INDEX

4-6-2 TENDER ENGINES

GRESLEY

Order
No.

Ordered
Engine
numbers

Built

Classes
293 10/1/1921 1470/71 1922 A1, A1/1
297 9/8/1922 1472-81 1923 A1, A10, A3
301 10/1923 2543-52 1924 A1, A10, A3
302 10/1923 2553-62 1924-25 A1, A10, A3
N.B. Loco. Co. 12/1923 2563-82 1924 A1, A10, A3

EARLY SCHEMES

George Jackson Churchward (1857-1933), Chief Mechanical Engineer on the GWR, introduced the 4-6-2 wheel arrangement with his GREAT BEAR, 1908), but technology had advanced some way since then.  In 1915 Gresley considered building a 4-cylinder Pacific, and an outline engine diagram was prepared.  This shows that the boiler was likely to have been a stretched-out Large Atlantic boiler, with the 5ft-6in diameter barrel 20ft long (requiring a lengthy smokebox).  The overall length of the firebox casing would have been 7ft-4in (instead of 6ft-6in) and the length at the foundation ring 6ft-9in (instead of 5ft-11in), providing an estimated 36 sq ft of grate area.  The four cylinders would have been 15in x 26in.  The decision depended upon satisfactory results from his 4-cylinder Atlantic No. 279.

In 1916 Gresley pushed ahead with his 3-cylinder 2-8-0 mineral engine with conjugated valve gear, the frames for which were ordered on 23 February 1916, in advanc of the Engine Order (8 December 1916), possibly to check first of all the valve gear arrangement.  This engine (No. 461) appeared in May 1918 and its success prompted Gresley to announce his intention of concentrating on 3-cylinder designs in future.  Two schemes were considered in 1918 for 2-6-2s, but weight considerations threw them into doubt.

Further 3-cylinder 2-8-0s were ordered in March 1919, with modifications to Gresley's 2-to-1 gear after Holcroft had suggested improvements.  But more important were the ten 3-cylinder 2-6-0s ordered in June 1919 (Nos. 1000-09).  These were able to confirm the suitability of his 2-to-1 gear on passenger trains.

Gresley then became impressed with the proportions of the Pennsylvania Railroad Class K4s 4-6-2, though some of the features were not practical e.g. 27in diameter outside cylinders and he would never accept a Belpaire firebox on one of his engines.  However, the K4s seems to have had a lengthy combustion chamber and this may have caught his eye.  Here was a method of shortening the boiler barrel, while still keeping its weight centred over the coupled wheels. The firebox casing sloped upwards ahead of the cab, so placing the safety valves on the slope would not foul the load gauge.  He then lost interest in 4-cylinder propulsion and concentrated his efforts on designing a 3-cylinder Pacific.

No. 1470 CLASS
GRESLEY CLASS A1
LNER CLASS A1

6ft-8in wheels, cyls 20in x 26in, boiler 6ft-5in diam, barrel 19ft-0in long, firebox casing 9ft-5½in long

A sketch was made (April 1920) of the proposed Pacific engine and just about all that remained to be done was fit a more suitable side-window cab.  Work started later that year on the boilers.  Steel plates were ordered for the first boiler (21/10/1920), before N380 boiler drawing was issued (12/1920), and almost three months before the Boiler Order and Engine Order were issued. 

Sketch of 4-6-2 engine prepared (4/1920) which closely resembled the finished product, except for its Ivatt-style cab,
Steel plates for the boiler were ordered 21/10/1920,
Cylinders dwg M268 (11/1920),
Cylinders dwg M269 issued (12/1920), perhaps one dwg was for outside cyls and one for inside cyls,
EO 293 was issued (10/1/1921) for Nos. 1470/71,
BO 653 was issued (10/1/1921) for Nos. 1470/71,
Short loop elements for the 32-element superheater were ordered 5/8/1921,
Frames were set up for No. 1470 in Doncaster Work (26/8/1921),
Firebox dwg N377 (-, reissued 7/1922) for No. 1470,
Boiler dwg N380 (10/1921) for No. 1470,
Number of smoke tubes increased (28/11/1921) from 157 to 164,
No. 1470 was completed (30/3/1922),
Sketch of 4-6-2 engine prepared (4/1922) which now has a side window cab,
No. 1470 entered traffic (11/4/1922),
General Plan dwg Q90 (29/7/1922) for Nos. 1470/71.

Gresley’s first two Pacifics (Nos. 1470/71) were ordered on 10th January 1921.  The engines appeared on 30th March 1922 and 10th July 1922 respectively. They were named GREAT NORTHERN (when new) and SIR FREDERICK BANBURY (towards the end of 1922).

The main frames were joggled inwards towards the rear followed by a parallel section under the cab 3ft-5in apart.  Separate outside frames, 1in thick and 6ft-0½in apart were bolted to the main frames.  Strengthening plates, 1in thick and almost 6ft long, were bolted and welded to the inside faces of the main frames at this joint.  This rear end provided a substantial support for the wide firebox.  These outside frames also supported the axle boxes for the trailing carrying wheels.  The centring device comprised Cortozzi slides, or Cartazzis as they were usually referred to at Doncaster, above the axle boxes.  The slides were inclined at an angle of 1 in 7.1 and used the weight of the engine at the rear for centring.  The bogies were constructed of 1½in thick steel plate, spaced 4ft-0¾in apart.  The helical bearing springs were stiffer to support the greater weight on the bogie.  The axle journals were 9in long as in all previous Ivatt bogies, and 6½in diameter.  The permitted side play of 3½in was found to be inadequate and there were signs of the rear bogie wheels having been in contact with the cylinders, and the maximum side plate with safety was deemed to have been 3¼in.  Part of the bogie frame casting was cut away (from August 1927) on existing and new Pacifics to permit 4in side play.

Gresley’s long firebox on his latest 2-6-0s (Class H4) had just about reached the limited expected of a fireman, but the wide firebox (as introduced by Ivatt for his large Atlantics) offered better prospects.  His Pacific boiler had a long barrel, 19ft between tubeplates, and the firebox casing was 9ft-5¾in long overall, i.e. measured from the rear of the firebox at its base to the firebox tubeplate, and 7ft-9in wide.  The working pressure of the boiler was 180 lb/sq in.  The front part of the firebox was just a combustion chamber to reduce the amount of unburned coal passing through the smoke tubes and then out of the chimney.  The firebox grate area was 41¼sq ft.  The original intention was for 157 small tubes x 2¼in dia, but this was increased to 168 (28th November 1921).  The boiler had a Robinson 32-element superheater as introduced by Gresley for the Ivatt large Atlantics (1918).  There were three cylinders 20in diameter by 26in stroke, with two sets of Walschaerts valve gear for the outside pair, and his patented 2 to 1 valve motion for the inside cylinder.  The bogie had the usual swing-link side control standard since Ivatt’s arrival at Doncaster.  The tender was huge; with eight wheels rigidly mounted, unlike the Baldwin tenders of a previous era, which were on bogies.  The capacity was 5,000 gallons of water and 8 tons of coal, suggesting Gresley could have had in mind through running between London and Edinburgh, though with a crew change en route.  Or would it have been London to York and back with one crew.  Certainly not to Leeds as it was a further ten years before they were permitted to cross the bridge over the River Calder on the approach to Wakefield.  Or was he making his mark to better his chances of becoming the C.M.E. of the anticipated new L.N.E.R.

On Sunday 3rd September 1922 a test run was made with No. 1471 hauling 20 vehicles, weighing 600 tons, from King's Cross to Grantham. Hitchin to Huntingdon was run in 25 mins at an average speed of 70 mph.  The final part of the climb to Stoke Summit was run at an average of 45 mph.

No. 1472 SERIES
LNER CLASS A1

6ft-8in wheels, cyls 20in x 26in, boiler 6ft-5in diam, barrel 19ft-0in long, firebox casing 9ft-5½in long, Gresley Dgm 1 boiler, LNER Dgm 94 boiler

Ten more engines were ordered on 10th August 1922 and the frames for No. 1472 were laid on 23rd October 1922.  The engines appeared shortly after Grouping, numbered 1472-80 and 1481N. 

No. 1481N incorporated alterations so it would pass the NBR load gauge.  Two spare boilers were ordered (21/9/1922) which was unusual for a new design, but perhaps Gresley was taking no chances in case there were unforeseen problems.  But there were no problems.  The engines were renumbered 4472-81 (1924-25).  No. 4472 was named FLYING SCOTSMAN (2/1924) in connection with its appearance at the 1924 British Empire Exhibition at Wembley. 

No. 2543 SERIES
LNER CLASS A1

6ft-8in wheels, cyls 20in x 26in, boiler 6ft-5in diam, barrel 19ft-0in long, firebox casing 9ft-5½in long, Gresley Dgm 1 boiler, LNER Dgm 94 boiler

Nos. 2543-62 were built at Doncaster (1924-25).

These engines were ordered in October 1923, followed a month later by two Mikados which would take the same boiler type. These engines incorporated alterations so they would pass the new LNER composite load gauge, which was more stringent than the NBR load gauge.  The Pacifics were built between June 1924 and July 1925) and the Mikados (Nos. 2393/94) appeared in June and November 1925).  The first use of a spare boiler was in January 1926 (for No. 2547), whilst the second spare was not used until April 1927 (for No. 4470).  This suggests that teething troubles with these new boilers were insignificant.

No. 2563 SERIES
LNER CLASS A1

6ft-8in wheels, cyls 20in x 26in, boiler 6ft-5in diam, barrel 19ft-0in long, firebox casing 9ft-5½in long, Gresley Dgm 1 boiler, LNER Dgm 94 boiler

Nos. 2563-82 were built by North British Locomotive Co. (1925) and were similar to the previous Series, though there were several points of difference.

LNER AND AFTERWARDS

LNER Class A1 was intact at Grouping: 2 engines in service and 10 under construction
LNER Class A1 (later A1/1) formed by rebuilding No. 4470 (9/1945)
LNER Class A3 formed by rebuilding from Class A1, e.g. No. 4471 (10/1942)
LNER Class A10 introduced (5/1945) for unrebuilt A1s (only applicable to LNER-built engines)

All that was left to be done was improve upon certain features, e.g. boiler pressure, cylinder size (related to boiler pressure), superheater size, ratio of lengths of smoke tubes to combustion chamber, improve exhaust through the chimney, fine turn the valve gear and improve bogie side control.  All these aspects were tackled, without any significant alteration to the basic frame arrangement (except in the case of Thompson’s rebuilding of GREAT NORTHERN).  The improvements made after Grouping are summerised as follows:

1924.  Superheater.  62-element type tried out on A1 2562.  Not a success.
1927.  Valve gear.  Improved valve gear with long travel valves fitted to A1 2555.  All engines altered with by 1931.
1927.  Boiler pressure.  220lb boiler fitted to A1 4480 (reclassified A3).
1927.  Superheater.  43-element type for A3s (and A4s later).
1927.  Cylinders.  19in dia for A3s.
1931.  Bogie side control.  Springs replaced swing links on A1 4478 for trial.  Majority of A1s and A3s brought into line during 1931-33.
1935.  Smoke tube length reduced by 1ft, combustion chamber length increased by 1ft, boiler pressure increased to 250 lb.  First boiler fitted to the first A4 2509.   The A4s also had a streamlined appearance.
1935.  Cylinders.  18½in dia for A4s.
1937.  Exhaust.  Double chimney fitted to A3 2751.
1938.  Exhaust.  Double chimneys fitted to new A4s 4468, 4901-03.
1938.  A4 4468 MALLARD achieves world speed record for steam traction.
1941-47.  General conversion from A1 to A3.
1942.  First Gresley Pacific withdrawn due to bomb damage, A4 4469.
1945.  Valve gear.  2 to 1 motion removed from A1 4470 and engine given three sets of Walschaerts valve gear. Reclassified Thompson A1.  Gresley A1s became A10.
1945.  Boilers.  A4 boiler fitted to A1 4470 when it was rebuilt with three sets of Walschaerts valve gear.
1947.  Boilers.  Last A10 rebuilt to A3 in December 1947, No. 47 (ex-2546).
1954.  Boilers.  Gradual fitting of A4 boilers to A3s, but working at 220lb.
1957-58.  General fitting of double chimneys to A4s.
1958-59.  General fitting of double chimneys to A3s.
1959.  First A3 withdrawn in December 1959, 60104 (ex-4473).
1961-65.  General withdrawal of A3s.
1962.  Solitary A1/1 withdrawn in November 1962, 60113 (ex-GNR 1470).
1962-66.  General withdrawal of A4s.
1965.  Last A3 withdrawn in December 1965, 60041 (ex-2506).
1966.  Last A4s withdrawn in September 1966, 60019 (ex-4464), 60024 (ex-4483).

No. 4480 was an early rebuild to Class A3 (7/1927).  No. 4471 was rebuilt to Class A3 (10/1942) but No. 4470 missed out.  The LNER engines Nos. 4472-79/81 were rebuilt (1941-47), by which time the engines were being renumbered.  Initially Nos. 4470-81 were to become 500-511, then this was altered to 113, 102-12.  No. 4470 was instead rebuilt by Thompson as his prototype express passenger engine.  Nos. 102-113 became 60102-13 (1948-49) and were in due course withdrawn (1959-64).  No. 60103 FLYING SCOTSMAN was fortuitously preserved.  Class A1/1 No.60113 was withdrawn in November 1962.

Both Nos. 60102/13 (the original GNR pair) latterly had A4-type boilers with their longer combustion chambers.

For details of LNER-built Pacifics refer to LOCOMOTIVES OF THE L.N.E.R. (RCTS) Part 2A.

PreamblePlant Works A 4-2-2B 2-2-2,  C 4-4-2,  C 4-4-2T D 4-4-0 E 2-4-0 F 0-4-2,  F 0-4-2T,
G 0-4-4TH 2-6-0J 0-6-0,  J 0-6-0ST J 0-6-0T K 0-8-0 L 0-8-2T MC Motor coach N 0-6-2T,
O 2-8-0