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Interesting post by one of the guys from Engine Dynamics Inc.(building race engine since forever). Long story short: the crank pulley on Honda's acts as a harmonic balancer because it has rubber in the middle. Without this you can get problems. Read on...
Bad Vibrations
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...
I'll begin to wind it up by stating what we do with the Honda engines. If the balancer has more belt grooves than the application needs, i.e. the power steering pulley, we machine it off. When it comes to the the pulleys that are actually a part of the outer portion of the balancer, we leave them intact. This procedure will not lighten the unbalanced hub substantialy, but the outer balancer ring will keep all its mass and function correctly...
It's especially important to keep the balancer "as is", if you're running an aluminum flywheel. The reduction in flywheel mass can also increase the pulsation shock strength and a higher level of vibration will immediately be observable. So if you lighten the flywheel,it's absolutely more necessary than ever to maintain the mass or the harmonic balancer. I realize that there's a lot of hype out there where manufacturers are promising this and that. The oversize crank pulleys can drive other geared or belted components faster due to the diameter ratio increase, but if you're deleting the balancer in the process, the short and long term side effects are going to hinge on your decisions. Larger diameter pulleys for the alternator, power steering and any other belt driven accessory are good ways to slow the speeds and drag of the those components, but when doing a large diameter crank pulley, the larger pulleys should actually be designed to fit "over" the stock balancer. Perhaps, someone will begin to make some good quality "functional" balancers some day, but until they do, you need to proceed carefully, as some good looks and minimal power gains can be off set by a ruined engine.
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