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    #31
    Originally posted by Lineman1 View Post
    ...What are we paying for in a Mercury Motor?? I would think that the MX6.2 was Mercury's HOT ROD small block.
    What I have found is a stock GM 2 bolt main block, light casting heads, stamped rockers. Outside of the stroked crank, better rods and pistons this is your average Malibu / Tahoe motor!!
    ...
    Mercury Marine and GM build a motor to particular price point that designed to perform well under the conditions it will see. I think they've done a good job considering how seldom the rotating and reciprocating components on these engines fail. I understand wanting a very durable motor, with 4-bolt mains, forged crank, etc, but all this is not necessary at the horsepower and RPM levels that these engines are operating at. These marine engines will fail due to top end wear, water intrusion, etc. way before the bottom end and valve train gives out.

    1999 3788, Cummins 270 "Freedom"
    2013 Boston Whaler 130 SS
    Anacortes, WA

    Comment


    • Lineman1
      Lineman1 commented
      Editing a comment
      That's kinda my thoughts at the moment. 325 350 horse from a 350+ ci. Small block is light on the hp. There are no shock loads to the motor. Like letting the clutch go at 5000 rpm. Unless you get the prop out of the water and slam it back in. Still with the torque load I would think a stronger bottom end would last much longer.
      The rpm range seems higher than most automotive motors see. I would have thought some valve train upgrades were in order. I understand why you cant run a big cam.
      Your probably right about top end failure or water ingestion being the leading cause of death. Or overheating. Like I said I'm not a marine mechanic so I don't see what kills boat motors.
      Merc is building a 383 on a 2 bolt main block with basically stock valve train , a comparison ratio for pump gas ,rating it around 325 hp , and putting there name on it. Something tells me they have the data to say this set up will stay together

    #32
    A 5.0 seems kinda light for a 24’ boat if that’s what you have? Here’s a potential alternative and will give you more power if it’ll fit your application. Not sure how the cost to repair your current engine stacks up but if it’s at all close this might be a good option.

    https://www.michiganmotorz.com/vorte...ment-p-58.html
    Jim Gandee
    1989 3888
    Hino 175's
    Fire Escape
    Fyrflyer@ca.rr.com

    Comment


    • Lineman1
      Lineman1 commented
      Editing a comment
      The 5.o alpha was kind small for a 2452 It might have been ok when new but I got it worn out. That's why I'm trying to get to 350 383 mpi and a b3

    #33
    All newer Mercruiser 6.2 is going to be 2 bolts main, but with 400 forged steel crank.
    4 bolt main is not necessary for these kinds marine engine RPM range.
    some 2 pc rear main seal SBCs were 4 bolt main & many BBCs.
    Almost all 1 pc rear main seal SBCs are 2 bolts main.
    Looks like it got hot enough to take the tension out of the rings at a minimum & #3, #7 hole discoloration... yup that engine was overheated severely .
    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


      #34
      Was starting to wonder if my old eyes and brain was playing tricks on me.

      Would not be surprised if the block itself warped .
      Be good, be happy, for tomorrow is promised to no man !

      1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

      '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

      Manalapan N.J

      Comment


        #35
        Lineman, it doesn't actually matter at this point.... but I believe this will be your # 7 cylinder..... not # 3.
        Depending on where the piston came to rest, standing water may have caused this discoloration.



        Click image for larger version

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        Please post photos of the pistons that were removed !





        .
        Rick E. Gresham, Oregon
        2850 Bounty Sedan Flybridge model
        Twin 280 HP 5.7's w/ Closed Cooling
        Volvo Penta DuoProp Drives
        Kohler 4 CZ Gen Set

        Comment


        • Nauti_Mike
          Nauti_Mike commented
          Editing a comment
          That was my thought as well. It's on the low side of the cylinder (outer wall) with a nice semicircle line as water finds its level.

        • 2850Bounty
          2850Bounty commented
          Editing a comment
          "with a nice semicircle line as water finds its level" ................ yes..... precisely!

        #36
        Standing water did cause the problem
        Rick
        you might be right about which hole is which. I was just snapping pix as I pulled parts. #3 hole had standing water in it when the head came off
        and is the one with the discolored wall. #7 cylinder was dry but rusted when the head came off and is pitted.
        I like that short block in the link you posted. A solid bottom end. It would be s bummer to give up my forged crank but that does sound like a good starting point
        I didn't get back in the shop Sunday and will be in the bay area all week I will get some pix up when I get back.
        1992 2452
        5.0 alpha1 gen2

        Comment


          #37
          ..........................................
          Originally posted by Lineman1 View Post
          Standing water did cause the problem
          Rick
          you might be right about which hole is which. I was just snapping pix as I pulled parts. #3 hole had standing water in it when the head came off
          and is the one with the discolored wall. #7 cylinder was dry but rusted when the head came off and is pitted.

          I like that short block in the link you posted.
          That's an image of an empty cylinder block that I found. ATK is the rebuilder.... I know zero about them.

          Ultimately, you will want something like this (or very similar).


          Click image for larger version

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          It would be a bummer to give up my forged crank but that does sound like a good starting point
          There is no reason why you could not re-use some of your existing parts!


          I didn't get back in the shop Sunday and will be in the bay area all week I will get some pix up when I get back.
          Rick E. Gresham, Oregon
          2850 Bounty Sedan Flybridge model
          Twin 280 HP 5.7's w/ Closed Cooling
          Volvo Penta DuoProp Drives
          Kohler 4 CZ Gen Set

          Comment


            #38
            I'm sorry I thought this link came from you Rick
            https://www.summitracing.com/parts/mll-bp3834
            1992 2452
            5.0 alpha1 gen2

            Comment


              #39
              Lineman1, it's more about torque numbers than horsepower numbers. There's a bit of a trade off, but you are looking for as much brute force over a long range of rpms as you can get. It's nice that an engine can produce 350hp at 5500 rpm, but if you are operating it at 3200, that's where you want your torque curve. Here's an rpm vs horsepower chart for a dodge hellcat https://www.google.com/search?q=hors...k_sNyrc6aOcBM: the max torque is in the 4500 rpm range while horsepower keeps growing. The torque isn't going to support the top horsepower and the car will be more sensitive to hills and drag. It the reason a 350 in a one ton truck is less than a Camaro, but the torque curves are much stronger and longer in the truck. Or, at least they were when I was a kid....younger than my kids are now.
              P/C Pete
              Edmonds Yacht Club (Commodore 1993)
              1988 3818 "GLAUBEN”
              Hino EH700 175 Onan MDKD Genset
              1980 Encounter Sunbridge "Misty Blue" (Sold)
              MMSI 367770440
              1972 Chevrolet Nova Frame off Resto-mod in the garage
              Boating on the Salish Sea since 1948

              Comment


                #40
                I'm sorry I thought this link came from you Rick
                https://www.summitracing.com/parts/mll-bp3834
                nope.... not me, and I'm not sure who posted that link.


                Originally posted by Pcpete View Post
                Lineman1, it's more about torque numbers than horsepower numbers. There's a bit of a trade off, but you are looking for as much brute force over a long range of rpm as you can get. It's nice that an engine can produce 350hp at 5500 rpm, but if you are operating it at 3200, that's where you want your torque curve.
                Yes... absolutely!

                Here's an rpm vs horsepower chart for a dodge hellcat
                https://www.google.com/search?q=hors...k_sNyrc6aOcBM:

                the max torque is in the 4500 rpm range while horsepower keeps growing. The torque isn't going to support the top horsepower and the car will be more sensitive to hills and drag. It the reason a 350 in a one ton truck is less than a Camaro, but the torque curves are much stronger and longer in the truck. Or, at least they were when I was a kid....younger than my kids are now.

                Basically, it all boils down to LPCP..... location of peak cylinder pressure..... of which is the main reason for a SBC Quench Effect build!



                Rick E. Gresham, Oregon
                2850 Bounty Sedan Flybridge model
                Twin 280 HP 5.7's w/ Closed Cooling
                Volvo Penta DuoProp Drives
                Kohler 4 CZ Gen Set

                Comment


                  #41
                  Originally posted by 2850Bounty View Post

                  nope.... not me, and I'm not sure who posted that link.
                  Just one of several
                  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


                    #42
                    Here's a couple of shots of a piston at TDC. Forgot about you wanting to see piston deck Rick. I kinda just started pulling things apart. Getting it ready to go to the machine shop.

                    Right now if the block checks out I'm thinking bore it 30 over. Leave the rest of the internals. Crank rods cam. Clean everything up maybe a set of main studs.and a good balance job.
                    What about pistons? I'm leaning towards a q e type that sits about. about 0.025 below the deck. With my heads I can come up with about 9.2 static compression ratio With a 0.015 stainless head gasket I will have 0.040 quench. Sound right?
                    How much am I going to benefit from this if I cant move the timing? At $700 a reflash I'm kinda leery about playing with timing over stock.?
                    1992 2452
                    5.0 alpha1 gen2

                    Comment


                    • builderdude
                      builderdude commented
                      Editing a comment
                      Of course, it’s been fitted with Ricks favorite pistons........ ​​​​​​​

                    #43
                    .......................................
                    Originally posted by Lineman1 View Post
                    Here's a couple of shots of a piston at TDC. Forgot about you wanting to see piston deck Rick. I kinda just started pulling things apart. Getting it ready to go to the machine shop.
                    Yep..... those are the dreaded GM full dished pistons!

                    Right now if the block checks out I'm thinking bore it 30 over. Leave the rest of the internals. Crank rods cam. Clean everything up maybe a set of main studs and a good balance job.
                    As you may know, you'll need to have your piston selection made prior to balancing.

                    What about pistons? I'm leaning towards a q e type..............
                    See my image in post # 37.
                    If you are using the Vortec cylinder heads, you will want to piston deck to mirror the cylinder head's quench surface.
                    If so, the piston profile will be what the industry calls a LCQ (low compression quench).


                    I'm leaning towards a q e type that sits about about 0.025" below the deck.

                    With my heads I can come up with about 9.2 static compression ratio with a 0.015 stainless head gasket I will have 0.040 quench. Sound right?
                    .040" minus .025" = .020".
                    In my opinion, a .020" compressed head gasket thickness may be hard to find.

                    Whereas if you shoot for a .015" to .016" deck dimension, you'll have more options regarding the compressed head gasket thickness.


                    How much am I going to benefit from this if I cant move the timing?
                    More than what Mercruiser will admit to..... especially if you were to build a 6.3L SBC Marine version!

                    At $700 a reflash I'm kinda leery about playing with timing over stock.?
                    OK..... here's what you need to know:

                    GM uses the full dished pistons for manufacturing economy and production build economy reasons.
                    One piston fits all eight bores..... the guy installing the pistons onto the connecting rods can be drunk while working!
                    The guy installing the rods/pistons into the cylinder block can also be drunk while working!
                    (I'm joking.... but hopefully you get my point!)

                    The Full Dished profile makes this a very "Detonation Prone" build.... in particular for a Marine installation!
                    In order to combat detonation, Merc holds back the ignition advance.
                    Holding back the ignition advance makes for a Lazy LPCP.
                    A lazy LPCP makes for less torque.

                    Remove the Detonation potential (by doing a Q/E build), and now we can throw more ignition advance at it, and improve the LPCP!


                    Before I can comment on what to do regarding your ignition advance, I'd need to know which one you have.

                    Originally posted by Dave
                    Of course, it’s been fitted with Ricks favorite pistons........
                    Yes, and they make excellent garden art!


                    Click image for larger version

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                    Rick E. Gresham, Oregon
                    2850 Bounty Sedan Flybridge model
                    Twin 280 HP 5.7's w/ Closed Cooling
                    Volvo Penta DuoProp Drives
                    Kohler 4 CZ Gen Set

                    Comment


                    • builderdude
                      builderdude commented
                      Editing a comment
                      .040" minus .025" = .020".
                      Need more coffee

                    • 2850Bounty
                      2850Bounty commented
                      Editing a comment
                      Ooops........ my bad! Thanks Dave.

                    #44
                    Talked to the machine shop today. If I can't get to 0.040 to 0.045 quench with a piston and head gasket combination I'll take 0.010 to 0.015 off the deck. Like I said before there's dosen't seem much I can do with timing. Unless anyone knows someone who has hacked the 555 ecm? There don't seem to be any "block boxes" for the 555. Again I don't understand the boating world. I had a tuner on my Harly's FI system 18 years ago.
                    1992 2452
                    5.0 alpha1 gen2

                    Comment


                      #45
                      There is, but expensive.
                      their is only one shop outside of Merc themselves that can flash those ECM 555, well maybe 2
                      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

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