Fortunately, inline 6 cylinders are very well-balanced naturally. It's not even necessary to use "bob weights" when spin-balancing the crankshaft due to the counterweights being spaced at 120 degree angles. Can't get away with that with a 4, a V8, or a V6 engine! As long as each rotating part gets balanced individually, the accumulated errors when the parts are assembled generally doesn't add up to enough to cause a significant amount of vibration.
Jerry
