How can I tell if a small block is internally or externally balanced?

Speaking of "factory harmonic balancers", if it's internally balanced the harmonic balancer will look the same all the way around front and rear. If it's externally balanced the harmonic balancer will look the same in the front but have a big thick groove like notch around about half of the back side of the balancer. Can you post a pic or two?

Only 400s were external balanced.

How can I tell if a small block is internally or externally balanced?

quick check,,, flexplate has a weight welded on it. 400 stock dampers have a relief cut out of the damper O.D. about 1/2 way arround and about 1/4" wide and about 1/4" deep.

if the pan is off or you have access to the crank,, it will have mallory metal plugs in the end couterweights if it was internally balanced. evidence of welding/grinding on the sides of the end counterweights.
andy

Only 400s were external balanced.

I thought the one-piece rear main engines were as well.

I thought the one-piece rear main engines were as well.

they're like the bastard child. 1/2 internal up front with a neutral balance damper,, and an external weighted flexplate in the rear. kind of a wierd deal with that one.

my description in the last post was about looking at a 400sbc factory setup,, just to clarify.
andy

Thanks Guys, the harmonic balancer that came w my new used engine is uniform front & back except for 2 shallow .5" dia. drill holes on the back of it. It is a couple of lbs lighter than the stock one on my old 350 so it had me wondering.

I thought the one-piece rear main engines were as well.


The way someone explained it to me....The 1 piece seal motors are internal. The thing is the rear of the crank doesnt have the counterweight as 2 piece do. To overcome that, the weight is on the flywheel.