If I was to install in a 686/690 piston, would I have to rebalence the rod?

 

No, you wouldn't have to. I would bet that 99% of the people that build 686/690's haven't done this. You could if you wanted to but the gains of rebalancing would probably not be noticable.

Also it is usually the crank that is rebalanced not the rod. The rod is usually weight to see how much both ends weight, but that procedure is only done when the crank is being balanced.

 

Great. Thanks for the information. i didn't know i it was something I should do, or something I shouldn't. I actually thought about installing a carillo rod if I went the route of building a 686 but if it's not required I'll have to think about doing it or not.