Quote Originally Posted by DennyW
You should have got a hold of a matched set of rods.

Did you double check to make sure you have the right balancer on there ? How about the flywheel ?

The rods should all have been weighed. Find the lightest one, and match the rest to that. You weigh the tops of the rods, and match, then the bottoms, and match them. Then, you weigh the total weight again.
I think Denny is on the right track.
If your rods vary in weight a little you would never even know it.