 Instead, they were equipped with smokebox blowdown valves on the right-hand side of the locomotive, the only NZR locomotives to be fitted with this modification.This was intended to increase the steaming capacity of the locomotives, making it easier to eject the ash, cinders and soot that would collect in the smokeboxes of the locomotives.A small port on the left-hand side of the smokebox was opened to assist this process, allowing one of the crew to brush down the smokebox and clean the spark arrestor.