Patent ID: 7011078

Claim:
A two-cycle internal combustion engine comprising: a piston, a cylinder bore, a crank chamber and at least one pair of C shaped scavenging passageways of a reverse flow system where at least one scavenging gas inlet port as well as at least one scavenging gas outlet port are both opened to the cylinder bore, wherein a scavenging gas introducing passageway for introducing an air-fuel mixture from the crank chamber into the at least one the scavenging gas inlet port is provided between the cylinder bore and the piston adapted to reciprocatively move up and down in the cylinder bore, and an effective opening area of the at least one scavenging gas inlet port is configured to be gradually decreased by the piston in the course of a descending stroke of the piston, wherein a cut-out portion for constituting the scavenging introducing passageway is formed on a lower external peripheral wall of the piston, and the effective opening area of the at least one scavenging gas inlet port is configured to be gradually decreased in the course of the descending stroke of the piston due to an upper external peripheral wall of the piston having said cut-out portion, the cut-out portion having a partially cylindrical configuration and being approximately a width of the at least one scavenging gas inlet port.