Seems like there has been a lot of talk on this lately, I will pipe in with what I learned, please add.
The gap needs to be small enough to essentially close up when the engine is at operating temperatures, but large enough that it does not bind. This measurement is based on the operating temperature, the bore and type of ring. Different metals expand slightly different. An engine that is operated at a lower temperature will have a smaller gap when cold.
The ring needs to be square in the bore to get an accurate reading, I push it down with an upside down piston.
I picked up a little tool for grinding the ends, it has a crank and an abrasive wheel. The grinding will produce a little burr on the end of the ring, make sure and clean this burr off when done grinding.
It is important that the ring grooves are CLEAN and square or they will not seal. It seems like most everyone replaces pistons now, but if not the groove may need to be machined. My dad did a lot of this in the 60s an 70s, he would turn the piston on the lathe, square up the grooves and put a spacer on the top of the groove above the ring.
The gap needs to be small enough to essentially close up when the engine is at operating temperatures, but large enough that it does not bind. This measurement is based on the operating temperature, the bore and type of ring. Different metals expand slightly different. An engine that is operated at a lower temperature will have a smaller gap when cold.
The ring needs to be square in the bore to get an accurate reading, I push it down with an upside down piston.
I picked up a little tool for grinding the ends, it has a crank and an abrasive wheel. The grinding will produce a little burr on the end of the ring, make sure and clean this burr off when done grinding.
It is important that the ring grooves are CLEAN and square or they will not seal. It seems like most everyone replaces pistons now, but if not the groove may need to be machined. My dad did a lot of this in the 60s an 70s, he would turn the piston on the lathe, square up the grooves and put a spacer on the top of the groove above the ring.