Thinking about buying a lightweight front pulley? READ THIS!

[JDM_GUY]

m making this thread so we can try and root out some of these dudes that keep on listing unorthadox pulleys and crap in there build lists.

First off this is what a harmonic balancer is (Also known as the "front pulley or crankshaft pulley)

Engine Harmonic Balancer

Every time the cylinders fire, torque is imparted to the crankshaft. The crankshaft deflects under this torque, which sets up vibrations when the torque is released. At certain engine speeds the torques imparted by the cylinders are in synch with the vibrations in the crankshaft, which results in a phenomenon called resonance. This resonance causes stress beyond what the crankshaft can withstand, resulting in crankshaft failure.

To prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft. The damper is composed of two elements: a mass and an energy dissipating element. The mass resists the acceleration of the vibration and the energy dissipating (rubber/clutch/fluid) element absorbs the vibrations.

Over time, the energy dissipating (rubber/clutch/fluid) element can deteriorate from age, heat, cold, or exposure to oil or chemicals. Unless rebuilt or replaced, this can cause the crankshaft to develop cracks, resulting in crankshaft failure.

There has been a trend at times by some "performance enthusiasts" to remove the harmonic balancers on their cars, usually when the balancer is attached to the crank pulley. The argument is that they aren't necessary and their mass reduces the performance of the engine. Others[who?] argue that this is not worth it, because the danger of damage to the engine from the vibrations the damper is intended to prevent is too high. Certain cars, however, do not come equipped with an external balancer on the crank pulley, and as such, can have the pulley replaced with a performance oriented product.

While net engine output can be increased without harmonic balancers, in professional race cars harmonic balancers are still commonly equipped, for reasons ranging from safety concerns to regulations. Almost all modern car manufacturers, even "performance" car makers and specialty tuners, include a harmonic balancer on their vehicles, and removal voids vehicle warranty.

Here is a quote from TOO (endyne)

Quote:
Originally Posted by TOO
The topic is that of aftermarket crank pulleys. 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.

A quick bit of history; Back in the late '70's, all the Pro Stock engines had been reduced in displacement to allow the cars to weigh less. At that time the vehicle weight was based on engine "type" and total displacement. Typically, the engines were in the 330 cubic inch range and running 10,000 to 11,000 rpm was normal, especially in high gear at the traps. There began to be a lot of engines that were "exploding" their harmonic balancers on the big end. Aside from cutting the steering in half and blowing the front tires, large hunks were also finding their way into the grandstands and there were numerous injuries, many of which ended in death. NHRA immediately mandated that solid "balancers" were to be used from that point on. Keep in mind that a balancer can't be solid and function properly, but the rules were the rules. Moroso and a couple other companies who were tight with NHRA began making aluminum billet "balancers" immediately and everyone bought them so they'd be legal to race. All of a sudden, racers were getting only 10 passes from their crankshafts, which had previously lasted an entire season. Initially, most people thought the cranks were "bad", but after destroying engine after engine, a few knowledgeable engine people figured out where the problem actually was coming from and several companies that were capable of making functioning harmonic balancers sprang up over night. They are all still in the business to this day and their units are actually much better than the factory units of years before, as they are made from premium materials and optimized for high rpm applications. With this short bit of history finished, 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. I also need to say that a large driven mass such as a blower or alternator, can have a slight dampening effect, but to actually work properly, the belt connecting the components to the crank would need to be 4" to 5" wide and the belt tension would be so great that it would wear out the number 1 main bearing as well as the bearings of the the driven parts in short order. 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. I'm sure that there will be some fall out regarding what I'm saying here and to that effect I need to remind everyone that we do not manufacture hubs, big pulleys, or harmonic balancers for Hondas and none of what I've said is the least bit politically motivated.

And yes, any engine with a non-functional hub or balancer can ruin the crank driven oil pump and a whole lot more.

Bottom line is do not use lightweight crankshaft pulleys. Alternator and a/c pulleys dont matter, but if you want your engine to last dont change the crank pulley.







**taken from http://d-series.org/forums/engine-building/98839-thinking-about-buying-lightweight-front-pulley-read.html

[JDM_GUY]

Sticky

[NY4PD]

very good info.
some one doing there homework.
nice to see this...