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 ; 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 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 , the spacer extending from between the connecting arms to between the first and second crankshafts , to prevent the first and second connecting arms 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 ; 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 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 ; 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 meshing with the drive ring ; the drive shaft being connected to the drive assembly and extending away therefrom, characterized in that <EOS>