Pushrod length question

Discussion in 'Engine Topic' started by buildinmy73, Mar 6, 2018.

  1. buildinmy73

    buildinmy73 Veteran Member

    1,029
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    Oct 20, 2007
    Bernardston, MA
    measuring for pushrods on my 427sbc and had a few questions .

    Do most use same length on intake and exhaust ?

    Most lobe lifts are diff for intake and exhaust so it would make sense to have diff lengths correct ? Or am I wrong ?
    Just can’t seem to wrap my head around this

    For instance my gross lobe lift is around 600 on intake and 580ish on exh . For my custom Straub camshaft

    What do others think ? .
     
  2. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

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    Nov 4, 2004
    Ringgold, GA
    You measure pushrod length when the lifter is on the base, not the nose of the cam, so cam lift does not come into play. You will want to rotate the engine a full turn to verify the rocker stays in proper contact with the valve. There are several good online sites, Comp Cam is one, that have some detailed instructions on measuring and verifying pushrod length. On a sbc, no offset rockers, all pushrods should be the same length.
     
  3. buildinmy73

    buildinmy73 Veteran Member

    1,029
    7
    Oct 20, 2007
    Bernardston, MA
    Thank u for the reply :)
    Much appreciated!
    The reason I brought up lobe lift is because Was taught that rocker should be at 90 degree to the valve at half the gross lift .
    And that it may take a diff push rod on exh vs intake to achieve this
    I’m def learning as I go
    I’m so grateful of all the great people and info on this site
    Dan
     
  4. czizza

    czizza Veteran Member

    860
    20
    Jan 8, 2004
    N. Massapequa, NY, USA
    Pushrod length is the used to ensure that the rocker maintains proper contact with the top of the valve stem through out the entire cycle of operation, this is known as geometry.

    How do you figure this out?
    1) Get some blue die
    2) Apply to the top of the valve stem
    3) Put the rocker on the stud and connect the push rod
    4) Tighten down to enough where the pushrod stops spinning
    5) Then rotate the engine several times working through the cycle
    6) Disassemble this and be careful not to ruin the mark left on the dye

    Do this for both intake and exhaust and examine the mark ... you want the marks and movement to stay in the center of the stem.

    [​IMG]

    As you can see that there is blue on the top and bottom ... some would want it more towards the front ... since mine are hydraulic and they were not pumped this is OKAY because the oil pressure will move it more forward ... I am going to recheck once I am done with my new heads install.
    [​IMG]

    [​IMG]
     
  5. buildinmy73

    buildinmy73 Veteran Member

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    Oct 20, 2007
    Bernardston, MA
  6. 77 cruiser

    77 cruiser Veteran Member

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    Nov 17, 2006
    Frostbite Falls MN
    You want the pushrod length that gives the narrowest sweep on the the valve.
     
  7. mrdragster1970

    mrdragster1970 Veteran Member Lifetime Gold Member

    .


    My guy bought a jig, that gives you the exact length needed, perfect to the thousandth.


    .
     
  8. 77 cruiser

    77 cruiser Veteran Member

    478
    14
    Nov 17, 2006
    Frostbite Falls MN

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