1. Web-fed rotary offset printing machine having several printing units arranged one behind the other, in each of which a printing material web (5) can be coated on both sides with ink, and a printing unit having an auxiliary drive (12 to 18) for flying plate exchange, in which a plate cylinder/rubber blanket cylinder pair (1, 2) for the plate exchange can be stopped and the other (3, 4) can be set against a common rotating impression cylinder (11), characterised in that in the printing unit, during the recto-verso print mode (Fig. 1), an impression cylinder (11) is used as a paper guide roller for the web (5) guided between the rubber blanket cylinders (2, 4), in that two gear wheels (11', 11") are positioned on the shaft (8) of the impression cylinder (11) and by means of couplings (9, 10) join the main drive (6, 7, 8) optionally with no drive wheel, with any one of the two or with both rubber blanket cylinder drive wheels (2', 4'), in that one rubber blanket cylinder drive wheel (4') mates with a double width plate cylinder drive wheel (3') and is axially movable so that in the recto-verso print mode it mates with the rubber blanket cylinder drive wheel (2') and in the single print mode it mates with one (11") of the gear wheels (11', 11"), in that in the insert print mode (flying plate exchange) the drive (1', 2', 11'; 3', 4', 11") of one plate cylinder/rubber blanket cylinder pair (1, 2; 3, 4) respectively can be separated by the couplings (9; 10) from the main drive (6, 7, 8) conveyed via the impression cylinder (11), and in that the auxiliary drive (12) can be optionally joined to one of the plate cylinders (1; 3) by means of couplings (16; 15) for the flying plate exchange.
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