A knotter system for performing a knotter cycle of a baler, said knotter cycle comprising at least a first knot forming cycle and a second knot forming cycle, said knotter system comprising: a needle configured for delivering a needle twine; a tucker arm configured for delivering a tucker twine; a billhook assembly comprising a billhook with a lower lip and an upper lip mounted pivotally with respect to lower lip, said billhook being mounted rotatably around a rotation axis and being arranged for receiving the needle twine and the tucker twine; a drive means adapted to make the billhook perform at least a first full rotation around its rotation axis during the first knot forming cycle and a second full rotation around its rotation axis during the second knot forming cycle; wherein the drive means comprise a pinion and at least a first and second gear stretch (504, 505) provided along the circumference of a disc, said pinion being adapted to cooperate with said first and second gear stretch (504, 505) for making the billhook perform the first and second full rotation respectively when said disc is rotated for forming the first and the second knot, respectively; characterized in that the disc is provided with a recess (550; 555) downstream of at least one of said first gear stretch and said second gear stretch, wherein an obstacle (560; 565) is arranged for engaging the pinion when moving in the recess (550; 555), wherein said recess (550; 555) and said obstacle (560; 565) are configured to rotate said pinion over a determined angle and back in order to move the upper lip of the billhook away from the lower lip and back after at least one of said first full rotation and said second full rotation. a needle configured for delivering a needle twine; a tucker arm configured for delivering a tucker twine; a billhook assembly comprising a billhook with a lower lip and an upper lip mounted pivotally with respect to lower lip, said billhook being mounted rotatably around a rotation axis and being arranged for receiving the needle twine and the tucker twine; a drive means adapted to make the billhook perform at least a first full rotation around its rotation axis during the first knot forming cycle and a second full rotation around its rotation axis during the second knot forming cycle; wherein the drive means comprise a pinion and at least a first and second gear stretch (504, 505) provided along the circumference of a disc, said pinion being adapted to cooperate with said first and second gear stretch (504, 505) for making the billhook perform the first and second full rotation respectively when said disc is rotated for forming the first and the second knot, respectively; characterized in that the disc is provided with a recess (550; 555) downstream of at least one of said first gear stretch and said second gear stretch, wherein an obstacle (560; 565) is arranged for engaging the pinion when moving in the recess (550; 555), wherein said recess (550; 555) and said obstacle (560; 565) are configured to rotate said pinion over a determined angle and back in order to move the upper lip of the billhook away from the lower lip and back after at least one of said first full rotation and said second full rotation.