It is generally known that the U.S. automotive manufacturers have reduced the cross sectional size of piston rings in the last few years. In reducing the cross-section, It is also necessary to reduce the depth of the groove to facilitate installation of the oil ring assembly.

Replacement piston manufacturers have in some instances stayed with a deep groove piston. In some other instances they have matched the O.E.M. piston and used a shallow groove. To give some reference to the "deep" and "shallow" nomenclature, a deep groove win generally be .190" or more while a shallow groove is .190" or less. To cover the possibility of two groove depths in one engine application, piston ring manufacturers have had to issue two differently dimensioned ring sets for the same engine.

If a deep groove ring set is used on a shallow groove piston there is a good possibility the ring will bottom in the groove resulting in severe engine damage.

To determine if this condition exists, install the oil ring in the groove in the normal manner. Push the assembly in as far as it will go in one side of the piston. If the rails protrude as shown in the sketch, the oil ring is incorrect for the groove.

A straight edge held against the rails and squared up will aid in showing if this condition exists. If it does, do not assemble the engine. Consult the manufacturer catalog to obtain the correct set of piston rings.

If a shallow groove oil ring is used in a deep groove piston, installation of the ring onto the piston will be difficult. The ring assembly will "pop off" the piston as shown in the sketch below.

If the oil ring is centered in the groove and does install in the cylinder, it will function normally. The major problem with this condition is installation of the oil ring assembly.

(P70-71)

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