The invention refers to a pump assembly, and more specifically to a chopping pump assembly comprising a cutting wheel mounted on a drive shaft in coaxial and co-rotational relation with a pump wheel, and a cutting plate stationary mountable in a pump housing between the cutting wheel and the pump wheel, the cutting plate having perforations forming passages there through for a liquid to be transported by the pump wheel in rotation, the cutting wheel and cutting plate in co-operation providing a shearing interface effective for cutting solid matter which may be entrained in the liquid. An axial clearance between the cutting wheel and cutting plate is established at all times by eliminating an axial play in a threaded engagement between the cutting wheel and the drive shaft. The invention also refers to a method by which an operative shearing action is securable in the pump assembly.