put a crankshaft in chevy 454 but when i tighten the rod caps on two cylinders the crank would not turn

I just put a crankshaft in chevy 454 but when i tighten the rod caps on two cylinders the crank would not turn wanted to know what would cause that

Answer:

2 things that will cause this
1) The clearance between the bearings and crank ( did you plastigage?)
2) If you are putting the rods and caps in the wrong direction it will cause them to bind.

Not just the caps being on the right way, but the rods aiming the the right direction. If the pistons have not been removed from the rods, you can use the small mark on top of the piston as a guide. The marks should all face the front of the engine when installed. There are different sizes available. specially if the rods have been reconditioned or the crank turned. I assume you are putting plenty of assembly lube on the bearing before installation and that the crank spun freely with the main bearing caps torqued to spec.