large coupled wheels, larger cylinders of bore by stroke were used. These, at a boiler pressure of , gave the locomotive a tractive effort of at 75% of boiler pressure. Each cylinder was cast integral with half of the smokebox saddle, which made the castings interchangeable. Given the successful operation of rotary cam poppet valve gear on the Class 19C, it was also used on the Class 16E. The valves were driven by outside rotary propshafts from turning mechanisms mounted on the driving coupled wheels. The valves were double-seated and housed at each end of the cylinders, an arrangement that resulted in short and straight ports between the valves and the cylinder barrels. The admission valves were in diameter and the exhaust valves . Most of the detail parts of the rotary cam gear, particularly the main drive and reversing gear, were interchangeable with similar parts on the Class 19C. The poppet valve gear gave the engine extremely free-running characteristics. The Class 16E was delivered with a Watson Standard no. 3A boiler, one of the range of standard boiler types designed by Watson as part of his standardisation policy. The boiler was designed for a maximum working pressure of and the boiler barrel plates and firebox outer shell were of nickel steel. The boiler and the firebox were entirely clothed with Alfol insulation. At above rail level, the Class 16E boiler centre-line was the highest-pitched on the SAR at the time. Because of this and the limitations of the loading gauge, the boiler was domeless with an inspection manhole on top of the boiler barrel where the dome would have been. Steam was collected through numerous small feeder pipes fixed into two collector pipes which were arranged as high as possible above the water surface. The collector pipes then joined together to form a main steam pipe, in diameter, which led to the superheater header and multiple valve regulator located in the smokebox. The steam pipes from the header to each cylinder were in diameter. The boiler was fitted with two large Pop safety valves mounted ahead of the firebox, one on either side of the boiler and angled about 80 degrees apart. The firebox had a power-operated Ajax fire-door and the grate was of the sectional pin-hole type, fitted with power-operated shaking gear. To assist in keeping within the axle load limits, the ashpan was constructed of relatively thin