Bandya Mama is a Travel Lover. To take or gather (something usable) from discarded material. to cleanse of filth, as a street. to expel burnt gases from (the cylinder of an internal-combustion engine). The three main types of scavenging for two stroke engines are cross flow, uniflow and loop flow. Notice on the below image that the cross flow and loop flow scavenging designs use ports only, whilst the uniflow design uses valves (for exhaust) and ports (for inlet).