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Johnson 115 HP Compression Test Readings

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  • Johnson 115 HP Compression Test Readings

    About the motor:It is a used 1975 Johnson 115HP (V)Outboard. The motor has sat outside for four years and was winterized the first year. I was told that the water pump/impeller needs to be replaced so the compression test I did was with the engine cold. About the test I did:The manual I have does not explain the proper test procedure or range. The choke was off and the gas disconnected. The spark plugs were in except for the cylinder tested. The cylinders were lubed with WD-40 before the test. I used two $30-40 compression test guages from the local auto parts store. I'm getting 90 psi in each cylinder whether I use the starter or the rope.Questions:Does anybody know what the compression should be?What is the proper compresson test procedure?Any other thoughts about the engine condition or things I should watch out for?

  • #2
    Re: Johnson 115 HP Compression Test Readings

    gt1000,I would like to see over 100 psi, yet being cold could explain that. Also, the throttle plates should be wide open for testing. That may have contributed also.The most important thing is that they are all close in readings. Anything over a 10 psi difference, would be a cause for alarm.


    • #3
      Re: Johnson 115 HP Compression Test Readings

      Thanks DJ, I'll have to re-test once I get the water pump installed. The booklet that came with the new compression tester seems to be accurate then.


      • #4
        Re: Johnson 115 HP Compression Test Readings

        Another altitude issue here that few understand....you are going to see 12%-15% LESS compression at 5500ft.90 to 100lbs. will be normal for you...If 90 is what you got, I see NO issues...