7.5hp Cranks OMC (Edited Journal Clearances)

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  • September 20, 2015 at 8:59 pm #2589
    chris-p
    Participant

      Does anyone know the difference between the cranks on a 1955 Evinrude Fleetwin 7518 7.5hp and a 1956 Johnson AD 7.5hp?

      They have different part numbers, but wondering if I can use the ’56 crank in my ’55 Fleetwin?

      The ’55 part number is 203375
      The ’56 part number is 203485

      They use the same connecting rods, so the journals must be the same.

      Reason I ask is I have a ’56 AD parts motor sitting around, and cannot seem to find a good crank for the ’55 Fleetwin that destructed from someone running it lean. Journals on the ’55 crank are well beyond polishing.

      Thanks for any help.

      September 20, 2015 at 10:02 pm #24267
      fleetwin
      Participant

        US Member

        OK, well the 203375 crank supercedes to the 203485 crank (according to marinengine.com). So, using the newer crank in the 55 Fleetwin should work out just fine.

        September 20, 2015 at 10:32 pm #24270
        chris-p
        Participant

          Aha, not sure how I missed that! Thanks Don! That works out just great for me.

          Assuming that the crank in this parts motor is ok. Has a big ole hole in the block from where she tossed a rod.

          I have a few 7.5hp blocks like that. Too bad.

          September 20, 2015 at 11:38 pm #24275
          1957evinrude
          Participant

            US Member

            Where would the numbers be stamped on the crank shaft ??

            September 21, 2015 at 12:23 am #24276
            dan-in-tn
            Participant

              US Member

              I have a brand new ’55 5.5 crank that has a circle dykem stamp on the taper with the part number in it. The OMC logo is there also, but it doesn’t stay very long usually if the flywheel has been pulled many times.

              Dan in TN

              September 21, 2015 at 7:51 pm #24333
              fleetwin
              Participant

                US Member
                quote Chris_P:

                Aha, not sure how I missed that! Thanks Don! That works out just great for me.

                Assuming that the crank in this parts motor is ok. Has a big ole hole in the block from where she tossed a rod.

                I have a few 7.5hp blocks like that. Too bad.

                So, your donor motor has a thrown rod? Unfortunately, the donor’s crank probably isn’t much good either.
                The rod bushings are definitely the weak link on these engines. Could be a messed up lower seal allowing water into the crankcase causing a slow death. Perhaps the previous owner followed the advice about "…..you can mix at 50:1 with today’s better oils….".

                September 26, 2015 at 12:52 am #24614
                chris-p
                Participant

                  Yeah, you were right Don.

                  I took some time to tear down that ’56 7.5hp with the thrown rod through the block.

                  I was hoping the crank would have been ok, but nope. Big end of the rod got melted in the journal.

                  Ah well, at least I finally got that thing torn down and put away in the parts bins. Been meaning to do that for a while.

                  September 26, 2015 at 4:29 am #24622
                  dan-in-tn
                  Participant

                    US Member

                    Pat & Shelly have two on Ebay at buy it now or best offer. I buy from them all the time. They are great to deal with. They run Pine Lake Boat & Motor in Plainwell, MI. This is the place that burned down and made it onto or old site 30 minutes later. If you just enter the old crank number the cranks will come up. Make an offer and most of the time Pat will go for it. Tell him Dan sent you and you are an AOMCI member. Good luck!

                    Dan in TN

                    September 26, 2015 at 4:48 pm #24638
                    chris-p
                    Participant

                      Ok thanks!

                      I have to start being careful on how much I spend on these motors though.

                      I always end up putting in too many NOS parts, on my restorations, then cannot even get what I have into them in parts when I sell them.

                      I don’t do it to make money, but cannot be taking a hit on every motor, lol.

                      I just cannot bring myself to scrap motors, I need to get them going again.

                      I have been spending my morning polishing cranks in my jig. Some I thought were scrap I may end up being able to use after polishing the journals.

                      I have about 20 cranks for the 7.5, almost all have a bad journal on the upper cylinder. Seems like all the parts blocks I have threw the top rod.

                      September 26, 2015 at 10:10 pm #24652
                      dan-in-tn
                      Participant

                        US Member

                        Chris, it doesn’t seem that way, it is that way! On the 7.5 anyway. These cranks from Pine Lake are used, but I understand what you mean by too much money in old motors. If polishing cranks, do you haven a micrometer? I’m sure someone here has the journal size spec. You can compare to the bottom journal to begin with. Needs to be real close (.001 or less) this is not an area where a little more space helps the rod get a little more oil. These little bushing rods do need the 16/1 oil ratio for sure. I haven’t had much luck saving one of these cranks, but it sure can’t hurt to try.

                        Dan in TN

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