The Influence of the Metallurgical Structure of Copper Lead Engine Bearing Alloys on Overplate Performance

Most overlay plated copper lead engine bearings have a nickel barrier underneath the overplate in order to minimize loss of tin by diffusion from the lead-tin-copper overplate into the copper lead. During engine operation the high dynamic loads on the crankshaft bearings of heavy duty engines result in breaks in the nickel above the lead phase in the copper lead surface. Loss of tin into the copper lead can then take place resulting in a deterioration in overplate performance characteristics. The coarser the lead the more likely is the occurrence of a break. A modified sintering process has the effect of reducing lead size, and is particularly effective with a new Cu Pb 14 Sn 3.5 alloy. The resultant lower frequency of nickel barrier breaks results in improved overplate performance during long term engine service.