Yes, Comp Cams is who I was refering to as my push rod vendor. That is the
method I used which I now believe to be incorrect. the second method I
described and that Bob posted a description of seems to be the proper way since
it reduces the loads on the valve guides.
Frank.
> Here is what Comp Cams says about it, although I like Bob's thinking
> better.
>
> http://compcams.com/information/Products/Pushrods/
>
> Craig
>
>
> Palmer, Robert L. wrote:
> > Frank,
> >
> > It seems to me that changing push rod length can satisfy one or the other
> > criterion, but not both at the same time; either you get maximum extension
>at
> > half lift (the 90 degree angle point), or you center the contact patch on
>the
> > center of the valve stem. If the rocker arm length equals the stud/valve
>stem
> > separation, then everything is fine; otherwise, some compromise will be
> > needed.
> >
> > Here's some instructions on how to pick the push rod length I found, which I
> > believe is what you described:
> >
> > "It is desirable to have the least possible amount of roller movement across
> > the valve tip as possible. This will provide maximum valve lift and minimum
> > wear and side loading of the valves and guides.
> >
> > To determine the roller movement across the valve tip, known as the "rocker
> > strike" or "contact patch". Apply a thin smear of bearing blue (Prussian
>blue)
> > to the valve tip, fit rocker arm and set lash clearance. Engines fitted with
> > hydraulic lifter cams set clearance to zero.
> >
> > Rotate the engine by hand at least on full turn watching the roller movement
> > across the valve, the roller should move forward across the tip until half
> > lift and them back to its starting position at full lift.
> >
> > The 'rocker strike' or 'contact patch' should be central on the valve unless
> > non standard length valves are fitted due to the intersecting angles of the
> > stud and valve centerlines.
> >
> > Geometry can be changed by fitting different length pushrods or valve lash
> > caps, shorter pushrods or lash caps will bring the starting point further
>back
> > from the center of the valve, longer pushrods will have the opposite effect.
> >
> > Ideal geometry will have a strike area of approximately .060" [1.5mm] wide,
> > central on the valve and have the major amount of roller movement at low
>lift
> > where the spring pressure is least.
> >
> > Before running the engine it is vital to ensure free operation and at lease
> > .060" [1.5mm] of clearance between arm and valve spring, retainer, base of
> > rocker stud and back of posilok nut.
> > Clearance should be checked at both closed and fully open valve positions."
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