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This is a good question. Actually, the torsional harmonics and transverse vibrations aren’t independent on a crankshaft. Also, the primary mode of damping for the harmonic damper is torsional damping, not transverse damping. I am sure this article written by Dinan does a better job of explaining the torsional harmonics and damping then I do. [ http://dinancars.com/whitepapersFile.asp?ID=5 ] So to answer your question, on a counterbalanced crankshaft, every additional degree of twist along the crankshaft length changes the counterbalance orientation relative to the next. The center of mass of the counterbalances must reside in a specific angular position to maintain the harmonic balance of the crankshaft. As the crankshaft twists from load and combustion energy, these relative angular positions will shift. This angular displacement shifts back and forth from positive to negative displacement (relative to unloaded neutral) due to under-damped elastic overshoot within the crankshaft. Therefore the crankshaft is constantly going in and out of balance depending on each counterbalance angular position. So the torsional harmonics (sinusoidal angular displacements) are the primary cause, and the transverse vibrations are the secondary affect. Therefore harmonic dampers are designed to counter the torsional harmonic components, the primary cause of the additional RPM dependent transverse vibrations. Compare this to any other object rotating at a high rpm. A simple example, if you change the angular position of a wheel weight, or the angular position of the balancing weight on a driveshaft, large transverse vibrations will occur. Some factory halfshafts (Honda comes to mind) also come with a torsional damper somewhere along the shaft. This is again the torsional damping helping to keep the transverse vibrations in check. So the torsional twisting of the crankshaft is what causes the angular change of the balanced mass, resulting in the additional transverse vibrations that you mentioned.
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