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1990 vs 1992 4.3 block swap

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  • #91
    unbolt flex plate, throw away. get manual transmission flywheel and bolt on. they are spec'd by GM to bolt on the flex plate and the flywheel have the same balancing. just get proper one for your generation of motor. that would be a 1989-1992 non-balance shaft motor.

    since your motor was already running, all youre doing is swapping out the automatic flex plate for a flywheel.
    Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

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    • #92
      Yup. Got that one from the mercruiser. Wasn't sure if,I can just replace the auto flex plate with the mercruiser one. From what I have read, they are balanced by themselfs.
      1990-4-3-century-2000-floor-transom-stringer-upholstery-project

      https://forums.iboats.com/forum/engi...4-3-block-swap

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      • #93
        you could have saved money and bought a flywheel from any auto parts store for a 1989-1992 GM vehicle with a 4.3
        Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

        1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

        Past Boats
        1970 Wooster Hellion - Merc 9.8
        2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
        1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

        What’s behind you doesn’t matter.Enzo Ferrari

        Comment


        • #94
          The flywheel is from the mercruiser. The stripped block will be my new one. That one had the auto flex plate
          1990-4-3-century-2000-floor-transom-stringer-upholstery-project

          https://forums.iboats.com/forum/engi...4-3-block-swap

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          • #95
            the flywheel is from one of GM's suppliers, sold to GM, sold to Mercruiser who in turn sold it back to you. its a $79 flywheel for a manual transmission application.
            Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

            1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

            Past Boats
            1970 Wooster Hellion - Merc 9.8
            2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
            1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

            What’s behind you doesn’t matter.Enzo Ferrari

            Comment


            • #96
              So I just got my camshaft out from the old mercruiser. Found two lobes damaged. Engine was still running good. would you say this one is toast? Look for another one with fuel pump lobe
              1990-4-3-century-2000-floor-transom-stringer-upholstery-project

              https://forums.iboats.com/forum/engi...4-3-block-swap

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              • #97
                I found a used one with the lobes to be still good. $50 with 15 shipping. Hard to find the older style camshaft with the mechanical fiel pump. And i don't want to pay at least 300-400 for a new one.
                1990-4-3-century-2000-floor-transom-stringer-upholstery-project

                https://forums.iboats.com/forum/engi...4-3-block-swap

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                • #98
                  Originally posted by Chris51280 View Post
                  I found a used one with the lobes to be still good. $50 with 15 shipping. Hard to find the older style camshaft with the mechanical fiel pump. And i don't want to pay at least 300-400 for a new one.
                  Make sure you know what the engine that that camshaft came out of was used for.. Needs to be a truck or RV... 'Normal' car is no good.
                  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
                  The world takes on a whole new perspective when viewed from 100’ below.
                  1972 Bertram ‘Bahia Mar’ 20
                  2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
                  (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


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                  • #99
                    It actually came from a 1988 4.3 mercruiser.

                    Chris, can I swap dampers from one engine to the other? It apears the mercruiser one is a bit heavier. Dont think it matters.

                    Whats your take on the crankshaft. Does it matter if its a light crank?
                    I'll take it that I can't use the old mercruiser crank?! It would be original with standard bearings. I would buy new bearings but not sure if it needs to stay together.

                    Both engines came out of Tonawanda if that matters
                    1990-4-3-century-2000-floor-transom-stringer-upholstery-project

                    https://forums.iboats.com/forum/engi...4-3-block-swap

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                    • The only things that need to be 'matched' are the pistons to the bores they were in, lifters to the cam lobe they were running on and rockers to the valves they were opening (unless you have the rockers 'faced', then put them anywhere you like). Everything else should be ok to swap around. If you prefer the Merc crank in the new block, as long as you check the bearing journal sizes and are putting new bearings in, that should be fine. Use the flywheel in place of the flex-plate, and the balancer that matches the crank (Merc crank, Merc balancer.) Remember, you're building up an an engine that will not turn any faster than 5,000rpm and produce no more than about 210hp. It's not stressing anything, you have lots of tolerance... If it was going to make 400hp and spin at 7,000rpm, different story.... That said, you can't be 'sloppy', do it all right and the engine will last longer than you.

                      That's my take. Others, like Scott and friends, have a little more experience building up engines, but I'm sure you'll be fine to do as above.

                      Chris.......
                      xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
                      The world takes on a whole new perspective when viewed from 100’ below.
                      1972 Bertram ‘Bahia Mar’ 20
                      2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
                      (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


                      Comment


                      • Awesome. I will do that. The only thing I have not watched out for are the lifters. Since I'm getting a different cam, I hope that won't be too much of a problem. Thanks for all the clarifications. I marked all the pistons where the go to and left the rods assembled. The chain from the mercruiser is a single roller chain and has 1/4" slop. The chain from the car is the link chain and streched. I think I can use the roller chain and be fine. It's within spec. i know that I should change it but I try to keep my budget low now. I'm in at 450 just for parts. Still got to do the stringers and floor. Who knows what else will come around. I would want to rebuild the carb and the trim cylinders.

                        Thank you for the info chris. Will post the progress here. Cam should ne here January 2nd

                        Merry Christmas
                        1990-4-3-century-2000-floor-transom-stringer-upholstery-project

                        https://forums.iboats.com/forum/engi...4-3-block-swap

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                        • If they are roller lifters, no problem as the retainers keep them aligned.

                          If you're carrying the chain across, take the sprockets too.

                          Chris......
                          xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
                          The world takes on a whole new perspective when viewed from 100’ below.
                          1972 Bertram ‘Bahia Mar’ 20
                          2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
                          (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


                          Comment


                          • So i cleaned the heads today and lapped the valves. I noticed a small nick at the top left where the combustion gasket ring will be. It was there when I took it off since im sure I did not cause this. I have noticed that the gasket in the merceuiser was a thin stainless steel sheet vs the automotive thicker gasket. I do have the one from the car but have more sludge on them. I would just change out the one that has the nick.
                            i have noticed that my mercruiser engine was rebuild at some point since it is .03 over and the crank is underside as well.
                            This brings me to the question, if someone would machine the heads, how would i know. Im afraid I replace one head that was machined with one that was not possibly. That would create different compression ratios.
                            I tested the compression before I took it apart and it was at 150 on all cyclinder
                            1990-4-3-century-2000-floor-transom-stringer-upholstery-project

                            https://forums.iboats.com/forum/engi...4-3-block-swap

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                            • Got most of my order from summit today and started assembling things. I checked the gasket design and it seems i won't have a problem with the little imperfection. I should also be ok with the oversize bore as described by felpro.
                              installed all of the freeze plugs but one. I have to install the cam bearing first. This way its easier to install the one on the transmission side without the plug right next to it.
                              1990-4-3-century-2000-floor-transom-stringer-upholstery-project

                              https://forums.iboats.com/forum/engi...4-3-block-swap

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                              • Sign up today
                                I assembled the cam bearings and the crank bearings and assembled the cam and crank. I checked the piston ring gap and cleaned the piston grooves. Top ring has .018" and second .02". Its on the high side but still within spec. The underside of the piston has alot of carbon build up. Not sure if it makes a difference. I was able to use the heavy crank instead of the light crank from this engine. Will use the damper that came with the crank.
                                1990-4-3-century-2000-floor-transom-stringer-upholstery-project

                                https://forums.iboats.com/forum/engi...4-3-block-swap

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