Internal combustion engine

A heat insulation construction for gasoline engines comprising

• a cylinder having a top,
• a piston reciprocably disposed in said cylinder, said piston having a top portion,
• a sub-piston projecting from said top portion of said piston,
• a cylinder head secured to the top of said cylinder having an inner wall forming a recess cooperating with said sub-piston such that the latter is inserted therein at a position near a top dead center of a piston stroke to form two independent combustion chambers,
• an ignition plug means provided in one of said combustion chambers in said cylinder head for igniting said one combustion chamber prior to communication of said two combustion chambers,
• said cylinder head having an intake passage and exhaust passage operatively communicating with said combustion chambers,
• first means for forming a heat insulating air layer provided in said top portion of said piston and said sub-piston, and
• a second means forming a heat insulating air layer adjacent to said inner walls of said cylinder head and said exhaust passage, said second means constituting a cast formed hollow structure made of steel plates cast in said cylinder head.