[Gaz64]

OliveR,

Can you please post a video of you moving the valve heads sideways from the combustion chamber side with the valve 1/4 inch off the valve seat please?

Can you also post photos of your rocker arms?

I would say you have had high rpm valve spring harmonics, where the valve spring and retainer oscillate in a circular motion.

Valve lift alone is not the sole reason that wears valve guides, especially if a roller tipped rocker is used.