STILLEN lightweight crank pulley

370ZDreamer

You are missing the point. I've had machine shops zero balance engines I have had built in the past. This does not mean you still do not need a harmonic dampener. A rotating assembly will always have harmonics that need to be dampened.

That is great that the pulley itself is perfectly balanced. That means the pulley itself will not introduce any additional harmonics. However it does nothing to absorb the harmonics that are inherent to the rotating assembly.

As the engine turns, the changes in direction from the pistons moving up and down and the forces exerted on the crankshaft by combustion force pushing the piston/rod down on the crankshaft produce torsional vibration. The crankshaft itself being perfectly balanced as it rotates is not where the harmonics come from. Sure an out of balance crankshaft will make things worse, but once the crankshaft is balanced, the forces at work on the pistons and rods exert their own forces which produce the harmonics in all engine rotating assemblies. That is why you need a dampener to absorb those harmonics.

If you look at this picture of the engine http://www.seriouswheels.com/pics-20...-1920x1440.jpg

You can see the ring bonding the inertia ring to the inner hub. It is a dampener and it needs to be there.

The reference to the shop manual that Wstar quoted further proves my point. You want to pull the dampener off from the center hub, not the outer ring because you could break the bonding and separate the outer inertia ring from the center hub.

I am a bit surprised at something like this from Stillen as I've always held your parts in high regard, but when it comes to this part, you wont be seeing my money for it. I don't believe its right.

wstar

Did you read the wikipedia quote above as well? They claim that while harmonic balancers are necessary for integrity reasons on larger V-8s, that newer, smaller-displacement engines (like our 3.7L V6, I would assume) only include damper-like rings to reduce noise, not to protect from failure.

I understand the basic theory going on here: since an ICE is acted on by the pistons in a pulsing pattern at odd angles, there will always be vibrations along the crankshaft, and that at certain RPMs these vibrations might be in tune with the natural harmonic frequency of the crankshaft itself, which would amplify the vibrations, potentially desctructively. I think the question is, in what configurations are those harmonics potentially dangerous? The wikipedia quote seems to indicate that smaller engines aren't susceptible to destroying themselves via harmonics.

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BlueR32

i'd hesitate to look at a picture of the crank pulley to decide if it is a harmonic damper.

the presence of elastomer or rubber on the pulley does not necessarily mean that it is required for torsional damping. it is common to have such on the crank pulley just for n/v/h.

to be a torsional damper, the pulley would have to have two rings whose movements are somehow isolated from each other, either by material or by springs. another format could be a viscous fluid in a circumferential cavity within the pulley.

stillen has looked at the pulley, and has said the configuration is not that of a damper. if there is doubt as to his expertise, then the only thing to do is to take one off and examine it in cross section.

wstar

Well, I've got my stock pulley sitting in my garage off the car, but I don't think I'm willing to slice it just to settle this. It's actually hard for me to tell the exact composition of the pulley and damper from the outside. There's definitely a very stiff rubber ring on the outer backside of the pulley, but it's molded right onto it in a seamless fashion, so it's kinda hard to tell where metal starts or rubber ends without, again, destructively investigating it.

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BlueR32

do you have a multitester? if one side doesn't conduct with the other, one might assume that the rubber layer, separating the two rings completely, may act as a harmonic damper. if they do conduct, i'd bet that the internal composition of the pulley is solid, and thus the rubber would be for nvh.

i'm really just guessing. where are the automotive engineer members of this board?

wstar

Good point. Using the sharp multimeter probes made it easy to tell which parts were rubber and which were metal too, I think I understand the piece now. It wasn't built like I though it was at first. First, here's some pics from my cellphone:

Front view:


Side view:


Rear view:


The pulley is constructed from two separate pieces of metal which are not electrically connected, but it's not a ring on the back like you would think. The inner part of the pulley (the hub and spokes) is separated from the outer part of the pulley (the outer ring with the grooves for the belt). The circular groove you see in the front and rear views is the layer of (very stiff) rubber between the two parts, as highlighted in red here:



I still don't know if that helps draw any independent conclusion. It's not like the design of V8 harmonic balancers I've seen in the past. Those are generally a solid complete pulley, with a ring (picture like a very large washer with a very large opening) mounted on the backside of the outer diameter, separate from the pulley by a layer of rubber. This could still easily be either a real torsional damper or just an NVH-reduction device to me, given how little I really know about the subject.

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370ZDreamer

This is the exact same construction used in Ford V-8 applications. Its a injection molded rubber that is bonded between the inner hub and the outer inertia ring. I deal with the O.E. supplier for Ford's dampeners. That is indeed a harmonic balancer and should only be replaced with a pulley that also is a harmonic dampener, period.