Walschaerts valve gear. All that waggly stuff on view makes the locomotive unusual amongst UK shunters - we preferred to hide all that stuff away even if it did make maintenance harder. When I'm operating the layout I love the look of all that moving metal. As a builder my enthusiasm is somewhat dampened.
Having recently build 4 sets for a Garratt this stuff doesn't scare me as much as it has in the past. I'd become used to the technique of using cooking foil to stop solder getting where it shouldn't. I've also started flattening the heads of the pivot pins to improve the appearance. The Garratt was 7mm scale though, the dock tank is 4mm.
I am having some success. The picture shows the return crank to expansion link assembly. There are 10 parts in there (Crank: 2 Rod:3 Expansion link:3 plus 2 pins). The rod is designed to be prototypicaly forked and it fits the link nicely, if you alter the front and back laminations to fit the fork by removing the bottom holes.
One improvement on this loco over my previous effort is that the waggly bits have much less slop in them. Hold the crank horizontal and there is no droop in the attached parts, in fact they are slightly tight so will need a bit of oil and running in.