A method and apparatus are provided for adjusting an impeller in a motor and impeller assembly of a pumping device. The method features steps of: tightening mounting bolts so as to move the motor and impeller assembly of the pumping device forward until the impeller touches a casing; inserting a feeler gauge in radial slots in a frame adapter and measuring a gap between a housing of the motor and the frame adapter; determining a desired impeller adjustment distance based on the gap and the desired impeller running clearance; selecting at least one shim having a thickness that corresponds to the desired impeller adjustment distance; loosening the mounting bolts and threading jacking bolts arranged in the rear of the pump frame adapter so that the jacking bolts push against the housing of the motor, and the shims can then be inserted into the radial slots; inserting the shims into the radial slots; backing out the jacking bolts; and securing the mounting bolts locking the motor and impeller assembly in position so that the impeller is at the desired impeller adjustment distance in relation to the casing. The frame adapter assembly features a frame adapter having four radial slots to enable access to the gap for measurement with a feeler gauge and for insertion of the shim to accurately set the impeller clearance.