Let me begin by saying that we have always called the pulley on the accessory drive end on the Honda cranks Harmonic Balancers. People never seemed to understand what we were talking about and so the word "pulley" was frequently used to avoid confusion. If you look carefully at a Honda "pulley", you'll find that it's not a single piece of metal. Typically, there's a nodular iron or steel hub and another "ring" of iron or steel surrounding it containing the belt grooves. The two parts are joined by a rubber layer, which is highly compressed and sandwiched between them. Why rubber? If you notice, many four cylinder engines over the years have used counter rotating shafts to help make the engine "feel" smoother. Reciprocating internal combustion engines and especially in-line four cylinder versions, all produce shock pulses, which are very apparent to the occupants of the car. Every engine produces a shock pulse each time an individual cylinder fires. So, in the case of the four cylinder variety, there are four large individual pulses for each 720 degrees of crank rotation. Each time there's a pulse, it causes the internal components to do a rapid acceleration-deceleration event. When you consider the mass of all the internal components and visualize all these parts stopping and starting during their reciprocating and rotating motions, the additional stress "spikes" tend to make it all the more reason for one to wonder how any of it can work for any length of time. The harmonic balancer is made with the rubber coupling so that, when the individual "spikes" occur, the inner portion may move with the crank, but the rubber connected outer ring's mass helps prevent the hub and crank from going as far or as fast during the spikes or pulses. Remember that the outer part had considerable mass, so it tends to want to stay in motion at the speed that it's traveling and that's why it can prevent excessive harsh motion by the crank and other internal parts. To put it simply, the harmonic balancer is a shock absorber for the engine and thus prevents the individual pulses from destroying everything in the engine.
