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  • Compression

    Would anyone know what the compression should be for a 1971 20hp Johnson. 20R71S

  • #2
    anything above 100 is good above 120 is great

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    • #3
      Thank you very much!

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      • #4
        Originally posted by flyingscott View Post
        anything above 100 is good above 120 is great
        How does 130 sound...both cylinders

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        • #5
          There are many , many of these motors around that have hardly been used over the years.------Some spend much time in proper storage.----Used for just a few hrs every year.----If you just bought it remove the flywheel to check the coils.-----Bonus if you finfd them cracked.

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          • #6
            Originally posted by racerone View Post
            There are many , many of these motors around that have hardly been used over the years.------Some spend much time in proper storage.----Used for just a few hrs every year.----If you just bought it remove the flywheel to check the coils.-----Bonus if you finfd them cracked.
            Not sure why you would want them cracked, didnt think they were like walnuts but am here to learn too

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            • #7
              Cracked means original and it probably hasn't been used for years and is most likely a low hours motor.

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              • #8
                Exactly----If coils are cracked then it likely has not been used for many years.-----Most likely then a low hrs motor.-----I see that all the time !!-----I have many new coils on hand here as it is a very , very common thing.

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                • #9
                  The comp readings: as long as they are even or real close.
                  Different gauges read differently.
                  Harbor Freight sells JUNK and they don't give the right readings.


                  Buy American made Cars and Trucks!!!Towing insurance for a boat,a GREAT thing.
                  ​Tools to make my life easier: Battery tester, die grinder, temp.gun, compression tester, DVA meter.

                  In Scenic , Beautiful San Sebastian by the sea Florida

                  88 Bayliner 21CC 2001 Mercury 225 HP EFI

                  PLEASE,NO PERSONAL MESSAGES IF THE QUESTION CAN BE ASKED ON THE OPEN FORUM I WON'T ANSWER AS MY SYSTEM CAN'T REPLY TO YOUR EMAILS

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                  • #10
                    Ahh interesting, "cracked" in that sense seems to be an exclusive North Americanism

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                    • #11
                      I see a lot of German, Japanese, and especially British Engineering that is Cracked

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                      • #12
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                        Originally posted by jimmbo View Post
                        I see a lot of German, Japanese, and especially British Engineering that is Cracked
                        I may have too, but at the time I probably considered it a misprint!

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