The Scat assembly was externally balanced and included the 9000 crank, rods, pistons, rings, 400 weighted flexplate and weighted harmon balancer. It included a balance sheet with weights of all parts. I tried my old balancer which was a 400 weighted piece from my old 383 to rule out a bad balancer. I put the new one back on though. If it was a balance issue, shouldnt the vibration get worse as rpm's increase?