Anyone using SB Lunati cam ending in 703 Part number?

Discussion in 'Small Block Mopar Engine' started by JKrebs, Sep 14, 2018.

  1. JKrebs

    JKrebs 68 GTS

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    If so I have a valve timing question. When adjusting the valves (first time fire up) and I'm at TDC the #2 intake is not on the bottom of the lobe. Either is the #8 exhaust. They both are close but not quite there. I don't know if the Lunati grind is a bit different. The Lunati literature calls for the intake to be adjusted when the exhaust starts to open and the Exhaust to be adjusted when to intake is fully opened. I usually use to TDC the turn 90 method but i'm concerned the a may have the cam a tooth off though i checked that more than once. I can call Lunati but i will need to wait until Monday and this will bother me. Thanks
     
  2. crackedback

    crackedback FABO Gold Member FABO Gold Member

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    Only if you are compression tdc can you do that and it still may not be good. Overlap period, no chance.

    I do it this way. Right when intake closes, do exhaust
    Right when exhaust opens, do intake.
     
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    • AJ/FormS

      AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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      You are on split overlap, go around, 360 crank-degrees. Split overlap usually occurs within 2 to 10 degrees or so of TDC..The 703 IIRC is a 268/276/110 fast-rate of lift cam. You probably installed it around 106, which would be 4 degrees advanced. You can verify your install by finding exact split overlap and reading your balancer, but the intake has to be off, so you can lay a straightedge across the two lifters and making sure all 4 edges are touching it. A bit tricky and only as accurate as careful as you are, but close enough to know you are not out a tooth,lol.
      crackedback has you covered with his method.
      When setting the lifter preload, I use the TDC compression method. A few thousands one way or another is hardly an issue........ IMO.
      I run a half turn preload. That way I get a full season or two of QUIET.
       
      Last edited: Sep 15, 2018
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      • JKrebs

        JKrebs 68 GTS

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        I was laying in bed thinking that I could not be a tooth off as I did degree the cam and numbers came out perfect with the info on the card. And yes 106 is correct. What is your method for finding zero lash? I would think that the whole procedure is not that precise as there is certainly some deviance in the zero lash starting point. I just turn the push rod until I feel like the rocker is making good contact and the slop is gone. Then i was using 3/4 turn as everything is new so there will be some seating in of things. Also I will be taking it all apart again after break in to install the second valve spring so I could set everything to 1/2 turn then after things settle in. Thoughts?
         
      • mderoy340

        mderoy340 Well-Known Member

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        use this chart.

        MoparValveLashSetup.jpg
         
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        • nm9stheham

          nm9stheham Well-Known Member

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          Did you verify that the damper mark is truly at TDC? If you timed the cam without the damper on, then the accuracy of the damper mark is not known.
           
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          • AJ/FormS

            AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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            If the intake is off, you can see and measure how far down the cup is in the lifter.
            Otherwise, and with empty lifters, it takes a delicate touch to find the starting point. I remember one time targeting 1/4 turn preload, with empty lifters. Hah, that wasn't the best idea I ever had............ It wasn't long and I had tickers in there. So I just cranked in another 1/4 turn to the tickers, and a couple of weeks later,different ones were ticking.
            Ok, I like to think I'm not a dummy, so I learned that my 1/4 turn target was not realistic, and started all over, but increased the preload to 1/2 turn. Problem solved.
            On the next build, I started with pumped up lifters,and set the preload before the intake was on,..... so finding the zero-point was a lot easier. And I started with 1/2 turn.
            Using pumped-up lifters tho has a different issue. Sometimes when you crank in the preload,the lifter does not bleed down, but instead the valve opens. So you have to trust what you are doing. No matter, by the time you finish setting all of them, some or most will have bled down....... BUT, you have to make sure that your preload is less than your piston to valve clearance, or you could end up driving the valves into the pistons, as you rotate the crank. This is usually not an issue, cuz who builds to that tight a PV tolerance?
            I think the adjuster threads are 32 threads per inch, so 1/2 turn is .0156 preload at the lifter times the effective rocker ratio, might be as much as .0234 at the valve(with a 1.5 ratio) if the lifter does not bleed down. You have to know your PV clearance because because the lifter manufacturer might spec a lifter preload of .080 ; Which, if the lifter would ever fully pump up, would be .128 at the valves with a 1.6 ratio,and almost guaranteed to bend a valve. At 32 threads per inch, .080 preload is 2.56 turns.
            My PV clearance is tighter than .128, which is why I run only a 1/2 turn preload. I like to buzz my engine up to 7000/7200, and if a lifter, set to .080 preload, should ever pump up on the trip, that would be an instant bent valve, actually probably at least 8 bent valves, and of course, the engine would lose all pressure and not idle, stall, and fail to restart. But the 1/2 turn is .050 at the valve in my combo, and so with say 8 pumped up lifters, I'm ok. The engine still would not idle, but if I kept her revved up a bit, she'd bleed down pretty quick. Proper springing of course should eliminate pump-up in the first place.
            So after this essay, you might think that setting the preload with pumped up lifters is a worse idea than setting it with empty lifters. And for a newbe, I'd have to agree with you.
             
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            • JKrebs

              JKrebs 68 GTS

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              I us
              I thought about this. And this could be my issue. I set the motor up with timing marks on the drivers side and it is now set up with mark on the passenger side. I do currently have a 68-9 balancer on the motor with TDC mark for passenger side cover. Any ideas on how to confirm at this point?
               
            • AJ/FormS

              AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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              Oh boy....
              You will have to create a new TDC mark on whichever side you want, or has easiest access.This is pretty simple. You don't even have to use either factory markers
              So to start, the engine has to be at TDC #1 or #6 , as determined and set with a piston stop. Then you can observe the balancer mark and put a new index mark on the cover adjacent to it. Or you can mark the damper adjacent to the cover mark. Or you can make TWO marks adjacent to eachother any where you want to; one mark on each part the damper and the cover .Now you have a TDC mark.
              Finally;now you can install a timing tape, which is a great aid to set the valves, to make setting the power-timing easier with a conventional light,and to configure the rate of advance, etc.
               
              Last edited: Sep 15, 2018
            • JKrebs

              JKrebs 68 GTS

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              Thanks for the detailed response. I do have a slight advantage as I am going to break in the motor on a test stand that I am setting up. So there will be no high revs until after break in and the install of the inner spring. So by then the lifter will be pumped up. I find it easier to find zero lash after the lifters are pumped up.
               
            • nm9stheham

              nm9stheham Well-Known Member

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              As above... use a piston stop to find exact TDC on 1 or 6 and confirm the mark's accuracy or make a new one as needed. And here's a 2nd vote for a timing tape...

              Not an unknown issue... many don't realize that confirming cam timing and confirming damper marks is 2 separate procedures.
               
            • JKrebs

              JKrebs 68 GTS

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              Do you think I could place a piece of rigid wire in the #1 hole and watch when it stops moving up and compaire it to the mark on the balancer for a sanity check?
               
            • nm9stheham

              nm9stheham Well-Known Member

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              Not nearly accurate enough for what you are doing. The piston motion at the top is so slow that you can be 5-10 degrees off. Then your ignition timing will be all screwed up....Though it will say if the damper mark is way off or not.
               
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              • JKrebs

                JKrebs 68 GTS

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                That makes sense. I am familiar with what a piston stop is and how it works. However I am confused on how to set the proper depth on the stop to confirm that the piston is truly at TDC. Or do I use degree wheel and rotate crank both ways and set the TDC 180 out of true TDC?
                 
              • mderoy340

                mderoy340 Well-Known Member

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                Put the piston stop in #1 and rotate CW, when it stops make a mark. Rotate CCW, when it stops make a mark. 1/2 way between the two marks is TDC.
                 
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                • crackedback

                  crackedback FABO Gold Member FABO Gold Member

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                  Stop making it harder than it needs to be is my suggestion.
                   
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                  • JKrebs

                    JKrebs 68 GTS

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                    Suggestion has been noted and implemented