Jeff,

There's so much more to it than that. You have to consider the fact that the crank goes through harmonic variations depending on load and rpm. The OEM crank pulley is tuned to fight the damaging harmonics. The flywheel or torque converter do much the same thing, but that end of the motor is also connected to the transmisson, directly or through fluid. There's all sorts of other dampening going on just "south" of the flywheel or TC. I'm not saying the connection to the driveshaft is helping quell crank harmonics on the flywheel end of motor, but the tranny does help things.

The overall math and concept is very complex. Proof of that can be seen in that crank pulley. All VQ pulley's have dimples on the engine facing side. That removed material serve as a counterweight for the crank. Sure, it's jsut a few grams of removed material, but the Nissan engineers saw fit to do it.

Finally, and I've said this numerous times, if someone says it's okay to remove the OEM pulley and add a non-damper pulley because the motor is "internally balanced", put your hands over your ears because whatever else they say is BS and they haven't a clue about what they're talking about. Yes, most every motor is interally balanced. Spin it with no load (ie the motor not running) and it's fine. Add some explosions to the pistons and that crank has to endure some pretty severe loads and harmonics. That's where the dampers come into play.

 

Well, we certainly got the nerds in here.

Jeff have you ever even driven a car with a lightweight flywheel?

They don't shake like you're letting on. Only under load at low RPMs in higher gears do they do that.

 

I had a fidanza on my maxima. But oem was a single mass also.

Dave. Read what the article says the dual mass unit's function is. And note the vibrations that people report after going to a single mass.

If you can actuall feel the chatter etc.. then that has to me way more vibrations than anything a light pulley would introduce. Then there's the vibrations you can't feel.

If you want to be specific, the DMF units are described as reducing driveline shock. Which is down stream of the engine. But I highly doubt vibrations travel only 1 way. I'll ask you the same question. How is a little rubber ring cancelling out less vibrations than the springs in the DMF unit? Especially when the diameters and total weight in question are very big relative to each other?

There's someone else that gave a very good description of the "merits" of eliminating the DMF units.

The only thing connecting the manual tranny to the engine is the case bolts and the pressure plate/clutch friction material.

 

I suppose that input from a manufacture is relevant to this discussion and I think that the information I can provide will assist in the understanding of this topic. To begin, it is important to understand that the flywheel's primary purpose is the transmittance of power from the motor to the transmission and thus the drive-shaft, differential and axels (on a rear wheel drive vehicle specifically). For decades the majority of manufactures used single-mass flywheels without question and even to this day a number of cars still do.

The recent (predominantly during the last decade) onslaught of dual-mass flywheels coincides with several factors. These include but are not limited too: Increased vehicle weight and the need for greater inertia to induce movement from a stop, a greater desire for more refinement and the subsequent negative perception of gear noise (a.k.a. clatter not chatter--this term is often misused and misunderstood) which is associated with the use of non-dampened flywheels, believed improvements in fuel economy (I have used a number of single and dual-mass flywheels and have never personally noticed any reduction in said fuel economy when using a lightened flywheel), and finally dampened clutch engagement and improved drivability in low RPM usage.

Initially, the above functionality was relegated to a clutch discs that used sprung hub carriers. With the advent of the dual-mass flywheel the majority of manufactures moved to rigid hub carriers with the exception of certain luxury brands which produce high power/high refinement vehicles (two that come to mind are the Porsche 911TT and the Audi S4).

I guess that this is enough of the history lesson…let’s move on the discussion at hand.
In light of the above information I assume that you now have a better understanding of the intent associated with the use of a dual-mass flywheel. But I am sure you are curious about how this relates to balance and harmonics and ultimately how this compares to the impact of a crank pulley.

DaveB seems to espouse that internally balanced motors really aren’t internally balanced…and that this inherent lack of balance is actually countered by a dual mass-flywheel and the vehicle crank-pulley. It is important to understand that balance, or lack there of, will be amplified as RPM’s increase (there is also a relationship between the imbalance and its proximity to the centerline of the rotating assembly as well but this is not mentioned so I will not address it in this discussion).

The most telling part of the Dave’s postulation relates to his reference to the dimples on the back of the crank pulley. If taken at face value these dimples could be perceived as counter-balance weights like those found on the flywheels used in Ford’s 5.0L motors and GM’s 5.7L LT1 motors. In reality the dimples are not intended for counter balancing…but rather are evidence of material removed during manufacturing to attain a 0-balance weighting for the part (in vehicle that are 0-balanced). As with any rotating component weight can be added or removed relative to the parts intended use and needed balancing (This is similar to having a wheel and tire balanced and it is done due to an outage in the parts when initially manufactured or as a result of the combined outage achieved in mounting the tire on the wheel).

In the case of the pulley and the flywheel there is no need for modified external weighting unless this is intended to offset an intentional externally dependent balance as in the aforementioned Ford and GM motors. If you are interested in checking this theory you can have a pulley or flywheel (intended for use on an internally balance motor) spun on a dynamic balancer. There will be an acceptable balance tolerance for each part determined by the manufacture. Outage is measured in oz-in/radius (this is how the location of the outage, relative to the assemblies center line, comes into play—I alluded to this previously). There are often bushings or cushion dampeners used in tandum with the pully to aid in reducing harmonics. These are generally rubberized, and a number of you have alluded to this already. I do not manufacture pulley's but I don't know why a rubberized dampener couldn't be built into an aftermarket pulley.

In preparation for Dave’s likely response I would like to provide further information relative to flywheels and the clatter that results from the replacement of a dual-mass flywheel with a single-mass unit. The sound actually originates in the transmission and not the motor. Clatter, which is also known as gear noise (it is called this for a reason), is dependent on the internal tolerances of the transmission used. Weaker tolerances and today’s more eco friendly petroleum distillates, specifically in this instance gear oils (as well as the use of lower viscosity fluids intended to further improve gas mileage) are what lead to the need for better dampening. Previously I mentioned the use of sprung hub discs for dampening, and though this is a great way to reduce the harshness of clutch engagement it cannot eliminate gear noise.

I hope this information helps. If you all have any questions or need further explanation please let me know. Thanks!

P.S. I am sure that you all realize that there is a difference between dampening and balancing. I took this for granted in the above post.

P.S.S Dave i only used your examples because they were already available in this thread...no harm intended! I am not trying to single you out...you simply provided the most complete support for your stance.

 

I agree, the drill marks on the oem pulley is to balance the unit itself and not to the crank. On the subject of sold/sprung clutch discs.

Seems both the oem and aftermarket are using sprung discs (at least for their oem/basic upgrade) So Nissan is using the DMFand sprung discs.

 

Jeff, you are correct...in providing the info in my last post I neglected to mention that the Z/G used the sprung hub as well. Nice catch regarding info! Let me know if you need anything else. Thanks!

 

I also noticed that you contend that the DMF units are designed to reduce the shock from the driveline (aka transmission) and not necessarily the engine. Now whether this is true or not, my original point still stands. Everone going with a SMF will have to contend with more vibrations regardless of the source. And since we are discussing engine vibrations, one has to assume that eliminating the DMF feature on the G or Z will result in more vibrations in the engine.

And my contention is that more vibrations resulting in the DMF elimination is much more than what an OEM pulley elimination would cause. Especially considering the weight being removed, the type of dampening being removed and the greater diameter of the flywheel vs a pulley

 

I think that the presense of resonance, associated with the elimination of the dual-mass flywheel, clearly indicates that the flywheel is less dampened...this is logical...expected...and it isn't contrary to my above post. My point of explanation was to clarify where the sound originated and to provide info relative to the cause and affect relationship that leads to this. It seemed that there was some confusion and subsequent lumping of lightened components into a "bad" category...which is unjustified.

There is also a line of thinking that fully believes that the lightening if components will cause less stress on the drivetrain. As long as there is no change in the balance associated with the ligntened parts then there should be no negative impact on the assembly.

But remember, there will always be a tradeoff when changing parts on any vehicle. To keep this discussion in the realm of dampening and vibration, look at the increased vibration associated with the fitting of stiffer motor or transmission mounts. Yes, with stiffer mounts the motor and trans are better able to transfer power but they are also less dampened and as a result the car will have more vibration. Keep in mind that a number of the concessions made relative to vibration and resonance are made to improve the perceived quality of the vehicle (we could follow this rabbit hole to China if we wanted too...) not as a result of any detriment associated with the use of lighter components.

 

I understand completely. But my original argument is that people are rating lightweight pullies as "dangerous" while lightweight SMF upgrades are not.

I only contended that it's either both are "dangerous" or both aren't. I believe you put these two into the same relative category. Which as do I.

 

Perhaps you felt as though my response was a rebuttle to your's...though I mentioned DaveB in the post (again this was relative to his well presented argument and clear adherence to what he believes to be the truth)...I am sorry if this is the case. I think that you and Dave present logical arguments...if anything I would say that I expected him to respond as my statements were contrary to his perspective. Again, no harm no foul!

 

So to cut to the chase; is a lightweight flywheel damaging to the engine or transmission in any way?

 

To make this as clear as I possibly can...a properly manufactured, balanced and installed lightweight flywheel should not have any negative affect. I am certain that my posts above will provide evidence of this and I hope that this response helps those of you that may not have read or understood what I hoped was clear in my initial post. Let me know if you need anything else. Thanks!

 

Oh, so now you change your story??? Is that how you do it?

I could have sworn you were trying to argue the other way around, that lightweight pulleys are bad, but lightweight single mass flywheels are worse becaust they introduce more vibrations...

 

No.

Look what happens when you swear?

This is my contention right from the beginning.

If further clarfication is needed, here it is.

People that are questioning the safety of pullies aren't questioning the safety of lightweight flywheels. If they aren't, they should be. Or they should say BOTH pose risks or BOTH pose no additional risks. NOT one is bad while the other isn't.

If you read Spec-01's replies, he implies if both are individually balanced, both introduce no more or less risk than their OEM counterparts.

 

Both are individually balanced for different reasons... you've been trying to argue that a lightened flywheel is worse on the motor than a lightened pulley. You've been trying to argue that a rubber strip around the pulley isn't enough to dampen the vibrations. I've been trying to tell you that dampening the motor's vibrations are the pulley's job, not the flywheel, so it won't matter if the flywheel is lightened.

I just love how you changed your views and stance and is now making a completely different arguement!..