I took the head of my ex motor (d16y8) and did some work, and then put it back on. It worked, and then I took the head of again to put on a new head gasket. When I try to start it, the crank will not turn. I turned the crank manually, and it has about 270 degrees of motion, and then it stops. I thought that a valve was hitting a piston, so I took the head off and tried to turn the crank. Still, it siezes... Any ideas??

 

I would drop the pan and take a look.

 

Not good. Drop the pan and see. Did you do ANYTHING else to the engine?