julianrowe

A while back I picked up a very cheap second-hand Hornby J15 on eBay that proved surplus to requirements. I then found this thread and, never one to dodge a challenge, I started to think about whether a J15-E4 conversion might just be possible. The big attraction of the project, apart from hopefully getting an inexpensive E4, was that I'm not great with chassis kits, and this way I should be able to retain the beautiful smooth running qualities of the Hornby mechanism in return for a little bit of hard work on the loco body.

I tried superimposing photoshopped drawings of the two classes on each other to see exactly how they differed. They have the same boiler, which is pitched higher on the E4. This is to clear the larger drivers and then a bit more on top of that. Because the boiler back plate is higher, the Great Eastern raised the height of the cab more or less in line with the boiler, which means the relation of the spectacle plate to the boiler is pretty much the same as on the J15. To make a conversion then, essentially it was a matter of reducing the height of the footplate by 1.5mm to compensate for the larger diameter drivers, raising the cab/boiler assembly, and doing whatever needed to be done in between the two. 

To interfere with the mechanism as little as possible I fitted Alan Gibson wheels to the existing Hornby axles, using bushes to compensate for the different axle diameter. Hornby's chassis is cast in what seems like the hardest alloy known to science and much grinding was needed to provide sufficient space for the drivers. The front carrying wheels run in a plain bearing made of a length of brass tube - crude, but it works.  To my surprise the Hornby model breaks down into more parts than I expected. In particular the boiler/cab is a separate component from the footplate. The latter had to be cleared of its splashers and cut away to accommodate the larger wheels. I gave it a new surface using very thin Plastikard, then built up the splashers, outside frames and smokebox mount on this. The Hornby cab contains some hefty sections of casting, so rather than cut it away and build a replacement, I applied the same thin Plastikard to create new cab sides, filling and filing the old cab to achieve the right profile. The overall result of this and the footplate mods only adds a couple of scale inches to the width of the loco. The rest was a matter of detailing, with a new chimney, clack valves, Westinghouse pump, external springs and pipework. Overall I'm pleased with it, except that the loco sits a little high for the J15 tender. It seems to be the scale height, but 0.5 mm lower would have made all the difference!