As with many commercial models, the engine truck for the Spectrum 4-4-0 is just along for the ride. It plays no role in supporting the cylinders, and doesn’t even guide the driving wheels into corners. Effectively, it is its own vehicle, shackled to the front of the frame. Consequently it needs to be as heavy as possible.
I made the replacement truck from a solid lump of brass with .020″ nickel silver frames soldered on the sides. As it happens, the frames could probably be heavier as there is a lot of play between the wheels and the frames. We’ll see how it fares once it’s on the line.
The wheels for this truck went much faster than any other set of wheels I’ve made so far. I modified the form tool width so that I could fit four tyres into about an inch of stock; this meant I could cut the stock to the flange diameter, and then simply form four treads without changing tools or parting off a wheel. I also found a drill bit that could turn the inner diameter; this didn’t need to be accurate because I could simply print the centers to the actual drilled diameter. The two innovations meant I could complete the set in little over an hour, and most of that time was spent turning down the 1/2 inch stock I started with. I installed the tyres according to my new heretical method.
I had a request for a video, so once the engine truck was installed again, I uploaded a quick shot of the engine navigating the test track. I’ve not tuned the decoder, and it lost connectivity at the end of the run, thus the abrupt start and stop. However, the drivers are the smoothest of any of my engines so far.
Pembroke:87 
I appreciated the video – nice to see it all come together. Will the decoder have a mechanical timer, or will you do that in the decoder alone?
Merry Christmas to you and your family Rene.
Merry Christmas to you too, Rob.
As with Percy, the idea behind 1120 is simply to learn and get something running. So, no mechanical timing for the decoder. I might spend some time working on tuning it, but that’s all.