1934 Johnson A-70

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  • August 25, 2017 at 1:57 am #8011
    10717
    Participant

      I have been working on cleaning up an A-70 to use on a Thompson car topper. I started it tonight for the first time and it ran very nicely. Alternate firing and underwater exhaust are big improvements over the 1924 A that was my last project! But how do you tell whether the cooling system that relies on the prop is working? It seemed to heat up more quickly than I expected. Thanks.

      August 25, 2017 at 12:18 pm #63753
      Anonymous

        This motor is a vacuum/pressure cooling system. When starting motor on boat you must go to max. engine speed to purge air from the cooling system. The motor will not cool in a tank or barrel. Touching the side of cylinder case on the opposite side from the muffler should be warm but not hot.

        August 25, 2017 at 12:34 pm #63754
        10717
        Participant

          Thanks. I had it in a barrel but was reluctant to put it on the boat in a lake until I knew it was cooling. Guess I had it backwards.

          September 11, 2017 at 1:44 pm #64669
          10717
          Participant

            Had it on a boat yesterday. As you said, the muffler side is hot but the spark plug side stays pretty cool by comparison. I have a short video of it running which I would be happy to share. Thanks again.

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