A wobble unit for a fuel engine with a drive shaft extending through an envelope having a recess opening through which the drive shaft extends, the said wobble unit comprising a central assembly having a ring provided with at least two coupling elements, for transmitting motions from pistons, whereby said central assembly comprising two parts (48A,48B) attached to each other, said parts having each a bore, said bores forming when the said two parts are attached together a passage through which the drive shaft extends, in which the first part forming one single piece comprises: a substantially cylindrical element (48A1) adapted to be lodged within a central bore of the ring, said cylindrical element having an axis corresponding to the central axis of the central bore of the ring, said cylindrical element having a bore adapted for the passage of a portion of the drive shaft, said cylindrical element (48A1) extending between a first free end and a second end, whereby the first free end of the cylindrical element lodged within the central bore of the ring is adapted to extend outside the central bore of the ring, a substantially circular plate element (48A2) extending outside the central bore of the ring, said plate element (48A2) having a face (48F1) contacting an outer face of the ring with interposition of a bearing, and an intermediate element (48A4) extending on the face of the substantially circular plate element not directed towards the substantially cylindrical element (48A1), said intermediate element having fins; in which the second part forming one single piece comprises: a substantially circular plate element (48B2) extending outside the central bore of the ring, said plate element (48B2) having a face (48F2) contacting an outer face of the ring with interposition of a bearing, a protruding element (48B3) having a bore adapted for the passage of a portion of the drive shaft, wherein the passage for the drive shaft formed by the bores of the first part and the second part forms an angle between 10° and 50° with the axis of the cylindrical element (48A1), and wherein the elements of the first and second parts are adapted so that the center of gravity of the wobble unit is located on the axis of the passage for the drive shaft, wherein the first part further comprises a tubular protruding element (48A3) attached to the intermediate element (48A4), said tubular protruding element (48A3) having a centered bore adapted for the passage of a portion of the drive shaft, whereby said protruding element (48A3) has a free end with a face extending in a plane perpendicular to the drive shaft, said tubular protruding element (48A3) having a length comprised between 2 and 10cm, whereby said protruding element (48A3) is adapted to extend within the recess opening of the envelope of the engine with interposition of a bearing to be placed in the said recess opening of the envelope, characterized in that said bearing is in direct contact with the outer surface of the protruding element (48A3). a substantially cylindrical element (48A1) adapted to be lodged within a central bore of the ring, said cylindrical element having an axis corresponding to the central axis of the central bore of the ring, said cylindrical element having a bore adapted for the passage of a portion of the drive shaft, said cylindrical element (48A1) extending between a first free end and a second end, whereby the first free end of the cylindrical element lodged within the central bore of the ring is adapted to extend outside the central bore of the ring, a substantially circular plate element (48A2) extending outside the central bore of the ring, said plate element (48A2) having a face (48F1) contacting an outer face of the ring with interposition of a bearing, and an intermediate element (48A4) extending on the face of the substantially circular plate element not directed towards the substantially cylindrical element (48A1), said intermediate element having fins; a substantially circular plate element (48B2) extending outside the central bore of the ring, said plate element (48B2) having a face (48F2) contacting an outer face of the ring with interposition of a bearing, a protruding element (48B3) having a bore adapted for the passage of a portion of the drive shaft, wherein the passage for the drive shaft formed by the bores of the first part and the second part forms an angle between 10° and 50° with the axis of the cylindrical element (48A1), and wherein the elements of the first and second parts are adapted so that the center of gravity of the wobble unit is located on the axis of the passage for the drive shaft, wherein the first part further comprises a tubular protruding element (48A3) attached to the intermediate element (48A4), said tubular protruding element (48A3) having a centered bore adapted for the passage of a portion of the drive shaft, whereby said protruding element (48A3) has a free end with a face extending in a plane perpendicular to the drive shaft, said tubular protruding element (48A3) having a length comprised between 2 and 10cm, whereby said protruding element (48A3) is adapted to extend within the recess opening of the envelope of the engine with interposition of a bearing to be placed in the said recess opening of the envelope, characterized in that said bearing is in direct contact with the outer surface of the protruding element (48A3).