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Changing from a 5.7 Liter OMC to a 7.4 454 Mercruiser

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    #16
    Originally posted by JJ_Parsons View Post
    Thank you all for the great responses and huge amount of intellect here!

    First, I want to note that my desire in looking at the 454's was due to their local availability only, not based on an upgrade in power. NOT that that's a bad thing in any way because, lets be honest..... ITS MORE POWER!!!! But in all honesty, they are at a great price and it would be a perfect opportunity to upgrade what is currently on the boat. Having said that though, I believe the overall aspects ($$$) of what may be required to fully take on this type of swap significantly outweigh my wants/needs and wifes desire that I not sink a ton of $$$$$$ into said boat! HA!

    Back on the hunt for a 5.7 L OMC!!!!!

    As always, my sincere thanks to all for the added advice and continued guidance!!!!
    You're being smart. When it was new, the 3255 was a 40 mph boat with twin 260 hp 5.7s.

    I also think you're being smart to replace both engines, not just one.

    I do not think twin 454s is the answer in this boat even if you did in fact replace the drives, which would have to be done to swap to a 7.4L engine. (Full disclosure, I am a "do it right the first time" guy).

    What you want is twin 383s. Actually, if I were in your shoes, I would look for a newer boat that has had a cabin fire and gut the drivetrains from that boat.....
    Matt Train
    BOC Site Team
    Chicagoland, IL

    Comment


      #17
      Matt,

      You got me going down a good path here!!!!!! That was awesome!!!!!! Duly noted and I will get on this!!!!!!

      JJ
      1987 Bayliner Avanti 3255
      Twin OMC 5.7L 4V

      Comment


        #18
        Originally posted by JJ_Parsons View Post
        Thank you all for the great responses and huge amount of intellect here!

        First, I want to note that my desire in looking at the 454's was due to their local availability only, not based on an upgrade in power. NOT that that's a bad thing in any way because, lets be honest..... ITS MORE POWER!!!! But in all honesty, they are at a great price and it would be a perfect opportunity to upgrade what is currently on the boat. Having said that though, I believe the overall aspects ($$$) of what may be required to fully take on this type of swap significantly outweigh my wants/needs and wifes desire that I not sink a ton of $$$$$$ into said boat! HA!

        Back on the hunt for a 5.7 L OMC!!!!!

        As always, my sincere thanks to all for the added advice and continued guidance!!!!

        Looking at Mercruiser 350 Mag/5.7L over the last few days myself, the best deal I seemed to find (~$7,500) was the below link (let me know if you have a better rate/choice please):
        http://www.boattrader.com/listing/20...tail-102073346
        2004 Bayliner Cierra 285
        1987 Bayliner Capri 1950 (sold)
        Intercoastal Panhandle FL

        Comment


          #19
          Originally posted by afchiefw View Post


          Looking at Mercruiser 350 Mag/5.7L over the last few days myself, the best deal I seemed to find (~$7,500) was the below link (let me know if you have a better rate/choice please):
          http://www.boattrader.com/listing/20...tail-102073346
          I'll be sure to keep you posted if I come across anything!!!!!

          JJ
          1987 Bayliner Avanti 3255
          Twin OMC 5.7L 4V

          Comment


            #20
            Originally posted by builderdude View Post
            Yatchman makes good point about loosing space and adding weight. 383's should be an awsome choice if you have to go with new power. Have you thought about a possible JB weld repair on the crack? I've never done this myself but others have saved engines doing this, might be worth a try if your engine was a strong runner previously.
            Builderdude and @dcmb JBweld was my first go to but as I look at these cracks more and more I just dont see that as being an option. I'm hoping I'm wrong because the search for this engine is driving me nuts. Indicator number one is the random amount of oil that I see in the water that had spilled from the engine. Beyond pulling the spark plugs and cranking the engine over to see if water comes out, I am somewhat convinced that I also have internal damage as opposed to just water jacket damage. I've pulled the dipstick out just about every time I get down to the boat and still see no water or water bubbles on it when I pull it but I believe there still could be internal damage.
            1987 Bayliner Avanti 3255
            Twin OMC 5.7L 4V

            Comment


              #21
              Originally posted by JJ_Parsons View Post
              Indicator number one is the random amount of oil that I see in the water that had spilled from the engine. Beyond pulling the spark plugs and cranking the engine over to see if water comes out, I am somewhat convinced that I also have internal damage as opposed to just water jacket damage. I've pulled the dipstick out just about every time I get down to the boat and still see no water or water bubbles on it when I pull it but I believe there still could be internal damage.
              Could you explain where this water came from that had oil in it. Also if the engine has not been run since the cracks were discovered you'll likely see no evidence of water on the dip stick as any water in the oil pan will settle to the bottom.
              Dave
              Edmonds, WA
              "THE FIX"
              '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
              (.030 over-Vortec top end-part closed cooled)
              The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
              Misc. projects thread
              https://www.baylinerownersclub.org/f...56-gctid789773

              Comment


                #22
                Originally posted by builderdude View Post

                Could you explain where this water came from that had oil in it. Also if the engine has not been run since the cracks were discovered you'll likely see no evidence of water on the dip stick as any water in the oil pan will settle to the bottom.
                Yes sir!!!!

                I had the engine running.......... and then I noticed the "boat loads" of water gushing from the sides of the engine.

                The water with the oil in it is the water that had pooled in the engine bay compartment right below the engine. If there is a possibility of oil getting into the water jacket, thus being flushed out as the water ran through the jacket and out of the cracks then, that would make sense to me, however; I dont believe (and this is completely under unsubstantiated and utterly false pretense) that the water jacket should generally have oil in it.

                Blown head gasket slowly creeps its way into a being plausible culprit now as well........

                Needless to say sir, its not a ton of oil, but its present enough to make me wonder.
                1987 Bayliner Avanti 3255
                Twin OMC 5.7L 4V

                Comment


                  #23
                  Compression test, cooling system pressure test is in order...
                  Easy to diagnose.
                  Joon, Kathy, Jaden & Tristan
                  Uniflite 42 AC, DD 671N
                  93 3058 sold
                  92 2855 (day boat)
                  91 Fourwinns 205 (lake boat)
                  Longbranch WA
                  Life is Good

                  Comment


                    #24
                    These are raw water cooled engines I’m assuming. The oil you saw may just be engine bay goo now floating around in the water that was added. Hard to get oil into the water jacket. A cooling system pressure test will likely just loose pressure through the crack.
                    Dave
                    Edmonds, WA
                    "THE FIX"
                    '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
                    (.030 over-Vortec top end-part closed cooled)
                    The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
                    Misc. projects thread
                    https://www.baylinerownersclub.org/f...56-gctid789773

                    Comment


                    • Nauti_Mike
                      Nauti_Mike commented
                      Editing a comment
                      I agree with Dave. What you are seeing is most likely oil that was already in the bilge. Can you post some pictures of the cracks?

                    #25
                    If it cracked due to lack of winterization they often crack inside the cam valley where the water passages around the head bolts are. So there is probably water leaking into the cam valley and mixing with the motor oil there, in addition to the external cracks. Did the exhaust manifolds crack too? They will spew plenty of water if so.

                    About replacing the engines, as all noted before, even if they fit, the 7.4s are too much power for the standard Cobra drive. OMC themselves thought this and used the Baby King drive for the Ford 460 (standard Cobra upper unit, with the larger V8 outboard gearcase). For the GM big block they used the Cone Clutch drive, even more beefy. So stick with the small block if you don't want to really spend a ton of money and keep your Cobras as long as they are serviceable. If the other engine is in good shape, you could try to get a re-man 5.7 of the same style you had (ie pre-vortec) so you can re-use your other parts easily, as long as they are in good shape. However, if the engine froze, that pre-vortec intake manifold probably cracked too and they are not easy to find in good shape. While it is possible to upgrade to the Vortec engines, there are slight differences that make swapping a bit more complex (ie, no heated exhaust cross over in the intake, so you have to convert the Q-jet carb to an electric choke). Staying with the pre-vortec makes it easy to re-use all your old stuff. I'd check on parts availability for some of these items before buying anything. Specifically, the exhaust manifolds (if bad and NLA they can be replaced with late OMC/Volvo style center riser units) and the intake manifold (get it checked by a machine shop).

                    PS did the mechanic do the winterization and if so, they should take responsibility for this!
                    88 Four Winns 200 Horizon 4.3 OMC
                    98 Jeep Grand Cherokee 4.0/Selectrac
                    07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

                    Long Island Sound Region

                    Comment


                      #26
                      http://www.michiganmotorz.com/marine...987-p-167.html
                      if you want a re-man long block
                      but keep in mind you will most likely need an intake manifold (may have cracked as well) and an exhaust system. The intake is tougher to find, the exhaust is easy to convert if you can't get the OE style log manifolds any more.

                      When I did my top end overhaul (re-man cyl heads, new head gaskets etc) I made sure that the original intake was in good shape before going forward and I bought a spare on on ebay just in case. At least for the 4.3 V6s the non vortec ones turn up now and then but they are not real easy to find. The V8s may be easier.
                      88 Four Winns 200 Horizon 4.3 OMC
                      98 Jeep Grand Cherokee 4.0/Selectrac
                      07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

                      Long Island Sound Region

                      Comment


                        #27
                        Originally posted by 88fourwinns View Post
                        http://www.michiganmotorz.com/marine...987-p-167.html
                        if you want a re-man long block
                        but keep in mind you will most likely need an intake manifold (may have cracked as well) and an exhaust system. The intake is tougher to find, the exhaust is easy to convert if you can't get the OE style log manifolds any more.

                        When I did my top end overhaul (re-man cyl heads, new head gaskets etc) I made sure that the original intake was in good shape before going forward and I bought a spare on on ebay just in case. At least for the 4.3 V6s the non vortec ones turn up now and then but they are not real easy to find. The V8s may be easier.
                        Cracked exhaust manifolds and the sudden "spewing of water" are what started this entire debacle to begin with. We had a bad cold snap here and as recommended all I had done prior to it was put a heater down in the bilge. Sadly, despite my efforts to avoid the freeze, both port side manifolds on Starboard and Port side engine wound up cracking. I have since replaced those and it was on my initial run, after replacing them, that I was suddenly introduced to the saddening effects of spewing water from the cracked block on the port side engine. I am completely lost as to how the port side engine wound up with all this damage yet the starboard side (minus the exhaust manifold) is fine. Honestly I have had nothing but trouble with the port side engine since I purchased the boat anyway and this is just the icing on the cake overall.

                        This past weekend I went down and did some thorough climbing all over the engine and was finally able to locate the block stamp. 14093638, which comes up as a small block Chevy. I found a rebuilt engine on Craigslist with the same block stamp and a 1 year warranty close to two hours away from me that I will be hopefully going to pick up next weekend as long as its still there. With the added info above on the intake manifold and possible damage there I will be sure to look over that as well and as you recommended, start looking for a spare. I actually found the numbers for that too, 14096244, mistakenly thinking that was the engine block stamp!

                        I will certainly post pictures of the cracks as soon as I can get them on my computer and uploaded.

                        1987 Bayliner Avanti 3255
                        Twin OMC 5.7L 4V

                        Comment


                          #28
                          Here's the pictures of the big crack starboard side of the port engine. If you look close enough you can see where it's actually spread out in various places. I'm calling this one a lost cause!
                          Attached Files
                          1987 Bayliner Avanti 3255
                          Twin OMC 5.7L 4V

                          Comment


                            #29
                            Looks bad but what have you got to lose by trying a JB Weld fix? There is no real pressure there and if that is the only damage a fix is possible. It may not be but I wouldn't give up on it just yet. Do the test suggested and if nothing shows, try the fix and run it. If there is other problems they will show up quickly and you are out nothing but a very few bucks and some time. Grind the crack to clean it up. There are a lot of engines here still going that have been fixed this way.
                            Doug
                            Started boating 1955
                            Number of boats owned 32
                            Bayliners
                            2655
                            2755
                            2850
                            3870 presently owned
                            Favorite boat. Toss up. 46' Chris Craft, 3870 Bayliner

                            Comment


                              #30
                              To me it looks like it has been cracked for awhile and it froze and cracked more. I could be wrong but it looks like it has old corrosion in part of it. Not that its.of any consequence
                              1989 Avanti 3450 Sunbridge
                              twin 454's
                              MV Mar-Y-Sol
                              1979 Bayliner Conquest 3150 hardtop ocean express.
                              Twin chevy 350's inboard
                              Ben- Jamin
                              spokane Washington

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