I really need help with my valves

[Mike Hewett]

I have a serious issue with my valves. I installed an edelbrock performer camshaft, 302 heads with bigger chevy valves, and stock rocker arms and a stock 1970 302 block with flat pistons.. When adjusting my valves, I proceeded to turn the crankshaft over and I heard some noise and it got somewhat hard to turn... so I stopped. My first reaction was that the pistons and valves were hitting, but I got to thinking maybe it was just the lifters riding up on the the cam lobes??? Ho do I know. I'm desperate for answers as I just spent 2500 on this motor and have been working on this bronco for 2 years

 

[broncnaz]

Ideally you should pull the heads back off and put some clay on top of one of the pistons the put 1 head back on and turn the engine over then pull the head again and check the clay if its squashed down the smallest thickness should be no less than .100 if its less you may need to get the pistons flycut for clearance.
to check without tearing it all back down. your best bet is to try and figure out which valve is opened up the most then look at the valve springs at full lift you need at least .060 clearance between the coils if you are more than good on that then you need to try and open the valve farther to see if its actually hitting the piston. if it is you may want to recheck the timing gears to ensure it is timed right. if that doesnt pan out I would say its back to the machine shop