A balanced rotary engine for applying torque to a drive shaft, the rotary engine comprising: an outer casing having a main drive case; a cylinder mounted in the outer casing; a piston mounted for longitudinal movement within the cylinder; and a drive assembly having: i) a first connecting arm and a second connecting arm, each connecting arm having a first connecting end and a second connecting end, the first connecting ends being connected to the piston; ii) a first crankshaft and a second crankshaft, each crankshaft being rotably connected to the second connecting end of the connecting arms; iii) a first drive wheel and a second drive wheel contra-rotably connected to the respective first and second crankshafts (60,62); and iv) a fixed drive ring having a circumferentially disposed drive member surface, the fixed drive ring being mounted in the main drive case so that the drive member surface is disposed towards the piston, the first and second drive wheels (68,70) meshing with the drive ring; the drive shaft being connected to the drive assembly and extending away therefrom, characterized in that the cylinder is rotatable within the outer casing; and wherein an arm spacer is located between the first and second connecting arms (30,32), the spacer extending from between the connecting arms (30, 32) to between the first and second crankshafts (60,62), to prevent the first and second connecting arms (30,32) from loosening and to distribute oil for lubrication during operation. an outer casing having a main drive case; a cylinder mounted in the outer casing; a piston mounted for longitudinal movement within the cylinder; and a drive assembly having: i) a first connecting arm and a second connecting arm, each connecting arm having a first connecting end and a second connecting end, the first connecting ends being connected to the piston; ii) a first crankshaft and a second crankshaft, each crankshaft being rotably connected to the second connecting end of the connecting arms; iii) a first drive wheel and a second drive wheel contra-rotably connected to the respective first and second crankshafts (60,62); and iv) a fixed drive ring having a circumferentially disposed drive member surface, the fixed drive ring being mounted in the main drive case so that the drive member surface is disposed towards the piston, the first and second drive wheels (68,70) meshing with the drive ring; i) a first connecting arm and a second connecting arm, each connecting arm having a first connecting end and a second connecting end, the first connecting ends being connected to the piston; ii) a first crankshaft and a second crankshaft, each crankshaft being rotably connected to the second connecting end of the connecting arms; iii) a first drive wheel and a second drive wheel contra-rotably connected to the respective first and second crankshafts (60,62); and iv) a fixed drive ring having a circumferentially disposed drive member surface, the fixed drive ring being mounted in the main drive case so that the drive member surface is disposed towards the piston, the first and second drive wheels (68,70) meshing with the drive ring; the drive shaft being connected to the drive assembly and extending away therefrom, characterized in that