Many of the geometric issues are addressed in
http://home.swbell.net/cartrip/RockerGeom.pdf , which assumes you have a
perfect arc at the valve end of the rocker arm and a perfect ball and
socket at the pushrod end. Changing pushrod length, valve length, or
pedestal height changes the initial angle, which has no effect unless it
also changes the contact points (lengths a and aR). The arc at the valve
end will have an effect, but we're talking about over 0.008 in of
deflection at full lift (with 220 lb spring force). I observed lift
ratios as low as 1.25. That would require the contact point to be moved
in about 1/4 inch. I also believe that if it is an issue of the contact
point moving outward, the curve would be much more linear. I suppose the
way to resolve this is to repeat the experiment with light springs.
Does anyone in the group know whether 60,000 lb/in is a reasonable
number for valve train stiffness in a pushrod motor? BTW, the
measurements were taken with stock TR4 pushrods, rocker arms, rocker
shaft and pedestals. I do know that valve train stiffness (or the lack
thereof) is a huge issue in valve train and camshaft design for pushrod
motors.
Greg Solow wrote:
>I don't think that is defection of the valve train due to spring pressure. I
>got 1.45: as a rocker ratio when I checked it years ago with light tension
>"checking " springs. The ratio will vary somewhat depending on how your
>rocker arm geometry is set up. The farther away from the rocker shaft the
>contact point between the rocker and the valve stem is, the higher the ratio
>will be because the lever arm length is longer. Raising or lowering the
>rocker shaft (or the end of the valve stem, or regrinding the end of the
>rocker arm and changing the geometry of the arc on the end of the rocker
>arm) will all change the rocker ratio.
> Greg
>Solow
|