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Ideally, you want the centerline of the valve to be perpendicular to a line drawn through the rocker stud pivot/roller tip axes at one half valve lift. The rocker tip would start out slightly to the inboard side of the valve stem tip at zero lift and the centerline of the valve at an angle of maybe 100* to the centerline of the rocker. As the valve advances to mid-lift, the rocker tip would roll outboard on the valve tip as the relationship of the valve centerline to the rocker axes moves to 90 degrees and the rocker becomes effectively longer from the pivot point on the rocker stud to the roller tip axis. As the valve advances to full lift, the centerline of the valve in relation to the rocker pivot axes would diminish to maybe 80 degrees and the rocker would become effectively shorter, rolling the rocker tip back to the inboard side of the valve tip.

As the valve begins to close and comes back to half lift, the relationship would again be 90 degrees, with the roller tip again moving to the outboard side of the valve tip. As the valve comes onto its seat, the relationship would again come to about 100 degrees and the roller tip would move to the inboard side of the valve tip once more, because now, the rocker would be effectively shorter again.

You would want the same scenario going on with the pushrod side of the rocker arm, with the 90 degree relationship between the pushrod centerline and the line established between the rocker stud pivot point and the pushrod cup pivot point at 1/2 valve lift.

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