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Pushrods too short

This is a discussion on Pushrods too short within the Internal Engine forums, part of the LSx Technical Help Section category; Couple quick questions. What ill effects (other than loss of lift/power and noise) would running shorter than needed pushrods have??? ...

  1. #1
    Slow'er'Ass Mr. Luos's Avatar
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    Pushrods too short

    Couple quick questions.

    What ill effects (other than loss of lift/power and noise) would running shorter than needed pushrods have???
    Would it cause power to flatline in the upper RPM's??

    Also...using a pushrod length checker I am going to get exact pushrods soon.
    Someone describe zero lash for me.

    Thanks in advance!!!
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    Veteran Hi-Po's Avatar
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    ill give a stab at it.
    You can determine correct pushrod length bycarefully watching the rockerarm from the side as it opens and closes the valve. Look at the end of the rockerarm as it sweeps across the vavle stem. Rockerarm should be slightly off center toward the inside edge(the edge nearest the rocerarm stud) with the vavle closed. As the vavle opens to about mid lift, the contact point should pass across the valve stem cenerline and move slightly toward the outside edge of the stem. The during the last half of the lift cycle, the contact point should swing back across the centerline and return to about the orginal postion just as the valve reaches full lift. Find the right lenth is kinda trail and error really. An adjustable length pushrod will simplify things. It has a threaded insert that can be adjusted to lengthen or shorten the rod. Having to short of a push rod will offset vavle train geometry. and will affect performance. Pushrod is the biggest part of vavle train geometry. Milling cyclinder heads, and engine block, installing over size valves, increasing valve stem length to accommodiate for larger valves springs and even grinding three way seats can affect this. Valve train geometry is the dynamic relationship between the rockerarm and valve stem during valve opening and closing.

    Lash, or clearance between the rockerarms and valve tips. So zero Lash would be ..... 0. Usually when people mean 0 lash, its at engine hot. after everything has been expanded. My Instructer usued to always talk about zero lash. From what i understand its harder done than said. He was a badass, actually had his own Nascar car/team that he build himself with a few others way back. Said he was forced out because he didnt have the money and the sponsers like all the big names Did all fab'in also. off topic.

    thats all i got pretty much.

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    Slow'er'Ass Mr. Luos's Avatar
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    Good info.

    Most of that I knew.
    Just double checking.

    Anyone else??
    Thinking my checker should be here tomorrow. Give me something to do.

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    Senior Member ninobrn99's Avatar
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    http://www.centuryperformance.com/valveadjustment.asp
    Its a pretty good link. Very informative. I also have a procedure on measuring your PR's with the checker. Your overall goal is to have the proper amount of lifter preload. Off the top of my head i think you measure at zero lash (hot/warm) then torqued @ 22lb.ft measure the difference and that is your preload. I have the preloads for differnet lifters somewhere..i just gotta find them. Let me know if you need them.

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    Slow'er'Ass Mr. Luos's Avatar
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    I know what the preload on my lifters is.
    Just need the checker at this point.
    Should be here today or tomorrow.

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    Senior Member ninobrn99's Avatar
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    oh.my bad..

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    Senior Member MadSeason's Avatar
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    mine were too short when the original owner put in the cam, casused a lot of backfiring issues when i was comming off the throttle. had 7.3 when 7.4 should of been in there

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    Slow'er'Ass Mr. Luos's Avatar
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    I know I am not that short.
    If anything, it is .025" off. 7.300" are in there now.

    I know too long can cause ALL kinds of problems.
    And yes, I know the hard way.

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