This review is from O Gauge Railroading,  June 2001. Reprinted with permission of Myron J. Biggar Group. 

Atlas O GM EMD SD-35/SDP-35

by George Brown

When I read or hear of a new product from Atlas O, accurate scale models with superb detail are the first things that come to mind. Although I’m not what one would call an O scale railroader, I really enjoy fine detail in 3-rail trains and I’m especially partial to large road diesels – similar to those I see on nearby Union Pacific and BNSF tracks. So based on my experience with prior Atlas O products, I had a definite level of expectation for their new models of the General Motors Electro-Motive Division SD-35 series of freight and passenger diesel locomotives.

Atlas O submitted two engines for this review:  a high-nose Norfolk & Western SD-35 and a Union Pacific SDP-35.  Actually, high-nose for the N&W engine could be considered a misnomer, since the N&W frequently ran their diesel locomotives long-hood-forward, as attested by the two crew figure in the cab – they face the long hood. Although the aesthetics, or should I say the lack of them, of solid black diesels don’t normally do much for me, the N&W SD-35 is more than an exception; it’s an unusually handsome model that appears much more massive than it really is.

As to Uncle Pet’s (UP’s) Armour Yellow and Dove Gray, this is a highly favored color scheme and much studied railroad, not only in the editorial train room but also in my library and at trackside.

Prototype Notes

The years 1964 through 1966 saw production of the 2500-horsepower SD-35 freight diesel and the SDP-35 passenger unit at GM’s Electro-Motive Division. Initially ordered by the Atlantic Coast Line, the SD-35 was a six-wheel truck variation of the GP-35 with four-wheel trucks; the six wheels enabled the SD-35 to operate on lighter rails than were required to support the weight of the GP-35

The EMD 35-series engines were considered early second-generation diesel locomotives and as such introduced the angular cab roof, a design style that continues with today’s hi-tech and high-horsepower third-generation diesels. GM’s venerable two-stroke turbocharged 16-cylinder 567 diesel was the SD/SDP-35’s prime mover; 567 is the cubic-inch displacement of one cylinder. With an overall length of almost 57’ between the pilot beams the SD-35 was the stubby fore-runner of EMD’s best-selling workhorses, the 16-cylider 3000-horsepower-plus SD-40 series.

Another southeastern road, the Seaboard, placed the initial order for a passenger train version, the SDP-35, equipped with a steam boiler for heating the passenger cars. This boiler was mounted at the back of the long hood, behind the area containing the cooling radiator and air pumps. Mounting a boiler with sufficient size and capacity to heat a train required extending the SDP’s rear frame and deck as well as extending and widening the long hood. The frame extension was also adapted to make physical contact with the diaphragm plate on the first passenger car behind the engine, a practice carried over from steam passenger locomotive design.

As a passenger engine, the SDP-35 did not need to carry the large quantity of fuel required for freight operations, but it did need to carry water for the steam boiler. As was EMD’s practice with first and second generation passenger diesels, the SDP-35’s fuel tank was actually two tanks, with the front tank for diesel fuel and the rear one for water.  Of course, the boiler burned diesel fuel to generate steam.

Between 1964 and 1966, 360 SD-35s were built for US railroads with 35 SDP-35s built in ’64 and ’65.

External Details

In a communiqué with Jim Weaver of Atlas O, he stated “Atlas’ penchant is scale models . . .” and the exemplary detail in their models of the SD/SDP-35 show it. From individually applied grab irons and scale-sized lifting rings on top of the long hood to sand pipes on the bottom of the truck frames, small details abound, many of which are not usually associated with mass-produced 3-rail locomotives.

At each end, the pilot has individual MU cables, complete with connectors and right-angle conduit molded in. Although the automatic coupler is the obligatory oversized knuckle required for 3-rail operation, a molded draft gear box covers its actuating coil. A moveable coupler pin lift bar, formed from wire, is on the face of the pilot with a molded plastic train line, complete with glad hand connector and isolation valve handle, realistically mounted beside the coupler.

Depending on the locomotive’s road name, each SD-35’s pilot has either a snowplow blade or brake-man’s foot boards, with the exception of the SDP-35s, which have only a plain pilot beam behind the rear truck. On the N&W engine, foot boards are at each end in keeping with the road’s real SD-35s, while the UP SDP correctly carries a plow on the front pilot. If the locomotive has a foot board assembly installed on the front pilot, Atlas O provides a separate snowplow blade, should you want to mount it. However, you have to surgically remove the footboards from the pilot before you can mount the plow.

Steps on the pilot and battery box are perforated in keeping with the steps on real EMD locomotives, as is the no-slip diamond pattern cast into the frame deck walkways. Handrail stanchions, some of them individually applied on the diecast frame, are the correct U shape, which I’ve not seen before on mass-produced diesels. An operating fold-down walkway bridge is on each end of the SDs, except on the rear deck of the SDP, which extended to accommodate the steam boiler housing.

Brake pistons and separate air lines mounted on the truck side frames again are details not normally applied to moderately priced 3-rail locomotives. A sand pipe mounts to the brake shoe hanger closest to the fuel tank, but I found it rather curious that these pipes were not present for the other wheelsets in each truck. The speedometer cable mounts prototypically to the left journal of the front truck’s center axle; a nice detail that is unique to the Atlas O SD/SDP-35s.

The fuel tank – oh what a visual difference a scale-sized fuel tank makes on the SD-35. It gives the realistic visual massiveness that is usually missing from O gauge road diesels that have narrow and shallow tanks for clearance with trackside obstructions, like Lionel switch motors. On each side of the diecast tank is the correct fill pipe and cap plus the sight glass, the visual indicator for fuel quantity. Even the placard “TANK FILL” is correctly applied to the frame above the fill pipe. On the SDPs, the casting appears correctly as two tanks for diesel fuel and water. Nestled in the cove between the fuel tank and the locomotive frame are the air reservoirs and air lines. As is fairly standard for models of road diesels, the fuel tank is the speaker housing for the on-board RailSounds system.

The Atlas SD-SDP-35s uses a diecast frame rather than a more conventional one of pressed steel. Atlas’ Jim Weaver explained that this frame adds needed weight to the locomotive as well as working effectively with the diecast fuel tank to provide better acoustics for the RailSounds system. It also provides a rigid mount for the scale cross-sectioned handrail stanchions.

Molded-in details on the plastic body shell are crisp and precise enough to look great under close scrutiny with a 5X optical viewer. Under this magnification, door release handles are so realistic, they looked like I could grab and pull them out of their recessed pockets to unlatch and open the access doors to the prime mover. At the left side of the front hood, the hand brake lever, gearbox, and chain are nestled in their cove, looking like they are ready to crank-on the brakes for parking the engine on a siding.

Formed wire grab irons are separately applied, as are rooftop details such as lifting rings and see-through fan housing grills, complete with moveable fan blades visible through the grills. One note of caution – the lifting rings on top of the hood are plastic and small, and as such, even the slightest contact can shear them off. Separate windshield wipers are correctly positioned over glazed windshields and door windows while two crew members are at their posts inside the enclosed cab.

On all versions of the Atlas O SD/SDP-35, the prime mover cover, with its integral dynamic brake resistor housings, is a separate molding and is removable from the main body. Jim Weaver explained that this separate molding models the crisp relief and appearance of the prototype resistor housings and is not intended for access to any of the locomotive’s internal components.

At the back of the SDP-35, the long hood extends rearward and protrudes out to the left side, modeling the housing for the steam boiler. Additional separately applied details on top of the hood depict the boiler flues and safety valves as well as the cap for the rear sand hopper.

Removing the body shell to install the RailSounds support battery, or for maintenance, is relatively easy and is adequately illustrated in the owners manual. Six small screws hold the body to the diecast frame, but unlike most contemporary models of road diesels, the handrails attach primarily to the frame, with their ends inserted into the cab. You have to disconnect the handrails from the cab and use care to prevent scratching the paint as you lift the shell free of the frame, not at all unlike working with Lionel road diesels made in the 1970s. In this particular situation, I’ve found inserting business cards or similar small pieces of card stock between handrails and the painted cab works great in protecting the paint during removal and installation of the body shell.

Spring pressure contracts on the body and frame electrically connect the body-mounted light bulbs to the frame-mounted electronics; there are no cables to disconnect during shell removal or wires to worry about pinching during reassembly.

Paint and Graphics

Overall finish on both locomotives submitted for this review is near perfection, smooth with a soft satin luster that hides none of the fine molded details on either the frame or the body shell.  Lettering and graphics are crisp and precise and, as best I could determine from photos I found on the World Wide Web, are prototypically correct for both locomotives. On the N&W, yellow-painted “safety” handrails correctly flank the steps at each end of the frame.

On the Union Pacific engine, I noticed some hand-done touch-up of the yellow paint across a few of the access doors on one side of the long hood (remember the 5X optical viewers I mentioned several paragraphs ago). I suspect this touch-up was to correct some minor masking bleed-under of the red paint into the yellow, but in normal light and viewing distance it was imperceptible.

Drive Train

On each truck, a can motor drives the center axle using a worm and gear, with spur gears transferring torque to the wheelsets at each end. Wheels on both ends of the truck are flanged and, although Atlas O ships each SD/SDP-35 with the center wheels blind, no flanges, the company also includes an extra center axle assembly for each truck, complete with flanged wheels and the drive gear. Experienced modelers who want to run all wheels flanged can replace the center axle assembly.

I emphasize “experienced modelers” because Atlas does not include any documentation or instructions for swapping the axles. It’s not a difficult job, as only a number 0 and 1 Phillips screwdriver plus a bit of study of the power truck design are really necessary. Personally, I consider the design of the power truck one of the best I’ve seen for mechanical operation and integrity as well as for effecting modification or repairs, without special tools. The truck block is essentially two halves that split horizontally across the center line of the axles. Recessed machine screws hold these halves together, so no wheel puller or press are required to change axle/wheel assemblies, or to replace a damaged part.

Traction tires on the wheels closest to the pilots, as well as on the center wheelsets, work well under most track conditions. However, if your layout includes Lionel automatic switches, the traction-tire-equipped lead wheelset may not conduct electricity from the common to the control rail for actuating the anti-derail feature of the switch. If you need all-metal lead wheels, you can disassemble the truck and swap the axles from one end to the other. This modification puts metal wheels at the pilot end of the truck with the traction tire wheels next to the fuel tank, and you’ll most likely need only to modify the engine’s front truck.

While I’m on the subject of the power trucks, should you want to separate the motor from a power truck for whatever reason, you’ll need to remove three screws: two screws holding the AC hot and common power wires to the top of the truck (next to the motor) and the large screw from under the truck that normally secures the motor to the truck. The two screws that hold the wire terminals also hold the motor base plate to the top of the truck.

Since the diecast frame for the SD/SDP-35 is rather soft, as is any diecasting used in model railroading, Atlas O assembles a steel plate to the frame above each truck to serve both as a bearing plate between the truck and the frame and as a reinforcement. This engine is really built!

Electronics, Lights, and Sounds

Lionel’s modular TrainMaster Command electronics control the motors and directional lighting, including headlights, illuminated number boards, and red rear marker lights. Freight engines have number boards and marker lights at both ends with headlights and number boards lit on the forward end and red markers lit at the rear, depending on the engine’s direction of travel. Passenger engines have headlights at both ends but number boards and marker lights are only on the front of the engine with the markers lighting only when the engine is running in reverse.

RailSounds 4.0 produces sounds of a GM diesel prime mover, very close to those reproduced on Lionel’s GP-9s. But then, the SD-35’s turbocharged GM 567 is the same basic diesel used on the early Geeps, so similarity between the two types of engines could reasonably be expected.

Considering the size of the speaker located in the fuel tanks, reproduction of the prime mover, horn, and bell sounds is good with the characteristic strong bass resonance that I’ve come to expect from diesel RailSounds. Simulated radio chatter is unintelligible, in keeping with other RailSounds crew chatter that I’ve listened to.

No smoke unit is included with the Atlas O SD/SDP-35s, and after taking the body shell off the frame, I could see why – no room for one exists. As for myself, the lack of smoke unit doesn’t bother me, since the only time I ever run one of them is to report on it’s out-put. You see, smoke and I don’t get along all that well.

Pulling Trains

The first time I eased the CAB-1 throttle open on the SD-35, I was immediately impressed with a smooth and effortless startup and run around the layout. Gearing is quite low and response to the CAB-1 throttle is outstanding – in fact, if the SD/SDP-35 is not the most responsive engine that I’ve tested in quite a while, it’s right up there with the best of them.

With the engine stopped and its sound system reproducing prime mover idle at full volume, the electronics pulled 0.5 amps. Its maximum effective tractive effort, without driver slip, measured a respectable 2 lbs. 9 oz. At 10 volts and drawing 4 amps. The 20-car test train that I chose for exercising the N&W SD-35 consisted of weighted scale 40’ boxcars that took about one pound of pull to get under way. So needless to say, the big black N&W had no problem with its train. At 60 scale miles per hour the SD drew 2.75 amps at 12 volts from a ZW, running in conventional mode of course.

Speaking of the N&W engine, it defaults to starting short-hood-forward. According to Jim weaver, the economics of mass production inhibit special motor wiring for one variant of a product line, such as the N&W SD-35, and Lionel’s electronics do not yet support an external switch for setting an engine’s start direction. However, a prototype-conscious owner can easily swap polarity of the two wires to both motors so the engine starts in the proper direction.

Six yellow and gray UP heavyweight passenger cars plus a scale UP express boxcar were the test train for the UP SDP-35 and again, the engine had no trouble pulling its load. Plus, the matching engine and cars made for a mighty attractive train, especially to a certain product reviewer and UP fan – me.

Both the SD and the SDP ran well and tracked without problems on all three loops of the editorial Carpet Central:  O42, O54, and O72 tubular sectional track, with Lionel O72 turnouts. With the engines running through the tighter turns, there was the expected slowdown because of their long wheelbase trucks, but I didn’t consider it at all objectionable. I also understand that Atlas O extensively tested the engines on several brands of track to ensure correct operation.

One of my initial concerns about operating was the size of each engine’s fuel tank and its apparent proximity to the rails. But after the big SD’s first run around the Carpet Central, my concern obviously had no foundation. In fact, throughout the next several hours of operation, with some of them over very uneven temporary roadbed, that beautiful wide and deep tank never contacted the rails.

Coil coupler operation was flawless, even at low track voltages not normally used for Command operation:  8 to 10 volts. And running both engines in a double-head lash-up was as much fun as running them solo – well, actually it was even more fun! As in solo Command operation, the lash-up’s response to CAB1-1 throttle control was precise and predictable.

Overall Impression

From unpacking the SD/SDP-35s for this review to repacking them for shipment to OGR Editor Fred Dole’s photography studio, I found Atlas O’s new road diesels downright exciting; not only for their faithful and abundant detail, but also for their smooth running and strong RailSounds 4.0 sound system. Best of all, the well-thought-out and executed mechanical engineering, primarily the on the frame and power trucks, make these engines truly unique within the hobby.

These two locomotives not only met, they vastly exceeded all of my expectations that I mentioned at the beginning of this article. Both the N&W SD-35 and the UP SDP-35 were a pleasure to just gaze at, to study closely, and especially to run.