Balancing a Scat cast crank

Small Block Mopar Engine

  1. pishta

    pishta I know I'm right....

    Messages:
    19,414
    Likes Received:
    8779
    Joined:
    Oct 13, 2004
    Location:
    Tustin, CA
    Local Time:
    10:43 AM
    The Eagle forged 434040006123 forged crank has a bobweight of 2050g, The SCAT being 1700g (!) is begging for tungsten!! I'd rather take weight off than add when it comes to a crankshaft and the price of heavy tungsten slugs. Cast cranks are lighter than Forged....sort of apples to oranges there.
     
    • Like Like x 1
    • Agree Agree x 1
    • Morten Stroem

      Morten Stroem Cuda67-Mortens

      Messages:
      8
      Likes Received:
      2
      Joined:
      Oct 27, 2017
      Location:
      Norway Askim
      Local Time:
      7:43 PM
      I'm about to build the strategy to correct the unbalance WITHOUT removing the engine and start the engine build from the start :). One option is to move to external balance solution and add weight to the balancer and to the flywheel/converter, still to be decided and still to be executed :)
       
    • mini

      mini Small Bore Long Stroke

      Messages:
      484
      Likes Received:
      267
      Joined:
      Jun 1, 2009
      Location:
      Chatham Ontario
      Local Time:
      12:43 PM
      Yeup CNC motorsports balanced my assembly with Mallory.
       
    • Morten Stroem

      Morten Stroem Cuda67-Mortens

      Messages:
      8
      Likes Received:
      2
      Joined:
      Oct 27, 2017
      Location:
      Norway Askim
      Local Time:
      7:43 PM
      :) I'm looking for some experiene when it comes to moving from a badly internal balanced 408 stroker to a corrected good balance external balanced engine with just added wights to the balanser and the flywheel. /Morten - Norway
       
    • TurboGLH

      TurboGLH Well-Known Member

      Messages:
      425
      Likes Received:
      481
      Joined:
      Jul 29, 2017
      Location:
      CT
      Local Time:
      1:43 PM
      My scat cast crank, with the scat I beam rods and Icon FHR pistons needed two slugs up front, and one out back. That's with a bobweight of 1770. If you're running stock rods and/or heavy pistons it can be a good bit higher.
       
    • TurboGLH

      TurboGLH Well-Known Member

      Messages:
      425
      Likes Received:
      481
      Joined:
      Jul 29, 2017
      Location:
      CT
      Local Time:
      1:43 PM
      You can't do what you're asking. If the rotating assembly is out of balance, just adding weight on the front and rear by using an external balance damper and tq converter won't work.

      You have some residual unbalance, obviously enough that you're feeling it in the car. The issue is you don't know how much, or the exact angle, of that unbalance. When you put the external balance parts on, you're adding weight of a specific amount, and at a specific angle, which aren't necessarily where you need the extra weight.

      Engine needs to come out, crank needs to go back, and be rebalanced with the external damper/converter.
       
      • Agree Agree x 1
      • flyfish

        flyfish C8H18+N2O = :-D

        Messages:
        2,212
        Likes Received:
        805
        Joined:
        Apr 16, 2007
        Location:
        Indy
        Local Time:
        1:43 PM
        I can't see doing internal balancing with a cast crank...just doesn't seem cost effective.

        For what its worth, my Scat forged crank, forged Icon flat tops & Scat I-beams did not need any heavy metal for balancing.
         
        • Like Like x 1
        • Agree Agree x 1
        • j par

          j par Well-hung Member

          Messages:
          27,206
          Likes Received:
          14686
          Joined:
          Jul 2, 2014
          Location:
          Portland Oregon
          Local Time:
          10:43 AM
          20141215_132248.jpg
          Mine...
           
          • Like Like x 2
          • Max1196

            Max1196 Well-Known Member

            Messages:
            926
            Likes Received:
            657
            Joined:
            May 12, 2016
            Location:
            Swift Current SK
            Local Time:
            12:43 PM
            I'm about to build the strategy to correct the unbalance
            I have an internal balanced 408 stroker setup


            Balanced ................................................Internal balanced, balanced assembly
            Connection Rods ....................................Chrysler Rod 6.123[/QUOTE]
            I'm not so clear as to how or what you have going on! If you had a shop balance it, and even ran it on a dyno, Why does the balance job need to be fixed? Do you have something else out of weight? As in the flex plate or torque convertor? OR, was it never actually balanced. Who assembled it? Was there malaroy metal added to the cast crank, it would have been obvious.
             
          • Morten Stroem

            Morten Stroem Cuda67-Mortens

            Messages:
            8
            Likes Received:
            2
            Joined:
            Oct 27, 2017
            Location:
            Norway Askim
            Local Time:
            7:43 PM
            Good thinking :) tnks
             
          • pishta

            pishta I know I'm right....

            Messages:
            19,414
            Likes Received:
            8779
            Joined:
            Oct 13, 2004
            Location:
            Tustin, CA
            Local Time:
            10:43 AM
            cast cranks are lighter by the manufacturing process. they are less dense than a forged (compressed) crank so your going to have to add weight to the throws to compensate for 1-heavier bobweight of rods and pistons or 2. lighter balance throws to begin with. I think your fighting 2, lighter throws. Tungsten is going to have to be added to the throws to make the bobweight compensation heavier. They had to use external balancing on cast crank 360 and 340 motors because the cranks were lighter by about 5 lbs with all other parts being the same as the forged crank motors so they had to add weight where they could externally, the balancer and the convertor or flywheel. I dont see an issue making it an external, you just have to supply and weighted 360 B&M flex plate and a cast 340/360 balancer, then weight can be taken from these parts. Anything can be internally balanced but at a cost of mallory metal/tungsten.
            normal_internalbalance.jpg
            If your going to start the balancing act, supply a weighted (cast 340 or 360) balancer to begin with. cheaper that tungsten.
             
            • Like Like x 1
            • Morten Stroem

              Morten Stroem Cuda67-Mortens

              Messages:
              8
              Likes Received:
              2
              Joined:
              Oct 27, 2017
              Location:
              Norway Askim
              Local Time:
              7:43 PM
              Tnks Pishta :)
               
              • Like Like x 1
              • Morten Stroem

                Morten Stroem Cuda67-Mortens

                Messages:
                8
                Likes Received:
                2
                Joined:
                Oct 27, 2017
                Location:
                Norway Askim
                Local Time:
                7:43 PM
                I'm not so clear as to how or what you have going on! If you had a shop balance it, and even ran it on a dyno, Why does the balance job need to be fixed? Do you have something else out of weight? As in the flex plate or torque convertor? OR, was it never actually balanced. Who assembled it? Was there malaroy metal added to the cast crank, it would have been obvious.[/QUOTE]

                This 408 stroker Mopar engine was purchased ready build and the history of balanced or not, will be unknown for all future
                 
                Last edited: Aug 5, 2020
              • PRH

                PRH Well-Known Member

                Messages:
                3,028
                Likes Received:
                4492
                Joined:
                Dec 14, 2018
                Location:
                So. Burlington, Vt
                Local Time:
                1:43 PM
                I built a 416 a few years ago.
                Scat 9000 crank, Scat I beams, ProTrue pistons.
                It balanced internally without heavy metal.

                I supplied the same part number crank and rods to another customer this spring, along with Icon pistons.
                Needed heavy metal for internal balance.

                For the next one I used a Molnar steel crank and h beam rods, same # Icon pistons.
                Had to take a bunch of weight out to balance it.
                 
              • RedB.

                RedB. Well-Known Member

                Messages:
                177
                Likes Received:
                75
                Joined:
                Feb 19, 2019
                Location:
                down south
                Local Time:
                12:43 PM
                so these 408 kits that are sold as balanced kits, need balancing ? I have been looking at the Scat 360/408 kits and some are sold balanced and some not balanced, so if the kit is going to need balancing why spend extra money on a kit that is balanced.
                 
              • TurboGLH

                TurboGLH Well-Known Member

                Messages:
                425
                Likes Received:
                481
                Joined:
                Jul 29, 2017
                Location:
                CT
                Local Time:
                1:43 PM
                You don't need to balance the kits sold as balanced. Some people prefer to have stuff balanced locally, and some people are ok with having scat balance them.
                 
                • Like Like x 1
                • Thanks! Thanks! x 1
                • gzig5

                  gzig5 FABO Gold Member FABO Gold Member

                  Messages:
                  1,545
                  Likes Received:
                  1602
                  Joined:
                  May 3, 2018
                  Location:
                  Mequon, WI
                  Local Time:
                  12:43 PM
                  They come either balanced or not. Balanced is usually a $200-$300 adder
                   
                • Morten Stroem

                  Morten Stroem Cuda67-Mortens

                  Messages:
                  8
                  Likes Received:
                  2
                  Joined:
                  Oct 27, 2017
                  Location:
                  Norway Askim
                  Local Time:
                  7:43 PM
                  tnks /Morten
                   
                • Idaho

                  Idaho Well-Known Member

                  Messages:
                  2,601
                  Likes Received:
                  260
                  Joined:
                  Oct 17, 2006
                  Local Time:
                  10:43 AM
                  My machinist told me when he has checked those that are SCAT balanced, they are not as well balanced as he likes. Course maybe he likes doing the work to pay for his machine.
                  Just an FYI, the flywheel for external balance is on the spendy side.
                   
                  • Like Like x 1
                  • Agree Agree x 1
                  • mini

                    mini Small Bore Long Stroke

                    Messages:
                    484
                    Likes Received:
                    267
                    Joined:
                    Jun 1, 2009
                    Location:
                    Chatham Ontario
                    Local Time:
                    12:43 PM
                    True. I don't have a problem with local machine shops paying for their balancing equipment.
                     
                    • Like Like x 1
                    • RedB.

                      RedB. Well-Known Member

                      Messages:
                      177
                      Likes Received:
                      75
                      Joined:
                      Feb 19, 2019
                      Location:
                      down south
                      Local Time:
                      12:43 PM
                      Would a flywheel or flex plate, or harmonic balancer from a internal balance 340 318 work on these Scat internal balance cast crank 360/408 ?
                       
                    • Wyrmrider

                      Wyrmrider FABO Gold Member FABO Gold Member

                      Messages:
                      3,611
                      Likes Received:
                      1745
                      Joined:
                      Sep 5, 2016
                      Location:
                      los angeles
                      Local Time:
                      10:43 AM
                      would depend on your bob weight
                      if heavier rod and piston the 360 parts save on balancing
                      get your numbers together and ask your balancer or post back
                      if tour question was if the rotating assembly is already balanced internally then yes 318 will work or forged crank 340
                       
                      • Thanks! Thanks! x 1
                      • Krooser

                        Krooser Reform School Graduate

                        Messages:
                        2,878
                        Likes Received:
                        2383
                        Joined:
                        Jul 19, 2015
                        Location:
                        Central Wisconsin
                        Local Time:
                        12:43 PM
                        All this balancing talk has reminded me I need to check some piston weights before I screw my fresh race motor together...new pistons new weight.
                         
                        • Like Like x 2
                        • furrystump

                          furrystump Well-Known Member

                          Messages:
                          1,199
                          Likes Received:
                          768
                          Joined:
                          Nov 13, 2004
                          Local Time:
                          6:43 PM
                          I have now run that crank externally balanced for over 1000 runs and a bunch of street miles. 55,000+. No issues, changed pistons a couple a years ago and had it balanced again externally. The REALLY old, REALLY smart guy who did it is kind of a perfectionist. IIRC Got it to within 1/2 a gram. Way closer than it really needed. Shift it at 6400 rpm.
                           
                        1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
                          By continuing to use this site, you are consenting to our use of cookies.