Has anyone ever hit water, or had a head crack after installing hard seats in 67 1.60 valve 915 heads. I think the book said a 1.78 hard seat is safe, any issues? These heads sonic checked .240 or better when they were 1.60 valve, machine shop installed 1.74 valve and you guessed it set them to deep. Valve stems are too high, ferrea only allows .010-.015 max stem machining, so need another answer.t