mdp c230k

Buell, you musy not have read my links. The idea behind a damper is not to be light as you suggest, it uses its weight to counter the twist. Try reading the links and learn about where your misconceptions are. The comment I made about springs is obviously misunderstood, there might be small pieces of spring steel linking the two parts of the damper withing the rubber. One of the links mentions the possiblity.

Yes, there have been 3 failures of SCs with the ring, tell me what was available other than the ring until recently on our cars? Also, remember that there are hundreds of people that are not on this forum with the mod that are not included in your sample size. I wonder how many SCs fail without mods, it would be no surprise if 3 is not out of the ordinary.

Again, read the links as it address' all of your points and shows where you went wrong.

avlis

Please. Cut the thing in half and end this debate once and for all.

I'm sure you'll find that thing is a harmonic balancer for sure. The weight is isolated from the rest of the pulley regardless of whether it's electrically isolated or not. I've got some flexable material here to show you that isn't an insulator. Continutity test proves nothing. If the damper isn't a damper...then what is the rubber there for? What's the weight there for?

Buellwinkle

Avlis, I'm not cutting it in half because a) I don't have the means to cut it in half, b) you'll just find something else to prove I'm wrong.


Mdp c230k, the crankshaft twists as a result of the load on the crankshaft. The pistons fire and create downforce on the shaft, if the less the shaft can freely rotate, the more twisting is must absorb. The obvious load of course is propelling your car out the back end of the shaft. By introducing a heavy mass on the front end of the crank the twisting motion has nowhere to release so it creates a vibration. Reducing this mass reduces the twisting motion, how much is speculation but like I said, no failures to date. The opposite is also true, increasing this mass creates more twisting altering the natutal frequency, possibly beyond what the damper was designed for. One car has had the solid pulley for 80k miles according to Kleemann. As for s/c failures, Kleemann only made solid pulleys for the previous C230 sedans and SLK230s, no ring was available and that has been out for years, yet one of the s/c failures on an SLK used a factory pulley with a ring attached. I guess it's pick your poison, there always risk in modifying your car, I felt my risk was justified and reasonably safe or I wouldn't have done it. You must think the modification you are about to take is reasonably safe or you wouldn't do it. That's why there are choices.

avlis

Your wrong about me.:p I don't post here for the sake of proving you or other people wrong. I'm just looking for answers to questions that people keep guessing on. One guy above is basing fact on an assumption and, for some reason, that bothers me.

You could always send me a factory pulley and I'll have my machinist cut it, but surely there's got to be an easier way...

Buellwinkle

Avlis, that pulley costs $302 and I may need it someday. What other way would there be to prove that the metal damper ring is indeed pressed onto the the body of the pulley. Maybe someone else can donate their unused pulley after their upgrade.

If you look at the back of the pulley there is indeed about a 1/4" bead of rubber that fills that gap. On the other side of the ring it has a small lip that is pressed against the body of the pulley. There is no gap, at least one that you can stick a needle through. I could stick a needle through the rubber on the back side on the inside edge to prove that it won't come out the other side. I can use a drill to drive the needle in.

20FHK02

Whether the pulley is press fit or spring loaded, it is just a methodology to put the outer piece (gray) onto the shaft piece (green) of the pulley. The fact is that there is the rubber filling (red) in between to reduce vibration of the shaft.

The 2nd link from mdp c230k's post has a graph (I name it Graph 1) comparing the vibration noises between a conventional pulley and a pulley with a damper. The pulley that contains a damper reduces the noise level significantly.

For a perfectly balanced pulley with no external force, there is no inertial vibration. However, there is force from the crank rods and the belts that will result in torsional vibration. Whether the pulley exists or not, the forces are always there and cannot be eliminated.

But the pulley is mandatory in order to drive the belts, and the forces will result in imbalanced loads on the pulley. The loads are magnified by the weight of the pulley and the rotational speed. The heavier the pulley, the higher the induced imbalanced load; the higher the rotational speed, the larger magnitude of the load (as seen on Graph 1).

So one concern in a pulley design is to reduce any additional loads created by the pulley. The goal is to "reduce" that addtional loads, not to "eliminate", because there cannot be a weightless pulley.

The rotational speed cannot be changed, so the only modification can be made or to play with the weight. For a factory designed heavy pulley, the weight is significant. This, in turn, yields the idea of a damper. The damper is to mitigate the weight effect (i.e., torsional vibration force) created by the pulley, but not to eliminate.

A super light-weight pulley with a damper is the perfect design, so the additional loads can be reduced to the minimum. But there is always the role of manufacturing cost, and this results in a heavy factory pulley with a damper.

Regardless of whether it is induced by a damped heavy pulley or a light-weight aftermarket pulley, a load is a load, and the shaft cannot determine where the load is from.

On one hand, you have the factory pulley with a damper, on the other hand, you have the after-market light-weight pulley with no damper. This is like remove conservatism on one aspect but add conservatism on the other aspect. The end result is two comparable designs. And the engine is already designed to handle that slight induced additional load by the pulley.

20FHK02

Opps... I forgot to attach my diagram.

Buellwinkle

I'm going to attempt to describe it because your drawing is all wrong. Picture a solid steel pulley, there is nothing between the hole in the center and the belt but solid steel. Now add a steel ring on the back that is pressed on and has a gap between it and the pulley that is filled with rubber. Also as you described the forced of the belt on one pulley plane, the other pulley plane has an opposite pull. Here's my convoluted drawing in MS Paint. Notice the Red part is a cross section of the damper and green part is the goo in between. The section where the red overlays the black is where it's pressed on.

20FHK02

Thanks Buell for the correction on the pulley for the Coupe.
What my diagram shows is just a representative setup, which is modified from the pulley picture showing in mdp c230k's link to show what it would look like if that pulley is a press fit.

20FHK02

And, for the counter pulling belt forces, note that the moment arms for the two forces are different. So unless the design engineers precisely calculate the required tensions for the two belts such that the moments induced by the two forces perfectly balanced each other, there will be a net pulling force.

My diagram shows a typical net pulling force to show the theory only. It is not intended to accuratly represent the specific pulley design for the Coupe.

Buellwinkle

The pulley is pulling belts attached to about 10 other pulleys (I include idler and tensioner pulleys as part of that). Each of these pulleys as well as the belts themselves must introduce vibrations of their own. Don't these vibrations transfer to the crankshaft?

20FHK02

Yes they do creat vibrations. But they are more of a concern to the attached engine block, alternator mounting bolts, etc. rather than the crackshaft itself. The engine block absorbs most of those vibrations before they are transferred to the crankshaft.

And, the governing force will be the one from the crank rods (this is the force being converted to drive the vehicle). I put the belt force just as an indication that there is some force from the belts, but not saying it is huge. (Note that Graph 1 does not even consider the belt force.)

avlis

Nice diagram Buell. What you drew is a harmonic balancer. But you still say it doesn't exist? Now I'm confused

Minor correction: I don't think the damper is pressed on. Instead, it's a close tolerance slip fit. This allows the damper to oscillate slightly yet is still retained radially. The slip fit also explains the continuity test. The pieces are actually touching, but are free to move relative to one another.

Buellwinkle

Aha, acknowledgement that they are in contact with each other. Baby steps. Now if we can get acknowledgement that altering the weight of the pulley, lighter or heavier alters the crankshaft's torsional twisting frequency or amplitude. Or in other words a heavier pulley (as in a factory pulley with a ring on it) would cause it to twist more and a lighter one would twist less (assuming the same damper or lack thereof). Also that the farther off center the weight addition is the more like it is to twist as centrifical forces come into play.

vadim

Well, let's hope my experience will settle this dispute.

I was instaling my ASP pulley yesterday (which I'll describe in a separate thread, a lot to be said about it). After the belts and the bolt were removed, the pulley wouldn't move when I tried to do it by hand, so I had to pry it off. In so doing, I could clearly see that the balancing ring moved with respect to the pulley body. This confirms that the balancing ring is connected to the pulley body by a rubber ring. This actually can be seen in the picture attached below.

This harmonic balancer acts as a rotational shock absorber. The diagrams shown in previous posts don't take into account rotational oscilations, but that's what this balancer is supposed to dampen.

eason

I can't wait for your post about the ASP pulley. Are you the first one in this forum installed this pulley besides Buellwinkle?

mdp c230k

Buellwinkle, I TOLD YOU SO! Now that you can see the rubber seperation maybe you can admit defeat. I knew there was no way for the thing to be one solid piece and function as a harmonic damper. Maybe you will now understand the importance of the damper in the system. I await a response to explain how your pulley is different than all the others.

Buellwinkle

I looked at mine again and it's touching. It could be a matter of tolerences. Yes, I admit defeat after seeing the picture.

Still doesn't answer the question of adding a ring to make it larger and it's affects on changing the natural frequency. And still doesn't prove that removing it has any ill side effects because nobody has had a crank or bearing failure in 5 years with the Kleeman alloy pulleys.

20FHK02

i agree! there is still some vibration on the damped factory pulley, and the damper only works at the design frequency. when the frequency is too low the damper ring simply oscillates in phase with the pulley which makes the matter worse. the load from a light-weight alloy is so subtle that the engine is capable of handling it.

plus, i'm not going to keep the car for 20 years to worry about that real long term effect (does anyone?). so if a Kleemann alloy pulley doesn't fail in 5 years, that's pretty much the length i'm gonna keep the car.

mdp c230k

The resonance of the damper ring would not change with the addition of a pulley ring, they are not attached. The added ring will not change the balance of the crankshaft as it is centered around the rotational axis. The only way to change the resonant freq of the damper ring would be to change its mass which a pulley ring does not. One of the links I posted goes through all the problems with changing the crank pulley, why take a chance if you don't have to? Someone here posted that there was much more wear on the bearings at the front of his engine with the pulley installed after 50k+ miles. No failures yet, but how about decreased engine life compared to stock? There is also a chance that the rubber used to isolate the damper is impregnated with something conductive to prevent static build up. This would explain the conductivity test results. At any rate, I'm going to use the ring and maintain factory damper.

Buellwinkle

Exactly, if you are going to mod your car for max ponies then don't plan on keeping it forever. I usually keep them 4-5 year or about 65K miles for good resale value.