from my experience looks like a cam failure from lack of oil, the first oil journel i open up to 2mm then chamfer the rest, at high rpms simply not enough oil in the head a common problem in other sohc engines too oil spray bar gets blocked very quickly or when hot the journels restrict oil flow. The cam aggressive ramp angles creates wear more than just lift or duration or valve springs tbh sadly pot luck the only cam i trust these days is catcams you can request specific case hardended and heat treated cam for extra life.