jeff, I've never seen the inside of a auto engine, I don't own one and I don't think my bro or parents would let me take one of theres apart

the hole balance thing has gone on and on, but the best way to say it is (this is for car engines not sure about plane engine though) you can't balance a single cylinder engine. you can balance it for a certain rpm but will not be balance in the other rpm range. so you just don't want to make the engine out of balance then it already is.