John Deere JX75 Engine Rebuild Issues (Kawasaki FC150V)

 So have been trying to rebuild my engine for my JX75 mower for some time now. I took it completely apart, replaced my piston rings, oil seal, gaskets, the top part of the crankcase, and my crankshaft. Everything went well until I attempted to close up the crankcase. I have the gears aligned correctly and I tuned the piston shaft, but every time I tighten the crankcase, the crankshaft will not turn. It turns fine right until I start to torque my cover screws. I cannot imagine what the issue is. It is not the oil governor, as I tried assembling it without it in and it still did not work. It's not just tight, I have tried everything to get it to turn, but once I torque it, it's like it's set in concrete. Does anyone have any ideas? I have put some serous cash into this machine, I don't want to get it all together, just to have it literally blow up in my face. If you can think of anything, please reply.
Thanks!