As well as the complete locomotive shells and bigger kits I also use 3D printing to make replacement parts for a whole number of repairs and improvements to my trains. In this post I will share with you my 3D design to replace a missing part from an old MRC/Rowa 2-8-4 steam locomotive.

The 2-8-4 Berkshire locomotive, pictured below, was made by Rowa who were a German manufacturer of European model trains. In 1969 they released this US model along with their impressive 2-8-8-2 Y6b. Both these models were imported to the US and sold by Model Rectifier Corp (MRC) and were very popular as they were and still are good locomotives. Compared to today’s offerings they are a little bit dated and smooth running at slow speed can be hard to achieve. There is no DCC readiness but a conversion is not tricky to do and they are still good-looking models; and if still running well are also reasonably good pullers.

Around 1977 Rivarossi acquired the tooling for this model and re-released it using Con-Cor as the importer.   Rivarossi made some improvements to the locomotive; the relevant one to this post was to the side rods and valve gear of the locomotive. Rowa’s locomotive had plastic side rods and valve gear which were colored gray. Rivarossi changed this to metal.

My 2-8-4 is one of the early ones made by Rowa with the plastic side rods and valve gear. As I have often seen when looking at second-hand Rowa 2-8-4 models the eccentric rod was missing from one side of mine. Below you can see one side with the eccentric rod and one side without.

The eccentric rod drives the valve gear in the top of the locomotive steam cylinders. This opens and closes the valves at the right position to allow steam to push the main rod in and out of the piston chamber. Although the eccentric rod has no real effect on the running of this model locomotive it is an important cosmetic part; the real locomotive could not operate without it and I would like to see this locomotive working properly.

The original plastic eccentric rod simply clipped into the C shaped mounts you can see in the photo above. There is one offset on the third driver, where the main rod connects to the side rod. The other is between the first and second driver just under the bell crank. The plastic eccentric rod has pins on the rear that fit into the C shaped mounts. It fits with a snap and the C shape holds it in place but allows it to rotate. Below is one of the eccentric rods removed from one of my other Rowa 2-8-4s.

I think it’s because the eccentric rods can snap out so easily that so many are missing from the secondhand models.

This was a very quick 3D model to draw and I was able to keep the part sizes the same as the original Rowa part without going below the recommended sizes for the material I want to use.

Oddly enough the pins on the rear of the eccentric rod are not in the center of the rounded ends but offset towards the ends as you can see from the rendering below.

These will be test printed in Shapeways Frosted Ultra Detail material which will give the best detail and should also ensure a smooth surface on the rod. As these parts are very small they can’t be printed individually so when I make them available it will be pairs.

These should be going to test print soon along with other small parts like the O Scale F9 gears from last week’s post. Once I get them I will share with you the results as well as some video of the new 3D printed eccentric rods powering my Rowa 2-8-4 Berkshire.