Today I was talking to a buddy and he said my LO3 was externally balanced. I could have sworn they were internally balanced. Who's right? Other than the 400 SBC, what motors were externally balanced? Thanks
-Rippin

 

All the one-piece rear main seal small blocks have a counter weight on the flywheel or flex plate.
The machinist said he needed the flywheel to balance my 305 motor because it has the last counter weight on the flywheel instead of on the crank like the 2 piece rear main seal cranks do.

It’s still internally balanced motor.

 

Yea its internally balanced, but the crank is slightly different than a 350 crank of the same era. If you take a 305 crank and lay a straight edge across the macined portion of the crank it will hit the crank on all of the humps. It wont hit every one on a 350 crank

 

MOSTLY internally balanced. The flexplate on these motors (305 and 350) has a "batwing" counterbalance on it that makes it NOT QUITE totally internally balanced.

I know, I know, it drove me nuts, too, but that's how they were made.