An internal combustion engine comprising: a cylinder; a piston reciprocably received within the cylinder; a pair of contra-rotating crankshafts (4, 5) rotatably mounted relative to the cylinder; a pair of connecting rods comprising first and second connecting rods (6, 7), each having a first end (61, 71) connected to a crank journal of a respective one of the crankshafts and a second end (62, 72) connected to the piston; a piston stabilising means comprising a knuckle housing to which the second end of each of the first and second connecting rods (62, 72) is pivotally connected, the knuckle housing being received within a cavity of the piston and surrounds and partially encapsulates the second ends of the respective connecting rods (62, 72) and piston connectors; wherein the connection between the connecting rods (6, 7) and knuckle housing and the axis of rotation of the knuckle housing relative to the piston forms a triangulated arrangement; and wherein the engine is configured such that the piston stroke in a first direction toward the crankshafts (4, 5) causes each crankshaft (4, 5) to rotate by a first angle and the piston stroke in a second direction opposite the first direction causes each crankshaft (4, 5) to rotate by a second angle different from the first angle; the engine being characterised by: a pair of stub axles located on opposing sides of the knuckle housing, which hold the piston stabilising means within the piston and allow it to rotate relative to the piston about their common axis, the knuckle housing being free to rotate relative to the piston about the stub axles such that any imbalanced forces cause the piston stabilising means to rotate relative to the piston and the piston remains balanced. a cylinder; a piston reciprocably received within the cylinder; a pair of contra-rotating crankshafts (4, 5) rotatably mounted relative to the cylinder; a pair of connecting rods comprising first and second connecting rods (6, 7), each having a first end (61, 71) connected to a crank journal of a respective one of the crankshafts and a second end (62, 72) connected to the piston; a piston stabilising means comprising a knuckle housing to which the second end of each of the first and second connecting rods (62, 72) is pivotally connected, the knuckle housing being received within a cavity of the piston and surrounds and partially encapsulates the second ends of the respective connecting rods (62, 72) and piston connectors; wherein the connection between the connecting rods (6, 7) and knuckle housing and the axis of rotation of the knuckle housing relative to the piston forms a triangulated arrangement; and wherein the engine is configured such that the piston stroke in a first direction toward the crankshafts (4, 5) causes each crankshaft (4, 5) to rotate by a first angle and the piston stroke in a second direction opposite the first direction causes each crankshaft (4, 5) to rotate by a second angle different from the first angle; the engine being characterised by: a pair of stub axles located on opposing sides of the knuckle housing, which hold the piston stabilising means within the piston and allow it to rotate relative to the piston about their common axis, the knuckle housing being free to rotate relative to the piston about the stub axles such that any imbalanced forces cause the piston stabilising means to rotate relative to the piston and the piston remains balanced.