Aasco flywheel is here.

[sb01box]

Originally Posted by JAAY

The sprung clutch just absorbs some of the initial shock but does nothing for the harmonics from my understanding. I am putting a stock flywheel back in. I just put the 3.4 in and do not want to chance something as stupid as a flywheel messing the whole thing up.

I've read somewhere where a secondary counter rotating shaft with weight is use to counter harmonics forstraight 4 cylinder engines - patented by Mitsubishi??? but these were basically directly driven via chain. is my understanding that DMFW has some sort of spring/elastomer coupling the two disks.

Question, with direct coupling, is the harmonics cancellation accomplished independent of engine rpm.
Question, with spring between the two, taking out harmonics from 700 rpm to 7000 rpm, 10x range would need spring to become 10x stronger??

I may have found answer to question here

http://www.exedyusa.com/multimedia/specsheets/ClutchFundamentals.pdf

RMS leaks are becoming VERY rare.

[jaykay]

this is good news but this is 2000 S 3.2 with only 18k miles on it I am talking about so it has not had enough running time to know

[Cartel]

My Aasco lwfw arrives tomorrow morning. I alongside my crankshaft are looking forward to it!

[jaykay]

hmmmm so you think it will keep it safe as per my original post?

[greggp]

I stumbled across this and read with great interest ...and also cringed at this misinformation mixed with correct information. I've spent 10y years of my life training people how to use balancing machines, and have been called into many facilities to balance something when no one else could do it. I have also spent another 8 years in the field of vibration analysis.

**) Balance has nothing to do with the total mass of the object, so a lighter flywheel does not change the balance of the the assembly. Unbalance is measured as mass x radius. There is no such thing as "zero balance". Zero balance only means "my balancer isn't accurate enough to measure this".
**) unbalance ALWAYS takes place at the same frequency as the speed of the rotating shaft ...no matter what speed the shaft is spinning.
**) Harmonics always take place at direct integer multiples of the shaft running speed (2x, 3x, 4x etc ...never 1.23x).
**) Unbalance can causes harmonics, but can never cure harmonics.
**) Assuming the shaft is rigid ...and it is safe to say all crankshafts are, (even though I know of 2 that were not), any Unbalance in the crank flywheel assembly can be corrected in two planes, but is best corrected on the crank, then add each component and balance that item in the same balance plane. This is the preferred way ONLY because it allows parts to be replaced without needed disassembly of the entire engine to re-balance it.

Given those statements of fact, a lighter flywheel will NOT change the balance of the system regardless of how much it is overhung away from the rear Bearing. RMS leaks are probably caused by bearing clearance issues and seal design issues, and can not be cured or made worse by any type of flywheel. A lighter flywheel will always make for a quicker reving engine, but some mass is desired to smooth out the pulses of the engine and more importantly to retain enough inertia to make starting from a dead stop easier. The heavier the flywheel, the more accurately it must be placed on the crank. If you mount a light weight and a regular flywheel that both have theoretically zero unbalance, the flywheel and pressureplate that weights 20 lbs and mounted to a flywheel with .0010" of clearance, would have half the residual unbalance as a 40 lb flywheel & pressureplate that have .0010" of clearance!

Now onto harmonic dampers. These are designed to reduce torsional vibrations. A person needs either 2 rotational accelerometers or 2 Polytec torsional vibrometers to measure these vibrations. While it can be done with one unit, it requires certain assumptions to be made. It can NOT be done with a regular accelerometer.
Piston movement turns the crank because the crank's rod journal is off the crank's centerline. The crank's rod journal acts as a lever arm attached to a shaft. The piston and rod push down on the lever arm, which rotates the shaft. That force is resisted by the entire weight and inertia of the car, which the driveline is attempting to push forward. It is impossible to create a perfectly rigid crank, so some of the energy from the piston bends the lever arm and twists the crankshaft.
When the force is reduced enough for the crank to spring back, it doesn't just return to its original shape immediately. Instead, the force of untwisting causes it to shoot past its original shape and twist in the opposite direction. This twisting goes back and forth a number of times until the crank settles down. The number of times this event takes place and its duration depends on the crank's construction (cast, forged, billet), mass, and quality of materials. When the engine moves through its rpm range, the speed at which the power pulses from ignition of the air/fuel mixture will eventually match the natural frequency of the crankshaft. When this happens, the vibrations moving through the crank will build upon each other and gain strength, often with damaging results. Running an engine without protection from these vibrations can cause flexplate or flywheel failure, loosened bolts, broken timing chains, along with erratic timing and valvetrain functions. The crankshaft will fatigue and eventually fail, usually at the snout. The purpose of the harmonic damper is to protect the engine from these damaging vibrations. Most quality harmonic damper designs reduce the vibrations traveling up and down the crankshaft by absorbing the vibrations and converting them to heat energy. Many racers use the words "balancer" and "damper" interchangeably, but since almost all engines are internally balanced, "damper" is the more accurate term.

There is a good reason that the damper is normally attached to the front of the crankshaft. The flywheel and the resistance provided by the rear wheels absorb crankshaft harmonic vibrations at the back of the crank. So if you run an engine without a damper, the crank will show greater twist the farther you get from the flywheel. Since the timing chain is normally at the front of the crank, running without a damper (or even with a poor-quality, inefficient one) reduces crankshaft life, but also causes the ignition and valvetrain to behave erratically. OEM manufacturers have started to place the damper in the flywheel to quiet transmission gear noise. As manufacturers have moved from very strong billet or forged cranks to sintered metal cranks, they are more susceptible to stress cracking due to torsional loads. Sintered metal is less expensive to produce, but the drawback is they break much easier. The harmonic damper (on the nose of the crank or built into the flywheel are both little more than a heavy rotating mass coupled to the crank by a rubber gasket with a specific damping frequency and with a very low Q. As the flywheel ages that rubber deteriorates and the frequency will change as will the Q. Eventually it will be damping the wrong frequencies and will become so compliant that it will break. This is the reason for not reusing a old dual mass flywheel. Unfortunately they are quite expensive, and the stock units are darn heavy and are not well suited to quick reving engines.

If you have made it to this point, you probably now know more that you really ever wanted to know about harmonic dampers, harmonics, and unbalance, (and according to ISO and ANSI it is UNbalance not IMbalance despite the high number of people in the industry that don't know the difference and even dictionaries that get it wrong).

-Gregg

[greggp]

Answers to Sb01box

"The sprung clutch just absorbs some of the initial shock but does nothing for the harmonics" 100% true statement. The sprung clutch helps reduce the shock of clutch engagement from being transferred to the gearbox. A dual mass flywheel makes the sprung clutch redundant. Never use a sprung clutch with a dual mass flywheel and don't use an unsprung clutch with a single mass flywheel.

"I've read somewhere where a secondary counter rotating shaft with weight is use to counter harmonics for straight 4 cylinder engines - patented by Mitsubishi??? but these were basically directly driven via chain." There is inherent unbalance that takes place at 2x the RPM of the crank rpm based on the weight of the rod ends attached to the crank in in-line 4 cylinder engines (not horizontally opposed engines nor V6 or V8 engines ...they have different issues). These 4 cyl engines use the timing chain to also spin two shafts that are intentionally out of balance ...and they spin it at 2x the crank RPM and a little above the centerline of the crank. This unbalance directly offsets the mechanical unbalance that takes place due to the positions of the 4 crank journals.

"is my understanding that DMFW has some sort of spring/elastomer coupling the two disks." Answer: Yes, and that is what acts as the damper or the shock absorber. The elastomer is positioned so it doesn't just allow the outside weighted ring to just bounce unrestrained like a spring, but rather it must overcome some friction like a shock absorber being expanded and compressed. It is less like a spring and more like a shock.

"Question, with direct coupling, is the harmonics cancellation accomplished independent of engine rpm." Answer: with direct coupling there is no harmonics cancellation, regardless of engine rpm.

"Question, with spring between the two, taking out harmonics from 700 rpm to 7000 rpm, 10x range would need spring to become 10x stronger??" No the harmonics are not due to the rotating mass or the RPM of the engine, but rather due to the power generated by each explosion of the firing cycle of the engine. While this does changes in force at different rpms, the damper is "tuned" to do the most damping at the specific frequency that the crank needs the most assistance. (if you ever saw the video of the tacoma narrows bridge, you have seen an example of something reasonably rigid that needed assistance at a specific frequency. Tuning of the harmonic damper is done by adding or subtracting mass from the outside rotating mass or by adding stiffness to removing stiffness from the elastomer ...In both cases this must be done equally 180 degrees opposite each other and with the same amount of weight (or elastomer stiffeners) or unbalance will be added to the crank assembly.

-Gregg

[stephen wilson]

Thanks for the detailed description. I remember harmonics being very interesting in my Physics class experiments. I noticed right away how soft gear-changes were when I bought the Boxster, due to the DMFW, You don't get that tire-chirping jolt with a hard shift.

[insite]

let's see, horizontally opposed engine with a SEVEN bearing main......and a LWF is gonna break the crank? please.....

if GT3's are breaking cranks, me thinks there is another issue. this occurs when the harmonics flex the crank back & forth until it fatigues (like a paperclip you bend back & forth until it breaks). i'd really like to see a photo of these failures to see if the fracture is indeed metal fatigue or if it's a helical separation, indicating something else all together......

[insite]

hmm. i may have to eat my words. Raby has some photos on his site of a broken crank from an X51. hard to say from the photos, but it looks like fatigue to me.....

IMO this is very bizarre in a flat6

[insite]

okay, this is driving me nuts. what would drive a harmonic in this engine that the DMF could actually balance out?

what i'm getting at is that this is a flat 6. it has inherent mechanical balance of 1st and 2nd order. further, the CG stays constant about the crank. the rocking couple of each bank is balanced by the other bank. harmonic balancer or no, this simply shouldn't happen w/ this configuration.

there could be some torsional harmonics, but the 1st order torsional (due to the engine pulses) is inherent to engines in general, since they create torque. IMO, this is just as well damped by a sprung clutch than by a DMF.

finally, the DMF is at the wrong end of the crank to really damp any higher order harmonics that may appear......


HMMMMMM: Jake - did the broken X51 crank come from a car with a solid clutch disk, or a sprung clutch disk?

[stephen wilson]

Well, I'm no expert, but you can have as many main bearings as you want, they do nothing to lessen the torsional forces, because by nature they provide almost no resistance to rotation, they only prevent bending. When tightening a bolt, whether you support the ratchet head or not doesn't change the torque on the bolt, just whether the socket will stay in line with the fastener or not.

[Cloudsurfer]

Originally Posted by insite

okay, this is driving me nuts. what would drive a harmonic in this engine that the DMF could actually balance out?

what i'm getting at is that this is a flat 6. it has inherent mechanical balance of 1st and 2nd order. further, the CG stays constant about the crank. the rocking couple of each bank is balanced by the other bank. harmonic balancer or no, this simply shouldn't happen w/ this configuration.

there could be some torsional harmonics, but the 1st order torsional (due to the engine pulses) is inherent to engines in general, since they create torque. IMO, this is just as well damped by a sprung clutch than by a DMF.

finally, the DMF is at the wrong end of the crank to really damp any higher order harmonics that may appear......


HMMMMMM: Jake - did the broken X51 crank come from a car with a solid clutch disk, or a sprung clutch disk?

If I remember it was from a LWF flywheel, tho I don't remember if it was a sprung disc or not.

I played it safe when I built my motor, and I have a dampened crank pulley on a dynamically balanced engine with a LWF and sprung disc.

[greggp]

I tend to agree with insite. There are numerous torsional forces in any internal combustion engine, the pulsing of the engine upon firing of each cylinder is easily heard as a car idles ...and the mechanics are the same at higher rpms, but not as noticeable to our ears. The absolute need of a mass damper to avoid breaking a crank seems pretty remote, but I guess it is possible - depending on what the crank is made of..

I would expect this would have everything to do with crank manufacturing techniques and engineering. There will always be resonant frequencies that every crank wants to vibrate at, and this is true in the torsional direction too. How compliant the crank is in the torsional direction is what matters, as also at what frequency the crank wants to recoil at when a torque load is released.as speed increases the the rotational forces will certainly cross that frequency and the crank will be excited. A billet or even a forged crank will by it's nature have a higher natural frequency than a sintered metal crank. They are also much stronger because of the way they were manufactured.

Personally I am not a fan of sintered metal cranks, I believe they are more likely to fail in torsional loading scenarios.
Are the cranks that have failed, all been sintered metal cranks?

[Cloudsurfer]

Originally Posted by greggp

I tend to agree with insite. There are numerous torsional forces in any internal combustion engine, the pulsing of the engine upon firing of each cylinder is easily heard as a car idles ...and the mechanics are the same at higher rpms, but not as noticeable to our ears. The absolute need of a mass damper to avoid breaking a crank seems pretty remote, but I guess it is possible - depending on what the crank is made of..

I would expect this would have everything to do with crank manufacturing techniques and engineering. There will always be resonant frequencies that every crank wants to vibrate at, and this is true in the torsional direction too. How compliant the crank is in the torsional direction is what matters, as also at what frequency the crank wants to recoil at when a torque load is released.as speed increases the the rotational forces will certainly cross that frequency and the crank will be excited. A billet or even a forged crank will by it's nature have a higher natural frequency than a sintered metal crank. They are also much stronger because of the way they were manufactured.

Personally I am not a fan of sintered metal cranks, I believe they are more likely to fail in torsional loading scenarios.
Are the cranks that have failed, all been sintered metal cranks?

Unfortunately, all M96/M97 cranks are sintered

[insite]

Originally Posted by Cloudsurfer

Unfortunately, all M96/M97 cranks are sintered

indeed. still, very bizarre that this happens. cloudsurfer - harmonic balancers are normally tuned to damp the natural frequency of the crank. who designed the damped pulley, & do we think it's tuned?

i wish i could get that broken crank under a microscope.......still, with it being sintered, it would be a lot harder to tell exactly what happened.

[Cloudsurfer]

Originally Posted by insite

indeed. still, very bizarre that this happens. cloudsurfer - harmonic balancers are normally tuned to damp the natural frequency of the crank. who designed the damped pulley, & do we think it's tuned?

i wish i could get that broken crank under a microscope.......still, with it being sintered, it would be a lot harder to tell exactly what happened.

Well aware The pulley I have came from RSS, and was "designed for the M97 3.8 engine to retain the factory damping characteristics" so honestly, who knows if or how well its tuned, but I figured it was better than having nothing, so it went on my motor.

I, too, would be interested to see the actual failure of that broken crank....

[insite]

here's the best close-up on flat6innovations.com:

[sb01box]

Originally Posted by greggp

Answers to Sb01box

"The sprung clutch .....................t (or elastomer stiffeners) or unbalance will be added to the crank assembly.

-Gregg

Thanks for the detailed explanation to my question!

[rightnwrong]

What happened to it insite? It looks, its been in trouble?