Rod balancing how important it is!

I am building evo 8 engine. I put rods on scale and all 3 rods are weighing exactly the same except the last one is 0.7 gram lighter. So I put all of them on connecting rod balancer fixture and I can't achieve repeatability. Every time I have different numbers which make me nuts. Should I leave it alone and keep going with assembly or is this good idea to just grind this 0.7 gram out of big ends to match overall weight without knowing where actually this 0.7 gram should be taken out. I know 0.7 gram is not horrible but I would like to be within 0.1-0.2 gram if possible but look like I can't achieve repeatability at all. Thanks!!

Personally, I'd call that within the range of repeatability, as you've found - certainly well within tolerances.

Remember, there will be varying amounts of oil flying around within the crankcase and so differing amounts on the rotating assembly at different times. Then there's the slight variations in compression pressures due to cylinder filling and the combustion processes within the cylinders.

Not to mention the possible differences in the piston assembly masses.

Thank you for help. Is it better to match heaviest rod with lightest piston or should I balance all pistons withing 0.2 gram and have 1 rod that is 0.7 gram lighter? Thanks!

Might be worth checking this - https://www.hpacademy.com/previous-webinars/268-balancing-pistons/

Generally, lightest piston with heaviest rod - preferably the one with the heaviest small end.

Got it. Thanks!!