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Mercruiser Alpha 1 transom seal

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  • Mercruiser Alpha 1 transom seal

    I have a Alpha 1 drive that is leaking from the transom. The boat when in the water slowly weeps water from the bottom of the inside transom mount plate. The bellows and seals are all new. Is it possible that the seal between the transom and the transom assembly is bad? How is this normally sealed? Having no experence with replacing a transom assembly, I dont know how it seals to the boats transom.


  • #2
    Re: Mercruiser Alpha 1 transom seal

    It's a big oring like seal that is about 3/4" diameter in it's cross section. They almost never just start leaking because the seal goes bad, what normally happens is the plywood transom starts getting soft (rot) and the bolts are then loose. The only good repair at that point is a new transom, then a new seal on the transom shield. Trying to tighten it down will just warp the fiberglass and probably make it leak worse.
    Check the transom for rot before you do anything.
    Don S.

    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.


    • #3
      Re: Mercruiser Alpha 1 transom seal

      what about where the hyd. lines attach to the block? 2 bolts and a gasket are the only things holding it in there.
      you don`t mention the year but if it`s 85ish, the exaust "Y" pipe may be corroded thru.


      • #4
        Re: Mercruiser Alpha 1 transom seal

        The boat was knocked around a bit during a hurricane (Katrina). That outdrive may have been loosened up as the boat hit stuff. The outdrive and transom assembly have been services since (new pump, bellows, seals, etc.) so I don't think thats it. I may be the Hydraulic lines, but I didn't take that out or loosen it. The Transom is good, but may I will try and tighten the bolts on the transom assembly to see if that helps. If I recall, the nuts are on the outside of the boat, under the anode caps, right?
        The drive in question (it a twin engin boat) is a 1988 Alpha 1, gen 1 drive. The leak is coming from the intersection between the inside transom and the engine mount plate/outdrive assembly inside the boat.

        Thanks for the help.


        • #5
          Re: Mercruiser Alpha 1 transom seal

          If I recall, the nuts are on the outside of the boat, under the anode caps, right?

          All the Nuts are on the Inside.......


          • #6
            Re: Mercruiser Alpha 1 transom seal

            and don't forget the big nut just aft of the helm.
            just because you found it that way does not mean it is supposed to be that way.


            • #7
              Sign up today
              Re: Mercruiser Alpha 1 transom seal

              I just did the transom seal on my Bravo 1 wich is the same as your Alpha .

              The motor has to be pulled or maby just loosend up enought to remove the transom sheild if your lucky...My machanic says you may be able to get lucky enough to tighten the bolts and stop a slight leak. It may not be a permanant fix but maby you can prolong the big work.

              I KNOW DON and the rest keep talking about rotted wood but there was 0 rot on my boat and the seal was bad. Problably due to recent prop strikes. Once by me and once by the previous owner.

              If the boat got knocked around because of katrina it is very possible that the seal got jarred around and ripped. Its a small 1/2" to 3/4" rubber / foam type of seal that sqeezes down when initially installed that creates the seal.

              My machanic even did a secondary seal by applying a bead of sylicone all around the edge of the transom sheild just to insure a nice water proof seal.

              Depending on how long youve had the leak you may need to check your U joints and Gimbal bearing. Mine G Bearing was shot and my joints were rusty but not damaged.

              I kind of find it interesting that all these posts have recently come up since I found my transom seal leak and had to under go the rerpair.

              I paid 2700.00 for transom seal, U joint replacement, Gimbal bearing replacement, lower shift cable replacement, upper shift cable replacement, new wheel bearings on my tri axel trailer. New master cylinder. assorted break parts for the 4 wheels. Carb idel adjustment. 24 hours of labor....The boat already sounds WAY quieter and smoother. I am looking forward to getting back in the water maby in a day or three.