The pistons are made of light metal and have a steel insert that reduces the thermal expansion of the piston. The pistons of diesel engines have as a feature on the upper plane a combustion chamber with a notch in the form of a number «8». This recess serves to better distribute the pressure of the burning working mixture. In the upper third of the piston, three elastic piston rings are arranged in grooves. They are pressed into the walls of the cylinder by spring force. The two upper rings block the ignited gas from the combustion chamber down to the crankcase. The topmost rectangular section ring has a special nickel alloy surface, thus avoiding too much wear on the top piston ring, which is subjected to the most stress. The bottom ring is the so-called oil scraper ring. It prevents oil from entering the combustion chambers.
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