is the 305 SBC externally balanced? i didnt think it was but a friend who has been workin on cars since the 70's says it is so i wanna know.

 

It is internally balanced.

I think the only externally balanced production sb chevy was the 400.

I hope you don't bring your car to your friend to have fixed

 

Well, to be technically correct the '55-'85 SBC (except for the 400) were all internally balanced. The '86-'9? were balanced differently than the early SBC, yet similarly to the 400s. Although they are not considered externally balanced because they truely are not, but rather there own type of balancing.

 

Agreed. In a sense, even the '55-'85 SBC's were "externally balanced" in that a counterweight existed on the crank external to the crankcase, but the flywheel/flexplate was "neutral" balanced. In '86, with the one-piece rear main seal, they couldn't have that counterweight there on the crank anymore, so they put the weight on the flywheel/flexplate. The harmonic damper stayed neutral, though, unlike the 400 SBC's.