Genesis BIG BOY 4005 User Manual Download Page 3

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The Union Pacific was built as the eastern portion of the

Transcontinental  Railroad.  The  original  line  was  built  west
from  Omaha  across  Nebraska  and  Wyoming,  into  Utah  to
a  meeting  with  the  Central  Pacific  at  Promontory.  Within  a
few years the junction was moved east to Ogden. In the early
1900s, the mainline of the Los Angeles and Salt Lake, an UP
subsidiary, joined the original Overland Route at Ogden. The
majority of UP’s traffic went through Ogden.

The line across the Nebraska prairies from Omaha to

Cheyenne,  Wyoming  had  no  serious  grades  as  it  followed
the  Platte  River  most  of  the  way.  West  from  Cheyenne,  it
was a much different story. First, the railroad had to cross the
Continental  Divide  on  Sherman  Hill.  West  of  Sherman  Hill,
the railroad encountered several grades near one percent as it
traversed the Basin and Range country. Eastbound trains faced
their toughest challenge immediately after leaving Ogden. The
Echo  Canyon  line  through  the  Wahsatch  Mountains  was  the
steepest grade on Union Pacific’s part of the Overland Route.
It  meant  that  most  of  UP’s  eastbound  traffic  had  to  contend
with the grade.

From 1918 through 1924, UP acquired a group of 65

compound  2-8-8-0  locomotives  to  replace  double-headed  2-
8-0s on the grades of Wyoming and Utah. The 2-8-8-0s could
handle the tonnage, but being compounds with 57-inch driv-
ers, they were not very fast.  2-10-2s, three-cylinder 4-10-2s,
and the three-cylinder “Union Pacific” type 4-12-2s were also
used. They could not handle as much tonnage, and the 2-8-8-
0s  remained  the  primary  locomotive  between  Cheyenne  and
Ogden.  By  the  1930s,  speed  was  becoming  a  much  bigger
factor,  but  with  the  grades,  pulling  power  was  still  the  most
important part. UP finally found a solution by splitting the 4-
12-2 design into a simple articulated locomotive. This resulted
in  the  Challenger  4-6-6-4  locomotives.  Fifteen  Challengers
were delivered in 1936 and twenty-five more in 1937.

The Challengers were much faster than the 2-8-8-0s and

only marginally less powerful. They were equipped with 69-
inch drivers and designed for 80 miles per hour. The Challeng-
ers were rated at over 5,000 tons across Nebraska and 4,290
tons  across  Wyoming.    But  on  the  grade  over  the  Wahsatch
Mountains,  they  were  limited  to  3,100  tons  eastbound.  UP
wanted  something  that  could  make  the  same  speeds  as  the

Challengers and could handle the same 4,290-ton trains
over the Wahsatch without a helper. In 1940, Union Pacific
President William Jeffers gave orders to the Department of
Research and Mechanical Standards.

Formed in 1936, the Department was under the leadership

of Vice President Otto Jabelmann. The easiest solution was to
scale up the successful Challenger design by adding another
pair of drivers to each half of the locomotive making a 4-8-8-
4 design. The task before Jabelmann’s department was to fit
such a large machine into the real world. To be of any use,
the new locomotive had to negotiate the existing curves and
fit within the weight limits of the railroad’s bridges.

They had an advantage in that the new locomotive was

intended for a limited operating area, where the mainline was
engineered for high-speed and heavy traffic. The basic Chal-
lenger  design  was  lengthened,  given  a  larger  firebox,  and
larger  cylinders,  while  the  driver  diameter  was  reduced  one
inch to 68 inches.  Other changes were the result of improved
technology  such  as  the  cast  frame  with  integral  cylinders
instead  of  the  built  up  frames  of  the  Challengers.  Like  the
Challengers, they were designed to burn the semi-bituminous
coal  from  Wyoming  mines.    The  tender  used  the  successful
“centipede” design from the 1939 built 4-8-4s. The coal and
water  capacity  was  based  on  calculations  of  usage  on  a  run
through Echo Canyon with yard delays and meets factored in.

Not every limitation could be overcome. One was the

length  of  the  locomotive.  The  boiler  overhang  would  have
resulted in sideswipe collisions on some double track curves.
These curves were widened a few feet to eliminate that prob-
lem.    The  length  also  meant  the  new  locomotive  was  too
long for existing turntables, so new 135 foot turntables were
installed  at  Ogden  and  Green  River,  the  western  and  eastern
terminals for the planned operation of the new locomotive.

In 1941, UP placed an order for twenty 4-8-8-4’s, num-

bers 4000 – 4019, with the American Locomotive Company,
or ALCO as it is better known. Each engine cost $265,174.
According to legend, an unidentified machinist at the ALCO
plant is responsible for the name “Big Boy”, having written it
in chalk on a partially complete locomotive. Although there is
some evidence that UP intended to call it’s newest and largest
locomotives “Wahsatch” in honor of the grade they were built
to overcome, the Big Boy name stuck.

The first Big Boy, number 4000, was formally accepted

by the UP at Omaha at 6 P.M. on September 5, 1941. Traffic
during World War Two resulted in 5 more Big Boys, numbers
4020 – 4024, being built in 1944. These were slightly heavier
due to wartime restrictions of various metals and had a differ-
ent arraignment of boiler tubes and flues.

In service, the Big Boys started out on the Ogden to Green

River segment. A typical freight train powered by a Big Boy
took four hours to go the 75 miles from Ogden to Evanston,
Wyoming, consuming 20 tons of coal and 12 to 13 thousand
gallons of water. Big Boys were also cleared to run from

Big Boy Locomotive Weights and Dimensions

4000 - 4019

4020 - 4024

Tractive Effort

137,375 Lbs.

Cylinders, diameter and stroke (4)

23.75 in. x 32 in.

Driver diameter

68 in.

Grate area

150 sq. ft.

Steam Pressure