R2. You need more than a scale for the rods. A rod is suspended by
each
end and in turn the big ends and the small ends are weighed, the C.G.
is
deduced. In other words the rotating and the reciprocating masses are

measured. Auto guys will then make up a bobweight of nuts and bolts

equal to the rotating part which they add to the crank throws and that
is
then spun on a dynamic balance machine

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This is correct to a point. I have balanced more engines then I care to
remember and I have never had a motor where I didn't weigh all the rods
as is. For instance if you have 8 rods and 7 weigh in at 580 or so
grams and one weighs 640, you can grind /machine /rub / pray,,, what
ever you want to do there is no way you can remove from the big end or
small end to get "that" heavy rod balance with the other seven. So the
point I was making is one could gram out the parts at home to find out
pretty darn fast is they have a bad match of stuff. Once the motor gets
to a quality auto machine shop they will put the rods on a fixture and
duplicate big end and small end weights.