All the valve stem heights HAVE to be very very near the same height, if a couple ( as in your situation) are higher than the rest, one of two things will happen: Lifter preload for that particular valve will be excessive If lifter preload is too excessive the valve will not close completely Regardless of Buicks shaft rocker system, valve tip heights should be nearly the same, even with a stud and nut set-up like Chevy, with un-even tip heights, lifter preload/geometry gets all screwed up. I'd bite the bullet and remove the heads and have the machine shop set all the valve heights the same, IF a few are off. Then, when you re-assemble, get a checking pushrod, find out exactly what length pushrods you need. Myself, I don't like running adjustable pushrods, I've had the adjusters bust off in my lap while adjusting
This problem has been fixed. I got adjustable pushrods and new rockers. I believe the problem was mostly the rockers were so loose that I had to over tighten them to stop the chatter which in turn kept the valves open.
The heads were milled .030 and only 2 valves would stay open. But when I say stay open, it was a only a difference of half a turn would seal them up or let them leak. Bottom line is that now each cylinder is producing about 150 psi and they are all very even. Very minimal rocker chatter. I may adjust the pushrods a bit more. The issue is that I still have poor vacuum and low end acceleration.
