belongs to "ltusler" over at renntech. this it "the one" that Jake Raby has posted about, including photos of it, and that everybody seems to always be referring to when they say that they know somebody whose crank broke because of a LWFW.

FWIW: it seems (as I read about it) that they were building a track motor, with a number of other modifications to the motor. It's also a 996 motor, so, more HP / torque being driven through that crank to begin with. Somehow the crank failure gets pinned on the LWFW, in spite of literally HUNDREDS of others that have used the LWFW without incident.

Here's the quandry I find myself in: I am not going to be able to do all of the testing myself.... and it would be foolish to do so anyway, when others have already done it. So I have to / get to rely on the findings of others. And frankly: the number of successes with a LWFW FAR outnumber the anecdotal evidence of failures. I say anecdotal, because, while I can (and have) talk with MANY, MANY who've had a success with the LWFW, I can find only ONE person who actually has a failure story.

JFP has just indicated that he has seen a few. I don't doubt he has. but this still resides in the somewhat nebulous territory of "I heard about", since I don't know any specifics (like mileage, other mods, usage, etc etc). On the other side: I can get all SORTS of details and specifics about the many people who have and are using a LWFW with success.

So as a newcomer, relying on what others have learned, what result SHOULD I come to?

You need to also remember that 90% of the single row cars never suffered an IMS failure either, but that 10% number is still very significant if it is you...…..

Porsche actually released a bulletin to dealers warning them not to warranty engine failures if the car has a single mass flywheel in it. The problem is somewhat more than "nebulous"...…………..

This is what I remember reading regarding a broken crankshaft referring to a light flywheel. I certainly would take the author's advise in what he is saying in the last paragraph of this article.


WOW, this is one of the more extreme failures I have ever witnessed from any engine.... Its not too often that a crankshaft shears on the track on an engine that has 7 main bearings, but this one damn sure did!

The engine has the 3.6 X-51 package and was making 325 RWHP and had seen TWELVE THOUSAND track miles prior to this failure. We had initially thought the engine had broken a rod due to the material that came from the oil sump, but as soon as the engine arrived at our facility a 5 minute inspection found the crankshaft to be in two pieces!

The material these cranks are made from is powdered metal, it's what most modern engines use for crankshaft and connecting rod materials and I am less than impressed with it thus far. I can't believe that a component with such mass could break so extremely.

I feel that this failure was attributed to by a couple of things-

1- The engine was "upgraded" to a lightened flywheel. This new flywheel was installed onto the existing stock engine without being balanced to that assembly. This created an imbalance in the rotating mass AND it did away with the factory dual mass flywheel.

2- The dual mass flywheel was removed to alow the single mass lightened unit to be installed. This eliminated ALL MEANS OF HARMONIC DAMPENING!! The crankshaft was forced to absorb ALL harmonics from the engine and transaxle when the dual mass unit was removed..

So- adding the light weight flywheel was a double negative, not only did it create imbalance, it also eliminated the harmonic dampening of the dual mass arrangement.

Due to this I feel that adding a lightweight flywheel to any existing engine is not a wise decision, and that they should only be added when the entire rotating mass can be balanced and indexed to accomodate the lightweight unit. This means engine disassembly, so I'd only add one of these when doing one of our performance upgrades so the entire assembly can be precisely balanced.


Jake Raby

This discussion raises the "performance vs robustness" argument. As I always mention, to each their own, but I gravitate toward longevity as I personally abhor failure that could be avoided, but then again, performance isn't my primary goal. As such, my decisions are left primarily to engineering (or my common sense version of form, function and durability) and in this limited case, I personally vote for the heavier flywheel (more robust) versus a lighter option that has *maybe* a few failures attributed...as even one failure would lead me to believe that this isn't the best design option. Again, I'm not the type of person to require volumes of information to prove (even if I want to believe otherwise) a failure *could* be extrapolated across an entire sample. I don't need to hit myself in the head with a hammer multiple times just to prove that indeed the first one truely hurt.

Regarding your choice (and again, to each their own), perhaps weigh the tangible performance improvements versus possibly having to do this all again....and forgive me for saying so, but it seems like you are in the "want to believe" camp (which for me always leads to poor decisions and/or injury); try to remove any preconceptions and just perform a mental pro/con analysis.

Whatever you decide, I always salute your wrenching, tinkering and thinking outside the box. You are also prone to call "BS" on a Porsche hardliner (which always makes me secretly smile); apply that same challenging thought process to yourself and I'm sure you will find your answer.

Let us know, and as always, I look forward to being completely and totally wrong. Lol.

Thanks JFP. to be clear, I'm not suggesting the problem is nebulous, but rather that the citations and references used when describing crank failures are. They almost NEVER come with pertinent details, with only one exception, and that being the sole, lone, single verifiable instance of a crank failure being attributed to a LWFW.

And lew just made the point. He cited "MANY", yet when pressed, he came back to the same one. ONE.

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Once again, we take the word of someone with an agenda (Jake raby) over hundreds of others with a successful record.

Look: if this were a widespread problem and everyone was trying to understand it, Jake's explanation would absolutely fit, and we could all put it to bed. But when his explanation is (as you showed us below) postulated to explain a single, specific failure, and then we ascribe it to ALL OTHER SITUATIONS ..... ignoring all of the rest of the successful uses, then we are fools.

Let's think like scientists for a moment, shall we?
We have hundreds of experiments, with as many variables. We have ONE failure (of the hundreds of tests). We blame ONE of the variables because it seems to make sense. We'd never get past peer review. Ever. If we published, we'd be laughed to shame.

All I'm asking for is more data. Not more requests that I just trust Jake.

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MWS, dude.... what a GREAT post.

Yes.... I'm guilty, as charged, of being squarely in that "want to believe" camp. And I've used LWFW on dozens of engine builds (not Porsche) and feel like I have a pretty good knowledge base. This also moves the needle for me. So yes, I also have an "agenda".

But I'm truly open to being moved to another camp. Especially if it saves me a motor! Haha.
I like your comment about there being a trade between longevity and performance. For me, the needle swings further away from longevity, and towards performance than for some others. I don't think I'm anywhere near "devil be dammed" on the scale though; somebody sway my opinion with some hard data, I'm not going to ignore it. I understand the science behind the argument, but I just don't see the data backing it up. In fact, I see the data debunking it.

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I'm a big fan of the scientific method (as it relates to OTHER people, lol), but I'm just too darn risk adverse to experience failure after failure just to prove a hypothesis to myself. I previously mentioned the example of hitting myself with a hammer, once is enough...now Im picturing a room full of scientists whacking themselves in their heads with hammers to replicate results then moving to another peer review group poised with hammers in hand and heads on the tables. Lol.

Also, I'm not in the camp of trusting one person, as even an "expert" has to pass my mental review process. I guess what I'm asking is "what design seems better to you, at least from a common sense point of view?" Using that criteria, you'll always be right...or at least for a few minutes. ;)

so now I'm looking at catalogs, and I'm forced to look at the cost:benefit as well. It looks like (just using Pelican as a source) I'm gonna spend most of $1000 MORE to do the LWFW and associated sprung-clutch, versus just replacing with stock-type components. (some of this is because of what looks to be a real bargain on a LUK clutch kit right now.)

is the increased performance, and the associated potential risk exposure, worth $1000 to me right now? (That's the question I'm posing to myself)

::sigh:: I hate it when I start to get pragmatic.

What is the difference in rotating mass?

From post #1 in this thread:

Lightweight Flywheel only - 13.0 lbs.
Lightweight Flywheel + New Sachs Clutch Assembly - 25.4 lbs. *
Stock Dual Mass Flywheel only - 26.5 lbs.
Stock Dual Mass Flywheel only + New Sachs Clutch Assembly - 38.8 lbs.
Lightweight Flywheel + New Sachs 4 Spring Clutch Assembly - 18.0 lbs.

I just gotta laugh at this....The name Maytag fits you perfectly....Wishy Washey!

The Devil made me do it! :D

5 to 1 odds you don't do it! Anyone else think that? :)

ahhh, say what you will, Lew.... but when I make the decision, it will be a decision I've made after I have considered ALL of the risks, benefits, costs, etc. Not because I have joined the rest of the sheep. Your silly taunting aside.

If cost is of no importance to you, congratulations. But cost (value) is ALWAYS a consideration for me. It WILL always be so. I'd enjoy you explaining to me why it shouldn't be thus, but I assume you would merely quote someone else again, since so far I haven't seen you present any of your own original thinking to the matter. Again, your silly taunting aside.

For the record: "Maytag" comes from being the guy who can fix or build ANYTHING track-side. I'd stack that name up against "lew" all day, and twice on Sundays. Since you asked.

18 lbs is a lot of rotating mass to lose. If you put a few back with the harmonic balancer for the crank pulley you still have a lot less mass to spin up. This will probably be my way to go when the clutch is due.

I'd have to say that almost every track boxster, 996, 997 and 987 is using a LWFW. Most motors I hear of go out because of oiling issues, spun bearings or rods. There has been a few cranks breaking but not many. I totally respect Jake's opinion on the M96/M97 motor but I have to disagree about using a LWFW. Maybe it's like the ims bearing and track cars don't have as many issues as the street cars?

Don't forget the cost to have the flywheel balanced, they are often way out of balance.

Thanks Woody.
That concurs with all of my own searching. I've read and read and read until my eyes glazed-over. I've spoken, to, visited, emailed and FBM'd with dozens of individuals representing (combined) hundreds of cars running LWFW on their 986 motors of every ilk, size, mileage, etc. I cannot find a single person who can offer me a solid "yes, I had a motor that had a crankshaft failure that I can attribute to a LWFW. Let me tell you about it". Except the one, single, lone example that everybody references. That guy is on renntech. His crank failed in his 996 motor with a LWFW and a SLEW OF OTHER modifications.

So I think I have proven beyond any reasonable doubt that the LWFW does NOT cause crankshafts to fail. I will state that unequivocally, based solely on the data. (I mean, as long as we're considering opinions to be facts, mine might as well be too, right?)

Yup. My machine shop is on standby. :-)

Did it. Parts are on the way. :dance:

Of course, I probably wont get to work on it for 3 weeks still..... sunnuva.....

dropped the flywheel and pressure-plate off to my machinist today. He'll balance and index them for me over the next couple of days.

I'm hopeful that tonight I can get to the garage before my wife or neighbors catch me, and I can get the IMS done, and the new halfshafts in, so I'm ready to install when the machinist finishes.

comin' back together!

I picked up my flywheel and pressure plate from my machinist, who was balancing them for me.
For what it's worth: the aasco flywheel was very close to balanced already: less than 1/2 gram out. The SACHS sport pressure plate was about 3 grams out. But now we're dialed-in.

I guess I love old threads..

So, how did this end up? Happy times or crank in pieces???

Happy times. Very happy times. Nothing but lots and lots of very happy times. [emoji6]

(Any awards for thread resurrection? [emoji38] [emoji1787])

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Enjoyed this thread but I have an unrelated question:

You mention installing your IMS bearing towards the end and curious which IMSB you used?

Lari, if you have an unrelated question, please post it in a new thread (or read the thousand imsb threads already published and make an educated decision for yourself). This is an exceptionally valuable thread and it should stay that way.

Yes, I'm an ****************************. No, I won't apologize. Since the moderators are now non-existent, someone has to say it.

On a related note, I'm curious to know if anyone has quantified the performance advantage of the lwfw with sprung clutch? Dyno results, track times, LTFT data, etc.

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