Magnificent loco Al, although way out of my modelling period I've always fancied doing a King! I guess it's because they were the pinnacle of GWR development and damn fine looking locos to boot!

Once you've crossed over to the "dark side" and started chassis building then there's no turning back!

Dave

Spent another evening trying to nail down that pesky short.

The loco has a live chassis with insulated wheels on one side only. The short seems to happen when the coupling rods on the insulated side - the one with pickups - are at 3 O'clock, such that the piston crosshead is at its maximum travel away from the cylinder. My first thought was that the crankpin boss on the leading drive wheel is occasionally contacting the crosshead, but after some head scratching I've convinced myself that it wouldn't matter if it did, since the cylinders, crossheads and coupling rods on both sides are all at the same polarity - the non-insulated side - anyway.

When the loco stalls at this 3 o'clock position, anyway, I can still run another DCC loco on the same piece of track. So maybe it isn't a short after all. Very puzzling. At anything above a slow crawl the loco's momentum seems to carry it through the short/dead spot anyway, and the thing can quite happily trundle around for hours without any sign of the problem. Got to be related to the drivers or motion/cylinders, anyway. I'll get there eventually but I always like to solve these "niggles" before starting another similar project.

ps - you should do a King, Dave! One done to the standard of your Edwardian locos would be quite stunning, I think. Go on go on go on...

It's all so very tempting Al! I keep repeating to myself, "stay focused and build the layout, stay focused and build the layout!" So far it's working, but I could very easily get led astray!

Surrender to the dark side of the Force, you must.

Barry Ten I must obey, I must obey; resistance is futile (and I'm not even Dave!!!!!)

P

It is the Lima body but with quite a bit hacked off and redone as separate bits. It was in a right state beforehand, after about 20 layers of green paint applied with a trowel during youthful over-enthusiasm.

Been away for a few days which gave me time to think about the King again and resolve to eliminate this intermittent short. In the end, I convinced myself that it wasn't actually a short at all, and after an afternoon of studying the chassis very carefully, with the main drive gear loosened, I decided it wasn't a mechanical issue either - I'd been wondering whether one of the slide rods might be occasionally fouling the motion support bracket, leading to a "twitch". But that didn't seem to the case either. That only left one thing, which was that there must be occasional problems with pickup. Now, I thought I had eliminated pickups as the problem but I suppose with a rigid chassis, you're more likely to encounter problems than in an RTR loco of the same wheel arrangement, where there tends to be a bit more "slop" in the assembly, as well as deeper flanges and wider wheel treads. Occasionally, with a totally rigid chassis, there must occasionally only be one wheel on one side of the chassis in contact with the track, and if that wheel then runs over a bit of dirt, then you've lost power. This could explain why the loco sometimes "snatches", especially at low speed.

There was no easy means of adding pickup to the bogie, but since I'd already located the decoder in the tender, it was a relatively straightforward job to arrange some additional top wipers picking up current from the front and rear wheelsets. Touch wood, but this appears to have eliminated the running issue, with the loco running smoothly and steadily at all speeds from a crawl to flat out.

Edit - that really seems to have done the trick. Spent an evening running the King at all speeds, with a decent load (5 Bachmann mk1s and a Hornby  Gresley) from a crawl to flat-out, with not a hint of jerkiness or stutter the whole time. I suppose the moral here is don't assume the thing you've ruled out is really ruled out...

Glad you've got it sorted Al, there's very little thats quite so annoying as an intermitent fault!

Indeed, Dave. To be honest I'm over the moon about it - that niggle has been there for years.

The King's been running like an absolute charm for the last week, so I think that box can be considered "ticked" - although now I realise I still have to add balance weights to those drivers! And, while we're at it, I'm tempted to add a firebox effect controlled via the decoder. Maybe a sound decoder would fit as well? Mustn't get greedy...