The locomotives did not change greatly during their NZR career. The first change was to fit Waikato-type spark arrestors to many of the North Island-based engines, resulting in a new 'pear-shaped' smokebox with an ash hopper at the base of the smokebox. The cast-iron smokebox doors were replaced by steel ones, and the brake pump was moved from its original location on the right-hand side of the smokebox to a new position, recessed into the running board, just forward of the cab on the same side.