Aasco flywheel is here.

[Jake Raby]

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?????

[edevlin]

Interesting stuff, I sure like learning more about our engines. In my case I have almost 3 years and 40K on my Aasco lightweight flywheel, and I love the driving experience with it, engine and car are much more responsive.

I did not think much of it at the time, but right after it was installed, it did seem to me that there was a bit more vibration comming from the engine compared to the factory flywheel, another subjective data point for the discussion.

As I said, I really like the performance of the car with the lightweight flywheel, but I must say, if I had known back then what I know now about the harmonic balancing function of the flywheel, I pretty sure I would have kept the unit stock, live and learn.....


:dance:

[JAAY]

Calling my Porsche buddy to see how much a stocker is. But. Why did my other go within 4k miles?

[Jake Raby]

Ummn, what do you think the components feel if they are screaming that way just at idle?

[timothy]

Just wanted to chime in and say thanks for a very informative (and civil!) discussion.

[jaykay]

Just curious as to whether anybody knows whether a light fly wheel could mitigate crankshaft and RMS damage by reducing the overhung weight at the back of the crankshaft. I would think the DMFW at 40 lbs, slightly unbalanced, on a slightly untrue crank could cause undue crank shaft deflection resulting in RMS damage and leaks. I would think by the time you have an RMS leak you already have engine damage.

I was thinking of a LWFW just to prevent this scenario but I am just learning about all the negatives associated with it. I have a very low mileage engine (m96) that I would like to make reliable.

What flywheel would I use to be safe? Do I need a clutch to go along with it? It is not a race car so I would like to keep it as streetable as possible. What are the risks? Will a dynamic balance problem be caused?

Thanks,

jaykay

[cnavarro]

It's questionable to put a lightweight flywheel on the engine without some sort of harmonic balancing to offset the loss of the dual mass flywheel. I have had many phone calls from individuals and shops alike with broken crankshafts, attributed to lightweight flywheels and it's bad enough that Porsche issued a TSB that use of a lightweight flywheel will void the warranty, likely due to harmonics I would imagine. It's been touched upon in this thread and I highly doubt that a reduction in mass would fix the RMS issue. Engines with multiple RMS failures are indicative of a larger problem - drooping of the crankshaft carrier in the crankcase.