difference between hydro and mechanical rocker shaft diameters

Small Block Mopar Engine

  1. pishta

    pishta I know I'm right....

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    Reading a Larry Shepard article about Mopar valvetrains: he mentions that the hydro rocker shaft is NOT round, and the mechanical shafts are ground round. Ever hear of this?
    "...The hydraulic rocker shaft is generally not used with the mechanical rockers. Either the T/A or the W2 shaft can be used... The T/A and W2 shafts were ground “round” and the hydraulic production shafts are not. Mechanical rockers need a round shaft.."

    I mic'd a set of hydros at .8740 every way I could, Summit lists the crane ductile shaft at .872 as well as all other non roller shafts. and I mic'd my 273's at .872x. Im not sure of my mic's accuracy but maybe someone in the know could tell me if there is in fact a diameter or cylindricity difference between the 2. I know the ductile iron fit on both with no binding as I modded a hydro shaft with additional oil ports to match the ductile iron rockers oil ports. I did have to knock down the hydros bolt holes of ANY flashing as it would stop the iron rockers progress down the shaft cold.
     
  2. Rmoore

    Rmoore Well-Known Member

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    Not round ? Or smaller , bigger ?
     
  3. '63GT

    '63GT Well-Known Member

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    I think Shepard overdosed on donuts that day.....
     
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    • Demonic

      Demonic Well-Known Member

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      Some of the editing/proofreading in his books leaves a bit to be desired.
       
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      • RustyRatRod

        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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        All of the rocker shaft stand saddles are the same diameter. Hydraulic or solid.
         
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        • famous bob

          famous bob mopar misfit

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          CHEVY BOY-----------
           
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          • toolmanmike

            toolmanmike Moderator Staff Member FABO Gold Member

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            Shafts not round? How does that work? The one he took off to measure was overtorqued and was egg shaped around the bolt holes. LOL
             
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            • Daves69

              Daves69 Well-Known Member

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              Sounds to me he's generalizing the different shaft roundness specs where as a hydraulic rocker is not as dependent on it as a rocker that has a bushing or bearing.
               
            • gregcon

              gregcon Well-Known Member

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              It would not be hard to make one out of round if you wanted to....but why would you want to?
               
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              • 69_340_GTS

                69_340_GTS Well-Known Member

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                I think what he meant was that the mechanical rocker shafts were made with a higher degree of precision. Could be a more highly controlled roundness, or just a tighter tolerance on the diameter during manufacturing.
                 
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                • abdywgn

                  abdywgn dismantler

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                  rocker arms for hyd do not have a round opening where they slide on the shaft;bottoms are,tops aren't is what I believe is the intended message.
                   
                • '63GT

                  '63GT Well-Known Member

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                  Lol exactly!
                  How many times has that happened? We got those shiny new hold-downs, and feels like a roll of toilet paper under your torque wrench.
                  I was so glad when Mopar came out with the 'heavy ' shafts.
                   
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                  • gregcon

                    gregcon Well-Known Member

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                    On further reflection, I think what he's getting at is the shafts made for stamped steel rockers were (probably) not ground at all. They were probably 'raw' shafts, kinda like DOM tubing. Only the shafts used on bushed rocker arms were ground. This would have been a cost savings, for sure, in production. So while both shafts are "round", the shafts used on bushed rockers are more rounderer due to being ground.
                     
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                    • 67Dart273

                      67Dart273 FABO Gold Member FABO Gold Member

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                      That's what I immediately thought..............
                       
                    • 66fs

                      66fs FABO Gold Member FABO Gold Member

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                      I have run hydraulic shafts with mechanical rocker arms. Apparently they worked fine for the general high performance I built it for. I only noticed it when we were noting differences in mechanical shafts.
                       
                    • 66fs

                      66fs FABO Gold Member FABO Gold Member

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                      If you mic'd them and they measure the same, that means they are round. Maybe not straight, but round. If your mic is off you still got .002 difference between hydraulic and mechanical shafts.
                       
                    • gregcon

                      gregcon Well-Known Member

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                      Well, nothing is really round if you get picky about it.
                       
                    • 66fs

                      66fs FABO Gold Member FABO Gold Member

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                      True, but plenty good enough for what we do.
                       
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                      • gregcon

                        gregcon Well-Known Member

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                        • Demonic

                          Demonic Well-Known Member

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                          I have no idea what that means.

                          Larry's books on differentials was a bit of a disappointment. No where does it mention the master pinion depths for the 8 3/4 carriers. Figures though, the FSM doesn't mention it either. Plenty of diffs get assembled without it, but if you have a depth mike and a bit of skill.....
                           
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                          • gregcon

                            gregcon Well-Known Member

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                            That's a good example of what I mean when I say the Mopar books are poorly written. Would it have been that tough for him to state "the stamped shafts were not ground; they were used 'as is' from the steel maker. Shafts used for bushed rockers received an extra grinding step to ensure roundness and to provide a finish compatible with the bushing material." ?
                             
                          • MOPAROFFICIAL

                            MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                            If you run the hydro shafts with mechanical rockers the oiling holes won't be clocked right, or let say it like this..they are in *different locations*
                             
                          • 66fs

                            66fs FABO Gold Member FABO Gold Member

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                            Actually, that is spherical.
                             
                          • 66fs

                            66fs FABO Gold Member FABO Gold Member

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                            True. I didn't mean to recommend it.
                             
                          • gregcon

                            gregcon Well-Known Member

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                            Yes, but it's also round.
                             
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