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  1. #1
    Cadet
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    Default 70 hp Johnson Compression ???

    What would the compression on a new 70 hp Johnson or even a fresh rebuild be? Wanted to compare the numbers with my 1988 Johnson. Have not performed the test yet, but I just wanted to know what to look for

  2. #2
    Admiral
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    Default Re: 70 hp Johnson Compression ???

    Expect healthy numbers to be over 100 and closer to 130-135 on that engine.Make sure all three are within 10% or closer.

  3. #3
    Cadet
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    Default Re: 70 hp Johnson Compression ???

    I have an '89 and it has 120 written on each of the cylinders. Hope that helps.

  4. #4
    Cadet
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    Default Re: 70 hp Johnson Compression ???

    slow-n-ez, Is that a stamped factory number?

  5. #5
    Admiral
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    Default Re: 70 hp Johnson Compression ???


  6. #6
    Admiral Chinewalker's Avatar
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    Default Re: 70 hp Johnson Compression ???

    I like to see the 49-cube OMC triple numbers in the 130+ range. They're designed as a fairly high compression engine. My '79 Stinger 75 still punches the gauge to about 145psi top to bottom. - Scott
    Share A Project Page for 1971 GW Invader Banchie 13
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  7. #7
    Cadet
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    Default Re: 70 hp Johnson Compression ???

    I'm getting a very small variation of 140 psi on all cylinders,1=1422=1393=140or at least that is as close as I can read the gauge.I know the boat has been used very little and you can tell the starter has some resistance on it as it tries to turn the motor over initially. I found a pull rope for the motor so I thought I would give it a yank just for funÂ… made me realize how big of a man I am not.

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