The PW201 has a horizontal boiler (4 3/16" x 1 3/4" diam.). It is fired by a meths burner with the wick inside a slotted tube, which is similar to the Dereham Bowman style but with several slots across the width of the tube instead of one along the length. The firebox is, unusually, made of aluminium. This was used, presumably, for ease of bending. Unfortunately, this also means that it unavoidably distorts as the screw holding the boiler strap is tightened.
The steam feed pipe exits from a dome at the top of the boiler. This feeds, via a removable coupling, to the single acting oscillating cylinder (5/16" diam. x 5/8" stroke), directly coupled to a pin on the flywheel. The crank shaft has a small 3/8" diam, pulley. The steam exhaust is fed to the bottom of the chimney, which fits on the steam dome on the boiler. The metal base is 5" x 4 1/2", with Meccano standard holes round it's periphery. It has felt feet attached at the corners by rivets. I'm not sure if these are original.
I purchased this toy in apparently functional but tatty condition, complete with the original cardboard box. It had already been repaired and repainted by a previous owner some time ago and was already getting tatty. The safety valve had been previously repaired using a 6BA screw for the central part. The steel spring had completely rusted away so was inoperable. The boiler had also been repaired with rather poorly soldered joints. I have fully cleaned and repainted the engine and replaced the spring in the safety valve. On first steaming after restoration, a leak was found at one of the boiler end caps, which has since been fixed