This is what Honda calls an "OEM engine" that Honda mfg. and supplied to a lawn mower manufacturer. The sleeve may be part of a pulley or drive system supplied by the mower manufacturer, can't say for sure. Based on the number, it's at least 7+ years old, and has a 7/8" crankshaft tip. Most likely had remote throttle and choke controls of some kind (again, supplied by the mower manufacturer).
Otherwise, it's a 160cc all-aluminum engine (no cast iron sleeve) rated at about 4.5 hp. Cast, manufactured and assembled at the Honda Plant in Swepsonville, NC.