Good evening

Hope you guys can help

Rebuilding a 1951 216 car engine

Here is some background
Engine was running when I started the rebuild but started smoking and leaking oil heavily on the block

This is the original engine and this was the first rebuild

I had the crank machined and it was in tolerance for original size bearing

After reasambly with all new bearing,rods,rings and tolerance set to spec

Once crank and rods are in and fully tightened the engine will not turn by hand,. Loosening the mains the engine will turn freely

Any ideas as to why it will not turn when fully tightened and what would be the next steps

Thank you