mcmonroe

Hey Guys,

Is a dual mass flywheel on a 1991 L98 a neutrally balanced flywheel? How about later years with the LT1, LT4? What about the dual mass on LT5's?

Many thanks,

Mark Monroe
Harrisburg NC

Exotic Muscle

The L98 (or LT1/4) flywheels are all the same unit (and even part number). The engine uses a zero balanced crank damper. However the flywheel has a balance factor built into which makes it an externally balanced flywheel.
Eric

mcmonroe

Hey Eric,

Thanks for the input. Another question or two if you dont mind. <smile>

So -- is the "balance" factor on all dual mass flywheels then the same? meaning that they can be interchanged?

I am looking to replace my stock L98 dual mass flywheel with a nice lightweight billet aluminum or steel unit and want to make sure that I get a unit with the correct balance -- either neutral or external balance. Would any replacement externally balanced flywheel work fine -- or would it need to be "match" balanced to the orginal flywheel that came off my car?

Many thanks,

Mark Monroe
Harrisburg NC

Exotic Muscle

Mark,

Don't get confused between internal and externally balanced on the Chevy motors. The L98 and LT1 are kind of weird in that the front of the engine is internally balanced (the Crank damper is Neutrally balanced)and the back is externally balanced because the flywheel has a small counterweight on it.

However, to throw another little twist, the Chevy Flywheels come balanced but with little metal weights that drive into drilled holes around the perimeter of the flywheel. When you replace your flywheel with another factory flywheel, put them next to each other and using the dowel hole in the flywheel flange as a reference point duplicate the factories weight placements on your new flywheel. The weights are available from General motors for the factory flywheels.

For any other non-GM flywheel for your L98 or LT1, most suppliers will offer a predetermined counterweight machined into the flywheel. The problem with universal fitments for flywheels is there is no way to have it precisly balanced to your engine. We've used flywheels from the same manufacturer (with the same weights) and be fine on one engine and have minor vibrations on others. The only way to be assured of a perfect balance is to balance it to your rotating assembly.

Eric@ Exotic Muscle


Eric@Exotic Muscle

mcmonroe

You have been great Eric,

I have both a brand new from Luk 1991 L98 flywheel and the orginal worn out one from my car. They both have the following part numbers on them -- 10174482 and 1020407400. I have placed both of them on an ordinary bathroom scale and they each weight about 38lbs. They both appear to be the same -- the holes on the outer each are the same, neither appear to have any additional weights placed in the outter holes, the holes on the backside appear the same also. I can see no realy significant differences between the two (other than one being worn out and shot obviously <grin>).

Do you think it would be necessary to have the new replacement balanced to match the original flywheel? Also -- since the old worn out flywheel has obviously seen several years of hard abuse I can't imagine that it would weigh exactly the same now as it did when the engine was built. Can I even trust that a good "reading" can be taken from the old flywheel? Would it best to simply install the new flywheel and go from there if there are vibrations and problems?

All ideas are greatly appreciated!!

Mark

corvette1990

ok here is another balancing question, now that you have peaked my interest. I swapped a ZZ4 crate motor into my car and used the original smaller front balancer (which shouldnt be a problem according to your summary about the front of the crank being balanced. I used the fly wheel that came with the ZZ4 so it should still be balanced at the back. Right? I wondered why the new motor came with a flywheel. Now when I build my 383, and order a new crank (one piece rear main seal). I will have to get a new flywheel and have it balanced with the crank? Can they balance it if I buy both from the same place? or does it need to be in engine to balance? You really have me curious now. Tks

Exotic Muscle

Like I said it's kind of a hit and miss deal with the "Chevy Balance". You might be able to put the flywheel on and have no vibrations or you might put one on and have a small vibration.

The best thing to do is get the rotating assymbly balanced with the flywheel but sometimes it is not feasible to do so. Or, you can take your chances. You will probably know if you have a little balance problem. it will vibrate more than it did with the factory Setup.

When you go to a 383 you won't have to get a new flywheel but it may be a good idea to get the assymbly balanced. I'm sorry that I'm starting to sound like a broken record but it's just so difficult with the L98/LT1 to KNOW if it will be balanced or not.

And your old flywheel should still be balanced although you might want to get it resurfaced depending on how it looks.

If you are going to go high horsepower, McLeod makes a great dual disk setup that comes with a flywheel (aluminum or steel) and is usually about the same price as getting a new OEM flywheel and aftermarket clutch and the clutch pedal effort is about the same as well. Just one option.
:)

Eric@Exotic Muscle