Just a minor update here on the perils of being too clever...

The Prairie chassis went together easily, and even though they had to be bent around the springs, the pickups were problem-free from the start. One of the good indicators of this is wheel cleanliness - if, after a few hours of test running, the wheels are still shiny, there's nothing wrong with the pickups. If pickup is intermittent, the wheel will begin to accumulate dirt which will only worsen things, leading to more dirt ... etc. I was very pleased with the Prairie as the wheels stayed shiny and it trundled over even my dodgiest of track areas without hesitation.

Once I'd got the cylinders working, I thought I'd be "professional" and add some heat shrink insulation to the pickups, just to avoid any possibility of a short against the chassis. The chassis on this engine is electrically dead, but if two pickups on either side were to touch it at the same time, there would be trouble. As I was considering dding DCC, I wanted to avoid any such possibility.

All seemed well, but over the coming days I noticed that the running was deteriorating, and the wheels were getting dirty ... very quickly. I'd clean them, and then they'd be dirty again after a couple of laps. The problem, it slowly dawned, was that the heat-shrink was impeding the springiness of the pickups. There was nothing for it, then, but to unsolder them and add completely new pickups - this time without any extra complication of insulation. This was tricky because I'd since added the brake pull rods, but it wasn't as bad as I'd feared. And they've been problem-free again and the wheels are still shiny. The moral here is that you can sometimes create a problem by anticipating one that hasn't happened yet...

A more pragmatic approach - and the one I've always used before - is to rely on the paint on the frames to insulate against shorts, and - if there's any doubt about that - add a smear of araldite where the contact might occur.

I've now fitted a decoder, incidentally, and the running is fantastic on DCC, with a barely perceptible crawl on speed step 1. That settles the identity of this engine so it's begun to be painted in BR black.