Red lamps were used to simulate blast furnaces and locomotive fireboxes. Steam was provided by six coal-fired boilers with twenty-six fireboxes. Eight trunk boilers, with four fireboxes in each, were divided into two boiler rooms. The increased distance travelled by many trains highlighted problems with the fireboxes and chimneys. The large fireboxes of these locomotives were made obsolete by better boiler design. Large fireboxes and Stephenson link valve gear ensured a free-steaming locomotive. The locomotives' fireboxes were also modified to burn diesel oil. It is typically specified in boiler work, especially locomotive fireboxes. The locomotives had standard Belpaire fireboxes, with a grate area of . Other railroads, such as the Great Northern and Illinois Central, had locomotives with Belpaire fireboxes. Each boiler had 4 fireboxes apiece for a total of 48. They had bar frames, steel fireboxes and three cylinders, each of . Again there was another round of cosmetic changes with updated boiler bands and fireboxes. Designated Class J, they had Walschaerts valve gear and Belpaire fireboxes and used saturated steam. Henry Fowler later rebuilt them with Belpaire fireboxes.