In 1935, Gresley convinced the LNER directors that, with steam, he could produce a far better commercial return than by following the German example of switching to diesel propulsion for high speed trains. The resulting A4 class were a significant step forward from his previous A3 class which were themselves a development of his original A1 class pacifics for the Great Northern Railway first introduced in 1922. The new locomotives made an immediate impact both through their looks and their performances on the new high speed services.
For a detailed history of this class, Part 2A of Locomotives of the LNER published by the RCTS is essential reading. Other valuable sources of information and photographs are:
Isinglass Drawings. Drg. No. 315 & Drg. No. 316.
Locomotives Illustrated 38 - Ian Allan
The Gresley Pacifics - O.S.Nock - David & Charles
Yeadon's Register of LNER Locomotives - Volume Two - Irwell Press
East Coast Pacifics at work - P.N.Townend - Ian Allan
The A4 Pacifics - P.N.Townend - Ian Allan
The Power of the A4's - Brian Morrison - Oxford Publishing Co.
The Book of the A4 Pacifics by Peter Coster.
The Book of the A4 Pacifics Accompaniments Compendium (Book of Series) by Irwell Press.
Chimney. Single and double chimneys. Double chimneys were fitted to all of the single chimney fitted locomotives between 5/1957 and 11/1958.
Frame rivets. The original engines were built using countersunk rivets and so give a smooth appearance to the frames. Many photographs show a gradual change to some rivets with a visible head as frames were repaired.
Extra roof vents. Fitted from 3/37
Casing access doors. There were two types, originally with a press clip fastener replaced, from 11/37 with the locking handle type.
Extra casing access doors each side of the smokebox. From 1938 locos 2509-11, 4488/90/91/99, 4500 & 4901-3 were fitted with these doors which had two hinges on their top edge. From 1939 these two hinge doors were replaced by a longer three hinge door; all 35 engines received them.
Lamp bracket - smoke box door. From March 1941 the top lamp bracket was moved 9" down the door.
Side skirting. Between 6/41 and 10/42 the skirting both in front of and behind the cylinders was removed from all the locos. This revealed that some of the locomotives had the GNR pattern valve guides ahead of the cylinders; these are provided in the kit.
Bogie dust shields. At first two small dust shields were fitted to the front of the bogie. From about 1941 these were replaced with a continuous one. Until this time the pipes from the middle cylinder drain cocks were not visible, but when the continuous dust shield was fitted these pipes were brought to the outside, one emerging either side beneath each outside cylinder to be clipped to the pair already there, thus making three pipes on each side from this time onwards.
Frame guard irons. Between 12/52 and 6/54 the large guard irons were removed and consequently the cylinder drain pipes cut back to a point level with the centre of the leading bogie wheels.
As can be seen from the table the locomotives were fitted with three types of tender as follows:
1928 Corridor tender - 10 tenders modified from the tenders originally fitted to the A1 and A3 unstreamlined pacifics. Easily recognisable because they retained their external beading.
Streamlined Corridor tender - 11 tenders built new for the A4s. They had no external beading.
Streamlined Non-Corridor tender - 14 new tenders. Easily recognisable because of their lack of a corridor and their narrower width over the tank. They too have no external beading.
Tender changes were not uncommon, so a dated photograph is needed to show the type of tender at a given time.
Bogie wheels 3' 2" diameter, 10 spoke, 5/32" diameter axle, Slater's Ref.7838GMF
Driving wheels 6’ 8", 20 spoke, 3/16" diameter axle, (3), Slater's Ref.7880G
Pony truck 3’8”, 12 spoke, 5/32” axle, (1), Slaters 7843NEMF.
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.
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.