I have put my cylinder head on my 16 valve 3 times now and the intake valves keep contacting the pistons. turning the engine by hand the marks come up perfect .I hand turn the engine 10 times. there is something weird going on does anybody know of something i can check?

Is this an 8cyl with 2 valves, or a 4 cyl with 4 valves? What kind of motor do you have sir? What year? What revision?

On the surface it may appear the heads are simply cut too short. Or the block was over-milled. Or the valve stems are too long. Or the valve seats have been shimmed. Or the pistons are too tall. Or there's carbon on the piston heads. Or the plugs are hitting the piston. Or the conrods are too thick. Or the wrong crank - maybe from a previous or different rev motor. Or the main bearings skewed in place. Or the head gasket too thin, or nonexistent. Cam lobes out of spec maybe? If it's a pushrod motor maybe the rocker arm tappet too close? Maybe the whole valve train timing is off. Or what we think is TDC is supposed to be a purposeful 5deg late. Or the wrong timing chain. Short toothed cam gears