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Results 1 to 4 of 4
  1. #1

    Default 1979 Johnson 70 hp compression

    What would be good compression numbers on a 1979 Johnson 70 hp.

  2. #2
    Join Date
    Oct 2011
    Location
    maplevalley WA
    Posts
    8,009

    Default Re: 1979 Johnson 70 hp compression

    What are the numbers you are getting? Did you check it three times engine cold WOT with all the plugs out? If the numbers are within 10% between the high and low numbers the engine should be still servicable.

  3. #3

    Default Re: 1979 Johnson 70 hp compression

    I have not checked the compression yet, it is a motor I am considering buying, I will be checking compression cold at WOT. My 4cyl Mercs all have about 120 lbs compression. I understand the 10% high low, but what is a good number for the Johnson ?

  4. #4
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,777

    Default Re: 1979 Johnson 70 hp compression

    The last 2 Johnson 3 cylinder motors I checked showed 150 PSI on a new gauge.

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