Don Allen’s

THE WORLD’S

BIGGEST LOCO -

UNION PACIFIC DD40X

The Bristol show always manages to produce a big model, or two. In 2013 it included a large model in 7.25” gauge of the world’s largest and most powerful prime mover.

Back in 1995 Don Allen received a Christmas present, a book entitled The Great Book of Trains. There he discovered the Centennial DD 40 X designed and built to commemorate its first 100 years. Some 47 were built, the largest locomotives to be built on a single frame. These diesel electrics produced  6600hp and could propel the engine at up to 90mph. Power was from twin General Motors 645E3A 16 cylinder two-stroke turbocharged engines driving a GM AR12 generator. It was supplied to the wheels via eight suspended electric motors.

Don made contact with the Union Pacific in Omaha, Nebraska in an attempt to obtain works drawings. Unfortunately, following a search, the archives contained only four black and white photos and a painting schedule. So he set about producing his own drawings of the 12’ long model - on his drawing board. The photos and info were scaled and converted to 1.5” to the foot. After some tweaking of the drawings, metal cutting started.

Some 18 years later, and 8500-9000 hours work, the model and its special trailer were complete.

Much time was given over to producing patterns, templates, formers, jigs, fixtures, benders and press tooling. Some 1778 nuts and bolts were used. To ensure adhesive weight the model is constructed entirely from steel. Tractive effort is also helped by having two motors on each axle. On the model, the diesel engines are replaced with six 110AAPH batteries to give sufficient power and long running times.

The half tonne locomotive was top model at Bristol.

Don says: “the whole project has kept me absorbed and entertained with thinking, sketching, drawing and learning new metalworking skills, but much more importantly keeping the brain working.

“I firmly believe if you make every part, no matter how small or insignificant, to the best of your ability the end result will benefit enormously.”

The Manchester Evening News reported that Don built the model for his grandson Jack, now grown up and just off to University. A 5-inch gauge loco had already been given to older brother, Robert. Don has three more grandchildren.