How do I tell if my 340 is internally balanced?

pt70 said
According to a 1971 FSM the weight of the pistons are all the same from std. to .040 oversize. KB brand also the same weight from std. to .060 o'size. There are pads cast into the bottom of early 340 pistons which are machined to achieve the proper weight. TRW is now Speed Pro.

According to the 1971 book, 340 piston weight is 719 grams. ----- 360 wt = 584 gms. ------318 wt = 592 gms.
Is this a misprint? Or are they really that heavy? -----
KB = 597 gms
Ross = 560/514 gms
Wiseco = ~550 gms

So if pistons are changed in an early 340, it is necessary to have the engine balanced [unless someone makes 719 gram pistons]?
Piston weights are tough to find sometimes. I gave up after my head started to hurt. I am not an expert on balancing , just find it interesting.

So maybe a cast crank heavy rod 318 c'shaft would end up being neutral balance in a 340 if the 597 gm piston was used? Pretty close!

Yes, I have dug out that same data of 719 grams. I had a set of 340 pistons that I got with some junk and that had been ruined by water; I weighed 1 or 2 as best I could with all the corrosion on them and that number looked right. They are heavy old slugs.

593 gr for the 318 is right too. FWIW.... 273 is around 548 grams but balances with the same crank as the 318's. The weight difference it made up in a super heavy pin used in the 273's to equalize the piston+pin weight between the 2 engines.

As for the weight being the same for all oversizes.. not what I have found. Example: spec sheet KB243 is 588 grams. Actual set of .020" oversize were weighed at 575 grams. Just sayin'...