inside a running engine

A Look inside of a 4-cycle running engine , FIRST the piston travels down the cylinder bore drawing in a fresh fuel/air charge, INTAKE VALVE OPEN. SECOND the piston ascends compressing this charge now trapped within the chamber, BOTH VALVES CLOSED. THIRD the spark plug ignites the compressed mixture causing a rapid expansion of burning gases which now propel the piston back down the cylinder bore. FOURTH, piston now ascends again to expel the now unwanted exhaust gases. EXHAUST VALVE OPEN. Process then repe