dual mass flywheel: LUK vs SACHS..?
 

I will be replacing the clutch with a Sachs performance clutch kit and I would like to replace the dual mass flywheel at the same time.

Rockauto have on their website LUK and Sachs, I was not aware that Sachs also manufacture flywheels, I like the Sachs brand and would rather but this one over the 'LUK'... any comments?

Thank you.

I have read peoples posts mentioning dual mass flywheels and I was curious what that is all about.

1) How is that different from a regular upgrade flywheel?

2) What is the purpose of dual mass and what is the benefit/drawback in having one.

I'm similarly uneducated on double clutches. What are they and how do they work?

Inquiring minds would like to be fed.

Guys please do a search here. The LUK I believe is oem. I may be wrong. But the dual mass is somewhat necessary.

The OEM dual mass flywheel includes what is essentially a vibration damping component between two different masses, hence the name, dual mass. Because part of the assembly actually flexes, it also wears out (when it flexes too much). Thus, it is common to replace the DMFW when the clutch is replaced.

The alternative is a common flywheel or what is more commonly called a light weight flywheel (LWFW) which is a standard aluminum flywheel. Because it does not contain the flexible damping material and the other mass, it weighs substantially less and thus, the engine will rev a bit quicker. The downside is that there is concern that the LWFW can result in engine failure due to undamped crankshaft vibrations.

Do a search on LWFW and you'll find the threads where this has been discussed with quite a bit of passion previously. :)

Yes, I am going to install a dual mass flywheel, the question arise when I saw the Sachs DMFW at the RockAuto website.

I am not familiar with the Luk brand, however I am very familiar with Sachs but I was not aware thet they manufacture the DMFW.

For this reason I created a new post since I did not find any posts that make reference to a Sachs dual mass flywheel...

but... the LUK brand is recommended at the Pelican site... :p

.

Ive never heard of boxster motors popping from a light weight flywheel, looks like I have some reading to do. How well documented is this? Is it a real concern?

http://i1140.photobucket.com/albums/...ps784a8d0d.jpg

Does that look serious enough? From one of Jake Raby's site stories on the subject of lightweight flywheels.....

I knew that this was going to happen....

Ok, before we scare everyone, I'd like to say that almost every Boxster Spec race car has a LWFW and the BSR/SPB fleet (which are driven harder than any street car) has not reported any such failure as common. I'm not saying that its not possible, just not common.

My Boxster has 136,000 miles on the engine. The last 45,000 miles have been with a LWFW and include 85 track days and over 10,000 runs to redline (and a few beyond redline :)), all without a problem. Your mileage may vary.

Most cars locate a "harmonic balancer" on the front of the engine, built into the fan belts/serpentine belt crank pulley. Porsche put the harmonic balancer on the other side of the engine, as part of the flywheel. Most cars can get away with a "lightweight" flywheel because the harmonic balancer stays in place. Do this to a Porsche design and you end up with no harmonic balancer at all.

As noted elsewhere the LUK 20-016 clutch kit includes a Sachs disc and pressure plate. For some reason it's cheaper than buying a Sachs clutch in a Sachs box.

Are you sure that was due to the LWFW and not due to the fact that these motors are made of explodium?

Visit Jake's website and read all about it. Yes, this was caused by the use of a lightweight flywheel, and the engine is actually an X51 version with all the oil system enhancements. When these things go bad, they go very bad..........

Fact of the day: 15% of all aluminum cans are made of recylced blown up Boxster motors.

Flywheels are usually out of balance especially the Aasco version. I would assume most spec Boxsters have thier's balanced before install.

Just read it, scary story. However it's just one case, at the beginning on the articule he states that hes never seen such an extreme failure. It seems low risk to me, that was also a very high powered race car with 12,000 track miles! Definitly something to consider but it doesn't seem probable.

Thanks for the explanation of the DMFW.

So you say the DMFW can wear out, what symptoms of that would you notice, just out of curiosity.

So are there light weight dual mass flywheels as well?

Seems prudent to keep the harmonic balancer function but at the same time a lighter weight would allow faster acceleration of the engine.

So if I understand correctly the LWFW does NOT have any harmonic balancing functionality?

I also wonder if the flywheel balancing can be done dynamically on the engine or statically before its attached?

Perhaps that is indy mech thinking and only worth it for racers if at all?

We have seen one as well, not as bad as Jakes, but bad enough; plus two complaints of drivability and vibration issues after the install of a lightweight unit, both of which were traced to significantly out of balance flywheels. We also had one in the shop that would not start after a DIY lightweight install that turned out to be problems with the CPS shutters on the flywheel. Some of the lightweight units just are not very well made.

A lightweight unit is a single mass with no dampening capabilities.

Yes, flywheels can be balanced by a competent balancer (requires special fixtures); but having the flywheel correctly balanced does not do anything for harmonic dampening, that requires the dual mass.

From Project 44 in Wayne Dempsey's book:

Good stuff, guys, thanks to JFP and others for sharing on the subject. I was totally into the idea of a LWFW but now won't even consider it. I don't track the car and I can live without the faster revving engine.

I plan to run a lightweight aluminum flywheel ( after taking to a machinist to balance ) and a SPRUNG clutch disc.

Some yes, some no. Mine, no.

This is usually where someone calls me an idiot (or some equivalent) because I have the original IMS bearing AND an unbalanced LWFW! Its a timebomb!

http://i1114.photobucket.com/albums/...ps45fb9f1b.jpg

But it has 136,000 miles and 85 track days without a hitch. So far, so good.

http://2.bp.blogspot.com/-7tELCIzSja...tman66bomb.gif





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I don't think this is an exercise in personal attacks, but a sharing of some hard learned information. You have had good luck, and that is a good thing. But others have not been so lucky, and some have experienced a disaster. Given the inconsistency in how these units seem to perform, I think it is a good idea that others be aware of it, particularly if they are paying someone to do the installation.

We do not do lightweight installations based upon our direct experience, that of other shops, and of course what Jake has seen. Porsche even released a dealer warning about the use of "single mass" flywheels, indicating that any damage would not be covered under warranty if the car still had one.

one person's 'luck' is another's 'caluclated risk'. folks have been taught to want black or white - it breaks or it doesn't. as soon as you get into 'it may break' you get conflict. people try to turn the grey into black or white. it 'may' break' turns into it 'won't' break or it 'will' break, and folks argue. 'i'm right' 'no i'm right'. you're both right. your both wrong. there are some that have broken, and some that have not. make a choice. try to base it on fact. ie, how may lw fw have broken vs how many are is use? ditto ims. ditto whatever. make your call based on risk vs reward - will a lw fw potentially fail sooner than a dual mass? perhaps. will it make driving more fun in the interim? perhaps. can you afford to deal with a failure if it happens? perhaps. ball it all up, make a decision and move on. all the feedback you get on the internet? worth what you paid for it. one failed flywheel with a sensational photo can morph into 'all lw flywheels fail' quite quickly out here in the ether. or a couple of success stories can send it the other direction (less frequently, however, as the interweb tends to attract the negative).

my personal story? i called the guys that made the dampened udps for gt3s and asked about an m96 application for use with lw fws and they told me that there was absolutely no need. i mean, is the oem flywheel dual mass in order to dampen harmonics, or is it heavier in order to allow use of a lighter unsprung clutch? it is a hairdressers car after all ...

Well played sir, well played

So what type of flywheel was on the batmobile? That is the way I'm going with my flywheel.

IIUC Porsche combined the effect of the front pulley harmonic balancer AND the springs in a traditional clutch disc in their dual mass flywheel. I suppose you could put on a single mass flywheel if you use a "sprung" clutch disc and a harmonic balancer belt pulley up front.

"Luck" also plays into it in a way very few even think about. By Porsche standards, the M96/97 engines are mass production items, and tend to have "broader" tolerances is several areas, including how well they are internally harmonically balanced. Unlike the Mezger lump that used to be used in the Turbo cars and is still in production in the cup cars, and which are refined to a very high standard, the M96/97's are not as closely held to the ideal specs. That is one of the many reasons the Metzger will set you back $50+K for a replacement, while an M96 is in the $15K range. Net result is that some M96/97's naturally produce more rotating assembly harmonics than others. And if "luck" has it that yours is one of the high harmonics engines, pulling the dual mass creates a lot more stress on the assembly. Plus, if your "luck" is really bad, and you get one of the lightweight units that is 10 or more grams out of balance on its own, it can become a recipe for a disaster.

When M96's are torn down and sent out to be internally balanced, some are pretty good, others not so much and require a lot more time in the machine shop to get them where they need to be. And it is a totally a matter of "luck" which one it will be......

THAT made my night. Thanks.....:cheers:

For the record..........I WAS going to go with a LWF but after researching it (beyond exploding motors, many guys had ongoing issues as a result of putting a LWF in) and coming to the conclusion it wouldn't be of any benefit to a street driven car I purchased a LUK Dual Mass unit off of Fleabay for significantly less than I could find anywhere else. I installed it along with a Sachs clutch kit in my 993 a couple of years ago, all is fine.

Lastly, I forgot to mention that if you do indeed test your DMF for in spec deflection and it passes with flying colors like mine did with ~35k miles on it (while I did the IMS bearing upgrade in my Box), you can simply clean it up with a palm sander since it cannot be resurfaced.

http://i46.photobucket.com/albums/f1...leanedFlyW.jpg

Dual mass actually can be resurfaced but the surface where the friction material touches must be clamped down in a fixture so it will not move. Here in OC there a couple guys who will do it, but shop around. the prices I found were as high as $450 and a low as $75.