Dual Mass Flywheel Problem?

[Hib Halverson]

(snip)

In the case of the LT1 and LT4 engine, the dual mass flywheel is used to quiet gear rattle and to balance the reciprocating engine mass.

On the LT1 and LT4 engine, the crankshaft is not balanced. The engine is not internally balanced. That job is left up to the flywheel and crankshaft damper. When one replaces a dual mass flywheel behind an LT1 or LT4 engine, the replacement dual mass flywheel must be balanced identically to the flywheel being replaced. If this is not done, vibration will inevitably harm the powertrain assembly.

Hope this clears up any misunderstanding regarding this marvel of automotive technology!

Actually, it continues to cloud the issue.

Again...the reason a dual mass flywheel is used, rather than a standard or "single-mass" flywheel on the L98, LT1, LT4 or LT5 engines is to damp gear rattle in the ZF S6-40 transmission. The election by GM to go to the dual-mass has nothing to do with engine balance, either internal or external.

With a dual mass flywheel on a Gen 2 engine, the wheel itself (the "primary" mass, if you will) has extra weight to balance the engine's rotating assembly. The secondary mass (what makes the flywheel a "dual mass" wheel) connects to the transmission input shaft and has no role in engine balancing.

You can put a 93-97 Camaro flywheel, which is a standard type or "single-mass" wheel on Gem 2 V8 and, if the trim weights are in the correct holes, the engine would balance.

As I've said several times in this thread, the dual-mass flywheel was chosen by GM for use in all applications fitted with ZF S6-40 transmissions to damp gear rattle...not to balance the engine.

Also, further clouding the issue is the statement that Gen 2 V8s have both externally balanced crankshaft vibration dampers and flywheels. As pointed out elsewhere, that's not correct. Only the primary mass of the flywheel is externally balanced.

 

[Hib Halverson]

I finally got into reading that patent information and in the Section titled "Description" in paragraph #0001 the following appears:

The invention relates to a device for damping vibrations, in particular between an engine and a drive train of a vehicle, forming a so-called dual-mass flywheel. The invention particularly relates to a dual mass flywheel, comprised of a primary mass, which can be connected to the output shaft of an engine, and to a secondary mass, which can be connected to the input component of a transmission, which are positioned relative to each other in a concentric and axial manner, and which can be rotated relative to each other, at least within limits, against the effect of a damping device with energy accumulators, in particular compression coil springs.

I'm surprised the person who posted this patent gobbledegoop didn't catch the part about the purpose of a dual-mass wheel being to damp vibration between the engine and the driveline. Further, I'm surprised the OP failed to notice that in that patent information, there is no mention of the purpose of the dual-mass flywheel being to balance the engine's rotating assembly.

You can Google "dual-mass flywheel" and in many of the search results you will find statements to the effect that the purpose of a dual mass wheel is to damp gear rattle not to balance the engine. One of the search results was a discussion on the Luk site (Luk is the company which holds the patent "LT4 Man" posted about). Here is the first part of it:

Modern engines can be driven at extremely low rpms. The trend is toward ever increasing engine torques. Wind-tunnel-optimized bodies are creating less wind noise. New calculation methods are helping reduce vehicle weights and weight-saving concepts are boosting engine efficiency as well. The addition of a fifth or a sixth gear can also reduce fuel consumption. Thinner oils are making precise shifting easier. In short: The sources of noise are increasing and natural damping is decreasing. What has remained is the principle of the internal combustion engine whose cyclical combustion processes excite torsional vibrations in the drive train – the unpleasant consequences of which are gear rattles and body booms.
Drivers who are accustomed to increased comfort no longer accept such background noises. The job of the clutch is now more important than ever – in addition to engaging and disengaging, it must effectively insulate the engine’s vibrations. Physically, this is easy to solve: The mass moment of inertia of the transmission must be increased without increasing the mass to be shifted. This dampens the engine’s torsional vibrations and brings about the desired comfort level. The process reduces load on the transmission at the same time.

So, again...dual-mass wheels exist to solve problems created by gear rattle not to balance the engine.

 

[CAJUN C4]

GM JUNKIE has a source of a shop that rebuilds them.

Might check with Him.