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Old 04-16-2014, 11:21 AM   #1
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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.

******************************** 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.
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Old 04-16-2014, 11:41 AM   #2
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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.
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Old 04-16-2014, 11:54 AM   #3
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Guys please do a search here. The LUK I believe is oem. I may be wrong. But the dual mass is somewhat necessary.
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Old 04-16-2014, 01:15 PM   #4
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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.
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Old 04-16-2014, 01:23 PM   #5
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Originally Posted by JAAY View Post
Guys please do a search here. The LUK I believe is oem. I may be wrong. But the dual mass is somewhat necessary.
Yes, I am going to install a dual mass flywheel, the question arise when I saw the Sachs DMFW at the ******************************** 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...

.
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Old 04-16-2014, 01:46 PM   #6
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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.
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?
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Old 04-16-2014, 02:13 PM   #7
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Does that look serious enough? From one of Jake Raby's site stories on the subject of lightweight flywheels.....
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Old 04-16-2014, 03:41 PM   #8
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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.
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Old 04-16-2014, 03:42 PM   #9
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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.
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Old 04-16-2014, 03:44 PM   #10
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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.
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Old 04-17-2014, 04:12 AM   #11
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Originally Posted by JFP in PA View Post


Does that look serious enough? From one of Jake Raby's site stories on the subject of lightweight flywheels.....
Are you sure that was due to the LWFW and not due to the fact that these motors are made of explodium?
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Old 04-17-2014, 08:40 AM   #12
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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..........
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Old 04-17-2014, 09:31 AM   #13
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Does that look serious enough? From one of Jake Raby's site stories on the subject of lightweight flywheels.....
Fact of the day: 15% of all aluminum cans are made of recylced blown up Boxster motors.
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Old 04-17-2014, 10:01 AM   #14
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Flywheels are usually out of balance especially the Aasco version. I would assume most spec Boxsters have thier's balanced before install.
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Old 04-17-2014, 11:20 AM   #15
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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..........
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.
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Old 04-17-2014, 11:43 AM   #16
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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?
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Old 04-17-2014, 01:17 PM   #17
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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.
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.
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Old 04-17-2014, 01:20 PM   #18
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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?
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.
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Old 04-17-2014, 02:27 PM   #19
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So you say the DMFW can wear out, what symptoms of that would you notice, just out of curiosity.
From Project 44 in Wayne Dempsey's book:

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Now, it's time to turn our attention back to the flywheel end of the engine. Porsche Tech Bulletin 8/02 1360 says to check the dual mass flywheel by twisting it approximately 15mm to both the left and the right, checking to make sure that it returns to its approximate starting position. If the flywheel can be twisted beyond about 15mm with no noticeable increase in spring force, or if it cannot be twisted at all then it probably needs replacement.
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Old 04-18-2014, 05:53 AM   #20
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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.
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