If there is plenty of assembly lube on the crank and bearings and its not wanting to turn when you tighten them down then either the following is happening or the problem:
Wrong size Bearings...What bearings are you using and are they the standard size or oversize. If they are oversize, that is the reason.
Warped or bent crank...Usually from storing it wrong/having it resting on its side or tetering on something to where it can flex/bend.
Warped block...If the block has been overheated
Or you dont have the main caps on the right way or the main caps arnt from that motor....The main caps for a motor go with the motor they came with and cant be used on any other motor unless you get it line bored.