An agricultural machine having a belt or chain drive system and a tensioning assembly for the belt or chain drive system, the tensioning assembly comprising a tensioning arm (41; 241; 341) pivotally mounted (41p; 241p; 341p) to the machine; a tensioning device mounted to the tensioning arm for contacting the drive belt or chain (60, 63) and applying a tensioning force (Ft) directly thereto; a bracket mounted to the machine; and a tensioning bar assembly comprising: • a longitudinal bar having a longitudinal axis, a top end and a bottom end and a threaded portion over at least a portion of the bar; • an attachment device coupled to the top end of the longitudinal bar and attached to the tensioning arm at an attachment point (41b; 103p); • a compression spring having first and second ends, said spring located around a portion of the longitudinal bar; • a first spring retainer for engaging with and retaining the first end of the spring; • a first locking nut fitted to the threaded portion of the bar for retaining the first spring retainer longitudinally in place relative to the bar; wherein the second end of the spring is in direct or indirect physical contact with the bracket, such that compression of the spring applied by and between the bracket and the first spring retainer provides a resultant force (Fa) applied to the tensioning arm, via the attachment point (41b, 103p), about the pivot mounting point of the tensioning arm, which produces the tensioning force (Ft) to force the tensioning device into contact against the drive belt or chain; characterised in that the longitudinal bar is rotationally freely coupled to the attachment device such as to permit free axial rotation of the bar about the longitudinal axis relative to the attachment device, and; there is further provided an engagement head (102h, 302h) attached to and located at or proximate the bottom end of the longitudinal bar, said engagement head for engagement with a tool to rotate the longitudinal bar. • a longitudinal bar having a longitudinal axis, a top end and a bottom end and a threaded portion over at least a portion of the bar; • an attachment device coupled to the top end of the longitudinal bar and attached to the tensioning arm at an attachment point (41b; 103p); • a compression spring having first and second ends, said spring located around a portion of the longitudinal bar; • a first spring retainer for engaging with and retaining the first end of the spring; • a first locking nut fitted to the threaded portion of the bar for retaining the first spring retainer longitudinally in place relative to the bar; wherein the second end of the spring is in direct or indirect physical contact with the bracket, such that compression of the spring applied by and between the bracket and the first spring retainer provides a resultant force (Fa) applied to the tensioning arm, via the attachment point (41b, 103p), about the pivot mounting point of the tensioning arm, which produces the tensioning force (Ft) to force the tensioning device into contact against the drive belt or chain; characterised in that the longitudinal bar is rotationally freely coupled to the attachment device such as to permit free axial rotation of the bar about the longitudinal axis relative to the attachment device, and; there is further provided an engagement head (102h, 302h) attached to and located at or proximate the bottom end of the longitudinal bar, said engagement head for engagement with a tool to rotate the longitudinal bar.