1986 EVO lifters - preload

Discussion in 'FXR Models' started by 86fxr, Jul 24, 2009.

  1. 86fxr

    86fxr New Member

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    Hello, new member here.

    Great forum; my question is about the lifters in my 86 fxrs (stock except
    for single fire, S&S carb, T/H pipes)

    About 10 years ago I replaced bottom jug gaskets and reused the stock
    pushrods with no problems.

    My rocker covers long ago shed their clear coat skin and recently the
    rocker box gaskets started leaking so I pulled them off and got a set
    of chrome (3 layer) from J&P.

    I think it makes sense to use adjustable pushrods (probably S&S c/moly)
    but I am confused about the lifters in this motor. The CSM - crummy
    service manual - says the stock rods should spin after bleed down when
    the cam is unloaded. I'm pretty sure this was the case the last time
    I put it together. This implies no preload.

    The tech tips here spec a preload of .05" to set up hydros.

    The question is: Are the stock lifters some kind of hybrid design that
    get set up like solids?

    Thanks
     
  2. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    No. You should have the specs from the pushrod maker or the lifters on the number of turns necessary to get to half (or a wee bit more) the lifter's piston travel. You then put that cylinder's piston at TDC and adjust both intake and exhaust. Leave them for 10-15 minutes until they have bled down (so they turn easily with your thumb and forefinger). Rotate the engine until the other cylinder's piston is at TDC and repeat for those pushrods. Button it up and back it out.

    TQ
     
  3. 86fxr

    86fxr New Member

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    Thanks for the info; two more questions/comments.

    A. should I worry about interference (S&S adj rods) to stock tubes?

    2. I have read numerous explanations (here and others) of how hydros work and I am still confused - if you preload the lifter (say .1" of the available .2" of travel) aren't you compressing the spring and if so how does it bleed down and release that tension (so that the rod can spin)?

    I'm gonna go back to the article on lifters and read it again as soon as I post this heh heh

    Got it now (I think)

    Wet lifter (bottom chamber full of oil) extended to its max length by the lifter spring is preloaded by lengthening the pushrod which opens the valve compressing the valve spring. The valve then slowly closes as the much stronger valve spring overcomes the weaker lifter spring forcing enough oil out of the bottom chamber until the valve seats and no longer exerts bleed down force. Now the rod can be spun because it is resisted only by the force of the much weaker lifter spring.

    Takes me a while to get it - 60 yr old noggin
     
    Last edited by a moderator: Jul 25, 2009