Balancing an engine

Coyote Jack said

I have small blocks so I figured I might as well ask this question here.
We all know that our engines came from the factory with the rotating assembly just bolted together. No special balancing.
My question is. Under what conditions is it required to get the rotating assembly balanced? ie: over a certain rpm, over a certain HP

Jack

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For me crankshaft rotating assembly balance is NOT important, you only waste time and money for it.

Before the engine assemble, engineer has calculated how part will be made, weight, length..etc to make sure that when they put them together, they will achieve the BEST balanced. As long as you re-use the crank and rod, even you has your cylinder bore and use a new piston, this will not effect bottom end.

Think about it, the motor have 8 piston and firing order go by 1 8 4 3 6 5 7 2 , ASSUME at every 90° angles, there are explodes stroke occur, so that mean the crankshaft does not turn freely but force by combustion 4 time in 1 revolution(360°) , how do you "mechanically balance" this? This can only be done by engineer by using math and physics formula to calculate at which angle(position) the crankshaft will has much/less force, then balancing the whole thing by drill a hole in balancer . The machine shop can only balance the bottom end when crank is free, no force, its a joke.