Multiple port cylinder for crankchamber precompression type two stroke engines

Claim 1

A multiple port cylinder for a crankchamber precompression type two stroke engine which includes a cylinder wall provided with intake port means and exhaust port means located at diametrically opposite portions along a longitudinal plane containing a longitudinal center line of the cylinder, a first group of three main scavenging ports formed in the cylinder wall at one side of the longitudinal plane, a second group of three main scavenging ports formed in the cylinder wall and symmetrical to the ports in the first group with respect to the longitudinal plane, a pair of auxiliary scavenging ports formed in the cylinder wall at a side opposite to the exhaust port means and symmetrical with each other with respect to the longitudinal plane, said main and auxiliary scavenging ports being connected respectively with mutually separated main and auxiliary scavenging passages which are oriented so that in a cross-section perpendicular to the longitudinal center line scavenging flows from the auxiliary scavenging ports do not substantially intersect with scavenging flows from the main scavenging ports before they reach the longitudinal plane, said auxiliary scavenging passages being oriented in the vicinity of the auxiliary scavenging ports further upwardly than the main scavenging passages.