273 crankshaft, 5.2 Magnum

Small Block Mopar Engine

  1. Maistrelli

    Maistrelli Active Member

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    Can a 273 crank be used in a 5.2 Magnum engine? Magnum damper on 273 crank?
     
  2. nm9stheham

    nm9stheham Well-Known Member

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    Balance has to be considered. I can't quite figure out if the crank balance is the same. Magnum 5.2L piston+pin+ring weights are very close to LA 318, but the Magnum rods may not be the same. I just don't have the rod data.

    What year of 273 crank?
     
  3. pishta

    pishta I know I'm right....

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    magnum rods have a different width little end, narrower. So thats potentially less weight right there. Also lack of fuel pump eccentric on magnum crank.
     
  4. Demonracer

    Demonracer 71 Demon 00 Ram 16 Chrysler 300S 05 Caravan FABO Gold Member

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    The fuel pump eccentric is on the camshaft, not the crankshaft.
     
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    • Maistrelli

      Maistrelli Active Member

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      1965
       
    • RustyRatRod

      RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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      It should bolt in and go. All 318s were neutral balanced that I know of.
       
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      • pishta

        pishta I know I'm right....

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        Doh! Of course I knew that....WTH?
         
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        • Plymouth 65

          Plymouth 65 Floorable Deplorable

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          The 1965 273 crankshaft has the small torque converter pilot diameter. Just so you're aware! 65'
           
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          • nm9stheham

            nm9stheham Well-Known Member

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            Yes, that's a fit problem for the trannie. The OP would have to have the crank pilot hole turned out.

            I worked out the bobweights with the data I have. 273 and 5.2L are pretty close but it still may be off enough to be 10-20 grams off of balance..... or some of my data is a bit off.

            I think RRR is correct on both being neutral balanced for the dampers and TC/flex-plate/flywheel.
             
          • pishta

            pishta I know I'm right....

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            I think 10-20g is within factory spec. Ive heard motors being much more out off the line.
             
          • toolmanmike

            toolmanmike FABO Staff Staff Member FABO Gold Member

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            If I was to mis match components I would have the machine shop properly balance the rotating assembly.
             
          • toolmanmike

            toolmanmike FABO Staff Staff Member FABO Gold Member

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            What we need to know is why the OP wants to put a 273 crank in a Magnum.
             
          • 318willrun

            318willrun Stomper 4x4... we kept energizer in business

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            probably wanting a forged steel crank instead of cast
             
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            • nm9stheham

              nm9stheham Well-Known Member

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              Well, the tolerance around a number may be that much, but what I am coming from is that the nominal numbers are that much off.

              BUT, the good news is that I just weighed some 2 BBL 273 rods & pistons and pins, and with the new data, the bobweight number is < 10 grams off from my 5.2L Magnum data. So this looks pretty decent for being balanced.

              Racing? No way. Going in the pickup to go out and cut firewood? A-OK

              I'm curious about that too.
               
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              • toolmanmike

                toolmanmike FABO Staff Staff Member FABO Gold Member

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                One thing you have to remember is how the rods are balanced. Not just total weight but end to end. 100_4954.JPG 100_4957.JPG 100_4956.JPG
                 
              • nm9stheham

                nm9stheham Well-Known Member

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                Absolutely.... I don't work out bobweight info unless I have big and small end weight data too. I've gotten to where I just give my bobweight number and crank to the machinist.
                 
              • RustyRatRod

                RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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                Why is that pertinent? Might simply be what he has.......OR as has been said maybe he wants a steel crank. The why really doesn't change anything.
                 
              • toolmanmike

                toolmanmike FABO Staff Staff Member FABO Gold Member

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                Oh just curious. Sometimes people have crazy ideas. It's more like why would you need to?
                 
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                • RustyRatRod

                  RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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                  Maybe he was gonna wear the rods as a necklace? LOL
                   
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                  • Maistrelli

                    Maistrelli Active Member

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                    Using an A833, crankshaft has pilot bearing.
                     
                  • Maistrelli

                    Maistrelli Active Member

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                    Because I have a good one and 5.2M crank needs ground.
                     
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                    • toolmanmike

                      toolmanmike FABO Staff Staff Member FABO Gold Member

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                      It might work but there will be other things that won't be right. Why take the risk. Just turn and polish the Magnum crank.
                       
                    • Maistrelli

                      Maistrelli Active Member

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                      I plan to have it balanced, new O.S. pistons, flywheel, clutch, PP and damper.
                       
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                      • Maistrelli

                        Maistrelli Active Member

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                        What's the average cost of -.020 rod & main journals? Anyone have crank ground lately? What others things won't be right?
                         
                      • nm9stheham

                        nm9stheham Well-Known Member

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                        Balancing is going to cost 2-3 times grinding a crank. If you are not racing, then changing pistons to oversize does not necessitate a re-balance. So haw hard are you going to be running this engine?

                        Just be aware: Since both the 273 and 5.2 are 'internal balance' engines, there is no need to balance the crank with the external parts. Each of those external parts are individually balanced.

                        $125-$150 as a guess on the regrind.
                         
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