crank shaft fly wheel with LWFW?

[Elombard]

I have been seeing some info about this lately; I guess it’s a known issue. I just heard about it recently. I was getting excited to get an old 996 to play with since the IMS bearing retrofit is now pretty mainstream (at least in our world). And the new failure detection thing from Jake Raby can give piece of mind.....although it gives me heart burn that it’s necessary.

What I 'read' is that the crank shaft is not a high 'quality' casting or the machining is not precision. Porsche designed the dual mass flywheel to work as a dampener (and clutch shock absorber I guess) and absorb any vibrations. Apparently it’s more of an issue on the larger displacement motors with the longer throw and the 2.5 motors in the spec boxsters don’t have an issue when you remove the 'dampener' and put on a LWFW.

I wonder if 'billet' cranks will become an option in the aftermarket. I know they do this in the domestic aftermarket; is it uber expensive?

What about a crank dampener pulley on the other end of the motor as is common in many performance aftermarket applications?

I also read if you are doing a complete tear down on the motor and the rotating assembly is carefully balanced it may not be an issue. What is the cost of balancing on top of a rebuild?

Its disappointing because I love the way a LWFW transforms the way a car feels, even for driving on the street. The down sides of a LWFW are completely eclipsed by the improved throttle/engine response and heel and toeing for me. I also understand why many folks would not appreciate it. I would not want a LWFW on a commuter where regular heavy traffic is experienced.

Maybe this is more evidence that Porsche determined that very few purchasers of the 996 new would get much into the upper rev ranges or track the car and so $$ could be saved on the crank and/or balancing?

I was hoping that with some of the reliability upgrades available I could track the car with some piece of mind. The idea that the crank is not 'high quality' makes me think I should stick with the old cars or at least something with a less expensive motor.

Am I overreacting? What are others thoughts?


Sorry about the mis-print in the subject - not editable.

[JFP in PA]

Do a search, this has been covered "ad nauseam" several times...................

[tdady]

If you're interested in buying a LWFW for your 996 let me know. I have a newly refubished AASCO one.

Tim

[Elombard]

Hmmm I did several searches, I found no mention of the crank shaft coming apart because of vibrations when the dual mass fly wheel is replaced with a LWFW? Is it inside of some other threads?

This has been covered some at rennlist but I do not want to become a member - I spend enough time here :-)

Can a mod edit the subject??

[JFP in PA]

From a discussion on the subject on Flat Six Innovations, along with a direct quote from Jake Raby:



"Installing this flywheel removes ALL harmonic dampening of your engine and transaxle..

One person has recently broken a crank... He didn't listen to me when I told him what caused his issue more than likely, so he reinstalled the same flywheel on his new crate engine. Two events later I got another phone call from him stating that he had broken another crankshaft and he should have listened to me. He is now on engine #3 and is broke, so broke that he is having to make one engine from 3 broken cores..

Another engine (2.7 DE car) had a knock, it was pulled apart and had a cracked and breaking crank.. When I threw the assembly for this engine onto the balancer it was immediately 10 grams out of balance, when the pressure plate was added that went to 19 grams and the flywheel was nearly new and had never been touched..

Both of these are in addition to the X51 engine that snapped a crank in half last year, also using a LWFW... There have been two other instances of similar consequence that people have contacted me about since the new year, but I did not see their parts first hand.

Harmonics have to go somewhere... The dual mass was utilized for a reason-Components that are forced to absorb them won't like it.. And it appears that these harmonics also end up being sensed by the knock sensors as possible detonation, so then the ECU retards timing and that reduces HP. I have gathered data that proves that these harmonics that can't be absorbed are directly related to reductions in net power, as much as 5HP in one instance from my test car.

Balance and harmonics are two different things... Sure an engine thats out of balance will have more harmonics, but even an engine thats perfectly balanced will still have harmonics that need to be absorbed..

The dual mass flywheel and it's dampening characteristics help to absorb these harmonics, the LWFW does not have any dampening capability because it has no second mass separated from the primary mass by absorption material.

Consider the fact that the dual mass flywheels that do fail may be failing because they are actually doing their job!! A flywheel is a wear item, it is a component that is designed to be disposed of after it's job is complete... A crankshaft is not a disposable item and if not absorbed somehow, somewhere these harmonics will find the weakest link and thats when things break.

With the M96 everything is rigid once the dual mass is removed, that means the harmonics from the engine, transaxle, CV joints and even the axle bearings are all going upstream directly to the crankshaft.

When the mass of a dynamic assembly changes as radically as it does when a LWFW replaces a DMFW the plane of balance must be compensated for, that means even if the flywheel that is placed onto the engine is perfectly balanced, when coupled to the rest of the dynamic assembly it will be imbalanced if the plane is not corrected.

The only way to do this is with the engine disassembled in a balance machine like mine. Thats why I refuse to install a LWFW onto any engine unless I am creating it's engine from scratch and can ensure the unit is balanced as a complete dynamic assembly then indexed for reassembly.

FWIW I have yet to see a single LWFW that has ANY balance marks on it brand new out of the box. Every unit I have spun up has had imbalance that exceeds my tolerance threshold...

When the second mass is removed where do those harmonics go?????"

Another from a similar discussion on the 986 Forum:



There was also an extensive discussion on this website, and others, about how poorly balanced some of the lightweight single mass units are, and the cost and effort to rebalance them, and the potential damage they can cause.............

Do another search, the data is out there.............

[Elombard]

Wow that is graphic.

Thanks for the links. Too bad there is not some other way to deal with the harmonics with a dampener on the pulley end.

At least Jake can balance on the ground up rebuilds and, if I read it right, it is safe to use a LWFW at that point. I wonder how that impacts the cost of a rebuild?

[ltusler]

Hi guys, those are pics from my engine. In full disclosure, it had around 10k track miles in it before the crank failed. Don't recall how many of them were with the LWFW before failure.
In the grand scheme of a full Flat 6 3.8 upgrade and rebuild, the full race balance and 2 flywheel indexing, one dual mass and 1 LWFW adds around $300.00.
We also magnafluxed the new factory crank to be sure it had no issues. We did explore a billet build but were not able to get it done at that time. I believe there is a solution now.
The engine has almost 3k track miles on it now and is performing beyond expectations. We built it for reliability and longevity before out right power, but only Cup cars and turbos are hard for me to keep up with on long straights. My 2 primary tracks are Brainerd and Road America.

Lon
1999 996 3.8 Moton Joengbloed Full Cage HoHo's

[Elombard]

Thanks for chiming in Lon. Great car!

So you are running a LWFW on the 3.8 with? $300 seems reasonable when doing a full build.

[ltusler]

Thanks, its a bunch of fun to drive. For saftey sake I'm running the dual mass. At the next clutch change I think I'll put the LWFW in.