Editing GWR 4000 Class (section)

==Prototype==
[[File:GWR 4000 Class No 40 4-4-2.jpg|thumb|left|Star class prototype No. 40 as built as a 4-4-2]]
In addition to acquiring the French compound locomotives Churchward built and tested his own prototype 4-cylinder locomotive [[compound locomotive|simple-expansion locomotive]], No. 40 North Star in 1906. As with some early members of the [[GWR 2900 Class|Saint class]] it was built as a 4-4-2 but designed so that it could easily be converted to a 4-6-0. It was completed at the [[Swindon Works]] of the GWR (Lot 161) in April 1906.<ref name=RCTS1>{{harvnb|le Fleming|1953 |p=H6}}</ref> It was numbered 40 and later that year was named 'North Star'. In November 1909 it was converted to 4-6-0. 

The new design incorporated many ideas from [[GWR 102 La France|the French locomotives]], in particular the four-cylinder layout, with the inside cylinders placed forward under the smokebox and the outside cylinders placed far back, in line with the rear wheels of the bogie; from this followed the [[divided drive (locomotive)|divided drive]] with the outside cylinders connected to the second set of driving wheels whilst the inside cylinders were connected to the front set of driving wheels.<ref name=Nock154>{{harvnb |Nock |1983 |p=154}}</ref> The valve gear was an unusual design, called scissors gear, which eschewed the use of eccentrics, but was basically a variation on Walschaerts gear. The prototype locomotive was rebuilt as a member of the Castle Class in November 1929.