Packaging problem

FR 20 approaches Mytholmes tunnel
[image courtesy of Furness Railway Trust]

Perhaps this project’s biggest challenge is squeezing a standard-sized motor into a boiler slim enough to look plausible. As you can see from the pictures, FR 20 has a boiler that is much narrower than the engine making it very hard to find somewhere to put the motor. In contrast, the Y9 has a generous amount of space inside its ample water tank to accommodate the power unit.

For my project I don’t expect to be able stick to the dimensions of FR 20 down to the millimetre, but the closer I can get to them, the more convincing the model will look. Nothing will spoil the illusion more than an incongruously large boiler. In fact, thanks to the size of my intended smokebox, which I’ll come to later, the largest diameter I can take the boiler out to is 19mm. However, the width of the motor is 20mm and simply will not fit.

What are the alternatives? A smaller motor is a possibility if I can find one that delivers similar power from a more compact package. However, before I set off trawling the internet for a possible candidate, I wanted to try another strategy.

The end profile of the motor is circular with flats on the top and bottom slimming the height down 16mm. If I could turn the motor through 90 degrees, it would effectively narrow the width of the motor and the top half would fit into the boiler while the rest could be buried out of sight in the chassis. But would it work?

I tried measuring the clearances, between the wheels and under the intended line of boiler top but couldn’t be sure. This is a game where half a millimeter counts and the only way to be certain is to try it and see.

I chamfered the sides of the chassis to find a little more space, but the big adjustment needed was going to be the mounting block. I had to file 2.5mm off the deck the motor sits on and hope for the best. Working slowly, measuring and test fitting again and again I eventually gained enough space for the motor to sit on its side.

But would it fit in the chassis, stay clear of the wheels and not sit too high? I assembled it all with trembling fingers wondering whether I had made a big step forward or just written off a previously operational loco. And the result? Success! It not only cleared the wheels by a good half mill, but it also will only raise the boiler height by one millimeter over the scale height of real thing. Phew!