They had 21-by-26-inch (533 by 660 mm) cylinders outside with outside Walschaerts valve gear, 6 ft 0 in (1.83 m) driving wheels and a boiler pressured to 175 psi (1.21 MPa). Weight was 62 long tons 5 cwt (139,400 lb or 63.2 t) for the locomotive and 42 long tons (43 t; 47 short tons) for the tender. Piston valve diameter is given as 10 inches (254 mm) (quite large for the period), but they had the conventional short lap, short travel valves. Bearing in mind that they probably spent a large part of their time slogging uphill or coasting down this was probably not too important. Total evaporative heating surface is given as 1,467 sq ft (136.3 m2), plus 256 sq ft (23.8 m2) for the Robinson type superheater, and grate area as 25.5 sq ft (2.37 m2).
Early in 1921 Clan Stewart was used for experiments with oil firing. This seems to have been successful, but was not applied to any other locomotives. Just when Clan Stewart reverted to coal operation does not seem to be recorded.
Baxter, Bertram (1984). Baxter, David, ed. British Locomotive Catalogue 1825–1923, Volume 4: Scottish and remaining English Companies in the LMS Group. Ashbourne, Derbyshire: Moorland Publishing Company. p. 202.