It's similiar in concept to tire/wheel balancing -- idea is to make sure the spinning pulley doesn't wobble a little bit and cause some small oscillations on the crank shaft. On the Z - it's a custom tuning of the pulley and the shaft. On the tires - little weights are added to make it all work right, amount of weights are customized for each tire.

Those small oscillations if not controlled properly can cause "harmonic resonance" which progressively adds wobble energy to the shaft and causes bigger issues.

UDs aren't dynamically balanced for the crank shaft on your car - ones that come from the factory are matched/tuned for it (specifically).

Hopefully I've explained this correctly??? Anyone else???



Post Edited (Feb 6, 2:58pm)

 

WHOA!!!!! UR SAYING PULLEYS ARE NOT INTERCHANGEABLE AMONG Z's???

that is a new one on me... I would've never imagined such a high grade of uniqueness....

so could you please just explain a little more on the "harmonic resonance"?

I see the whole picture, but its just that I like to know the details... you never know when you'll need all this info =D

 

Actually a better way to explain it is like this. Picture the crank shaft as being made of rubber. The firing of each cylinder tries to push that particular crank throw around. The crank throw then stretches a small amount on the initial force and then springs back. This event occurs every time a cylinder fires. This is a normal and not destructive under normal use. The problem is that any primary or secondary imbalances tend to create a wave like effect through the crank. Some are twisting forces and some are longitudinal and others are more horizontal in nature. At certain RPMs and loads these effects are additive and others are negative. The resulting force, if not held in check, can cause sufficient stresses on the crank and bearing assemblies to cause failure or premature wear. Here enters the harmonic balancer. The way it works is like a counter spring in order to dampen these vibrations. When engine designers create an engine they, through calculation and measurement, determent what the "harmonic frequency" of the rotating assembly is. They then determine what mass and elastimer (springy thing) is needed in order to either avoid the harmonic or move the harmonic to a more desirable frequency. Ideally one that is outside the normal operating RPM range. The stock balancer has mass. It's heavy for a reason. It also has a rubber isolator between the pulley surfaces and the center section (the part that bolts onto the crank). This mass and isolation is what was determined to be needed in order to dampen any effects of the crank and accessories that are belt driven.

Here's the good news... The VG30DE/TT engine is fully counter balanced and is a 60 degree V6. What this means is that most of the primary harmonics and many of the secondary harmonics are either non existent or are so small as to not constitute any long term issues. At least that's the reasoning behind using the lighter solid UD pulley assembly. Is it true that it's not needed? Well not from Nissans point of view. Lets face it. If Nissan could have made the front pulley assembly cheaper to produce and lighter (less rotational mass) then why would they have not done so. The answer is the warranty on the engine and the conservative nature of Nissan's history on engine design. They still felt that the harmonic balancer would benefit the engine in the long term.

It's really your decision as to if you think it's worth it. If you lower the mass and gain some HP. You can do it on the crank nose or the flywheel. Either one will do the same from a performance stand point. One will effect the harmonics while the other will do so to a lesser extent. Will it cause engine damage? Only time can tell to what extent Nissan was "overly conservative".



Post Edited (Feb 6, 7:04pm)

 

No Subject

Post Edited (May 18, 6:58pm)

 

gee guys! thanx a million... you know those articles should go to some reference section... I mean now... I can say there is no doubt about it... thanx a million for taking the time to educate me on that matter... really appreciate it

 

Isn't like the blood vessels in your body vibrate @ like 7hz or so and if soundwave at that frequency are at a loud enough level it actually causes them to rupture. German scientist experimented with that during WWII. Thats kinda like what would happen to the engine if the harmonics weren't right. It would rupture.

 

JT240Z = THE MAN!

 

http://en.wikipedia.org/wiki/Torsional_vibration

and no, NO engine, no matter how well balanced it is (balance has nothing to do with tortional vibration), is immune from torsional vibration. It is the most deadly thing to an engine with the exception of oil starvation. Removal of a fluid based damper in exchange to a solid pulley style can increase vibrations through the crankshaft by up to 4 times their prior strength.

 

alright red_october.... the floor is yours and the spotlight is on you....

explain what you just said plz =D

"Removal of a fluid based damper in exchange to a solid pulley style can increase vibrations through the crankshaft by up to 4 times their prior strength"

 

you have harmonic resonance in the crankshaft when you perform a combustion cycle. this occurs in all piston driven engines. This resonance is a sound wave with what is called an amplitude. The dampener "muffles" this wave by absorbing energy cutting the amplitude of the wave (strength).

 

Actually "torsional vibration" is minimized in the VG design by virtue of the fully counter balanced crank (each crank throw has it's own pair of counter balancers) design and more importantly the even fire 60 degree V6 block design. This makes the crank a very stout piece with fewer primary and secondary harmonic components in the firing order. This doesn't eliminate the harmonic effects entirely, but it does reduces the number of variables and their effects.

Agreed with Red in that there is no way to "eliminate" the torsional effects. You can suppress them to some extent and you can change the harmonic frequency, but you can never eliminate it completely. Even the stock balancer does not eliminate all of the harmonics as there is still a primary harmonic along with a 2nd, 3rd 4th... order harmonic component as well. As I said in my earlier post... The choice is yours, but do understand that there are side effects to the elimination of the balancer. Will it cause you a problems in the short run? Probably not. Will you be able to "feel" the difference? Also probably not, but the fact still remains that you've eliminated one of the features that Nissan engineered into the design of the VG and the long term effects may still be there. If you planned on keeping your car for the next 100K miles, then you may consider not adding a solid balancer for an added safety measure. Also keep in mind that as you add HP and Torque, you're adding additional stresses on the same components (crank and bearings). Is saving 5 to 10hp really worth it? On an NA, maybe, but on a TT there are just too many other ways to make up for the difference. You want to lighten the rotating assembly? Then I'd use the lighter flywheel 1st.

So many people argue the point "It hasn't caused a problem on my car, so it must be OK". That's like saying "I can't see, hear or feel the carbon monoxide in the air, so it must not be there". The fact is, it can still be a killer even if you don't see it, feel it or hear it.

 

I disagree with your claim that the design of the engine being a 60V6 removes the torsional vibration effect. I still affirm that the balance of the engine has an insignificant effect on the tortional vibration of an engine. The vibrations are caused by the explosions occuring.

 

I agree with red, that no matter what design if it combusts in a cylindrical unit that when it is changed to rotational mass that it is impossible to remove the resonance. Question though - Does a rotory motor not have a harmonic balancer ?

 

I say u get AMZ/ATI harmonic race damper

-93 2+2 RIP
-92 2+2 tt

 

"What happens if there is no harmonic balancer and your crank is close to out of spec for balance? Then given the right conditions (load, RPM's, piston weight differences) you put much more wear on the crank and journals - but only at those conditions. Harmonic resonance is the formation of a standing wave but it would only happen at steady state conditions, meaning for our car; if everything is just right to make harmonic resonance happen then you will be putting a much greater strain on the crank if you held it at those same RPM's."


What happens is the engine comes apart. Catastrophic engine failure. The motor in a semi is close to 13 liters in displacement. The motor is stout, makes an abundance of power...but the tolerances are nowhere as close as a VG's. The most common cause of death for the big diesels is overrevving. They have enough power and torque to change the rotation of the earth, but overrev them once and they shatter like glass.

 

No Subject

Post Edited (May 18, 8:13pm)

 

Let me correct my previous statement. I did say that "torsional vibration is minimized in the VG design". What I ment was simply this. In addition to common rotating couples of varying magnitudes (torsional vibration) there are other vector components associated with additional primary and secondary harmonics by design. I did not say that it can ever be eliminated. The reason that the 60 degree V6 design "helps" (as opposed to say a 90 degree V6) has to do with those additional primary and secondary harmonics, the associated couples and the additive nature associated with them rotating couples. Any 4 cycle 6 cylinder design that can have its primary and secondary couples eliminated must fall into one of 4 designs.

1: The inline 6 with one throw per cylinder and an associated counter balance at each throw

2: The 180 degree "V6" with 6 throws and no counter balance

3: The 120 degree V6 with a 3 throw crank shaft and 2 rods per crank journal

4: The 60 degree V6 with 6 throws and associated counter balances. (VG design)

All other V6 designs will not only have common harmonic issues will also have additional issues related to

We're arguing a moot point here. Simply stated, the VG design tries to minimize harmonic effects, but CAN'T eliminate them entirely. The balancer only helps to minimize the issues, but CAN'T eliminate them either. Removing the balancer will only hurt the final product in terms of balance and associated harmonics that are the main cause of engine damage not related to oil starvation.

What I've been saying over and over is just this... If you feel like it's worth the risk of not using the stock balancer, then go ahead. I personally wouldn't, but if you feel like you want to shorten the life of your engine, then go ahead. Just make sure you understand that it's not without risk and is not good practice by design. You ARE risking your engine in the process and anyone who doesn't see this is being blind or ignorant.

 

No Subject

Post Edited (May 18, 6:58pm)

 

Yikes, that is no bueno

 

sounds like what you are saying is that the VG engine reduces rotational vibration (balance) due to its design, but has no effect on torsional vibration.

 

Exactly. Rotational balance and torsional balance issues can be additive. One can be reduced or even eliminated, while the other has no direct way of being counter acted from a balance standpoint. The VG design minimizes those interactions but the truth off the matter is it can not eliminate them altogether.