Okay. What many don't know about balancers is the press fit is just as important as the bolts torque. If the balancers fit is too loose, it will move back and forth so little you won't be able to see it. All the while it's doing this the back and forth motion is working against the bolt until it breaks.
This is what happened to my 4.3 V6. When it did it broke the balancer in half and sheared a section of cast iron out of the cranks keyway about a 1/4 inch wide so the crank was ruined. So there I was with a engine I had just rebuilt with only about 10,000 miles on it and I had to put a crank kit in it, but first I had to get the new crank balanced which ran me another $150.