How do I know the difference? Ordering a flexplate soon?
I'm having a brian fart moment.

 

Forgot to add that the last time I built this engine the machine shop balanced it and had my balancer and flexplate but there are no signs of adding weight or taking weight away from either.

 

Olds engines are external balance from the factory. Switching to internal takes significant work on the crank. So if you didn't pay someone for that, then you have an external balance.
The flexplate should have a weight on the back, just a curved piece of metal welded on. Most shops focus on the crank when doing the balancing so you can, in theory, swap out balancers and flexplates as necessary.

Note that the new flexplate *will* have a different balance. It may or may not be worth rebalancing the entire assembly, though.

 

I'll add that there are two types of flexplates/flywheels for stock Olds motors, the 64-67 style and the 68-90 style. The difference is the bolt pattern on the crank. Unfortunately, in our Chevy-centric world, vendors for some reason think this means that two different designs represent internal/external balance.

 

Thanks guys. This is pretty much what I figured but wanted to be sure.

I'll be swapping out a Mondello heavy inertia wheel for a lightweight SFI replacement from Rocket Racing.

The Inertia wheel does have a weight bolet to it and my 445 is a 68 block with a 70 N crank.

 

Does Brian Fart sell flexplates? Lol

 

Maybe. HaHa! This was a beer induced type-o. Good catch.