I remmber reading some where!! that the GEN 1 SBC with the single piece rear main seal in externally balanced? is this true or not? I am haveing to rebuild mine and wnat to upgrae the harmonic ballancer and possibly go to an aluminum flywheel.

thanks
steve

 

The only factory Gen I SBCs that were externally balanced were the 400s. All others are internally balanced.

 

i am wanting to say that it is internally, but i would wait on a second person to answer since i am not 100% sure

 

Internally balanced. The flywheel does have an external counterweight on it due to the one piece rear seal, but the engine is internally balanced.

 

The harmonic damper will need to be a neutrally-balanced part.

The flywheel will need to be a one-piece rear main seal part, which means it will not be neutrally balanced. But, that doesn't mean it is the same as a 400 flywheel.

This whole "internal vs. external balance" thing with one-piece rear main seal cranks is kind of silly. Technically, two-piece rear main seal cranks were "externally balanced", because the counterweight was outside of the crankcase - but, it was part of the crank. However, since one-piece rear main seal cranks cannot have the counterweight outside of the crankcase, the factory chose to put a weight on the flexplates/unbalance the flywheel to provide that function. As stated, the 400 engines were "externally balanced", because the damper and flexplate/flywheel were weighted to complete the balancing.

 

57, nailed it!