3SX or other non-OEM Custom Crank Pulley vibrations vs STOCK CRANK PULLEY smooth ???

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Originally Posted by BigTyla

Pretty much. Being more educated in vibration analyses has made me paranoid. :)

OEM pulleys sitting on a shelf should not be of any worry. Stored properly, a 10+ year-old pulley with the rubber ring would be just as good as one made within the last year.

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agreed. just know that "stored properly" would mean inside an airtight bag (or close to it) with a thin amount of lubricating oil as a preserver.

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Originally Posted by ProwlerGT

Frankly BigTyla... I'm surprised you got rid of yours. I guess expense finally caught up with ya.

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Not expenses. Three things:

1) The wife. :D
2) I was living in an apartment and working on my Master's degree, leaving me no tinker time.
3) I had a 350Z to fill the void.

Can't argue with my decision looking back. I do wish I would have been able to keep it though, especially after what the guy I sold it to did to it.

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Originally Posted by BigTyla

Not expenses. Three things:

1) The wife. :D
2) I was living in an apartment and working on my Master's degree, leaving me no tinker time.
3) I had a 350Z to fill the void.

Can't argue with my decision looking back. I do wish I would have been able to keep it though, especially after what the guy I sold it to did to it.

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Those are pretty damn good reasons. OUCH on the "I know what the next guy did to it". I don't think I'd want to know what someone did to my car after selling it, especially with all the labor of love and sentimental value it (mine or yours) has/had.

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Originally Posted by ProwlerGT

Those are pretty damn good reasons. OUCH on the "I know what the next guy did to it". I don't think I'd want to know what someone did to my car after selling it, especially with all the labor of love and sentimental value it (mine or yours) has/had.

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car's worth more to me on cinderblocks in my backyard than it would be 100% running and sold so some random dude.

I hope the people in this thread that justify using a solid crank pulley by saying... "the engines are balanced from the factory" take or read an engine vibrations book. The crank pulley is there to damp TORSIONAL vibrations in the crankshaft... IE the twisting back and forth caused by compression and combustion events. You tune the rubber thickness and material so that you can damp the natural torsional vibration frequency. In most 6 cylinder crankshafts its in the 1800-2500 RPM range. The exact range that most of our engines spend their time operating in... UH OH. But remember... any deviation from the natural torsional frequency is good... less amplitude... less stress. Only bad part is... none of us actually know the exact RPM location of the natural torsional frequency. A permanent marker and a strobe light and a good shaker rig would tell us. The vibrations at high RPM are of little to no consequence. If anyone has seen a frequency response curve of any dynamic system, they will know what I'm talking about.

I'll see if I can call in a favor in my spare time and have one of our crank dampers tested to see the rpm that they are calibrated for.

PS... I know these tid bits of knowledge because... I used to work in an engineering office that designed crankshaft dampers. Rubber and Viscous dampers.

Forged crankshafts of today are not as sensitive to the cast iron cranks of the past. However, I bet if you shot a crank with a Cobalt 60 source to do an "X ray" of the crankshaft then you would see some micro cracking on cranks that don't use the stock damper.


Just some food for thought fellas! The world of Vibrations is a bitch and a half sometimes.

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Originally Posted by VR4Drive92

I hope the people in this thread that justify using a solid crank pulley by saying... "the engines are balanced from the factory" take or read an engine vibrations book. The crank pulley is there to damp TORSIONAL vibrations in the crankshaft... IE the twisting back and forth caused by compression and combustion events. You tune the rubber thickness and material so that you can damp the natural torsional vibration frequency. In most 6 cylinder crankshafts its in the 1800-2500 RPM range. The exact range that most of our engines spend their time operating in... UH OH. But remember... any deviation from the natural torsional frequency is good... less amplitude... less stress. Only bad part is... none of us actually know the exact RPM location of the natural torsional frequency. A permanent marker and a strobe light and a good shaker rig would tell us. The vibrations at high RPM are of little to no consequence. If anyone has seen a frequency response curve of any dynamic system, they will know what I'm talking about.

I'll see if I can call in a favor in my spare time and have one of our crank dampers tested to see the rpm that they are calibrated for.

PS... I know these tid bits of knowledge because... I used to work in an engineering office that designed crankshaft dampers. Rubber and Viscous dampers.

Forged crankshafts of today are not as sensitive to the cast iron cranks of the past. However, I bet if you shot a crank with a Cobalt 60 source to do an "X ray" of the crankshaft then you would see some micro cracking on cranks that don't use the stock damper.


Just some food for thought fellas! The world of Vibrations is a bitch and a half sometimes.

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There's no doubt of the function of a damped pulley vs an undamped one. The balancing comments were from concerns of the decreased mass of the pulley independent of vibrational considerations.

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Originally Posted by BigTyla

There's no doubt of the function of a damped pulley vs an undamped one. The balancing comments were from concerns of the decreased mass of the pulley independent of vibrational considerations.

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But yes! There in lies the issue at hand. Swapping to a light weight flywheel and or light weight pistons changes your engines natural frequencies. A stock damper wasn't ever designed to deal with that. The lighter the stuff the higher the natural frequency RPM becomes. It shifts up.

It's the big catch 22. Which is where the love of fluid viscous dampers comes from. They can damp a broader range but the damp less than a rubber one. The rubber is tuned to a very small range but has exceedingly good damping characteristics!

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Originally Posted by VR4Drive92

But yes! There in lies the issue at hand. Swapping to a light weight flywheel and or light weight pistons changes your engines natural frequencies. A stock damper wasn't ever designed to deal with that. The lighter the stuff the higher the natural frequency RPM becomes. It shifts up.

It's the big catch 22. Which is where the love of fluid viscous dampers comes from. They can damp a broader range but the damp less than a rubber one. The rubber is tuned to a very small range but has exceedingly good damping characteristics!

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This is certainly true. Nevertheless, the rotating assembly is still internally balanced.

You're preaching to the choir here. :)

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Originally Posted by BigTyla

This is certainly true. Nevertheless, the rotating assembly is still internally balanced.

You're preaching to the choir here. :)

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It is balanced but remember... the balance of the motor has nothing to do with the torsion vibrations. They are created from the combustion events. Every engine has torsional vibrations. They can't be smoothed or balanced... merely damped.:D

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Originally Posted by VR4Drive92

It is balanced but remember... the balance of the motor has nothing to do with the torsion vibrations. They are created from the combustion events. Every engine has torsional vibrations. They can't be smoothed or balanced... merely damped.:D

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Again, preaching to the choir. :p