A screen door assembly (61) on the bottom of a combine serves to screen large pieces of foreign material from air flowing to a fan (49) and to provide access for service personnel to an interior cavity (53) of the combine. A screen (62) is moved between a closed horizontal position and an open position, shown by broken lines (62"), by a crank arm member (63) which can be operated (pivoted) by a wrench (91) engaged with the hex head (89) of a shaft portion (86). A pin (111) locks the crank arm member (63), and the screen in their screen closed position in which the screen and arms rest on laterally inward extending flanges (106, 107). The rear edges (116, 117) of the flanges (106, 107) serve to guide the screen (62) to its open position as the crank arm member (63) is rotated counterclockwise, as viewed in FIG. 2 from its full line screen closed position to its screen open position shown by broken lines (63").