UD pulley Question

[19Cutlass94]

About the UD pulleys, Ive heard that by taking off the stock crank pulley and replacing it with the UD pulley, can be harmful. I just need someone to clear this up. ive heard it several times but everytime I search every forum, I dont quite get the answer Im looking for. So here we go:

Does the stock crank pulley ( well use the pulley from a '94 3100SFI since thats what I have for this example ) act as a damper? Now I know that crank pulley's and harmonic balancers are completely different. The fact that I have heard that this pulley does act as a damper, in which this case if you used a UD pulley, you would be hurting the engine. Since all the vibrations of the combustion chamber would transfer down to the crank etc etc. Now if the crank pulley, is just that a crank pulley and doesnt not act as a damper this will not hurt the enginer. But question? Is it? Or is it just simply a pulley? No matter how many times Ive searched, I could never find if this was just a pulley or a pulley/damper. I know its not a harmonic balancer.

Sorry to sound like a noob with this one.

[robby1870]

I'm pretty sure the stock pulleys have a rubber O-ring to help with vibration absorbtion and the UD ones don't. However, the UD has been around a while and I dont think anyone has had a problem yet. I know some people won't run them because of not having the O-ring, but that's a personal choice.

[napatiger]

mine works fine.

[jackal2000]

this has been debated for a while. 60* v6's are "internally balanced" so a dampner is not necessarily mandatory but yes it is worthwhile.

[CNCguy]

Yes this topic has been debated alot. All I will say is that manufacturers put them on there for a reason. Auto makers spend hundreds of millions of dollars finding ways to reduce weight/costs and would eliminate the harmonic dampner if it wasn't absolutely needed.

Do all of you naysayers really believe that automakers put them on engines at an additional expense for no reason when they are always trying to reduce costs and weight? I can't think of a single contemporary auto engine that doesn't have one... can you?

[torq455]

mine's been on for 2 years and about 15K miles. who knows what the automakers do for their reasons. they put the o-ring to help reduce vibration. the same reason some automakers use a timing belt instead of a chain. some figure the belt will help dampen some of the vibration--which it will to a point. kinda of the same principle when we lean out our A/F mixture and add more timing. they have a rep to protect so add a few buffers to help protect their products. food for thought

[sharkey]

a crank pulley, balancer, and damper are 3 different things.

-a crank pully is just that, something to run a belt off of to run accessories. this is what all the aftermarket underdrive pulleys are.
-damper- dampens the engine vibrations to stop them from causing damage.
-balancer- used on some externaly balanced engines. it is a damper with an offset weight to help with engine balancing.

just because an engine is internally or externally balanced doesnt mean it neeeds a damper or not. in fact, all 60 degree v6 engines, both internaly and externaly (pre 88 motors) balanced, use a neutrally balanced damper. there is no offset weight on them.

dampers are used on all oem engines. as stated, do you think an oem would put something on a car if they didnt need it??? with higher hp motors, engine builders often use high dollar dampers, mostly fluid dampers (these use fluid instead of rubber to dampen vibration). why do they use them??? because all engines produce vibrations. some vibrations you can feel, others you can only hear (harmonic vibrations). both can be very destructive.

use a damper.

[torq455]

so i take it you don't have one....

[discostu]

Don't forget that automakers offer up to 100,000 mile warranties on powertrains, so of course they are going to take extra precautions to make sure their oem will outlast that warranty period. Also, they have to take into account people who don't properly service their engines, or drive the hell out of them.
If you built a 300+hp 3400, would you expect it to last well over 100,000 miles?

Sharkey is right in that high powered engines use expensive dampers, but for the average joe engine builder, you could get away with it because you aren't producing that much power... An underdrive pulley could give you +5% power at the expense of -5% engine longevity. Everything in engine building is a tradeoff, somehow, somewhere.

Me personally? I'll take my +5% power... I'll more then likely tear down the engine before something grenades on me anyways... Sorry to be so long winded lol.

[gpse3400]

In school I was tought that the torsion damper aka harmonic dampener is there and it was explained well to me. My text books, hot rod magazines, even my own father states you hurt the engine by not running that. And no the serpentine belt dosen't act in the same way the elastomer in the the torsion dampener does, just because it's wound up to it. In fact it'll be harder on the accessories as the belt will trasfer the same actions .. Its not just the elastomer, its a combinnation of the the hub, the elastomer and the outer ring/ pulley. When the rod comes down on the power stroke, the crank deflects momentarilly. That gets tranfered to the flywheel, flexplate torque converter, and to the hub on the accessory side. Obviuosly one side is taken care as far as torsional vibrations. But the other side needs containment as well. When the crank deflects it will momentatriily increase speed and then decelerate. This rubber band occillation effect gets trasfered to the hub, were the elastomer and outer ring are pressed on. The hub starts to change speed, that gets trasfered to the elastomer, but because the outer ring is pressed on to the elastomer there is a momentary lag in the speed chang of the outer ring. This action then gets retransfered back down the hub which then contains a substantial part of the speed changes. This all of this happens in an fraction of a second, uncontained can cause crankshafts to sever, and main bearing failure. Now factory dampers supossedly have a speed where they really work well, but make no mistake they are always working. And the elastomer is more than just an o ring or a rubber band.

I acknowledge the fact that there are plenty of cars with this pulley on it but when they die I do expect to see cracks in the crank and flattend, beaten bearings.

My 3400 as of now has a huge operating range from just off idle to as high as 7000 rpm. My next rebuild I plan to wind it higher. Eitherway I will not be without some sort of torsional vibration protection. And even if I had an old 2.8, I wouldn't run it with out a dampener either. The Theory is too ingrained into me. I'll get my 5 extra hp with the next cold front blows in.

[Rhedalert]

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[97cutlas$upreme]

i put mine on about a year ago and the only problem it gave me was that it threw the SES light on but thats just because i forgot to transfer the crank trigger ring for the cps to read off of.. i changed the ring out already and no problem

[sharkey]

most people here wont care about engine life because they will rip their motors apart before they are worn out. but why build a motor and not expect it to last, or have to replace extra parts when you shouldnt have to??? all for mabey 5hp.

[torq455]

that's cool, but with 147K on my old 3.1, i'm not too worried about shot bearings. and i don't plan on keeping a 300 horse 3.1 together for 100K either. in other words....to each his own. and where the hell are we getting 5HP from??? did someone dyno their UD pulley?

[discostu]

I thought I saw a dyno graph somewhere that a UD pulley was good for almost 10 whp on a stock 3.1L at the top end...
That's about an 8% gain, assuming a stock engine puts out 120 whp...