There are two styles of rider rings: A split rider is commonly used that is installed on the piston similar to a piston ring. A “band type” rider ring is also used in many cases; this style is a single piece continuous ring that contracts into the piston groove (like a rubber band) to provide a snug fit on the piston

The split type rider ring must be replaced when it is worn to an extent where the metal piston is within 0.25 mm of the cylinder bore at the bottom. This clearance can be measured by using a feeler gauge under the outer end of the piston. Because the split type ring is free to turn, this results in practically even wear around its periphery and re-positioning the ring will not restore the required bottom end clearance.

When the band type rider ring is used, the ring normally remains tight on the piston which results in localized wear at the bottom of the piston. When this wear at the bottom of the piston within 0.25 mm of the cylinder bore, the bottom clearance can be restored by turning the piston and rod assembly in or out of the crosshead. Refer to the following instructions which apply specifically to the band type rider ring.