak down cylinder tests and elevated crankcase pressure? How about exhaust valve guide leakage into the valve covers and onward to the breather? The pressure can come from some source(s) including the front crankshaft oil seal mentioned.

        I know for some air cooled motorcycle engines that fail to break-in properly and have a good piston ring seal it's common to have excessive crankcase oil and fumes directed into the intake where they are plumbed.

        Correlation isn't necessarily causation as some scientists like to say.

        Gary
        piston ring blow by will give a higher case pressure if its bad enough.

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        • #5
          One of the most common things I've found is a dip in the breather line. That's caused a lot of messes. I did have one engine that they said was puffing smoke after a few hours of running. I knew it wasn't on the test cell, so I went to investigate. They had the breather outlet facing forward...... go figure.
          John
          I'm so far behind, I think I'm ahead

          Comment


          • #6
            Originally posted by N96337 View Post
            One of the most common things I've found is a dip in the breather line. That's caused a lot of messes. I did have one engine that they said was puffing smoke after a few hours of running. I knew it wasn't on the test cell, so I went to investigate. They had the breather outlet facing forward...... go figure.
            John
            My Taylorcraft breather goes out the bottom, I dont go over the top like some do.
            N29787
            '41 BC12-65

            Comment


            • #7
              Blowby? May be >

              Poor break-in and/or piston ring seal throughout stroke
              Exhaust valves to guides loose
              Flat prop so low BMEP load on pistons and rings
              Too low cruise rpm and manifold pressure
              Too much sump oil
              High oil temps
              Breather outlet in low air pressure zone
              That front crank oil seal air leak
              Oil that turns dark quick is an indicator for some of the above

              Gary

              N36007 1941 BF12-65 STC'd as BC12D-4-85

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