Union Pacific 4005, 4006, and 4012(4-8-8-4)

UP 4005, 4006, and 4012 are three of eight surviving Big Boy (4-8-8-4) articulated locomotives. Built in 1941, the locomotives have 68" drivers. The combined engine and tender weight is about 600 tons and the combined length is 139' 10". The four cylinders are 23-3/4" in diameter with a 32" stroke. Since the Big Boy uses simple expansion rather than compound expansion, this locomotive is not a Mallet. UP 4005, is on display in very cramped quarters at the Forney Transportation Museum, Denver, Colorado, UP 4006 is on display at the National Museum of Transportation, Kirkwood, Missouri, and UP 4012 is housed at Steamtown, Scranton, Pennsylvania.

Copyright 2004, 2006 Donald Nute

This page last modified:7/17/2007.

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