Bulletin: TB1044

Subject: Piston Ring "TOP" Marking

Engine: All

Perfect Circle Part Number: All

Explanation:  We have had some installers ask why some piston rings which appear to be symmetrical have one side marked "top"; for example, the top ring in our RS6454 Premium Plus ring set for Cummins 855 engine applications.

In appearance, these barrel faced keystone top rings may seem to be symmetrical. However, there may be very small differences in the ring side angle or face profile which make them perform better in one direction than the other. In most instances, these differences are very small; they may only amount to the way in which manufacturing tolerances are specified, but these slight differences have a definite influence on performance.

Rest assured that if one side of a ring is marked "top", there is a reason for it and the ring should definitely be installed with that side toward the crown of the piston. Besides the word "top", other methods of indicating the top side of a ring are either a round or an elongated indentation.