I know internal balancing you have to take it to a machine/speed shop and they balance out the crank rods and pistons, but how exactly do you externaly balance? The 383 crank I got says it shud be ext. balanced, meaning I have to get a 400 flywheel and balancer. But, is that it? Do I still need to take it to a machine shop and let them balance it with the balancer and flywheel, or what?

 

An externally balanced engine has a special harmonic balancer and flexplate/flywheel. If you look at any of them you'll see they have a counterweight incorperated into them. The balancer has a larger section cut out of the rear. The flexplate will have a weight welded onto it. This adds the required weight to the crankshaft balance.

Internally balanced engine have neutrally balanced balancers and flexplates. All the balance weight is on the crankshaft. Normally an engine is externally balanced because there's not enough room inside the engine to allow the extra weight on the crankshaft.

You can have a 383/400 internally balanced but it would cost more than buying the proper balancer and flexplate. They would use an expensive and heavy metal called mallory metal to add the extra weight.

All the BBC engines are internally balanced up to but not including 454 CID. Above that displacement, they're all externally balanced.

 

When you take an externally balanced engine to the machine shop to be balanced, you take everything you would normally take for an internally balanced engine plus the balancer and flexplate/flywheel. Without them, they can't balance the engine.

Anytime you change internal parts such as con rods or pistons, everything should be rebalanced because the weights are not the same as factory production weights.

 

so as far as the machine shop balancing out everything, it wud be about the same for internally balancing as it wud be externally? just the prices for the flywheel/balancer wud be a little different?

 

Cost to balance the rotating assembly is the same. Cost of a internal balanced balancer and flexplate should be about the same as the external balanced ones.

A factory replacement internal or external balance 8" balancer is the same price. Performance balancer's will vary in price depending on which one you use.

SBC flexplates are roughly the same price also.

Now if you want to have an externally balanced engine internally balanced to try and claim to only have a 350 engine, then it will cost you a lot more for balancing. Anyone who knows SBC engines can easily look at the balancer to see it it's an internal or external balanced engine. Seeing a 400's balancer means you either have a 383, 400/406 or possibly a 434. Throw a chrome cover over it and the'll never be able to tell anyway.