Flywheel for 1 Piece Rear Main

[Windycity1]

Does anyone know what flywheel I use for an internally balanced chevy 383 motor with a one piece rear main seal?

[toxicz28]

Anything for an '86-up 350. (not sure about LT1 flywheels though) Also, the tooth count on the flywheel will effect bellhousing clearance.

[TPI Monte SS]

I think the LT1 flywheels are different; you'd need the whole clutch/bellhousing assembly as well to use the LT1 flywheel. If you're building a mild motor, you can use a stock flywheel for an '89 F-body. I'm using a stock 16 lb. nodular flywheel with a RAM clutch behind my ZZ4-cammed 355, and it behaves nicely.

[TD509EFI]

Don't use the 1986 and up flywheels if your running an internally balanced rotating assembly. GM doesn't offer a neatral balanced flywheel for one piece seal crankshafts, so you'll have to go aftermarket. MacLeod, Hays, Fidanza, Spec, etc should have a neutral balanced one piece seal flywheel that you need.

John

[KeislerRich]

Don't use the 1986 and up flywheels if your running an internally balanced rotating assembly. GM doesn't offer a neatral balanced flywheel for one piece seal crankshafts, so you'll have to go aftermarket. MacLeod, Hays, Fidanza, Spec, etc should have a neutral balanced one piece seal flywheel that you need.

John

+1 I agree. The '86 and up motors are not internally balanced and require a counter balanced flywheel. My guess, is you'll have to have a custom one made.


Richard
Tech Support

[GMJim]

Yes GM does make a counterbalanced flywheel for THEIR 383 crate engine. (If that is what you are referring to) It's the same flywheel as used on the 350 ZZ engines. When GM went to the one piece rear main in 1986 the flange/counterbalance on the rear of the crank had to be removed and the weight was added to the flywheel. The ZZ one piece rear main engines are still considered internally balanced however they use a counterbalanced flywheel. Most people selling parts for this engine still refer to it as internally balanced. The 10105832 is a popular 30 lb. flywheel for ZZ350 and ZZ383 Engines and is still available from GM. http://www.who-sells-it.com/cy/gm-pa...-fullsize.html

A stroked 383 (two piece rear main) uses a externally balanced flywheel and balancer. These days it's easy to get confused with flywheels. The after market builds cranks for stroker engines in both configurations! Be careful.

[TD509EFI]

JIm,

With all respect, I think your statement that all ZZ ( and by inference, all one piece seal engines) are considered as internally balanced really adds to the confusion concerning the question that Windycity1 posted. Are they internally balanced? The answer is no, you can't put a neutral balanced flywheel ( which is what you would use on an internally balanced engine) on a ZZ style or one piece crank UNLESS that crank was internally balanced by a machine shop. Unmodified one piece seal cranks from GM must use a counterbalanced flywheel. Aftermarket one piece seal cranks that state they are internally balanced ( or can be modified for internal balance) can, if the necessary balance is done.

Not trying to be stupid about this, just hate to see someone use the wrong flywheel.

For anyone that's unsure, here's an exerpt from a GM Performance Catalog:

"In addition, all cranks which use a one piece seal require a counterweighted flywheel for proper balance"

John

[GMJim]

JIm,

With all respect, I think your statement that all ZZ ( and by inference, all one piece seal engines) are considered as internally balanced really adds to the confusion concerning the question that Windycity1 posted. Are they internally balanced? The answer is no, you can't put a neutral balanced flywheel ( which is what you would use on an internally balanced engine) on a ZZ style or one piece crank UNLESS that crank was internally balanced by a machine shop. Unmodified one piece seal cranks from GM must use a counterbalanced flywheel. Aftermarket one piece seal cranks that state they are internally balanced ( or can be modified for internal balance) can, if the necessary balance is done.

Not trying to be stupid about this, just hate to see someone use the wrong flywheel.

For anyone that's unsure, here's an exerpt from a GM Performance Catalog:

"In addition, all cranks which use a one piece seal require a counterweighted flywheel for proper balance"

John

John
No offence taken! You are correct that a neutrally balanced flywheel won't work on a ZZ engine.

What I said was
"The ZZ one piece rear main engines are still considered internally balanced however they use a counterbalanced flywheel. Most people selling parts for this engine still refer to it as internally balanced."

Maybe I should have said, still considered by many to be internally balanced?

And
"The 10105832 is a popular 30 lb. flywheel for ZZ350 and ZZ383 Engines and is still available from GM."

My explanation was to eliminate the possibility of installing the wrong flywheel, not to confuse the issue.

I have a stack of GM publications that refer to the 86 and up one piece rear main engines as internally balanced so even GM is guilty of making this more confusing.

We deal with this issue every day and sometimes It can be a challenge to get the info right as even GM publications contradict each other.

With respect to you, your GMPP excerpt "In addition, all cranks which use a one piece seal require a counterweighted flywheel for proper balance" is not necessarily correct with GM (Callies) and other manufacturers. It is true with most stock GM cranks but GM, Eagle and others make a one piece rear main crank that can be either internally or externally balanced and I have had close up experience with this issue.

The 572 for example is a one piece rear main crank (Callies) but uses a neutrally balanced flywheel.

Excerpt from GMPP.
This engine uses a Gen VII internally balanced Flexplate part # 12561217 & 6 bolts part # 3727207. If a manual transmission flywheel is needed, part # 12555135 & 6-839756 flywheel bolts must be used,Remember that unlike the 454 and 502 engines, this engine is internally balanced. Using the wrong flywheel/flexplate can destroy the engine due to a severe out of balance situation.

Check one piece rear main column.
http://www.eaglerod.com/products/Che...%20cranks.html

I really believe conversations like this help everyone understand that things can change quickly and we can all learn from each other. Don't feel bad about having a little debate from time to time. I can be wrong and I know it!
Regards

[TD509EFI]

JIm,

I'm in complete aggreemnet with you, some of the statements made in GM publications, and others can be misleading, especially for beginners.

I can just see a newbie going to the parts store and asking for a flywheel for his 350:

Nebie: "Need a flywheel for 1987 350"

Parts Guy: "Is that internally or externally balanced?"

Newbie: (thinking about what he read on the 'net and in some books)

"ït's internally balanced"

Get's home, installs it, takes it out for a drive and proceeds to shake his fenders loose from the frame, and pop the fillings from his teeh.

I know... a little extreme, and probably not likely to happen, but you never know....

Thanks for the great write-up you posted on this. Hopefully, we all learn a little bit from your research.

John

[andrewb70]

There are two things to consider. First the flywheel register diameter and then whether the engine is internally or externally balanced. The early engines had a different flywheel register diameter on the crank as compared to the later engines. All later engines were externally balanced in stock form. That is the reason that GM changed the register diameter so an early flywheel would not work on a later engine.

Now a later engine can be built so it is internally balanced so in that case a "hybrid" flywheel must be used. One that is neutral balanced but has the later flywheel register. Clear as mud!?!?!

Andrew

[GMJim]

Ah yes ! Isn't life interesting?

I have given up trying to remember all this stuff.
Jim

[BritishGreen68]

Just went through this myself.. kind of...
I had a ZZ4 350 and you did indeed need a flywheel that has a counterweight on it.
IF your 383 is built by a machine shop and is truly internally balanced, then you need a zero balance (ie. non counterweighted) flywheel obviously, that will bolt to the one piece rear main seal engine, which from the sound of it has to be after-market. If you buy the GMPP flywheel that's for the ZZ4 or ZZ383 for your custom built internally balanced 383, it will be the wrong fly wheel as far as counter weight is concerned.