Mobile machining system for turning machining of inner faces of hollow-cylindrical components , in particular for machining of valve seats, comprising - a base part , - a rotation part of hollow configuration which extends through the base part , is mounted on the latter such that it can be rotated about a C-axis of the machining system , and defines a first flange region on the end side, - a guide rod , - a first motor which is connected fixedly to the base part so as to rotate with it, and drives the guide rod via a first drive train so as to rotate about the C-axis, - a support which is held on the guide rod such that it can be moved to and fro in the direction of the Z-axis, - a second motor , - a tool holder which is held on the support such that it can be moved in the direction of an X-axis of the machining system , which X-axis extends perpendicularly with respect to the Z-axis, - an outer clamping device which is connected fixedly to the base part so as to rotate with it, and is designed to fasten the base part centrally to an end side of a component to be machined, and - an inner clamping device which is mounted on the guide rod and is designed to support the machining system on an inner face of the component to be machined, characterized in that - the guide rod has, at its free ends, a second flange region which is connected fixedly to the first flange region of the rotation part so as to rotate with it, and which defines a Z-axis of the machining system, which Z-axis extends parallel to the C-axis, - the second motor is connected fixedly to the rotation part so as to rotate with it, is supplied with energy via a slip ring and drives the support via a second drive train, - the machining system comprises a third motor, which is connected fixedly to the rotation part so as to rotate with it, is supplied with energy via a or the slip ring, and drives the tool holder via a second drive train. - a base part , - a rotation part of hollow configuration which extends through the base part , is mounted on the latter such that it can be rotated about a C-axis of the machining system , and defines a first flange region on the end side, - a guide rod , - a first motor which is connected fixedly to the base part so as to rotate with it, and drives the guide rod via a first drive train so as to rotate about the C-axis, - a support which is held on the guide rod such that it can be moved to and fro in the direction of the Z-axis, - a second motor , - a tool holder which is held on the support such that it can be moved in the direction of an X-axis of the machining system , which X-axis extends perpendicularly with respect to the Z-axis, - an outer clamping device which is connected fixedly to the base part so as to rotate with it, and is designed to fasten the base part centrally to an end side of a component to be machined, and - an inner clamping device which is mounted on the guide rod and is designed to support the machining system on an inner face of the component to be machined, characterized in that - the guide rod has, at its free ends, a second flange region which is connected fixedly to the first flange region of the rotation part so as to rotate with it, and which defines a Z-axis of the machining system, which Z-axis extends parallel to the C-axis, - the second motor is connected fixedly to the rotation part so as to rotate with it, is supplied with energy via a slip ring and drives the support via a second drive train, - the machining system comprises a third motor, which is connected fixedly to the rotation part so as to rotate with it, is supplied with energy via a or the slip ring, and drives the tool holder via a second drive train. <EOS>