Question on balancing

[ss3011]

If your parts are out of balance, the vibration you feel is a force or load. This force will increase exponentially with increase in rpm. Those forces could fail parts, depending how high the load gets, compared to how strong the parts are. Bottom line, stuff needs to be balanced !

[Mike Schwartz]

I guess I need a little schooling too. How is the process of equalizing the weights of the pistons, rods, pins, etc related to the overall balancing process? Isn't that done first before making adjustments to the crank bobweights?

[Mike Taylor 3601]

I'll go through basics first, rods,pistons are weighed you find the lightest piston ,lighten others to match,how close varies, I balance +/- 1/2 grams or within 1 gram whichever way you want to say it. Weigh big ends rod find lightest,lighten rest to match,weigh small end find lightest,lighten rest to match.
Then you start figuring bobweight, reciprocating side uses piston,pin, locks, rings,small end of rod,then that weight is totaled and mutiplied by number of rods per throw ,V8 would be two, is mutiplied by recprocating factor normal 90 degree v8 use 50 % this is factor that is changed to over or underbalanced.
rotating side uses big end of rod,bearing,usaully we add 3 grams for oil then this weight is mutiplied by number of rods per throw,V8 would be 2.
then rotating and reciprocating are added together to make up what bobweights will weigh then bobweight s are installed on rod throws and crank spun on balancer,then crank is corrected for unbalance.

Are far as over or underbalance I never have done either,I know alot of blown alky,and big inch,and ultra high rpm 10K+ change percentage.
I would'nt worry about over or undrer balancing unless I was having vibration/unbalance caused problems
Hope this answer your question if not I try to answer them.
Mike Taylor 3601

[DIV3CR]

Back in the 60s &70s we would over balance some race engines,
we never under balance. If I remember correctly we added weight
to the bob weights to compensate for the centrifugal force of the
rod journals at high RPM. We over balance up to 50%,

[Mike Taylor 3601]

to over or under balance you change the percentage of 50%to to percentage of more or less as example 48% or 52%
Mike Taylor 3601