Modern highly loaded engines, particularly long life diesel engines, require main and connecting-rod bearings that combine fatigue and wear resistance with ability to combat dirt and slight misalignment. With the extended oil drain intervals, corrosion resistance is also ever important.
When the tribology of connecting rod bearing and cranckshaft main bearing systems in an internal combustion engine is concerned, it should be remembered that the said systems are supposed to operate in the full film lubrication regime over their lifetime. In this regime, friction modifiers have no effect on the system tribology. Moreover, deployment of certain friction modifiers, such as molybdenum phosphothioates or thiocarbamates, in engine oils has been indicated as a potential cause of copper/lead/tin bearing corrosion in diesel engines.
If the engine bearings or crankshaft journals become worn, oil pressure will drop and the engine may start to burn oil. Under normal conditions, bearing wear occurs immediately after a cold start, before the normal oil pressure builds up. The main journals and the connecting rod journals of crankshafts are hardened so that excessive wear of the shaft itself is rather uncommon.
Triboconditioning of cranckshafts (main journals and the connecting rod journals) improves lubricant film strength and system resilience to crankshaft misalignment and oil contamination.
Due to incompatibility of WS2 with copper-containing alloys used in engine bearings, triboconditioning of cranckshafts requires use of sulfur-free process fluids, resulting in a different tribofilm chemistry.