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Kitbashing an HOn3 Centercab- Part 1

August 7, 2008






After accidentally discovering a long-abandoned N scale Bachmann F7A from a train set I had long ago, I decided to give it a new life as the centerpiece of a new project: An HOn3 Centercab locomotive. After researching a variety of Narrow Gauge diesel locomotives, of which you can witness an extensive collection of photographs here: <–This is an EXCELLENT reference site BTW. I decided to take styling cues from 1940’s center-cab locomotives, like the Whitcomb, GE and Vulcan locomotives that this locomotive would be a contemporary of (late 1930’s/early 1940’s)

Recognizable parts are the following for this first part of scratch building:

-Bachmann F7A “Plus”, or Cheapie, both run well.

-0.60 styrene (lots of styrene)

-0.30 styrene less than 1/4 sheet

-Small styrene “L” shape

-Two winterization hatches off of Proto 2000 SD60M or GP38 (You can buy cannon& Company hatches instead)

-HOn3 Couplers

-Small gauge metal (non-electrical) florist wire, 16 gauge.

-Cab from Athearn GP9/SD9.

-Thick molded metal roofwalk from Athearn, Front Range, or MDC boxcar.


Bachmann F7 Drive and new frame

After cutting the cab shell in half on either side of the horn bracket, removing roughly 1 scale foot, make the frame out of 0.60 styrene The Frame is 30 feet long, and 8 feet wide. The cab walls should be flush with the sides of the frame.

re-gauging wheelset

Next, I took a small jewelers screwdriver and popped the wheels off. Using a pair of needle-nose pliers I bent the brass electrical pickups outward, to reach out to the newly re-gauged wheelsets.
Then I pushed the wheels in carefully and gauged them to HOn3.

frame with cab

I then proceeded to carefully cut a hole into the solid styrene frame so It can slip over the bachmann chassis, which has cast-metal “lips” on both ends. The front of the locomotive has an angles lip, you you need to sand down the front inside frame to make the frame ride level and flush with the chassis.

sand the cab's inside walls to fit on the chassis

Now, your cab is a tiny bit too narrow to fit snugly on the frame. Go in with a flatfile and widen the inside edge of the front and rear cab walls to slip snugly on the frame, adjust until it fits.

In the foreground are the winterization hatches. The Dark Gray one is from an SD60M, and the white one is from an GP38. The SD60 needs to be cut at the seam so you get the correct height hood to put atop your locomotive.

preventing shorts with electrical tape

Next, I placed a strip of electrical tape over the split frame to avoid causing shorts in the future.

adding weight

…because next you add 1/4 and 1/2 oz lead weights to both ends of the hoods, atop the chassis covered with the electrical tape. Make sure to center the 1/2 oz weight over the trucks.

ALSO REMOVE THE LIGHTBULB if you havent already. It isn’t wired in, it just slips out easily using a toothpick or exacto knife to guide it out of the split-frame.


Next, you assemble the hood sides. This is made from 0.30 styrene. (0.20 works well too.) Make sure they’re as high as the grilles, or you’ll have to do what I do in this next step.

too-short, but matching hoods

These hoods are too short in height, but I fixed the problem by layering one layer of 0.60 styrene atop the sides, then adding another custom-cut layer that includes roof vents.

hood access doors

You can scratchbuild your own access doors for the engine. I did this on two of my four hood sides, and wasn’t pleased with the results. Use an aftermarket detail part for this. Cannon & Co, or Details West makes access doors for diesels.

next, the roof

Add a cut-to fit 0.60 styrene roof atop either hood.

new roof

Here’s an exotic extra: atop the roof I added a debris shield. Often used in Steel mill locomotives, it can also be useful on mining railroads to keep foreign objects and debris out of the engine compartment, like if the train is loaded by a excavator or steam/electric shovel. The raw ore could fall off the top of the full bucket and foul parts inside the locomotive.

Notice for the second layer of 0.60 roof styrene, I added the roof vent, made from a front range or athearn 40′ boxcar roofwalk. The styrene parts on either side are 0.60 and cut to fit.

debris shield

The trucks were typical roller bearing Blomberg type “M” trucks (oddly enough, they weren’t type “B’s”), too recognizable to be on a 36″ narrow gauge locomotive. so I filed off the roller bearings and the brake cylinder and using a razor saw, cut off the friction journal bearings off of a mantua caboose truck, also cutting the coil springs off the caboose trucks and sanding that part to half it’s thickness produces a more unique truck, reminiscent of ALCo’s HI-AD trucks. As a final touch, I added small styrene “L” shaped ‘steel’ parts along the bottom of each truck to completely hide the EMD Blomberg heritage. To further disguise the truck I also filed off the “wingtips” on each end of the top of the truck.



Stay Tuned for PART TWO.


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