Cylinder bore polishing is considered one of the most serious life limiting factors in heavy duty diesel engines. The origin of bore polishing is described. Reasons for expected increased occurrence in the future are discussed. Long stroke engines with more favorable surface to volume ratios will become more prominent. On the other hand, lower engine profile requirements dictate less favorable r/1 ratios for the crank mechanism. In addition, other development targets such as higher power density and increased cylinder pressures for efficiency improvements have an effect.Bore polishing prevention by traditional methods such as the use of small topland clearances, and alternatively large topland clearances is described. Potential problems with each approach are discussed. In particular, the detrimental effects of large top-land clearance on performance due to parasitic losses are described.The successful application of a “calibrating ring” insert in the Copland area of the cylinder liner is described. Bore polishing was totally eliminated, parasitic losses were minimized, engine efficiency was increased, exhaust smoke and oil consumption were reduced.