Pistons (VW Golf 3)

The pistons are made of light metal and have a steel insert that reduces thermal expansion of the piston. Diesel engine pistons have a special feature on the upper plane of the combustion chamber with a recess in the shape of the figure "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 laid in grooves. They are pressed into the cylinder walls by a spring force. The two upper rings block the path of ignited gas from the combustion chamber down into the engine crankcase. The uppermost ring with a rectangular cross-section has a surface made of a special alloyed nickel alloy, thus avoiding excessive wear of the upper piston ring, which is subject to the greatest stress. The lower ring is the so-called oil scraper ring. It prevents oil from penetrating into the combustion chambers.