Home Forum Ask A Member Compression

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  • #245195
    Boonie
    Participant

      Canada Member

      I have two 1956 Evinrude. #1 is a Fleetwin 7.5HP
      #2 is a sportwin 10 Hp
      What should compression be?
      What is acceptable compression.
      Early testing is at 80 psi

      #245199
      Bob Wight
      Participant

        US Member

        Both motors should run OK with 80 psi. If the motors have been sitting idle for some time, rings could be slightly stuck and compression might come back up a bit after you run them. My 1958 and 1959 10hp Johnson both run great with about 80 – 85 psi.

        Bob

        1937 Champion D2C Deluxe Lite Twin
        1954 Johnson CD-11
        1955 Johnson QD-16
        1957 Evinrude Fastwin 18
        1958 Johnson QD-19
        1958 Johnson FD-12
        1959 Johnson QD-20

        “Every 20 minute job is only a broken bolt away from a 3-day project.”
        "Every time you remove a broken or seized bolt an angel gets his wings."

        #245200
        Mumbles
        Participant

          I’m not aware of any published compression ratios for these motors but 80 might be a bit low for the 7.5 while I think the ten would be better in the 90’s. If you can get the motors running for a while, the numbers might come up a bit.

          #245208
          Bob Wight
          Participant

            US Member

            A correction to my previous post after looking back thru restoration notes – I had initial tests of 80-85 psi on my 10hp Johnsons. After replacing the head gaskets and getting some running time on them, I ended up around 90 – 92 psi on both.

            Bob

            1937 Champion D2C Deluxe Lite Twin
            1954 Johnson CD-11
            1955 Johnson QD-16
            1957 Evinrude Fastwin 18
            1958 Johnson QD-19
            1958 Johnson FD-12
            1959 Johnson QD-20

            “Every 20 minute job is only a broken bolt away from a 3-day project.”
            "Every time you remove a broken or seized bolt an angel gets his wings."

            #245215
            Boonie
            Participant

              Canada Member

              I’ve heard people on here talk about sea foam. What is its purpose? Is it a fuel additive?

              #245217
              outbdnut2
              Participant

                US Member

                I’ve heard people on here talk about sea foam. What is its purpose? Is it a fuel additive?

                Sea Foam is a fuel additive available everywhere from auto stores and WalMart to Menards. It’s been around for many decades. My opinion is that it’s way over-rated – considered a cure-all by many. It has cleaners and lubes in it and who knows what else. If you have a dirty carb problem, there is a chance it may cure it, but best to take the carb apart. It can also loosen dirt in the tank and send it to the motor where it causes problems. The only use I believe in and use it for is storage of 4-stroke car-type engines. In my I/O ski boat that has a 4.3 Chevy engine as a MerCruiser factory setup, I put it at a fast idle and slowly dump 1/2 can into the carb, then shut it down for the winter. This provides valve and upper cylinder lubrication and coating for winter storage. Years ago a friend with an inboard cabin cruiser told me all the people at the St. Paul Yacht Club do this and they claim that engine storage problems went away and motors are much easier to get started in the spring. This came form a good friend who rebuilds these engines, so I trust his judgement. The stuff runs from $7 to $10 for a 16 ounce can. Some use it as a gas stabilizer for winter, but it contains 18% alcohol, so that could actually add to the fuel storage problem. I do not believe in adding it to gas and think that’s a waste of money. Most people who swear by it say they “always use it and never have a fuel problem” – my opinion is that they wouldn’t have had a fuel problem anyway. That’s my 2 HP on the subject. You will likely get a lot of opinions here. I hear a lot of the same claims for Marvel Mystery Oil that’s been around since the 1920s or 30s.

                • This reply was modified 3 years, 8 months ago by outbdnut2.
                #245273
                Boonie
                Participant

                  Canada Member

                  Thanks for the info outbdnut2. You either schooled everyone or scared the heck out of them.🥺

                  #245277
                  outbdnut2
                  Participant

                    US Member

                    Thanks for the info outbdnut2. You either schooled everyone or scared the heck out of them.🥺

                    Yeah – I’m really surprised I haven’t gotten a lot of disagreement on my opinions about Sea Foam. I bet if I posted that at he AOMCI facebook site, there would have been a lot of emotional commentary!

                    Dave

                    #245293
                    kerry
                    Participant

                      US Member

                      You can put Seafoam down if you wish. I have been using it for almost 20 years after some of the AOMC elders suggested it and swear by it, not at it. I use it in all of my lawn and garden equipment as well as outboards and have not had ethanol fuel issues. Snowblowers start in the fall, mowers start in the spring. Until it stops working, I will continue to use it.

                      If you have too many, AND not enough, you're a collector.

                      #245295
                      2fast4me
                      Participant

                        Seafoam/Deepcreep, might be the same formula, has worked for me on More than a few engines that were stuck. Some struck from old oil some from overheating. Tune up in a can not do much…

                        2Fast4Me

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