When I get ready to install my new piston is it really necessary to gap the rings? I have helped my dad rebuild a couple motors and I hardly ever remember having to gap piston rings before we installed them.
improperly gapped rings can be a big hp robber, they can also wear your cylinder out much quicker especially on nikasiled cylinders.
not to mention the oil stuff
a lot of the piston companies will make them very close like dl said so sometimes it may not be as necessary but you always need to check. CP generally are tight i have had them lots of times overlap themselves so it would almost be hard to install them without some gapping. This is a good thing imo so you can set the proper gap.
this includes oil rings and compression rings and oil ring spacer (waffle ring) the oil rings are the toughest thing to gap correctly and take a lot more time most people will generally just gap them rings themselves but after they get gapped they should be installed on piston with waffle ring and check tension getting pulled through cylinder (needs oil) you need to similate what it will do in real life. modifying a waffle ring is a lot tougher and usually those are real close a tiny modification will create a big result and they are easy to make them to loose where it will burn a lot of oil. i generally spend a good amount of time properly gapping rings sometimes up to an hour to make them like i want. but properly gapped rings can be the difference of quite a few hp