The Ring belt
It is most important that this part of the piston be accurately made. In particular, each ring groove should lie in a plane at right angles to the cylinder axis. This part of the piston is generally given more clearance in the cylinder than the skirt, and does not normally bear against the cylinder. The ridges which separate the grooves are called lands.
There are usually three or four of these grooves above the skirt, and sometimes one in the skirt below the gudgeon pin. These are discussed in greater detail later in this chapter in connection with piston rings.
Pistons that are prone to ring groove wear can be fitted with an iron ring carrier which is metallically bonded into the piston. This process provides good heat flow and ensures that the ring life is extended.