The S Scale Journal
Converting the American Models GP-9 to a GP-7
The American Models GP-9 is a fine starting point toward creating a very nice GP-7. Historically the GP-7 predated the GP-9 with the first production models introduced in 1949. Aside from EMD’s less popular BL-1 and BL-2 models it was the manufacturer’s first successful road switcher with 2,729 units produced and originally purchased by more than 50 railroads.
For the S Scale modeler interested in modeling the GP-7 few options exist. American Flyer produced a GP-7, but converting this particular model to scale would be a significant challenge because the only usable feature would be the body shell and the shell itself is a crude representation of the EMD car body. Sunset Models imported an S Scale brass version in the 1980s. Outwardly the models were quite nice but those modelers that purchased the units have complained about mechanical problems.
By contrast, the American Models GP-9 is a relatively smooth running locomotive that has for the most part been accurately modeled in S Scale. So it would be only natural that their GP-9 would make a fine starting point for modeling the GP-7. In addition, a few years ago Des Plaines Hobbies produced a GP-7 long hood specifically intended to convert the American Models (AM) GP-9 in to an accurate GP-7. I purchased the long hood and related parts a few years ago and decided to give it a try recently.
The prototype for my GP-7 conversion is PRR 8551, which was a very unique version of EMD’s first road switcher. The Pennsylvania Railroad purchased 66 GP-7s and only three were ordered with roof mounted air tanks. PRR nos. 8551, 8552 and 8553 were passenger units equipped with steam boilers and the space in front of the fuel tank, where the air tanks would normally be mounted, was occupied by a cab signal equipment box. Of the thousands of hood units order by the Pennsy, only these three have roof-mounted air tanks. I model the PRR’s Elmira Branch in the mid-1950s and 8551 and sister unit 8552 were frequent visitors on the branch. They mostly handled freight assignments when they weren’t handling the remnant of passenger service from Canandaigua to Williamsport.
The techniques that I’ve use for building the GP-7 can be applied to any prototype and thanks to suppliers such as Des Plaines Hobbies (DPH) and Bill’s Train Shop (BTS) just about any version of the GP-7 can be modeled in S Scale. I’ve included a parts list at the end of this article, but the most important item that you’ll need is the GP-7 long hood conversion kit from DPH. This is a beautifully reproduced plastic casting that is designed to replace the AM GP-9 long hood. You could also purchase the DPH short hood as well, but there is really nothing wrong with the AM short hood. I chose to replace mine with the DPH version because I like the detail of the hood doors which were flush like the prototype instead of the raised door panels on the AM version.
The DPH GP-7 long hood represents a Phase I GP-7 car body with 86” high engine access doors. There are subtle differences in the door height arrangement in the various phases. Chances are that if you’re building one of the later phase units no one would notice difference in door heights particularly on a non-dynamic brake unit. The real PRR 8551 is actually a Phase III GP-7.
An excellent article along with plans for the EMD GP-7 appears in the October 1982 issue of Mainline Modeler (long out-of-print but back issues can be found on-line). The plans are drawn in 3/16ths in scale and are accurately drawn.
The first order of business is removing the long hood from the GP-9 body shell (and the short hood if you go that route). This is where an extreme amount of care needs to be exercised because you don’t want to mar the surface of the portion of the Geep body that must remain. Before making any cuts remove the cab body section and completely cover all walkway surfaces with masking tape. I cut the long hood from the GP-9 with an X-acto™ no. 13 micro saw blade in an X-acto™ knife holder and made the cut flush with the top surface of the walkway. The DPH hood is designed to sit on top of the walkway so after making the cut sand any remnants of the old hood flush with the walkway tops. Pay particular attention as to how the DPH shell fits around the raised portions of the walkway as additional vertical cuts are needed in those areas to properly seat the new long hood.
Once the new long hood is in place the remainder of the details can be installed. Regardless of which version of the GP-7 you build, the roof top cooling fans need to be installed. All GP-7s had four cooling fans – two above the rear radiator section and two above the generator area. These are available from BTS, or alternately, you can use HO cooling fans from Details West. As it turns out, 48”dia. HO fans are very close to 36” dia. fans in S Scale. The conversion kit does not include exhaust stacks, but brass stack castings are also available from BTS. I added lift rings using Northeastern Models eye pins which are a bit oversized but they look much better than the HO equivalent. On my version of the GP-7 I installed the roof mounted air tanks, Pennsy antenna wire conduits, steam generator details, and a three chime air horn. If you’re modeling a dynamic brake version of the GP-7 you can use the AM GP-9 dynamic brake components without modification, otherwise your roof details are complete.
One thing lacking from the DPH long hood components is the raised marker light assembly. I fabricated mine from a piece of 1/8”- O.D Evergreen plastic tubing cut on an angle and glued in place. I then filled in with putty adjacent to the tubing to provide a smooth taper to the car body. I chose not to illuminate the number boards so I mounted strips of 0.02” styrene behind the openings. This created too deep a recess and I then added another piece of 0.02” styrene to fill the recess and bring the number board surface closer to the face of the car body. DPH produces a set of air intake screens that mount on the sides of the long hood below the cooling fans. The AM intakes will work fine but the DPH screens are see through and have much nicer detail. I also added grab irons fabricated from 0.015” dia. brass wire to the ends of both hoods. The DPH hood ends are pre-drilled to ease the installation of the grab irons. To complete the long hood I added a BTS lever-type hand brake casting.
One important detail that distinguishes the GP-7 from the GP-9 is the set of louvers located on the battery box door below the cab window. All GP-7s had these louvers while the GP-9 did not. Fortunately, plastic louvers are available from DPH. They come on an injected molded sheet and must be cut out individually. They are very thin in cross-section but I chose to make them even thinner by sanding the back side of each louver until they resulting thickness was about 0.005” thick. Even with that, the edge of the louver material is still visible, but the end result is certainly not objectionable.
The prototype GP-7 was offered with two different fuel tank options. A combined fuel/water tank was provided for passenger Geeps and a fuel only tank was available for freight units. The AM model featured the passenger version. The cross-section profile of the two tanks is noticeably different. The passenger tank is more rectangular in cross-section and the freight version is more rounded on the bottom. I used the AM tank which is approximately 6-scale inches too short meaning it rides too high above the rails. I extended the sides of the tank by adding 0.08” strips to compensate for the difference and added a spacer under the mounting tab. If you’re modeling the freight version, I recommend using the AM fuel tank from their GP-35. This has the correct cross-section, but may need to be shortened to the proper length.
Another area on the AM body shell that definitely needs improvement is the pilot/coupler mounting area. The AM pilot has a large opening where the coupler mounting tab from the frame protrudes through the pilot opening. This opening is extra large because the AM GP-9 is designed to accommodate the American Flyer coupler used on the hi-rail version of the model. I chose to body mount the scale couplers in lieu of using the frame mounted tabs. In order to do so, you must cut off the die cast frame extensions and build up the area behind the pilot and beneath the end platform to accept the scale coupler. The pilot opening was altered with styrene strips following the plans in Mainline Modeler in an effort narrow the opening and create a draft gear box to mount the coupler.
The GP-7 had distinctive handrails stanchions that were not used on subsequent EMD road switchers. I used the early GP-7 handrail stanchions which were originally available as brass castings from DPH, but are no longer listed on their web site. Fortunately, they are available from BTS as part no. 02066. The stanchions are very delicate but well worth the effort in completing the finished model. I used 0.015” wire for the handrails. Though the handrail stanchions are located at the same locations on both the GP-9 and the GP-7, the mounting hole on the AM GP-9 are too large for the mounting pins on the brass handrail stanchion castings. I filled the AM holes with 0.035” styrene rod and drilled new holes in the correct diameter.
Most GP-7s were ordered with multiple unit capabilities, so adding the MU cables and MU stands are a necessary feature. BTS offers different versions of the MU stands and MU hoses though most early Geeps were ordered with high MU stands. Other pilot details worth considering are drop steps at the end platforms to enable worker passage between units when MU’d together; coupler pin lift bars; pilot steps; a front grab bar, and a small section of chain spanning the end handrail opening above the drop step.
The AM GP-9 corner step wells are not accurately represented on the body casting. The tread portion of each step is too short. I chose to modify the steps so that each tread was closer to the scale dimension. To do so, I removed the riser from each step and applied a new 10” wide tread as an overlay to the old tread. For this I used a strip of 0.01” styrene and perforated each tread using a no.72 drill bit to represent the pattern on the prototype. Once these were glued in place, I added new risers made from strips of styrene.
Since I went through the effort to keep my crews safe by perforating the ends steps, it is only natural that I would want to have a non-skid surface on the walkways. To achieve this I used the new tread plate texture made specifically for S Scale Geeps by Archer Fine Transfers. The texture is applied in a manner similar to applying decals and once set resembles a metal surface with small raised dimples just like the prototype.
I painted the body shell with Scalecoat™’s PRR Brunswick Green. I didn’t prime any of the surfaces because I applied a dark color, but if you’re using a lighter color, I would definitely recommend priming all surfaces before painting. The Scalecoat™ finish creates a glossy enough surface so that decals can be applied without applying a gloss coat. I painted the window frames silver to represent the aluminum frames found on the prototype.
I have not solved the headlight lens issue yet as no commercially available clear plastic lenses are available as inserts for the dual headlight castings. Recently I found some clear plastic rod that is close to the diameter of the opening, but as of this writing I have not installed them.
I installed DCC with sound and mounted the speaker in the short hood above the gear tower. The space is rather tight, but I used a rectangular speaker with enclosure and mounted it to the gear tower support by fabricating a bracket from styrene and securing it to the tower with short 2-56 machine screws after drilling and tapping the tower support.
PRR 8551 is now ready for service for just about any assignment from hauling passengers to helper service to everything in between. Truly a General Purpose locomotive as EMD had intended.
#SSA160 – GP-7 Long Hood Kit
#SSA164 – GP Short Hood Kit (optional)
#SSA123 – GP-7/9 Grills
#SSA122 – EMD GP/F/FP Louvers
# 64-45 – PRR Single Stripe Diesel Decals
#02057 – Pilot Steps
#02002 – Air Horn
#02004 – Exhaust Stacks
#02062 – Drop Steps
#02065 – MU Stands, Early
#02302 – Air Hoses, Flexible
#02015 – 36” Cap-Top Cooling Fans
#02055 – Torpedo Tube Tanks and Pipes
#02058 – Hand Brake
#02066 – Handrail Posts, Early GP
#02012 – Steam Generator
#CF-143 HO 48” Cooling Fans (alternate cooling fan source)
Archer Fine Transfers
GP-7/9 deck tread plate transfers
Northeastern Scale Models
Various sizes of Evergreen Styrene, brass wire, plastic cement and paint