Hydraulic Lifter Preload Excessive?

Engine, Trans & Driveline

  1. EngineerDoug

    EngineerDoug Well-Known Member

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    All I can say is, "wow, am I learning a lot from this build!". I just mocked up my 906 heads onto the 383 block, with my Summit K6400 cam and lifters, and Comp Cams 911-16 springs installed. As far as I know, the only thing non-stock about this motor are the cam, lifters, & springs. With a 0.020" nominal head gasket, and a spring installed height of 1.850", the lifter preload is a whopping 0.130". My understanding is that this preload needs to be 0.040" to 0.060" for proper operation.

    I used a dial indicator to measure the compression applied to the pushrod & lifter, and am sure the lifter was on the base circle of the cam. With such a mild cam, is this a surprise? I suppose now I have to get some shorter-than stock pushrods?
     
  2. khryslerkid

    khryslerkid FBBO Gold Member FBBO Gold Member

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    Yes, get a checking rod, watch for the lenth capabilities because there are different ones. I used Smith Brothers for the new pushrods. Fast turnaround, Great product!
     
  3. charger318

    charger318 Well-Known Member

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    Things like decking the block, shaving the heads, different thickness head gasket, or change on the base circle of a camshaft will all effect the pushrod length needed for the correct preload. What kind of rocker arms? Stamp steel or adjustable? A cam with 488 lift or 588 lift just tells you how much it opens the valve, you could of had a camshaft with a smaller base circle and new cam is larger causing the extreme preload.
     
  4. lewtot184

    lewtot184 Well-Known Member

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    there's no way i would use those springs at 1.85" installed. according to comps catalog that's 140+lbs on the seat, and 300lbs+ over the nose.. that cam is just a generic version of a stock magnum cam that had about 115lbs on the seat and 240lbs over the nose. you can get adjustable push rods from smith bros; just did this a couple of weeks ago.
     
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    • khryslerkid

      khryslerkid FBBO Gold Member FBBO Gold Member

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      I found the same thing useing a Sum 6401cam. They recommend the 911spring. They are useing a higher installed height to get their numbers and thats just wrong. Doing the math they were way too strong. I went with a Crane 99839 spring. I'm not sure if that would be the right diameter for your app. I did some machining for the spring seat on my 452 heads. (Check out "My Photo Garage")
       
    • Badvert65

      Badvert65 Well-Known Member

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      I placed shims (about .045" in my case) under my rocker shafts to reduce preload. That was about 30 years and a few thousand miles ago (1/4 mile at a time) Haven't had any problems with it.
       
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      • Garys1969RR

        Garys1969RR Well-Known Member

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        You know Doug, I had the same problem with my 451 build, 509 cam, stock valve train. The plunger was way down in the lifter. I like it to be near the top. So I simply made steel shims from an old .020" steel head gasket, and stacked 2 shims between each pedestal and the rocker arm shaft, with the bolt going thru the center hole of the shim. That brought the plunger to near the top of its travel, very near the retaining clip. That set up ran great at the track for 4 years!. 40 or 50 mid 12 second passes. I think that reduced pre load by .040 on the valve side and .040 on the push rod side, for a total of .080" less pre load. Am I looking at this correctly? There are also rocker shaft shims available thru various sources.
         
      • Garys1969RR

        Garys1969RR Well-Known Member

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        With 080" less total valve train length , that would move your plunger up to .050 pre load. .130 less .080 equals .050". That would be right where you want it.
         
      • texas69bee

        texas69bee Well-Known Member

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        Was the dial indicator over the push rod or over the spring?
         
      • Garys1969RR

        Garys1969RR Well-Known Member

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        Yea that would make a difference. It should be directly over the push rod to accurately measure lifter pre load. My question would be, how do you bring the plunger up to measure how far down it was? Or do you tighten the shaft bolts until there is no preload, then measure how far down it goes when the rocker shaft tightens against the pedestal?
         
      • khryslerkid

        khryslerkid FBBO Gold Member FBBO Gold Member

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        I tried shims once. Changed the geometry of the rocker tip to valve stem travel. The rocker tip started off center and ended up near the edge of the stem.

        You have to use a pushrod checking tool to get the proper lenth measurement and have them made. Or use the adjustable pushrods.
         
      • miller

        miller Well-Known Member

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        That preload distance is measured from the top surface of the tappet 'cup', to the bottom of the retainer clip. That's the only way I measure it.
        Only reason for the preload, is setting it all for positive contact, push rod to rocker arm, allowing for the 'soft' hydraulics to work through the cycle. Main thing (like a busted record) is keeping the tappet cup off the retainer.
        Methinks I'll leave it at that.
         
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        • lewtot184

          lewtot184 Well-Known Member

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          this is what i recommend and have done. the 911's diameter is too big for stock retainers; cranes will work with stock retainers. the 6400 cam should work ok with stock magnum springs.
           
        • lewtot184

          lewtot184 Well-Known Member

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          rocker shaft shimming can be a blessing or a curse. it shouldn't be done without checking the scrub pattern at the valve tip. mopars tappets have a lot of plunger travel, .200+". i've found that .060"-.090" works ok. if you can get by with less thats ok too, but don't let the push rod cup come in contact with the retaining clip.
           
        • Challenger340

          Challenger340 Well-Known Member

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          You mention installing the 911 Comps at 1.85" ? Probably too much seat & over the nose V/spring pressure for my liking ?
          but,
          what are your actual Valve "tip" Heights as measured from the un-machined V/Spring seats that you have .130" Lifter preload ? and, how much Block/Head Milling was done?
          I see shorter, or adjustable pushrods in your future.
           
        • lewtot184

          lewtot184 Well-Known Member

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          factory stuff always had a lot of preload. probably well over .100".
           
        • EngineerDoug

          EngineerDoug Well-Known Member

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          The issue with the springs has got me concerned - these are the springs the tech line at Summit recommended. Sounds like I need to look into a different spring. I did check the preload at the rocker arm cup (where it contacts the pushrod). These are stamped steel rocker arms. I don't have measurements of the valve tip height, but I don't think any block or head milling has been done. Dead stock.
           
        • lewtot184

          lewtot184 Well-Known Member

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          i don't have a $1000+ Rimac spring tester but my little hobby cheapie tested a 911 at 145lbs@1.90" and 155@1.85". the 911's spring rate is 373lbs per inch according to comp cams.
           
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          • Garys1969RR

            Garys1969RR Well-Known Member

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            Doug, what is your method of measuring the pre load? I don't understand how you are doing it. It would be the distance from the top of the plunger travel, to where it is when the lifter is on the base circle and the valve train is in place. Seems like it would hard to do with stock rocker arms. How do you do that?............. And as far as valve springs are concerned, I wouldn't use any more pressure than the cam manufacturer recommends. You don't want to lose a cam lobe.
             
          • EngineerDoug

            EngineerDoug Well-Known Member

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            Yes, I would estimate the open/closed pressures to be 314/141 lb, respectively - using 1.85" installed height. Looking at the Crane 99839 spring, I compute open/closed pressures to be 307/103 lb. I called Crane to chat with them, and they also recommended this spring. They indicated it would work with stock retainers and no head machining required.

            If I use the Crane springs, do I need to shim them to bring up the closed pressure at all? Is 103 lb high enough?

            Thanks.