Whether or not the harmonic balancer enters into the dynamic-balance equation depends on the particular engine. Chevy V-8's can be either internally or externally-balanced. 265 through 350 engines are all internally-balanced, and have harmonic balancers that neither add nor subtract from the overall dynamic equation as long as they don't vibrate when spun. 400 cubic inch smallblock engines have a weighted flywheel and harmonic balancer which must be attached to the crankshaft during the balancing operation. Ditto for Ford 302's, which use external balancing. Some John Deere Diesel tractors use gear-driven timed balance shafts to offset harmonics in the rotating assembly that can and will break crankshafts if they're timed incorrectly. Chrysler 2.5 liter 4-cylinders use a chain-driven balance shaft for the same reason. Chrysler 440 engines can be either internally or externally-balanced, depending on connecting rod design. Using a 305 Chevy crankshaft in a 350 causes vibration problems, even though they're dimensionally identical.
Anything attached to the crankshaft must either be dynamically balanced, or add a calculated amount of shake to the assembly. Offsetting torsional harmonics gets added into the mix after the assembly is able to spin vibration-free. That ability to dampen out harmonics is very RPM-dependent, and there will be nodes above and below the normal operating range where the harmonics can't be controlled effectively. That's where balancer technology gets out of the realm of the average engine builder.
Jerry
