Rocker geometry

[Stangman]

How do you figure out the proper rocker arm  geometry,I seen the post below and didn't want to bud in I have FPP which are the Ones from Precision  oil pumps I believe it has to do with threads on the adjuster bolt but want to be sure

[e philpott]

rocker geometry is how the roller tip makes contact with the valve stem , when you have good geometry the tip will be "centered" in the valve stem and stay centered the whole lift .....

to check I paint the valve stem , install pushrod and rocker , then rotate engine , remove rocker and look at the witness marks on the valve stem to verify geometry .....

to adjust you have to change valve stem height or rocker stand height to center tip ,

[blykins]

The thing is, though, perfect geometry is not always in the dead center of the stem. I usually try to look for getting the most lift that I can. Now that's not saying that I will put the roller on one extreme edge of the tip but I won't be upset if it's not perfectly centered.

Usually when you go through several iterations of either stand height or pushrod length on a stud mounted rocker, you will gain varying amounts of lift by having different patterns. Sometimes it's in the center, sometimes it's off-center a little bit.

I will often mount a dial indicator to the head so that the indicator is on the valve spring retainer. You can measure the net lift this way and see how much you lose.  You will inevitably lose a little bit just because of pushrod deflection, but on a serious application you want to lessen this as much as possible

[RJP]

I seldom see any one addressing the geometry issue of the adjuster side of the rocker. Check what happens when the adjuster is shallow or high in the rocker as opposed to deep into the rocker. The pivot point is changed between the high and low set point of the adjuster ball. Only fix is different length pushrods or rocker stands but I believe it could be a potential problem that could add to or cause a geometry problem. Any thoughts?

[blykins]

Yes, you can waste a lot of lift that way, if the adjuster is way down.  The pushrod will make more of an arc instead of translating itself into movement that's important. 

If the adjuster is way up, then you can get into pushrod cup/rocker clearance issues. 

[Stangman]

Thanks guys I put them on and I never had a problem before the only thing I changed is instead of 598 lift  i have 624. Never really noticed how much the rocker actually rocks I could just imagine 700 plus lift