Loads of folks here will know better than me, but I feel I should contribute when I can, so here goes . . .
The crankshaft suffers through loads of force in the process of torque-creation. All the controlled explosions in the cylinders translate their force to the crank. As the crank turns, the engine wants to turn the opposite of the crank. And the off-set combustion in the cylinders puts different twisting force on different parts of the crank at different times.
The vibration dampener acts like the shock absorber on a tennis racquet. The rubber in the dampner helps absorb and redistribute the shocks of the crankshaft forces, providing for smoother turning action. The other name for the dampner, the Harmonic Balancer, I think refers to the vibrations set up from all these forces, which are measured in sine-waves, much like music can be. I guess it keeps the competing forces "in harmony", by "balancing" them out.
OK . . . I think I may have made that more complicated than it needed to be . . .
Must me readin' too many books.
PS: I didn't think our trucks HAD timing marks on the dampner, only on the flywheel - I don't recall my dampner being indexed at all to the crank shaft?
-Michael
