So I recently rebuilt my 03 VQ, go to start it, won't fire. Pull front timing chain case to double check timing even though I triple checked before reassembly. Long story short I redid everything timing wise per the FSM I'm 99% sure it's correct as of right now. That being said I still cannot manually turn the engine over 360 degrees. Turns about half way then feels like it hits something and refuses to budge. I'm completely out of ideas as to what the hell could be wrong. Any help would be greatly appreciated.

 

If the pistons are catching or impacting something then don't force anything. Obviously something is wrong. Pictures of the timing would be awesome! Possibly have it mis-aligned or maybe a problem in one of the pistons/heads? Have you pulled the valve covers to visually inspect the top of valve trains? Just a thought. Was this just regular maintenance or in response to a problem?