In 1924 Mr. C.B.Collett responded to the Running Department's request for a more powerful mixed traffic engine to surpass the 43xx Moguls by rebuilding one of George Jackson Churchward's classic 'Saints' (No. 2925 'Saint Martin') with 6ft. coupled wheels. In 1928, after four years of extensive evaluation, the first of 258 production engines were introduced with several differences from the prototype including increased boiler pitch, reduced bogie wheel diameter, outside steam pipes and modified motion and frames. For a detailed history of this long lived class, Part Eight of The Locomotives of the Great Western Railway published by the RCTS is essential reading. Other valuable sources of information and photographs are:
Collett & Hawksworth Locomotives - Brian Haresnape - Ian Allan
The 4mm Engine - Guy Williams - Wild Swan which includes some of the drawings.
Valve spindle crosshead guides. These were fitted new but later removed.
Spring compensation beams. These were fitted new but gradually removed.
ATC equipment. This was fitted to 4921 onwards when built and applied to Nos. 4901-4920 in 1930.
Top feed pipes. The top feed pipes on 4901 to around 4922 passed through the footplate in front of the centre splasher. On later engines, it passed over the centre splasher and through the footplate alongside the rear splasher. Lamp bracket. This was moved to the smokebox door between 1934-39.
Rear sandboxes. These were originally placed under the cab floor and filled from inside the cab. Later they were replaced with boxes behind the rear steps and filled from outside the cab.
When built the first 20 engines, or so, were paired with second-hand 3500 gallon tenders of standard Churchward design. At least two, Nos. 4959 & 4960, were paired with 3500 gallon intermediate tenders. Many, but not all, from 4922 up to around 4958, were paired with new Collett 3500 gallon tenders. From 4961 new 4000 gallon Collett tenders became the norm, although several including 5900 came out with Churchward tenders. At various times Nos. 4918 & 5919 ran with the eight-wheel 4000 gallon tender. Subsequently the Collett 4000 gallon tenders became standard for the class although this process was very protracted some engines not receiving this tender until after WW2.
Bogie wheel - 3' 1" diameter, 10 spoke, 5/32" diameter axle (2), Slater's Ref.7837MF
Driving wheel - 6' 0", 20 spoke, 3/16" diameter axle (3), Slater's Ref.7872GWH
Motor/Gearbox. A Canon motor with a SDMP 40L/15 gearbox (available from Finney7) or an alternative such as an ABC VML2 gearbox.
Crankpins. Heavy duty crankpins are available from Finney7.
Inside Motion. A separate kit is available from Finney7 to construct the working inside motion.
To obtain a pdf copy of the instructions please click on the links below; the pdf will open in a new window. Unfortunately the A4 and A3 pages have to be in different files.