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1963 75hp Lower Unit Level and Fill Plugs

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  • 1963 75hp Lower Unit Level and Fill Plugs

    My parts manual clearly shows the same part for both top and bottom plugs: "307551: Plug and Washer". These are parts #37 and #75 in the exploded view.

    ​I had previously bought NOS plugs and I recently looked at my stock of them. It seems that I have 2 sizes of plugs. The threads seem to be the same but the diameter of the heads are different. There is also a dimple in the end of one of them (to differentiate it?).

    ​It seems that the small-head-diameter plug fits into both holes, but that the large-head-diameter plug will only fit into the upper (Level) hole. There also seems to be nylon washers that have different ODs. One is black and one is white. During a recent trip to a local marina, the guy told me that I shouldn't be using the nylon washers but I should instead be using the composite seal washers in the pic below.

    ​Does anybody know the story behind the plugs and seals and which ones are proper?

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    1963 75hp Starflite V
    Selectric Shift with 5" Extension
    Model #75383E

  • #2
    ??---Use smaller plugs and the white washers.-----Been done for 50 years or more

    Comment


    • #3
      Anybody know the part numbers for the smaller plug and white washers? Also the larger plug and black washer so that I know what to avoid?
      1963 75hp Starflite V
      Selectric Shift with 5" Extension
      Model #75383E

      Comment


      • #4
        If you look on that same diagram now #75 is omitted. #37 is part number 0307551. Note these are allen head screws with washer included. IBOATS has some part number 18-4255. I did not see a listing for just the washer but I think it is 0311598. And probably there is a part number for a bulk pack but I dont know it.

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        • #5
          I found another thread on this topic: http://forums.iboats.com/forum/engin...plugs-obsolete

          ​I wonder if 18-4255 is the smaller-diameter head like in my first post. If it's the larger diameter with the dimpled end, then it won't fit into my bottom drain hole.
          1963 75hp Starflite V
          Selectric Shift with 5" Extension
          Model #75383E

          Comment


          • #6
            Can you machine / file down the bigger plug so it will fit ?

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            • #7
              Sign up today
              Yeah racerone, I could do that. I think that I go ahead and order one of the plug/washer combos (18-4255) and see if it is the smaller diameter. If so, then I'll just get a few of those and use them in the top and bottom holes. If not, then I'll file down the 4 or so large diameter plugs that I have and keep them in my stock. I'll post back here once I get the item and can compare.

              In the meantime, I was just wondering how it came about that OMC has these two oh-so-slightly different plugs and also why the holes that accept the plug head differ between the top and bottom on my lower unit.
              1963 75hp Starflite V
              Selectric Shift with 5" Extension
              Model #75383E

              Comment

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