TWO CYCLE ENGINE

PURPOSE:To make it possible to obtain a high output by increasing the primary compression ratio of air intake by a method wherein in the case of the titled engine in which the primary compression of air intake is performed within a crank chamber, a chamber is provided in communication with the crank chamber and the opening degree of the chamber is adjusted in proportion to the rotating speed of the engine. CONSTITUTION:When a piston 2 is in its upward stroke, sucked air is introduced into the crank chamber 4 from an air intake hole 6 and after the sucked air is primarily compressed during the downward stroke of the piston 2, it is filled into a cylinder 1 from a scavenging hole 7. Further, the chamber 8 is provided on the outer periphery of the crank chamber 4 independently of the crank chamber 4. The chamber 8 opens toward the crank chamber 4 and is divided into a plurality of small chambers 8a by partition walls 9 which chambers 8a are opened and closed by a changeover valve 10 in sequence in proportion to the rotating speed of the engine. As a consequence, the changeover valve 10 is rotated in the direction (f1) with, for example, an increase in the engine speed so that the small chambers 4 are opened in sequence and therefore, the capacity of the crank chamber 4 is increased gradually to thereby lower the primary compression ratio of air intake.