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GE's 25-ton switching locomotive is another one of those locomotives that's made in every scale except O. But now that I'm on the case, it won't be so for much longer!


I first heard about these a few months ago when my friend @RSJB18 mentioned them. The Long Island Railroad had a few of these little locomotives that they referred to as "Dinkies". There were hundreds of these Dinkies around from the 1940s through to the present, and many have survived in museum collections-- here's a website with many past and present photos. I thought I had seen one of these locomotives recently, and it turns out I had. I was at the Seashore Trolley Museum in Maine last summer and photographed their "Dinky", which happens to be a former Providence & Worcester locomotive from my neck of the woods.


Once I knew what I wanted to make, I had to find a suitable donor frame-- in this case, a K-Line Plymouth. Just about everyone has one or two of these around their layout (or maybe more if you're @gunrunnerjohn).


After dismantling the Plymouth,I was left with a big pile of parts. I want to reuse as many of these as possible in the 25-tonner kit. The motor frame, reversing unit / interior insert and the couplers seemed most reusable. The smoke unit would be a challenge since it's such a snug fit into the Plymouth and the Dinky is even shorter.


I started the digital design by making scale drawings of the two most critical parts-- the motor truck and the reversing board.

plymouth switcher motor and reverse board

Working around the drivetrain, I produced a new body and frame, including the screw hole pattern for both the original 3-rail couplers so they can be inserted into the pilot. I had to widen the frame to squeeze everything in, but the overall length is very close to 1:48th scale.

plymouth switcher mk1 body and frame assy

The first prototype came out pretty good in both materials. I can 3D print with two different methods and for this project I am advantageously using both-- the UV-cured resin for a highly detailed body and the ABS filament for a sturdy, durable frame. I was able to do a test build with a little bit of filing and snipping.


The couplers were just the right height and the electronics fit snugly inside. Perhaps the original smoke unit could be incorporated, although it would need to be carefully modified to neck it down to fit the 25-tonner's narrow little stack. I'd rather leave space for a command control board in my personal build, so I'll leave the smoke unit out.


Here's a video of the prototype running on my layout.

The second version of the kit fits beautifully, so this weekend it's going into my workshop for paint while I start on forming the grabirons from wire. Stay tuned for updates!



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Original Post

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Cool build, I'd suggest one of the much smaller smoke units if you want smoke, an MTH HO smoke unit would be a good fit.

For command, you can get the Lionel RCM2 from Lionel Parts.

For sound, you can use the ERR Gas Powered engine board.  I managed to cram those two boards into the Plymouth, so you should be able to get them into your creation.


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Last edited by gunrunnerjohn

This is a great post, especially for the people building steel mills. Thank you Ken! As I have posted before, my Father was an open hearth charging foreman at US Steel's ET Works. When USS went from steam to diesel (early 50's), he procured the whistle off a steam dinky for me.  My question, for the RR history people is, what steam power did the diesel dinky replace.  Could it be a 0-4-0 engine that is already available in O gauge or could it be, like this build,  a relic of the past that may know longer exist?  or has never been  offered in O.

Very cool!  Our local museum (Connecticut Eastern) has one of those, a former electric utilities unit, built in 1958.  I so admire people like you who don’t take no for an answer, just go ahead and make their own!


Thanks everyone for the encouragement! I've been to the museum in Willimantic a few times. Looking through my photo archives from my last visit, I turned up this photo of the CERRM's 25-tonner inside their roundhouse. Quite a striking livery!


I've just finished the primary paint on the model in my garage. I'm pretty pleased with how the red and brown came out-- there's a few small runs that got through the painter's tape, but I should be able to cover them up with the white stripes.


I have some leftover LNE pinstripe decals that I'm going to use to add the white accents to the ladders and body. Once that's done, I can bend and glue in some handrails. Hoping to squeeze that in sometime this week.



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Over the course of the past week, I have been applying decals to the P&W Dinky. I'm using K4 Decals, specifically a mixture of leftover LNE stripes and New Haven lettering. I use Micro Set to place them and a little Micro Sol to melt them in place.


Early this morning the decals were done and the paint was just cured enough to take a topcoat. I used my usual clearcoat, Rustoleum Matte Clear.


The clearcoat is already halfway set, so this model will be ready for railings and window glass this weekend.



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The "Dinky" is finally done!


Since last weekend, I've put some window glass into the model with my usual technique-- clear plastic scavenged from food containers, cut to shape and held in with silver tape.


I started hand-bending railings from 0.050" wire in my usual fashion, but I felt like I could do a little better.


I designed and printed up some little tiny bases that act as shoulders to set the handrails in at the right heights. This makes them easier to put in and better looking too.


Again, here's what it looks like all put together.


Here's a view from the rear. I'm going to run this as conventional for a little while, but in case I ever go for a command control and interior lighting update, I have left the railings unglued so they can be removed for disassembly.


Despite the galvanized grabirons, it still looks pretty prototypical.


While I get started on the production run of kits, here's the video of the 25-tonner crawling along with that slow and smooth K-Line worm drive. Thanks for following along!


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@TheRambles posted:

Awesome project!

FWIW, k-line hand cars have the same/similar drive mechanisms. Rather than sacrificing a Plymouth Switcher, hand cars could be a cheaper option.


That's a really good tip, I'm looking into that now. I'd like to try modifying my Pennsy Street Tractor kits to fit it to one of those. I checked the dimensions in Fusion and it looks like the K-Line motor frame is around 1/4" longer than the MPC era Lionel one I used for the street tractor. I anticipate some strategic rescaling and screw boss moves will be involved.

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