A harvesting reel assembly for a header of an agricultural harvester is disclosed. The harvesting reel assembly includes a central rotatable shaft, a plurality of support members, a cam assembly and an extendable reel arm. The plurality of support members extend widthwise across the reel assembly and connect to the central rotatable shaft for rotation therewith. The cam assembly guides rotation of the plurality of support members. The extendable reel arm includes a first end engaged with the central rotatable shaft for rotation therewith. The extendable reel arm also includes a distal end opposite the first end connected to one of the plurality of support members.