An internal combustion engine comprising a conversion mechanism, the conversion mechanism being operable to convert pivotally reciprocating motion of an output member about a prime pivot axis (30.1) into rotational motion of an output shaft about a rotational output axis (40.1), including: a cam housing which is fast with the output member for movement about the prime pivot axis (30.1) and which is pivotally displaceable relative to the output member about a cam axis (74.1) which is transverse to the prime pivot axis (30.1), the cam axis (74.1) being movable with the output member about the prime pivot axis (30.1), the cam housing defining at least one cam member; and a cam follower on the output shaft, the cam follower having a wobble axis (80.1) which is titled or inclined relative to the rotational output axis (40.1), the cam member of the cam housing being in pivotally reciprocating engagement with the output member and being operable to engage the cam follower, thereby to convert the pivotally reciprocating motion of the output member to rotational motion of the output shaft about the rotational output axis (40.1), the output member and the output shaft being drivingly connected together; and at least one piston which is movable in a cylinder (24, 26) for driving the output member in response to combustion of fuel in the cylinder (24, 26), the piston being in the form of a vane, each vane (34, 36) are equi-angularly spaced about a central hub and project radially outwardly therefrom, the hub is right-circular cylindrical and is pivotally mounted or mountable in an engine block for pivotally reciprocating motion about the prime pivot axis(30.1) which is co-axial with the cylindrical hub, the engine block defining cylinders (24, 26) shaped to accommodate pivotally reciprocating vanes (34, 36), and a set of intake and exhaust valves (42, 44) on either side of the cylinder (24, 26), thereby defining two combustion chambers per cylinder, one on either side of each vane (34, 36), the output shaft including a worm gear assembly which is in drive communication with at least one intake and exhaust valve (42, 44) present in the internal combustion engine. a cam housing which is fast with the output member for movement about the prime pivot axis (30.1) and which is pivotally displaceable relative to the output member about a cam axis (74.1) which is transverse to the prime pivot axis (30.1), the cam axis (74.1) being movable with the output member about the prime pivot axis (30.1), the cam housing defining at least one cam member; and a cam follower on the output shaft, the cam follower having a wobble axis (80.1) which is titled or inclined relative to the rotational output axis (40.1), the cam member of the cam housing being in pivotally reciprocating engagement with the output member and being operable to engage the cam follower, thereby to convert the pivotally reciprocating motion of the output member to rotational motion of the output shaft about the rotational output axis (40.1), the output member and the output shaft being drivingly connected together; and at least one piston which is movable in a cylinder (24, 26) for driving the output member in response to combustion of fuel in the cylinder (24, 26), the piston being in the form of a vane, each vane (34, 36) are equi-angularly spaced about a central hub and project radially outwardly therefrom, the hub is right-circular cylindrical and is pivotally mounted or mountable in an engine block for pivotally reciprocating motion about the prime pivot axis(30.1) which is co-axial with the cylindrical hub, the engine block defining cylinders (24, 26) shaped to accommodate pivotally reciprocating vanes (34, 36), and a set of intake and exhaust valves (42, 44) on either side of the cylinder (24, 26), thereby defining two combustion chambers per cylinder, one on either side of each vane (34, 36), the output shaft including a worm gear assembly which is in drive communication with at least one intake and exhaust valve (42, 44) present in the internal combustion engine.