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Big Boy Heavy Freight Locomotive

HO Insider Model for 2001

The World's Largest Steam Locomotive

In the center of the Union Pacific's route network, between Cheyenne and Laramie, lies the Sherman Hill grade. It leads to the Wasatch Range and beyond, heading westwards via Great Salt Lake. As freight trains became ever longer and faster, this grade by the late 1930s could be negotiated only by the time-consuming and expensive process of hitching several locomotives to the train. The solution was a specially built new locomotive of truly gargantuan dimensions. The performance required and the correspondingly enormous weight had to be distributed to the track via an articulated chassis that could negotiate relatively sharp curves. The American Locomotive Company (ALCO) developed a colossus with a 4-8-8-4 wheel arrangement, a service weight over 500 tons and a length of almost 132 feet or 40.5 meters. This giant was known respectfully in the workshops as "Big Boy" and the name stuck, becoming the symbol of the world's largest steam locomotive.

Over One Million Miles per Big Boy!

The Big Boy is an articulated locomotive with two groups of driving wheels and four cylinders. In contrast to the principle behind the Mallet locomotives, with their linked high and low pressure cylinders, the Big Boy has four identical direct-feed cylinders. This generates an extraordinarily high performance - at a price! The locomotive's performance was around 31 mph or 50 km/h at 8,000 horsepower, with a rarely reached top speed of 70 mph or 112 km/h. This enormous power carried a heavy price tag: The entire supply of 28 tons of coal and 25,000 gallons or somewhat under 100,000 liters of water lasted barely two hours when running flat out. Since human muscle power was not up to the task of keeping this Moloch supplied, a mechanical "fireman" stoked the firebox from the tender.

A total of 25 Big Boys were built between 1941 and 1944. They remained in service in Utah and Wyoming for two decades and each one in the first series racked up over one million miles. In 1959 the last Big Boy was used to haul a regularly scheduled freight train. A couple of the locomotives were kept in running condition until the final end came in 1961. Eight locomotives still give an impression of their size. Only three of these museum locomotives are technically capable of being restored to operating condition. Several groups of interested people are considering the restoration of one of these historic giants.

HO Insider Model for Märklin Club Members

This year we have dared to undertake the largest, most powerful steam locomotive ever built, the Big Boy. Building an 18-5/16"/46.5 cm long model so that it can negotiate 14-3/16"/360 mm radius curves is of course equivalent to squaring the circle! But we did it! Despite its ability to handle curves, the model has not been shortened, but is in exact HO scale. All of the driving axles on the model are powered. The two center driving axles are sprung to maintain efficient contact at all times. To get an idea of the dimensions of the model, each of the sets of running gear on the Big Boy are larger than the entire running gear on the class 41 3082/3382, which is itself not exactly a small locomotive.

Metal Construction

The model is made largely of metal construction. Not only the boiler, but also the cab and tender superstructure are diecast. The separately applied grab irons are of course made from steel wire and the pipes are of etched steel plate. The drive rods, except for a few small parts, are also made from the same material. The bell is brass, as on the prototype. The hefty Big Boy model weighs in at over 2 pounds 10 ounces.

The Propulsion and Running Gear Technology

The model of the Big Boy locomotive is powered by a high-efficiency can motor with a bell-shaped armature. Its advantages are high power, smooth running and excellent control features. Also, this motor is so compact that it will fit in the boiler. A flywheel smoothes out the motor's performance and helps the locomotive over contact gaps. The kinetic energy stored in the flywheel overcomes the tendency of worm/spur gear drives to lock up, so that the locomotive does not come to an abrupt stop in areas of track without power.

All eight driving axles on the model are powered. The motor transmits its rpm to two of the driving axles by means of cardan shafts, and worm and spur gears. The other axles are powered through side rods as on the prototype. Four traction tires increase the locomotive's tractive effort. The model's total weight of over 2 pounds 10 ounces or 1.2 kilograms contributes to this pulling power.

DELTA and Digital Multi-Train Control

You have easy access to the electronic circuit for the locomotive's motor, after you remove upper parts of the boiler. The DELTA electronic circuit can be set for one of four addresses for multi-train operation. The load compensation feature will also work to a limited extent. The headlight/backup light smoke generators and sound effects circuit are on constantly in conventional and DELTA operation.

On the digital model two digital decoders are used to control an unusually wide range of functions. The first one is in the locomotive's boiler and is responsible for the motor and the headlight/backup light. The locomotive can be set for one of 80 digital addresses by means of the dip switches. Two potentiometers are used to set the acceleration and braking characteristics as well as the maximum speed. In addition, the long distance headlight, the regular headlight, number board and cab lights can be turned on and off. The second decoder is built into the tender and controls the sound effects circuit.

Realistic Sound Effects in the Digital Version

Both the decoder and the speaker for the sound effects circuit are located in the tender. The cylinder exhaust sound for this steam locomotive is synchronized with the driving wheels by means of a contact generator. In addition, the original sounds of the bell and whistle for the prototype, converted to a digital format, are stored in the sound effects circuit. All of the sound effects are called up with the function buttons on the 6021 Control Unit - the whistle as a short impulse, the steam locomotive sounds and the bell as continuous sounds that can be turned on and off. The volume can also be adjusted with a control.

Description of the Model

34990 DELTA Big Boy Heavy Freight Locomotive

Prototype: Union Pacific Railroad (U.P.) class 4000 "Big Boy" Locomotive no. 4013 as it was around 1960.

Model: Special version DELTA electronic circuit. High-efficiency can motor with bell-shaped armature and flywheel in the boiler. 8 axles powered. 4 traction tires. Articulated frame to enable the locomotive to negotiate curves. Boxpok wheels. Center driving axles are spring loaded. Maintenance-free LEDs for the headlights, tender light and number boards. Coupler hook can be inserted into the pilot. Close coupling between the locomotive and tender. Steam lines can swing out with the cylinders. Separately applied metal grab irons and railings. Many separately applied details. Can be retrofitted with 2 Märklin 7226 smoke generators. Figures of a locomotive engineer and a fireman included for the engineer's cab. Length over the couplers 18-5/16" / 46.5 cm.

37990 Digital Big Boy Heavy Freight Locomotive

Model: Same as 34990, but with 2 digital decoders, controlled high-efficiency propulsion, sound generator and additional auxiliary functions. Headlights, and smoke generators that can be retrofitted on the locomotive are conventional in operation, can be turned on and off digitally. Steam locomotive, sounds that vary with the speed of the locomotive, bell and whistle, long distance headlights, number boards and engineer's cab lighting as well as acceleration and braking delay can be turned on and off with the Control Unit 6021. Powerful speaker in the tender, volume is adjustable. Sound effects are synchronized with the motion of the locomotive by means of a contact generator in the frame.

The 34990 and 37990 Big Boy Heavy Freight Locomotives in this version presented for the first time, are being produced in a one-time series for Märklin Club Insider members. Delivery is planned for the end of 2001.

Important information about the operation of this locomotive: This locomotive can be used on curved track with a minimum radius of 14-3/16"/360mm, but we recommend larger radius curves. Due to the overhang of this locomotive's long boiler, signals, catenary masts, bridge railings, tunnel portals, etc. must be set out further from the curved track for clearance. The track must be well mounted for the high weight of the locomotive. The locomotive can only be run over the turntable and transfer table, it cannot be turned or moved by them.

An interesting book on the Big Boy:

Title:  World's Greatest Steam Locomotives
(A comparison of the Union Pacific 4-8-8-4, Chesapeake & Ohio 2-6-6-6, and the Norfolk & Western 2-6-6-4 steam locomotives.)

Author:  Dr. Eugene L. Huddleston
Cost:  $29.95 + $4.00 shipping and handling
Publiher:  TLC Publishing
Address:  Department MRN
                 1387 Winding Creek Lane
                 Lynchburg, VA 24503-3776

Order Procedure for Insider Models

Märklin Club members receive a reservation form for Insider models in their Insider magazine mailings.

  • A reservation is placed by the Club member through their authorized North American Märklin dealer.
  • One model per member.
  • Delivery is made to your dealer at which time you purchase and pick up your model.

How to join the Märklin Club and receive information about future Insider models.

To learn more about the Märklin Club and to join on-line or download an application, which can be mailed with your payment, just click on the appropriate links.

Although the reservation period has passed, please keep in mind that each year the Märklin Club offers special Insider models for its Club members in all scales, so please watch your Club magazine Insider for news about upcoming Insider model offers. If you have any questions about the reservation process, contact the Märklin Club at:

Freight Cars to go With the Big Boy

Available on an open order basis from Märklin dealers.


45656 Boxcar

Prototype: Union Pacific Railroad (U.P.) type B-50-24/B-50-27 boxcar. Standard 40 foot design.

Model: Metal frame and floor. Detailed trucks with special wheel sets. Sliding doors that can be opened. Roof walk, ladders and other details separately applied. Couplers can be replaced with other types. Length over couplers 6-1/8"/15.5 cm.

DC wheel sets are being readied for this model.

Important: This model is being produced under the same item number with 10 different car numbers.

Hopper Cars

45800 Car Set - 4 Hopper Cars

Prototype: Union Pacific Railroad (U.P.) type H-70-1 hopper car. Design with 3 bays.

Model: Metal frame. Detailed trucks with special wheel sets. Ladders and other details separately applied. Couplers can be replaced with other types. Length over the couplers 6-3/8"/16.2cm.

DC wheel sets are being readied for this model.

Important: The 45800 car set contains 4 cars with different car numbers.

45702 Caboose

45702 Caboose

Prototype: Union Pacific Railroad (U.P.) type CA 3/CA-4 caboose. Design with center cupola.

Model: Metal frame and floor. Detailed trucks with special wheel sets. Platforms at both ends with hand brakes. Roof walk, ladders and other details separately applied. Couplers can be replaced with other types. Length over the couplers 5-9/16"/14.2 cm.

DC wheel sets are being readied for this model.


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