I have sealed power .40 over pistons installed on std rods. I did not weigh these parts separately for balancing prior to putting them together, but weighed them assembled.
There is a 5 gram diff. between lightest and heaviest piston/rodd assembly, with caps.
Where should I shed the excess weight?
Also, Caps vary among between lightest and heaviest by 10 g. Can I lose the weight in the cap only? Or do I go through time and expense of Taking pistons off and weighing, then reassemble? Thanks, folks.

Take them apart! Weighing the piston is completely diffrent than weighing the rod. The rod is roational and linear so you need the proper set-up to measure it(read my article on Rod Polishing). There are two "pads" at the top and bottom where you can shave metal as needed. The pistons you can simply throw on the scale and they have pads right underneath the pins, or just inside metal will be fine. If you don't/can't take them apart don't bother, you can easily do more damage than good.

Thanks.
On the other hand, Could a matched set of Sealed Power pistons be off by 3-5 grams from lightest to heaviest? Yeah, I know, take 'em apart and check. By the way, this car will not be raced. But I will try to see how fast it can go!

Raced, driven, idled it could tear your engine apart. I have no idea about the weight differences of the pistons. We can only measure as human to a certain accuracy, so your assuming that the connecting rods are perfectly all the same weight and that all the variances are in the pistons. If you were to take them apart and let's say match all the pistons weights that will certain help. For a street car this should be fine, or maybe you want to weigh the pistons and drop the rods off at a shop. Assuming your not going to balance the crank which I don't hear a lot of right now this could be a good way to save some money. Or you could take the money you saved with the pistons and have the rods/crank shot peened. Just bouncing ideas.
The overall it's smart your touching on balancing your internals it's a good move. I know when I was a more of a novice engine builder (in otherwords when I was 16) I was more concerned with more carb and headers. Well, the engine is a machine that depends on all parts being matched and it's alot easier to do internals now than later. Sorry if this sounds like a lecture it's meant to be a compliment and advice.

Chances are good you'll never feel the difference between balancing your parts and leaving them as-is. Nothing is going to blow up or fail just because one rod and piston assembly is 5 grams heavier than the lightest. I would worry more about cleanliness, the bores being straight and round, bearing clearances being correct, etc.

_________________
Joshua

I agree with Josh. If your not making over 200 HP you could spend the time elsewhere.

I have 40 over stock style pistons and rods (sans Balancing) and my slant is smoother running than my fully balanced 400hp/cid sbc.

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

I'm a touch over 200 horse, and I have never balanced squat. Were I building something that was going to rev 7000+ or something I was looking for every last 1/1000th of a horsepower I would do it, but reality here is that we are building a Slant.

_________________
Official Cookie and Mater Tormentor.