Jim,
The information on that web site is not fully correct:
" The need for a Harmonic Balancer often stems from increasing the stroke of the engine which makes the crankshaft overly flexible (twisty). If something is not done to keep this flexing vibration to less than 1/2 of one degree of twist from one end of the crankshaft to the other, then the crankshaft may develop cracks over time.The harmonic balancer consists of the hub (bolted to the crankshaft), an outer weight ring (usually of cast iron) and a sandwiched layer of flexible rubber. This rubber absorbs the energy of the vibrating crankshaft in the form of heat, damping the amount of vibration to within safe limits."
Torsional excitations are a product of the power pulses (and compression pulses to some degree) in the engine by twisting the crankshaft on the power stroke in one direction and then the crankshaft snapping back. These excitations will grow to an alarming peak at the natural frequency of the crankshaft, flywheel, gear train system to break the crankshaft or shafts or any gears in the torsional resonance system. The flywheel is like a filter that keeps the harmonics from going into the transmission, drive shaft and so on. The harmonic balancer (that's not the correct name for it, people think it balances the rotational parts), is like a torsional excitation absorber, it absorbs some of the twist during the power stroke, but it gives it back to further resist the snap-back. I true harmonic damper is very hard to come by, because it is designed to absorb that adverse twist and turn it into heat. The rubber that you talk about can be considered as a "spring" that is connected between the crankshaft and the heavy metal ring. Consider this as a rotational pendulum that is "tuned" to the torsional excitations.
That's it in a nut shell.....There is more to this.
Jan
