Abstract: A rotary sprinkler is provided with structure for adjusting the force applied to the impact arm by the impact arm spring. The sprinkler has a laterally directed nozzle cooperating with the arm to rotate the nozzle and an impact arm journaled on a shaft extending above the nozzle. The arm is mounted within a cage extending above the nozzle. The cage includes a pair of arms extending from the nozzle on opposite sides of the shaft and terminating at their upper ends remote from the nozzle in a top plate. A helical spring surrounds the shaft and is secured at its lower end to the arm. A bushing assembly is mounted in the top plate of the cage and receives the top end of the spring. The bushing assembly may be manually adjusted relative to the top plate to vary the force applied by the spring to the impact arm. The sprinkler is mounted in a bucket-like housing positionable within the ground such that the mouth of the housing is flush with the ground surface.