Stock rocker arms 509 cam?

Big Block A body Tech

  1. EvilScamp

    EvilScamp Well-Known Member

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    I recently built a 383 for my Duster i used a 509 lift mopar performance cam with stock rocker arms, it runs rough and when i bring up the RPM's it cracks and bangs out the exhaust.
    I have been told i need to use adjustable rocker arms with this big of a cam and the issues i'm having is caused by the valves not opening and shutting correctly.
    Do i need to go with roller rockers or am i overlooking something? I have a set of 1.5 rockers but i have no idea how to set them up because i never used them before.

    A little more info. it's bored .040 over and i'm running a 750cfm carb.
     
  2. GEO

    GEO Sarcasm Inc.

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    What springs did you use?

    The stock ones will not work well with this cam
     
  3. moper

    moper FABO Gold Member FABO Gold Member

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    You've also got an overcammed engine situation... The .509 can be run with stock rockers but with the right springs you will have a lot of rocker flex. That usually would mean bent pushrods and a limited rpm potential. From what you're describing it may also have tuning issues. Was the cam degreed when you installed it?
     
  4. EvilScamp

    EvilScamp Well-Known Member

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    The cam was installed straight up, the springs are the correct ones for the cam but i don't remember exactly what they are off the top of my head.
     
  5. RustyRatRod

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

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    You can run the old MP heavy duty version of the stock rockers. They are a lot thicker but they are almost impossible to find. With a cam that big, it is best to run adjustable rockers though.
     
  6. 70aarcuda

    70aarcuda Master Hoader of SBM FABO Gold Member

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    Mancini racing still has them under their own brand name.....but i would spend my money on adjustable rockers too.
     
  7. EvilScamp

    EvilScamp Well-Known Member

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    I do have a set of adjustable rockers for it but i don't know how to set them up.

    What is the best way to adjust them and what do i need to know in order to do so?
     
  8. RustyRatRod

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

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    What kind of adjustable rockers do you have first of all? You'll need different pushrods of course. Tell us what you have first and we can go from there.
     
  9. RustyRatRod

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

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    Really? I wasn't aware of that. Thanks. Seems Mancini makes a lot of the stuff MP used to.
     
  10. airgrabber

    airgrabber Well-Known Member

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    Get the motor warmed up and back off each rocker, with the cam lobe in the closed position, til you can spin the pushrod between your fingers. Then tighten the adjuster til the pushrod JUST starts to lose all the slack up and down, then go 1/4 turn more and snug up the adjuster. Bump the motor over til the next valve is definitely closed and repeat. A more correct way is to use the chart MP made and do it while watching the timing marks and such.
     

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  11. RustyRatRod

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

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    It depends on which rockers he has. If he has the factory adjustable rockers, they will need some small modifications before they will be reliable with a cam that big. That's why I asked.
     
  12. moper

    moper FABO Gold Member FABO Gold Member

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    He'll also need pushrods.
     
  13. EvilScamp

    EvilScamp Well-Known Member

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    They are 1.5 ratio rockers and pushrods from 440 source for B block with hydraulic cam and roller rockers.
     
  14. txstang84

    txstang84 Well-Known Member

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    There are a couple different ways to go about adjusting them once you find the correct length pushrods and ensure your sweep across the valve stem is good (checking rocker geometry) as mentioned by moper and RRR--strongly recommend you borrow/beg/buy an adjustable and ensure you buy the right length pushrods.

    Here's one I found from Comp's instructions...keep in mind they're written for chevies, but the process can be used similarly

    "
    Section I. Setting preload with ADJUSTABLE ROCKER ARMS​
    Turn the engine in the normal direction of rotation. Start with cylinder number one (1). When the​
    exhaust valve begins to move, adjust the intake valve to the correct preload. To reach zero, take the​
    pushrod between your finger tips and move it up and down while you tighten the rocker arm. Once​
    you feel the pushrod has no more vertical slack, you are at zero preload. Make sure the pushrod is​
    in the lifter and the rocker arm seat when making valve adjustments. As stated before the best​
    setting is .030” to .040”, or ½ to ¾ a turn of the wrench past zero. Now, you can move on to the​
    exhaust valve on the same cylinder. Begin by rotating the engine over again until the intake valve​
    reaches maximum lift and is almost all the way back down. Then set the exhaust valve using the​
    same method as the intake (.030” to .040”, or ½ to ¾ a turn of the wrench past zero). Continue​
    adjusting the valves on each cylinder in this manner until all valves are adjusted."

    The above method in post #10 works well, but I never did well that way...I always did better one cylinder to the next...also, the amount of preload you put into it will change the way it runs. Too light, and it'll be a little noisy, and it'll essentially lose some duration/lift...too much and you can actually push the valve off the seat on the base circle...no bueno.
     
  15. EvilScamp

    EvilScamp Well-Known Member

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    Thanks for all the info.
    I'm gonna take a shot at the roller rockers tomorrow, hope there are some improvements with them.
     
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