STILLEN lightweight crank pulley

370ZDreamer

Does the lightweight crank pulley bolt on to the front of the factory dampener or is it completely replacing the factory dampener?

wstar

From what I read here before, there is no real harmonic dampener on our engine, it's internally damped/balanced. Our stock pulley has an integrated NVH (noise/vibration-something) that reduces noise, which the replacement doesn't have.

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370ZDreamer

All internal zero balance engines still need a harmonic dampener. You still have harmonics in any reciprocating assembly. The pictures I have seen of the factory crank pulley show it has an inertia ring, so it is a dampener like its supposed to be.

I would never replace the crank pulley on my car with a pulley not built as a dampener.

wstar

Can you elaborate on the above? The service manual doesn't really go into this sort of detail, although it does call the ring a "damper", when it says "Never put suitable puller tab on crankshaft pulley periphery, because this damages internal damper." (by which they mean, attach the puller to the insides of the pulley, not the outsides).

Wikipedia has this to say, although I wouldn't consider them very authoritative on the subject: Harmonic balancer - Wikipedia, the free encyclopedia.

Have people actually seen crankshaft failure from this sort of thing?

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Josh@STILLEN

As long as you are going with a reputable pulley manufacturer who understands how to build a perfectly balanced pulley, there have been zero problems. We've been producing pulleys for superchargers on down for years, and have never had a failure.

There are thousands and thousands of pulley sets being run on 350Z's, G35's, G37's and now 370Z with no problems at all. The factory crank pulley does NOT have a harmonic balancer, the engines are internally balanced.

Again, this is not the type of item you want to take a risk on ebay by just anyone who thinks they can cut a pulley, but have been a proven power-adding modification that provides great results.

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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Skorch

Quick question - have there been dyno results for the Stillen lightweight pulley? Not the underdrive, just the lightweight one. I'd appreciate the info or a link to the thread with it - I can't seem to find any.

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wstar

I believe RCZ has the light, non-underdrive pulley, but hasn't installed it yet.

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RCZ

Yes he does. He will get it installed soon. We ran into some difficulties and decided to leave it for another day.

wstar

Back on this subject of harmonic balancers and all that jazz, here's a better wiki link: Underdrive pulleys - Wikipedia, the free encyclopedia. To quote from the end of that article:

Again, it's wikipedia and with no citation, so take it for what it's worth.

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SOLISIMO

You two get a room

ssqpolo

i dont know about a nissan engine designer, but RCZ should have this puppy on soon, so time will tell if the mythcial harmonic balancer (or lack thereof) will rape this motor or not.