Work was done by PO and no extra/trick balancing was done.
This LWFW topic is not fully understood by many of us.
... and somewhere between the careless/uninformed and the world-is-going-to-end-fearmonger lies a balanced and harmonic explanation.

If you know the reason some LWFW work and others destroy the engine, it would be a generous gesture to share your wisdom.
Otherwise the cryptic comments are gratuitous. We are trying to help each other ,not play smarty-pants.
I suspect that much depends on the harmonics in frequently used rev ranges. The Luk tutorial I posted alludes to this .YEMV.

Seeking an answer too. "...not fully understood by many of us" includes me :)

An indication of how poorly understood this issue is - nobody seems to know the answer to the simple and very conventional question "Why not just fit a harmonic-balancer front pulley ? It works for many engines,light,cheap, simple,long-lasting but effective?

Same here. I'm not here to get into right/wrong should/shouldn't. I just want to contribute to the community of information so folks can make their own decisions. I'm glad we've got voices from all sides of the issue.

Inadvertently I think we are on a previously well researched path. Curious that no product has yet emerged. I googgled "Porsche+996 harmonic+balancer" and #1 was this = day jar view?:
Snapped Crankshaft (with pics) - 996 Series (Carrera, Carrera 4, Carrera 4S, Targa) - RennTech.org Forums
http://www.renntech.org/forums/topic/32521-installing-m97-38-harmonic-damper/

I think one of the biggest issues was mentioned by poster #2 in that first thread; "RFM "is a retired Porsche engineer living in Belgium that worked on the design and production of the M96/97 during his career with them. He knows an awful lot about these engines, and their weaknesses.

Poster #12 quotes the following advisory from Porsche NA to their dealer network concerning warrantees and the use of single mass flywheels on their 997 GT3 cars (which they expected to be wailed on at the track):

"• The single-mass flywheel causes fluctuations and vibration in the lower rpm range, thereby reducing the smooth-running performance of the engine.
• The crankshaft is subjected to one-sided loading, causing stress peaks that can result in damage to the crankshaft.
• The one-sided loading of the crankshaft can cause the pulley to come loose, resulting in damage to the belt drive and engine.
• Any damage relating to conversion or damage that can be attributed to conversion is not covered under warranty"

Jake (and others) have also noted significant unbalanced conditions on certain brand light weight single mass flywheels right out of the box. One was a much as 15 grams out of balance, brand new. Others of the same brand were much better balanced, but still not perfect.

I don't think anyone with serious experience with engines would deny that lightweight flywheels have certain inherent advantage's over heavy units. But in this case you are dealing with a number of uncertainties; the engine has certain design elements, such as the component spacing and material of manufacture in the crankshaft, which when combined with inconsistent inherent balance characteristics of the lightweight replacement flywheel itself, can lead to a complete disaster. Some work fine, others shake the crank apart; the problem is that you don't know which engine and flywheel combinations will work, and which ones won't without doing a lot of work before trying the lightweight flywheel. This is why both some engine builders and a lot of shops back away from using them, we don't want customers coming back with two or more piece cranks.

JFP
Thanks for sharing your knowledge and experience with us.
Since the LWFW subject comes up frequently (like the why do I need to lock the camshafts when I do IMSB job?) - I suggest your response becomes a Sticky or at least a copy+paste response..
People who blunder in to this thinking -Hey LWFW worked on my Miata/Mustang/whatever ,it will work on a flat 6 just as well... Could be an expensive mistake.