Union Pacific 4-8-8-4s

Big Boy is the American Locomotive Company 4000 class of 4-8-8-4 articulated, steam locomotives built between 1941 and 1944 and operated by the Union Pacific Railroad up to 1959. The Big Boy locomotives were the only locomotives to use the 4-8-8-4 wheel arrangement, comprising a four-wheel leading truck for stability entering curves, two sets of eight driving wheels and a four-wheel trailing truck to support the large firebox.

They were built to operate the Union Pacific main line over the Wasatch Range between Green River, Wyoming and Ogden, Utah, a single engine replacing previous double-heading. To avoid locomotive changes, the new class had to pull long trains at a sustained speed of 60mph (100kph) once past mountain grades. In fact, it could travel at 80mph (130 kph). Train load was 3200 tons.

The Big Boys were articulated, like the Mallet. They were designed for stability at 60 miles per hour and built with a wide margin of reliability and safety, as they normally operated below that speed in freight service. Peak horsepower was reached at about 35 mph (56 kph); optimal tractive effort, at about 10 mph (16 kph).

The Big Boy locomotives burned coal and had large grates to burn the low-quality bituminous coal from Union Pacific’s mines in Wyoming.

Locomotive 4005 was converted to burn oil.

Wheelbase was 72’ 5.5” and the locomotive was 85’ 3.4” long - the longest steam loco ever built. Overall length was 132’ 9.25” and the combined loco and tender weighed 1,250,000lb.

Twenty five Big Boys were built and eight survive. Union Pacific recently bought back number 4014, which is undergoing a restoration for excursion service plus conversion to oil firing.

This brief outline of the Big Boy is to introduce a 5” gauge model built by Alberto Celot of Treviso, Italy (below). We will be looking at Alberto’s build of this outstanding locomotive in the coming weeks.

Go to Big Boy build part one.

Alberto Celot’s Big Boy in 5” gauge.