I have a 85 mustang with a 331 that was running when I bought it and the cam bolt backed out sheared the pin in the cashaft ruined the whole top end so I put all new valves pushrodscam ect. but when i went to adjust the vavles it sheared the pin again any ideas on the cause by the way it has flat top pistons eldelbrock preformer rpm heads and a x303 com

 

with clat top pistons and the x cam first thing id do is check piston to valve clearance, also make sure your using the right lifter/cam combo