[Born Lucky]

Originally Posted by Killer Bee

engine make, model, and detailed explanation of work done and parts replaced would be optimum for troubleshooting via interwebs..

for what's posted, my swag would be to verify con rods/caps mated and proper size bearings installed correctly..

then torque with plastigage one at a time and verify bearing clearances..

http://www.plastigaugeusa.com/how.html

this is per what is previously stated to imply crank and pistons fitted and installed correctly..

good luck!

engine 350 SBC 1996
machine shop honed,cleaned block, polished crank.
Pistons and bearing(main and rod) were provided by machine shop.
Plastic gauge was done and were within specs.