A crop harvesting header comprising: a header frame structure arranged for movement in a direction of working movement across ground carrying a crop to be harvested; a cutter bar arranged across a forward edge of the header frame structure for cutting the crop; a cut crop transport arrangement mounted on the header frame structure for receiving and transporting the cut crop for further processing; a reel for controlling movement of the crop in the area over the cutter bar; the header frame structure comprising at least two reel mounting arms for movement therewith in the direction of movement; the mounting arms being mounted on the header frame structure for upward and downward movement relative to the cutter bar; each mounting arm having a reel mounting assembly supporting the reel on the mounting arm for rotation about a reel axis generally parallel to the cutter bar; each reel mounting assembly including a component for moving the reel forwardly and rearwardly along the respective reel mounting arm; the reel having a plurality of reel bats at spaced positions around the reel axis each reel bat having reel fingers projecting generally radially outwardly from the reel axis, the reel bats all lying on a common bat circle around the reel axis so that rotation of the reel causes the reel bats to follow a path of movement lying on the bat circle; each of the reel bats being pivotal about its respective bat axis parallel to the reel axis so as to vary the angle of the fingers about the bat axis as the reel rotates; at least one of the reel mounting assemblies including a control component arranged such that, as the reel rotates, the control component cooperates with the respective bat to cause pivotal movement of the respective bat about the bat axis; and an adjustment component responsive to the forward and rearward movement of the reel along the mounting arms which causes the control component to be rotated about the reel axis to different adjustment angles in dependence upon the position of the reel along the mounting arms; characterised by the adjustment component comprising a linkage interconnecting at least one of the mounting arms and at least one mounting assembly, the linkage including a guide plate fixed to the mounting arm and having an elongated guide track formed therein and a guide track follower fixedly mounted to the control component and slidably received in the guide track wherein the control component rotates about the reel axis in response to longitudinal sliding movement of the guide track follower along the guide track. a header frame structure arranged for movement in a direction of working movement across ground carrying a crop to be harvested; a cutter bar arranged across a forward edge of the header frame structure for cutting the crop; a cut crop transport arrangement mounted on the header frame structure for receiving and transporting the cut crop for further processing; a reel for controlling movement of the crop in the area over the cutter bar; the header frame structure comprising at least two reel mounting arms for movement therewith in the direction of movement; the mounting arms being mounted on the header frame structure for upward and downward movement relative to the cutter bar; each mounting arm having a reel mounting assembly supporting the reel on the mounting arm for rotation about a reel axis generally parallel to the cutter bar; each reel mounting assembly including a component for moving the reel forwardly and rearwardly along the respective reel mounting arm; the reel having a plurality of reel bats at spaced positions around the reel axis each reel bat having reel fingers projecting generally radially outwardly from the reel axis, the reel bats all lying on a common bat circle around the reel axis so that rotation of the reel causes the reel bats to follow a path of movement lying on the bat circle; each of the reel bats being pivotal about its respective bat axis parallel to the reel axis so as to vary the angle of the fingers about the bat axis as the reel rotates; at least one of the reel mounting assemblies including a control component arranged such that, as the reel rotates, the control component cooperates with the respective bat to cause pivotal movement of the respective bat about the bat axis; and an adjustment component responsive to the forward and rearward movement of the reel along the mounting arms which causes the control component to be rotated about the reel axis to different adjustment angles in dependence upon the position of the reel along the mounting arms; characterised by the adjustment component comprising a linkage interconnecting at least one of the mounting arms and at least one mounting assembly, the linkage including a guide plate fixed to the mounting arm and having an elongated guide track formed therein and a guide track follower fixedly mounted to the control component and slidably received in the guide track wherein the control component rotates about the reel axis in response to longitudinal sliding movement of the guide track follower along the guide track.