Tick Tick goes the magnum.

Magnum Engine Swaps

  1. Slantsix64

    Slantsix64 Well-Known Member

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    Hey guys, so i had a couple questions, i upgraded my magnum camshaft, along with hughes springs etc, i kind of knew the stock push rods would work but tried to get an idea and yup the stock rods at 6.900 were too short the rockers were all loose.

    So bought a push rod checker used a sharpie to mark the top of the valve honestly that method didnt really show me a clear mark (maybe i needed a paint marker) but it looked like the motor was wanted a 6.945 pushrods so i ordered some 6.950 Hollow Pushrods.

    After starting the engine i can hear it tick!!!! Not extremely loud but mild, i can hear it thru the carb, i also can hear like cylinder pressure if that makes sense while the engine is running feels like its got a vacuum leak or something.

    Could the push rods be too long?? or Too Short??
     
  2. RustyRatRod

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

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    Can you describe in depth how you measured? Here's how I do it. I order a pushrod checker straight from "whomever" I plan to buy pushrods from. Done this before with Smith Brothers, so lets say them. I get the checker. Get the camshaft lobes on the base circle. Now adjust the checker to take all the slack up, plus "however much" preload I think will work best for a given situation. I prefer a light touch with preload so I normally go .025"-.040" after all the "up and down" slop is taken out. Then, I send the pushrod checker back to Smith Brothers telling them "I need X number of these".
     
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    • Slantsix64

      Slantsix64 Well-Known Member

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      thanks for the reply, so i installed the the pushrod checker until there was no slack, rotated the engine a couple times by hand after marked the top of the valve tip, trying to get the pattern in the middle then measured it. ordered the push rods, although i did not account the preload, so how would i account for this, so if i get a measurement of 6.945 accounting for preload i should go 0.25-0.40 longer so in the 6.975 range? these are magnum stock roller lifters and stock rockers 1.6
       
    • Bobzilla

      Bobzilla Well-Known Member

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      You cannot try checking sweep and all that stuff on this system if you are running factory Magnum rocker arms. There is only two measurements on these, right and wrong.

      The procedure RustyRatRod outlined is 100% correct way to do it on this one. The rocker arm position on a factory system is fixed, so all you are doing is measuring the length needed to take up all slack WITHOUT pushing the lifter plunger down at all, and then adding the desired preload to that measurement. Done.

      Try measuring again with Rusty's method and your adjustable checking pushrod and report back with findings.
       
    • Slantsix64

      Slantsix64 Well-Known Member

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      Thanks yeah I guess I been doing it wrong this whole time, I shall return and measure again, and add the preload to my measuring
       
    • Bobzilla

      Bobzilla Well-Known Member

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      Are the heads, block, and head gaskets all original? Maybe the stock pushrods will work after all. It sounds like the length you added was just enough to hang some valves open a tiny bit.
      When you say the rockers were loose with original pushrods, were they flopping around, able to move the pushrods up and down, or do you mean you were able to push down on the rocker arm and it was “springy” on the pushrod side? You will be able to easily compress some of the lifters, so it’s easy to get a false measurement that is too long. Easy to see with intake off, but more just feeling it when intake is on.
       
    • Slantsix64

      Slantsix64 Well-Known Member

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      but if they were to long to hang the valves open why do i hear lifter chatter? the stock push rods had a huge amount of play. Im thinking like 0.80-1.00 play.

      I did have some 7.000 Pushrods laying around and tried them the valves wouldnt close resulting in no compression.

      As of now i tried 6.900 (stock) Pushrods being way too short,
      7.000 being way too long
      6.950 working but alot of chatter when reving. (measured incorrectly With no preload added)

      Going to use the push rod checker again on on #1 cylinder when the valves are closed get that measurement and add 0.25 to it. Going to do it on both intake and exhaust.
       
    • DionR

      DionR Well-Known Member

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      I don't think you want to add 1/4" to the number. I'm guess that is a typo, but just making sure.
       
    • RustyRatRod

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

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      Yes, .250" is way too much. ....and if he means .025" that's not enough. I'd go probably .050-.060 after all the slop is out.
       
    • Slantsix64

      Slantsix64 Well-Known Member

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      Lol yes typo
       
    • Slantsix64

      Slantsix64 Well-Known Member

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      update, just got the number 1 cylinder to tdc and with the 6.950 pushrods still in the rockers had some play in them! so i guess they are a bit short, going to use the checker and get an exact measurement and add 0.050 as RRR recommends thanks!
       
    • Slantsix64

      Slantsix64 Well-Known Member

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      so i got 6.890 getting the slack out the rocker arms, Hughes recommends 0.080 preload for the magnum roller lifters 6.975 is what i need.
       
      Last edited: Jan 18, 2022 at 11:13 PM
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      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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        You do not need .080 preload.
        That amount is given, mostly so that over the life of the lifter/lobe, you may never experience noisy lifters.
        Every 5000 miles, the lifters and lobes may show measureable wear. So then, 50,000 miles from now, your .080 will no longer be .080. Hopefully you will still have "some" preload, and so the engine will still be quiet which is the whole reason for having hydraulics in the first place. But there is nothing magical about .080.
        In fact, if your piston to valve clearance is less than .080, and if it should happen that you rev your engine past an rpm where the springs lose control; it could happen that the lifters pump up and drive your valves into the tops of the pistons and bend the stems.
        My 367 has adjustable valve gear, and I run about .020 preload. I can rev it to 7500 with no problems. If the lifters were to pump up, .020 is nothing to worry about. If it ever happened, it would only cause a rough idle until the preload was re-established. The penalty for this, is more frequent valve adjustments, perhaps once a year or every other year.
        I am not telling you to run .020.
        I am telling you that the preload can be anything you want it to be, so long as it less than your piston to valve clearance , and more than zero(lol). Anywhere from .020 to .080 should be just fine.
        If the preload gets to be less than zero, as in there is some lash, I can tell you that a small amount of ticking is not a big deal. My engine gains torque with a few ticking valves . I only reset the lash when it starts to tic on more than 4 or so cylinders, or if it develops a clack.

        If you are getting noise from valve lash, with .065 preload, something is wrong.
        You may have other problems, or the noise is being misinterpreted. It could be that the tips of the stems are not all at the same height, and so in it's worst case, this could require 16 different-length pushrods.
        Or the pushrods could be hitting the sides of the tunnels, etc.
         
        Last edited: Jan 18, 2022 at 10:19 PM
      • Slantsix64

        Slantsix64 Well-Known Member

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        UPDATE!!!! i was wrong the pushrods were too long!! causing the valves to stay open a bit, i found this out by inspecting the rockers and seeing that one of them had a crack from were the push rod seats. also those trickflow push rods measured with my caliper at 6.965 instead of 6.950. So with the reading i got with my new measurement on the base of the camshaft im just going to add .035 preload end up with 6.935
         
      • MOPAROFFICIAL

        MOPAROFFICIAL FABO Gold Member FABO Gold Member

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        If it hisses out the carb...
         
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        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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          Good call
           
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          • RustyRatRod

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

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            I think that's a very accurate recommendation from Hughes. I was not taking into consideration it being a roller. Those profiles normally require more preload than a flat tappet. I think their recommendation will be right on the money.
             
          • RustyRatRod

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

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            Make up your mind, dammit. lol
             
          • RustyRatRod

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

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            That means there's a snake in it.
             
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            • Slantsix64

              Slantsix64 Well-Known Member

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              Lol I know
               
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