Sunday, 10 July 2016

Remotoring a Roundhouse Boxcab

The defunct Model Die Casting used to make a nice little boxcab kit in plastic. For years, it's been a favourite of modellers who wanted to get a boxcab at a decent price.

Unfortunately, the motorization is absolutely garbage. I tried a few time to figure out a way to salvage as much as I could from the old drive, but came to the conclusion it was useless. In fact, the way trucks are powered by middle of the engine makes it absolutely unable to manage sharp curves. Given Harlem Station sports prohibitive 13.5" radius curves in some parts, I had no choice but to think about an alternative.

However the year, a common trick had been to replace the original drive with a Bachmann GE 44-ton drive. The most popular method is to sit the boxcab shell onto the 44-ton frame. Most people keep the pilot of the GE switcher which is plain wrong and looks silly. Also, the GE truck sideframes are kept in place emphasizing the weird look of the loco.

To be noted, the GE wheelbase, wheel diameter and wheel spacing are wrong too. Now, I had a challenge in front of me. How to make the GE 44-ton mechanism more acceptable and prototypical.

The new styrene undreframe
The first thing I did was building a styrene frame of similar size than the original metal frame to which I would attach the MDC "correct" pilots. It was a fast and easy build. Vertical styrene walls were built to prevent the frame to warp. They also provided a nice surface to add self-adhesive lead weights which is always a good way to improve performance. There's still a lot of space for a sound decoder and speaker.

Lead weights added to the new frame
The next step was the trucks. I decided to accept the wrong wheelbase as an inevitable trade off. However, the small GE 44-ton wheels had to go. Fortunately, the person who sold me the kit also provided an European Bachmann streetcar drive. The drive is exactly the same but the wheels are the correct diameter for a boxcab. It was just a matter of swapping the wheels and that big problem was now a thing of the past.

The shell is sitting to high on the frame

The last thing I wanted to correct was the sideframes. While the Roundhouse sideframes are a little bit crude, they are still better than keeping GE trucks. To make them fit the new drive, I cut the metal pins behing the truck, grinded the bushing behind the journal boxes and slightly reduced the depth of the peg securing the sideframe to the truck.

One could get rid of everything located at the back of the sideframes
With drill bits and cutoff wheels, I was able to notch the metal peg in such a way the sideframes could be mechanically attach to the truck's plastic pins. Be aware you will have to take time to adjust the sideframe height. Yes, the sideframe isn't a perfect match for the wheel, but it's almost imperceptible.

If I had to redo this, I think I would grind completely the sideframe metal peg and replace it with styrene. That way, it would be much easier to adjust the height.

Finally, my last modification was to remove about 0.75mm of material on the shell ends to make sur the carbody would sit correctly aligned with the pilot beam. The original Roundhouse design was a little bit weird because it didn't align. Now the shell sit properly!

I'll probably remove large part of the underframe diesel tank. Since I changed the wheel diameter, the trucks can't swivel freely. Also, only an air tank existed under Erie #20 and I'd like to follow the prototype as much as I can. It will also look more prototypical and eliminate the last visible remnant of the GE 44-ton.

Another challenge will be to find a way to mechanically fix the shell on the underframe. I don't have yet an idea how I'll do it. Once done, the fun part starts by detailing and painting the locomotive. It shouldn't be too hard. In that regard, I don't plan to buy parts since I consider this a low budget conversion.

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