A coupling device for a ride lawnmower engine and a rotary pump is a device that is utilized to connect and transmit power between two shafts such as the driveshaft of a ride lawnmower engine and the input sleeve of a rotary pump. The device features a tubular coupling shaft with an axial motor adapter used to connect the driveshaft and the input sleeve. A compression spring is mounted within an open end of the tubular coupling shaft and is able to vertically lower the tubular coupling shaft towards the driveshaft in order to allow the axial motor adapter to engage the driveshaft. Conversely, the compression spring is compressed when the tubular coupling shaft is vertically raised. A height adjusting clamp is utilized to regulate the vertical positioning of the driveshaft coupling device in order to allow manual engagement and disengagement of the ride lawnmower engine and the rotary pump.