Many of the current throughbolt and valve issues are linked to hydraulic lifter introduction, sorry Rutan it wasnt a good move. Keep in mind you still have to open rocker covers anyway to tension headbolts.
Maybe Rod should simply copy an IO550 and make his half size. Then the engines would see a TBO of 2 - 3 thousand hours and the owner would never have to adjust a tappet or remove a rocker cover.
