From Valves to Rocker Arms "98 V11EV

[Tom H]

Thank you for clearing that up for me. I thought that Guzzi "basically" pushed straight down, not wiped. I will remember that.

Tom

[s1120]

Tom,

On your BMW the valve stem keepers are full half circle and they butt to form a full circle. The circle diameter is ever slightly larger than the valve stem. Your valve stem probably has 3 grooves to give a greater surface area to wear as the valve rotates.

Moto Guzzi keepers are just shy of a half circle. So the pair does not butt when they drop into the top collar. Instead they clamp on to the valve stem and keep it stationary rotationally.

You do indeed get a line across the top of the where it is wiped by the tip of the rocker. The wiping action also wears the tip of the rocker.

Properly set up the tip of the rocker should wipe across equally both sides of center as it pushes the valve open. I smoothed the valve ends square and flat. I stoned the tip of the rocker to remove any uneven wear from 7K miles.

I did the installation and applied Prussian Blue to the valve ends and cycled the crank and valve train.  A subsequent examination showed that the rocker tip wiped a clean patch that was symmetric about the valve centerline. So I've got a perfect, flat contact patch on the valve stem. This rebuild should last as long as the original assembly.

https://www.lunatipower.com/how-to-verify-valvetrain-geometry
It's not a motorcycle engine but it illustrates the variations in contact patches produced by valvetrain geometry. On the BMW (/2) you would move the patch by shimming the rocker pylons.  Those butterheads frequently needed shimming. Don't remember having those problems with the '89 R100RS.

Building auto engines, thats something you need to do when you start swapping, heads, cams, rockers, etc. I built a few adjustable pushrods over the years, to measure for custom length ones to get it right.