original 8 inches to inches, the plate frames continued to crack especially in the region of the firebox. While many repairs were undertaken to fix the frames, this problem was only solved by replacing the frame with the new design constructed for the KA and KB classes. This was only done as the replacement was required; as a result not all of the class received the new frames. After the Second World War, a coal shortage occurred and NZR converted a large number of locomotives to oil burning. The K class were a prime candidate due to the large size of the grate. The conversion process was concurrent with that of the KA class. As time went on members of the K class gained improvements and additions from the KA class, and some locomotives had the Westinghouse cross-compound pump added in place of the original twin single-stage pumps. Withdrawal and disposal In 1954, mainline dieselisation began and progressively displaced the K class, especially as the DA class locomotives introduced from 1955. Some of the class were rebuilt with new frames in 1955-57 but most of the class were in storage by 1961 and the decision was made that year the class would receive no more A-grade overhauls, other than K 911. The withdrawal of the class began in 1964, and all members exited service by 1967. Three of the class were retained by Hutt Workshops for use as stationary boilers, replacing three Garratt boilers from the G class. These three heavily stripped members of the class lasted in such use service until 1988 when they were auctioned off. Preserved locomotives K 900 was donated to MOTAT, and prior to being delivered to the MOTAT site, it was put on display outside Sims Pacific Metals until 1975 when it was replaced by DF 1301. It was then transported to the main MOTAT site and placed at the rail pavilion in the company of AB 832, F 180 Meg Merrilies, J 1236, WW 491, and diesel-electric locomotive DA 1400. It has remained on display at MOTAT since then, initially in the open but later under a shelter roof. Physically, K 900 retains its original boiler, tender and plate frame, the latter showing evidence of extensive welding repairs due to the weak nature of the original construction. It appears much as it was when withdrawn, with the recessed K-style headlight, but with a