| The original bulders photo for UP 4022. The second group of 5 Big Boys was nearly identical to the earlier set of 20, with a few minor exceptions. Due to a wartime rationing of alloy steels, the 4020-4024 series was slightly heavier than their earlier siblings, and the units also had their air-brake cooling pipes moved from the front handrails to behind the air pump shield over the front pilot. By 1951, the original 19 Big Boys had been rebuilt with the pipes moved to this location as well. The tenders were also redesigned, with the mechanical lubrication system removed, allowing for an extra 1000 gallons to be carried in the tenders, which were classed as 25 C-4 and numbered 401-405. Obtained from Union Pacific Steam: Big Boy Portraits (Bush, Ehernberger) |