What requires a rotating assembly to be rebalanced?

If a rotating assembly was previously balanced and one or a combo of the following was performed does the rotating assembly need to be re-balanced?

Recondition connecting rods
Replace pistons rings
Replace rod bearings
Polish crankshaft

Is there a general guideline of when a rebalance should take place?

A before and after of the rods would've told you but I doubt their weights changed enough to make a difference. Were they resized?

No repairs have been performed...

It's a general question

No reason to re-balance unless some weight is removed or added.

Changes have to be pretty substantial in most cases to need a rebalance. Anything you mentioned is miniscule

Recondition connecting rods----- No but a quick check never hurts.
Replace pistons rings-----No
Replace rod bearings-----No
Polish crankshaft-----No


I have a gram scale that I balance my pistons and rods before I even take them to the shop. That way we can double-check each other. I always ask for a copy of the balance sheet for every assembly I have done. They also keep a copy too.

As far as recondition connecting rods, if you have them resized and or replace the bolts your probably good, if your replacing the original rods with a different set of recondition rods I would definitely have them check for balance on both ends and length I went through around twelve sets of LY rods years ago when I was still racing NHRA stock, the factory standards for production motors is not real precise
I've saw .017 in length and a hoop of weight differences (35 grams from the lightest to the heavy one) in those rods

Most shops know that about a little under 30 grams anywhere and you better redo it--under that --it is usually ok---many factory tolerances would accept that back in the day--I agree with the others NO need to re-balance even if you grind crank--go to different rod bearings etc--No worry!

Don't laugh when I ask this. But you definitely need to rebalance when you replace pistons correct?

i would guess only if they are heavier, or lighter than the original, balanced, set. unless the total set is only 10 grams or so[? amount] different in weight. of course, you would weigh each piston and get each to weigh the same as you would normally. is this a correct assumption ? if not, please correct me with the weight difference for the re balance necessity.