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Internal combustion engines normally use a pair of flanged bearing whose purpose is to carry axial loads resulting from the clutch system action and/or crankshaft impacts which unavoidably occur under real running conditions. There are alternative solutions to flanged bearings like, for example, thrust washers positioned directly onto the engine block but structurally decoupled from the respective main bearing. An engine designer's choice on the subject depends, in many cases, of his knowledge of similar engines with a reliable track record or of his personal preference for a specific solution that he is fond of However, the trend towards smaller and compact power units, i.e. of high power density (kW/L kW/cm2) has, as a result raised the mechanical loading imposed upon thrust bearings, in a number of cases, the thrust loads foreseen at the conception of the original design were exceeded by far. This factor alone results in excessive wear of the thrust faces.

Combustion in reciprocating engines relies on in-cylinder gas motion to speed up the process and enhance burning efficiency. A number of factors capable of influencing such motion can be listed. Among the most important are intake port and piston top geometry. The latter normally referred to as combustion bowl shape is a subject of intense research activity in the Diesel field,in stark contrast to the mild endeavours prevailing in the Otto-cycle partisanship. However, today's environmental and energy resources availability considerations demand that cleaner and more fuel efficient engines have to be made available. Homogeneous mixture Otto-cycle powerplant improvements in fuel economy are hampered by knock incidence, among other factors. It is known that piston top features do interact with the combustion flame front in both negative or positive fashion. In order to better understand how sensitive this interaction is, four piston top shapes were tested in a 4-cyl.