to replace the engine with a used VQ35DE from a 2003 Maxima; it has 86K miles. I thought I would replace the secondary timing chain before I put it in the car. I rotated the engine so number 1 was at TDC and removed the chain. The chain and guides really don't have much wear, but I put a new chain (from Nissan) on anyway. I decided to turn the engine over by hand several times and recheck to be certain the cam timing is correct. After a couple of full turns it came to a stop like a piston hit something. I pulled the timing chain and I have turned the cams on both heads a little at a time to close valves that may be hitting a piston. With the timing chain off, the crank will only rotate to a certain point and stop.I really don't want to pull the heads and I really don't think that I have a piston hitting a valve. Is there something else that would cause this?HELP!!