50’s 18hp OMC retrofit question

Home › Forum › Ask A Member › 50’s 18hp OMC retrofit question

Viewing 10 posts - 1 through 10 (of 26 total)
1 2 3
  • Author
    Posts
  • April 14, 2019 at 9:02 pm #173404
    shoestringmariner
    Participant

      Hey folks, I’m wondering if my 1957 18hp Johnson’s internals can be upgraded with internals from motors of later years like I believe the 58 QDs can? If not 57, than 58?

      What about 25-30 hp’s Up to 58?
      I would like to get away from 16:1 ratios but keep an iconic motor on my 1957 wooden runabout.

      One outing with my 57 and the transom is covered with a grey oil film.

      Thanks in advance

      April 15, 2019 at 1:43 am #173413
      garry-in-michigan
      Participant

        Lifetime Member

        Swapping out with a low ’70s 25 horse powerhead should work . . .

        April 15, 2019 at 5:25 am #173414
        frankr
        Participant

          US Member

          Wanna start a fuel mix war? You say your goal is to get away from 16:1 mix. In the first place, 24:1 is the correct mix for your ’57. Now for the war: Show me the difference between the ’57 guts and something like ’70, which is a 50:1 motor.

          April 15, 2019 at 5:52 am #173416
          shoestringmariner
          Participant
            garry-in-michigan wrote:

            Swapping out with a low ’70s 25 horse powerhead should work . . .

            Excellent, thanks I did not know that was possible!

            April 15, 2019 at 5:59 am #173417
            shoestringmariner
            Participant
              frankr wrote:

              Wanna start a fuel mix war? You say your goal is to get away from 16:1 mix. In the first place, 24:1 is the correct mix for your ’57. Now for the war: Show me the difference between the ’57 guts and something like ’70, which is a 50:1 motor.

              Oops, my bad, I was thinking about my TN28’s. But yes, 24:1 is too rich and 50:1 is what I’m trying to achieve.

              And not trying to start a fuel war, I’m just trying to clean mine up is all

              April 15, 2019 at 6:11 am #173418
              rudefan29070
              Participant

                I just recently have poured over parts for ALL the years of 18’s looking for pistons for my rebuild. Frank is right there isn’t much difference in them at all. If I had a 1950’s era 18 I would surely run a leaner mix than 24:1. The oils we have available today are MUCH better. I have a 1968 18 that I run basically a 50:1 mix and I throw in 1 more oz for a 6 gallon tank, instead of 16oz of oil per 6 gallons I mix 17. The motor doesn’t complain and it runs like a cat kicked in the butt and doesn’t foul plugs. My best friend has a 1965 18 that I maintain and he too runs the mix I do and doesn’t have any trouble with his either. We both run the Johnson Evinrude TCW3 2 stroke oil that they sell at Walmart by the gallon.

                April 15, 2019 at 9:03 am #173425
                shoestringmariner
                Participant

                  As it so happens, I happen to have a 1969 18hp that could work. I’ll probably use my 57 until I pick up a 58 since I prefer that colour scheme.

                  My 57 runs so good it would be a shame to cut it up

                  April 15, 2019 at 9:34 am #173431
                  frankr
                  Participant

                    US Member

                    There was a change in the powerhead base mounting pattern around 1960-ish. Not sure they can be interchanged, or not.

                    April 15, 2019 at 9:55 am #173432
                    shoestringmariner
                    Participant

                      Where do you guys get your sources when it comes to parts diagrams? If I could look those up I could look through them to see if I can determine what years are compatible.

                      This junction, I think I’d rather go 25 or 30 horse if I’m going to all this work. Electric start if available in those years will be nice too as this runabout is dual cockpit without a pass-through. Kind of awkward to get back to the motor

                      April 15, 2019 at 10:44 am #173439
                      wbeaton
                      Participant

                        Canada Member - 2 Years

                        Well, you aren’t going to get 25-30 hp out of that 18 hp without swapping power heads and I don’t believe any 25-30 powerhead that will swap. At best you could swap in a 70’s 25 hp powerhead, but I don’t think it will be easy. Plus it won’t have the mounting points for the cowl.

                        24:1 shouldn’t be as messy as you are experiencing. If it’s still too dirty and you aren’t willing to use 50:1 then I suggest finding a newer motor in the hp range you want. I don’t mean that to sound harsh. I just don’t see an alternative.

                        Wayne
                        Upper Canada Chapter

                        uccaomci.com

                        • This reply was modified 5 years ago by wbeaton.
                        • This reply was modified 5 years ago by wbeaton.
                      • Author
                        Posts
                      Viewing 10 posts - 1 through 10 (of 26 total)
                      1 2 3
                      • You must be logged in to reply to this topic.