Move flywheel rapidly back and forth within the half inch it takes the balancer.what you want to listen for is the clunk and to determine location of it, yes you may have a broken crank, but you may also have a loose flywheel.if it is possible to look up between oil pan and flywheel you may be able to see the end of crank when you move flywheel back and forth and see if moves at all.if not drop oil pan.then you will see what is going on for sure.
