An adjustment mechanism for reel-to-bedknife clearance includes an adjuster base having an internal bore, an adjustment knob attached to a rod extending through the internal bore to engage one of the reel or bedknife, and a detent spring captured between the adjuster base and the adjustment knob and biased against the adjustment member to resist rotation of the adjustment knob. The detent spring may engage radial notches on the adjustment knob at a plurality of reel-to-bedknife clearance positions.