More usually seen built in 2 inch scale, Robin Dyer's popular design for the Clayton undertype steam wagon scales up very happily to a 4 inch engine. We've been running this one round the garden all afternoon, all in the interests of testing of course (although it's funny how often intensive tea drinking and testing sessions coincide with sunny afternoons!).
Silver-soldered copper boiler by Morewood, working pressure 100 psi, fed by mechanical pump and highly effective injector. The engine is slung beneath the chassis, enclosed in an oilbath apart from the crossheads. Mechanical lubricator for cylinders, slide valves mounted beneath with pole reverser in cab.
There is a very comfortable drivers seat which fits onto the tow ball on top of the trailer. Whilst not best-suited to very rough ground, on mowed grass or a hard surface the thing will chug round gently with the regulator just cracked open, give it some steam and it takes off like a rocket!
Overall length 64 inches
Weight approx 500 pounds
Length 80 inches
Total length engine and trailer coupled 128 inches