The influence of oil balls on the premature overlay removal of diesel engines connecting rod bearings is discussed. Oil balls are discrete spherical particles which embed in the bearing overlay. The elemental composition of oil balls include calcium, phosphorus (2:1 ratio), zinc and barium; elements which are also present in oil additives. Diesel engine manufacturers have observed a high incidence of premature overlay removal in upper connecting rod bearings.An in-depth metallurgical analysis of field returned connecting rod bearings and laboratory engine tested connecting rod bearings indicated that bearing overlay was removed prematurely due to fatigue aggravated by corrosion. The oil balls, embedded in the bearing overlay, are considered one of the contributing factors in premature overlay removal, although their exact formation and embedment mechanisms are not understood.