500 piston got chipped

When you say "at the top" , if it isn't damaged at the top ring groove, and just at the top edge/corner, I would polish out the nick and use it. Sort of depends on the damage to the side surface.
You would have to get an identical piston if you replaced it, because of a possible imbalance problem. Is a single piston available from your supplier??
Most vendors usually sell in sets only.

its just on the top not near the ring so sealing shouldnt be a promblem

In that case I would use it. You may want to be sure the ring groove isn't "squeezed" in any way where the nick is, and the ring fits the groove normally.
BILL

If it was my piston that was dropped(especially since it is likely a cast aluminum piece) i would check it to make sure that no hairline cracks have occured via dye penetrant, you can do this yourself with a can of wd-40, just spray the entire part down with wd-40 and let it sit until it mostly dries up and anywhere there is a crack will show up being outlined by the wd-40.

That's a good idea. I use dye-check on aircraft parts, but hadn't heard about the WD40 trick, neat!!

BILL