Hole-Shot

How do the two differ from each other?
What are the advantages/ disadvantages of each???

Thanks!
:cheers:

Monty

An externally balanced engine uses a damper/balancer and flywheel/flexplate with counterweights. An internally balanced engine uses neutral balanced dampers and flywheel/flexplates. It can be a little confusing, because externally balanced engines can still have the cranks balanced by either removing material, welding on materal or adding mallory slugs, but still uses counterweghted damper/balancers and flywheels/flexplates.

Advantages/disadvantages of each? Depends on who you ask. Both have been used in production vehicles and have proven themselves in all types of applications. SBC 400's and big blocks were externally balanced from the factory. Internally balanced engines allow greater freedom/selection in dampers and flywheels/flexplates, and some will argue are better because you don't have the counterweights on the extreme ends of the crankshaft. For high-output, high-rpm applications, I prefer internally balanced.

HunterRose

Hi Monty,

I've been curious about this situation too (since I'll be dealing with this very issue in the future)...

So, if I buy the rotating assembly elements already balanced (to much better tolerances than production 400 assemblies came, I would hope!), then external balancing elements aren't really necessary?

Tony

jburnett

Not all OEM big block Chevys are externally balanced. Just the 454 and the 502 crate motor is... The 396's and 427's with the 3.75" stroke are internally balanced. The 400's are externally balanced and the majority of the street 383's are also externally balanced. Monty's descriptions of the differences are spot on. The main advantage of the internally balanced motors are better high rpm stability and the ability to use lighter flywheels/flexplates and harmonic dampers. Here's something even more interesting...Some motors are 'split balanced' meaning they are different from front to rear...The LT1's are an example of this; internally balanced front and external rear...Weird, huh?
-Jeb Burnett

aobrien

http://forums.corvetteforum.com/zerothread?id=263852

This thread goes over externally/internally balanced pretty well.

Basically, if you have your components internally balanced then you don't want to use externally balanced flywheel/damper because your parts are already balanced.

Hole-Shot

I may need to replace my flexplate in the future (chipped teeth). My 383 currently has a 400 small block, 153-tooth flexplate. The flexplate does have a spacer/balancer plate on it. If I replace the flexplate, will I mess up the balancing of the motor?

What if I were to reuse the spacer/balancer? Would my motor still be properly balanced? Or would I need to have the motor re-balanced?

Thanks!!
:cheers:

jburnett

You will need a matching flexplate to keep your externally balanced 383 in balance when you replace it. To go one step further (or at least what we do) is have the new flywheel spun up to ensure that it matches your old one correctly, if it is off that will need to be rectified. It's basically "match balanced".
-Jeb Burnett

Hole-Shot

Jeb,

Do you have/know of a shop that you could recommend to do the "match balance" work to my flexplate?

Thanks!!

vette punk

So how would a 383 small block being used with a ZF 6 transmission and aluminum flywheel be balanced?
Jim B.

jburnett

A good flexplate/flywheel manufacturer (RAM, McCleod, etc) will be able to match them, otherwise a good engine machine shop should as well. In response to VettePunk's question it kind of depends. Are you building an externally or internally balanced motor? If it's externally balanced there are single mass aluminum 153 tooth flywheels that have a counterweight on them for use in externally balanced motors. If you choose internally balanced you simply get a neutrally balanced 153 tooth flywheel.
-Jeb Burnett