Discussing with my cousin if his engine builder properly balanced his Pontiac 400 crank. My understanding is that the Pontiac 400 is externally balanced.

What is the proper procedure to balance the crank assy for an externally balanced engine?

Use the correct damper and flex plate / flywheel.

My issue with that is that the damper is not a rigid device. How do you get a correct balance if you have a non-rigid device on the rotating assembly?

If the counter weight was cast in the outer ring , it could have conceivably moved.
But verifying TDC with the timing marks AND with the piston will tell you if it has moved.
You will have slight variations in balance as things move.......that's how it works. The differences are so small that they are not an issue unless the weight moves to someplace it shouldn't be.
If you roll the dice with a stock balancer , that is what you get.
A quality SFI rated piece takes care of that.
But stock pieces obviously do work.
How old is the one you are thinking about using ?
They do wear out.

IIRC, the Pontiac is externally balanced by the flywheel/flexplate only, the damper is neutral balanced.

Thanks for the replies.

The damper is a new aftermarket elastomeric type. The builder did balance with the flywheel and damper.

I have not seen it, but my cousin says there are no weights on the flywheel (flex plate). Is that normal? The balance weights would not be on the torque converter - or would they? The flywheel is a new Hays unit.

I am trying to understand that everything was balanced correctly, but I am struggling..........

I understand the concept that if the crank is externally balanced with the flywheel then the flywheel needs to be installed on the crank during balancing - but if there are no weights on the flywheel????? And if the engine is only balanced with the flywheel, then I would not have expected him to balance with the vibration damper installed.

Here's the answer:
Pontiacs are not "internally balanced". There is a slight imbalance (about 6"-oz.) at the rear. Rather than adding weight like chevy and Ford, Pontiac removed some weight from one "side" of the flexplate/flywheel to bring it "in". The front portion IS internally balanced, so the balancer is "neutral".

Thanks to Mr P body on another forum.

R.