The research is relevant because oil supply processes in the cylinders of four-stroke piston engines with traditional cranking mechanism and combined lubricating system are understudied. The research aims to receive the experimental data on pattern of motor oil distribution by circumference of cylinder for the specified type of internal-combustion engine. The measurement method is based on organization of drainage and following quantity control of oil that is removed by piston rings from internal surface of the cylinder. Experimental device corresponding to this method represents the low-sized high-speed four-stroke air-cooled TMZ-450D diesel engine having a cylinder with six oil-catch through holes executed in its bottom support belt and supplied with thin-walled tubes. Tests were performed under rotation of crankshaft by means of outside source (balanced engine) with nominal speed. The oil filling of any first of six tubes was considered as a moment of ending for each experience. The quantity of oil in tubes was controlled by measuring of oil column length in every tube. During cranking both with air compression and without it, experiments show that quantity of motor oil removed by piston rings from non-loaded cylinder wall side in all cases is more by 15-18% than from the loaded one. Such pattern of oil distribution by circumference of a cylinder at which non-loaded side receives more oil than the loaded one, points to the infringement of principle of coordination between lubricating and loading conditions. That increases the risk of wear and bore scuffing in cylinder-piston unit. In spite of limitation by only one method and one object, the received results show the expediency of following studies of features of cylinder oil supply for the specified type of engines to increase their work reliability.

The study actuality is connected with a problem of high mechanical losses due to friction in naturally aspirated high-speed low-cylinder four-stroke diesel engines. The research aims to check the efficiency of application of an experimental piston with rigid skirt that according to preliminary data provides the decrease of mechanical losses in the cylinder-piston group. The check method consists in comparison of benchmarks of a serial piston and an experimental one. Following indices are accepted as benchmarks: the piston friction force and mechanical losses formed by its work; the temperatures in characteristic zones of the piston; the temperatures of cylinder wall and motor oil caused by the piston friction; the moment of resistance to turning of crankshaft of installation with piston in the cylinder. The comparison is made by means of both modeling and experiments on a model installation designed on the base of 1Ch 85/80 (TMZ-450D) low-sized diesel engine. The comparison objects are a serial piston of diesel engine and an experimental piston with improved rigidity of skirt provided by special stiffening ribs joining the skirt wall with piston bosses. The results of modeling show the advantage of the experimental piston over serial one by signs of decrease of mechanical losses by 4%, of skirt wear by 33%, of temperatures of combustion chamber center and piston top edge accordingly by 5 and 10%. The experimental check allows to establish that the experimental piston with other equal conditions of turning without compression, combustion and cooling provides the decrease in the moment of resistance to turning by 3%, in temperatures of cylinder wall by 9% and motor oil by 6%. The results of comparative modeling and experiment highlight the certain prospect of substitution of serial piston for the experimental one, which is caused by possibility of significant decrease of temperature of the piston top and mechanical losses.