These engines are not externally balanced,the flywheel is neutral ,as is the damper.The alignment dowels insure the flywheel is positioned correctly on the crank,for lining up the timing marks,not a balance issue.Unless the crank was altered during the rebuild,the engine should run as smoothly as before the rebuild.The piston and rod weight is not important on an inline 6 so long as they all weigh the same within reason.
Does the vibration get worse with higher engine speed,or it it worse around 2000 rpm?
