Pistons are made of forged aluminum. They have three rings and aluminum buttons retain the steel wrist pin. The piston is anodized and Teflon coated to prevent galling during the high thrust load operation encountered. The top ring is an L-shaped section "Dykes" ring that provides a good seal during combustion but a second ring must be used to prevent excessive oil from entering the combustion chamber during intake strokes as the Dykes-style ring offers less than optimal reverse gas/oil sealing. The third ring is an oil scraper ring whose function is to scrape the majority of the oil film off of the cylinder wall as the piston descends, to prevent oil being exposed to combustion heat and contaminating the upcoming round of fuel/air. This "oil scraping" also provides a key heat removal step for the cylinder walls and piston skirts, the oil film is renewed as the piston moves upward after BDC.