[Mike Taylor 3601]

Phil,
Did you find piston/valve clearance problem? In picture you sent me it looked like you had some intake and some ex but not all of either hitting with it being somewhat random I would look at valves see if all same thickness and setting same depth,if they are the same probaly getting valve float with it being kind of random springs may not be set up evenly and have some with less pressure, all that is ok double check actual clearance piston to valve clearance.
I know valve broke had head popped off of stem that alot of times is sign of valve float,hitting piston did'nt help head stay on valve,but float will pop off heads of valves stretch and burr keeper grooves,can leave X or * asterick pattern on tip off valve where roller on rocker is beating on it,and timing chain stretched ,valve guides wollared out prematurely are all symptons of valve float.
Mike Taylor 3601