LWF a bad idea?

My 3.4 is being rebuilt. Some 'while we are at it' items are a given. Clutch and flywheel incuded. My car is not a daily, but i will be driving it as much as possible to get max value from the incoming expense. I have driven an early Cayman with s LWF @nd liked it. Some say it is courting disaster, sends bad resonance to the crank and can also stress the gearbox. Any truth in this? anybody had problems? or are lots running them without issue? I will deffinately be having stiffer than stock engine mounts and a new transmission mount with one of the softer inserts to keep it honest. The car is stiffly sprung on Ohlins R & T which are well bedded in after 3 years. I dont find the spring rates too high. Looking forward to the wisdom of the collective

Interested in this as well for when I drop the gearbox, probably early next year.

I'm also interested in this having had a few cars with lightened flywheels in the past but have also read of problems arising from lightweight, single mass flywheels leading to damaged cranks. I think it was on Rennlist in the USA as I recall and apparently the harmonics? Vibrations? Not sure but they were blamed for a snapped crank. Given how hard replacement cranks are to source that sounds.... bad. Hopefully one of the 'Grown ups" will be along soon to explain it. Maybe Barry Hart? I seem to recall they fit an additional end bearing to support the flywheel which probably allows the fitment of the LFW but I won't even try to put words in his mouth. As I say, look forward to hearing a learned response; I think that the LFW would really suit my 3.4 Carrera's rev you nature well. Oh and mine also runs the Ohlins R&T and I also don't find them to be excessively stiff though it seems we may be in the minority!

Had a LWFW in my car for about 30+k miles without issue....just sayin?

This is talking about the Carrera engines, not the M96.7* engines which are known to operate well with a LWFW. I have heard various things from it messing up the timing to problems with vibrations. I don't know how much is from direct experience and how much from conjecture repeated from a variety of sources. Somebody like Baz will be best to give actual experiences I would think. MC

apologies Martin, , ,

If your using a light weight flywheel ideally the whole crank/pulley/flywheel/clutch cover etc want balancing as an assembly. If you put a component on like a new flywheel the whole rotating assembly COULD be out of balance. It really is pot luck but if there is enough vibration the crank COULD break. You might well be lucky and it makes no difference you would notice. It a gamble.

Edited with apologies to Parsley. I personally feel wildly unqualified to comment on this matter having had no experience in the possible difficulties involved in fitting a lightweight flywheel; my experience being limited to 'Stuff read on the internet". I am more than happy to bow to anyone who has greater knowledge than I, this is simply something I found online which had an impact on my decision to not fit a lightweight flywheel on my own car at this stage. I found the article I had read previously on Rennlist which made me wary of a lightweight flywheel on a non Metzger engine. https://rennlist.com/forums/996-forum/570732-lightweight-flywheel.html I believe (That's 'I believe" rather than 'I know to be a fact") that the Carrera (Non Metzger) engines have their rotating assemblies balanced... adequately. We all know the engines were designed to a budget. Any secondary vibrations that might occur from car to car would be absorbed by the dual mass flywheel so protecting the crank from harsh vibrations while the engine is running. Without the dampening effect of the dual mass flywheel all of this vibration has to be taken by the crank. In addition I believe that the Carrera engine has quite a long length of crank hanging unsupported by a bearing at the flywheel end, to the extent I think Hartech sometimes add an additional carrier (Once again Barry apologies if I'm wrong) so I guess stopping the end of the crankshaft from 'Whipping" due to any vibration or imbalance. As I say, this is NOT based on science or experience but simply based on reading stuff on the internet... with all the facts, lies and bullxxit that entails. What I would say though is that it was enough to give me pause in my headlong rush to go for a lightweight flywheel on mine.

I take exception to your opening sentence.Thats a very dismissive statement considering you know nothing of me or many other people on this site.

Parsley I'm very sorry if that was taken as a comment in any way against you. My reference 'Until Barry comes along with something based on science and experience" was meant entirely to say that I myself have no empirical evidence nor engine building experience from which to comment, It was not meant to imply a lack of useful knowledge on the part of anyone other than myself. My humble and unreserved apologies Parsley for any offense caused.

No worries at all mate. I perhaps took it a little seriously. Apologies for firing back like that. :thumb:

I run one and have had no issues, there are others whom also run them without issue. Prior to fitting the only issue I could find is the rennlist thread, which it appears that everyone bangs on about whenever a LWF is mentioned. M96 has a large unsupported section of crank, reducing the load hanging off said crank by circa 6Kgs is a good thing. Mine was dynamically balanced to the crank during a rebuild and is coupled to a sprung clutch. As I track my car I also opted for a custom additional bearing to support the crank overhang. Others however have retrofitted without balancing or an additional bearing. You get a little more mechanical noise on tick over, that aside it's no more difficult to live with than a DMF. You pays your money............

This is one of the greatest features of this forum, that the members can take offense and still have the maturity to work things out rather than start a war, which is what would happen almost anywhere else on the internet. Kudos to both you guys.

I have had a SMF fitted for just over 5k mile now without any balancing carried out on my 3.4. The Porsche specialist who did the work said he had fitted a few to 996's and 986's. which had been used as road cars and on track without any issues. I naively listened to his advised and had one fitted when my clutch needed replacing. So far fingers cross without any issues. When I read treads like this it does fill me with dread that it might be a costly mistake. However my experiences of having the SMF are positive. The engine rev's more freely and feel more energetic. Yes there is chatter at idle and it can be noisy at low rev in a gear too high. It took a bit of getting used to in traffic but touch wood, so far I'm happy with it.

Thank you all for the insights. On ballance I have decided to have a new DMF instead. I just dont want a LWF nearly enough to suffer any nagging doubt! I will instead try to sharpen up the car a little with some semi solid engine mounts (SSR seem to generate good opinions?) a new gearbox mount. (possibly with a stiffening insert) a stock 997 shifer and new cables. And because my old manifold looks very gnarly, a new stainless set, probably Top Gear if they re stock in time. Then if I can still afford petrol, I will have to do as much driving as possible to spread the cost per smile.