the bolens and troy built are the same engine, more commonly known as the Ryobi 31cc (oddly enough not really used on ryobi weedie's anymore)

well, I just ran my MacCulloch 32cc that's running on gas/glow today, got an RPM of 7500 with mild porting and a worn ring on an APC 18 8 prop, according to thrust calc it said about 17.5lb thrust, I didn't get a weight on the engine in this configuration though, I don't have a ryobi on the bench or I'd offer to give you a weight, people seem to be getting about 7300rpm on 18 8 props on the ryobi's too I think, someone else will chime in I'm sure