Alright, I know the difference between the two.

All I need to know is if an externally balanced engine that was attached to a manual tranny (flywheel) can be rebalanced to work with an auto tranny (flexplate).

What is involved and how hard is it to do?

Thanks

 

Is it a stock balance or custom?

 

If it is a 383 you need an external balanced 400 flexplate.

 

I had an issue with a motor that was built for an auto, and had an externally balanced flex plate.

I decided to fit a manual box, so purchased a new (stock balance) externally balanced flywheel as recomended by the engine builder.
After firing up, I had engine vibrations from 4000 rpm up.

Pulled trans off, removed flywheel and clutch pressure plate, and sent them off along with the originally fitted externally balanced flex plate to an engine balance workshop.
I didn't see the procedure, but this is how it was explained......

They placed the flex plate onto a similar crank as mine, and zeroed their instrumentation for neutral balance.

They then removed the flex plate and attached the flywheel, and compared the "balance" of the flywheel to the flexplate.
Balance was out by 55 grams. Flywheel was drilled to compensate.

Then the clutch pressure plate was attached, and balance rechecked...
a further 17 grams of correction was required.

Flywheel and pressure plate have been re-installed on motor, and the vibrations at 4000 and up have diminished.

I guess in your case, you could match the external balance weight of the new flexplate to the balance weight of the original flywheel.

I've learnt my lesson though..... in future I will insist on an internally balanced rotating assembly. Saves a lot of mucking around.

 

The externally balanced GM production engines were compatible with both their corresponding flexplate or flywheel. This way an engine could be either mated to a production flexplate/auto transmission or a production flywheel/manual transmission on the assembly line.

My ZZ4 came with a counterweighted flexplate. I replaced it with a stock counterweighted flywheel. The ZZ4 is externally balanced.

I think that engines should be internally balanced. It just has to relieve a lot of crankshaft stresses. Also, as noted above, an internally balanced engine means you can switch flywheels or convert to a flexplate with out concern (assuming the flywheels/flexplate is self balancing.)

 

So, an externally balanced 400 flexplate is my solution? I was told to buy one that is SFI approved.

The engine is a 406 and it will be backed by a TH350C.

How's this one?

 

ttt

 

Back to bashcraft's post (#3). is it a standard balance or custom? If the builder built and balanced the engine to stock GM external balance then a stock-type flexplate will work. If he custom balanced everything together as a unit then you'll need to balance the new flexplate to the same as the original one.

 

Custom balance.....So I should be alright just match balancing the flexplate to the flywheel.

What about reinstalling? Does position matter? I would think if the flexplate is modded to match then it has to be installed in the same position as the flywheel. (referring to position of mods, example: drilling or weight added)

 

You won't be able to match the totsl weight- it's the mass of the counterweight that you'll need to match. Should be no problem for a good shop.

If I recall, there is an offset bolt hole so either the flexplate or the flywheel will only go on in one position. Can't miss.