BRITISH RAIL CLASS 74

British Rail 'class 74' was an electro-diesel locomotive that operated on the Southern Region of British Railways, rebuilt from redundant class 71 locomotives in the late 1960s. An electro-diesel locomotive is one that can operate either from an electrical supply, such as overhead catenary or an energized 3rd rail, or from an on board diesel engine.

Contents

History

Power supply

Complications arise with the build of E6102

Operations

The end

Departmental use

External links

History

Twenty-four examples of British Rail Class 71 (pre-TOPS type HA) were built in 1958 at the British Rail works in Doncaster, and in 1964 ten examples were deemed surplus to requirements, withdrawn from service and placed in storage. The Southern Region was highly impressed with the "little-ED" JA/class 73 locomotives and were keen to see a higher power locomotive with the same flexibility. Instead of being scrapped the ten moth-balled members of class 71 were sent to the British Rail works at Crewe, where they were rebuilt into type HB, later class 74, electro-diesels. During this rebuild, buck-eye couplers and high-level control & brake jumpers were fitted to facilitate working with other EP stock - especially TC units in push-pull mode. Also, two-tone "raspberry" airhorns were mounted on the cab roof, replacing the original air whistle of class 71.
They were intended especially for use on the Southampton and Weymouth boat trains, whose routes included sections of non-electrified track (with some tramway along the public thoroughfare). The elimination of the locomotive change (at either Southampton or Bournemouth) was envisaged, and their dual power capability would greatly accelerate timings and reduce operational requirements.
Originally, plans had been to number them E7001-E7010, but once rebuilt they were numbered E6101-E6110 instead. Later they were renumbered 74001-74010 under the TOPS system.

Power supply

In common with the first SR DC electric locomotives (class 70), class 74 utilised a 'booster' set (a motor-generator and flywheel combination) to overcome the problem of gapping. Booster set 836/2D had been designed by English Electric for use in class 71 and this was retained in the rebuild. The compact size of the booster permitted a small diesel engine and generator inside the body shell (only a single booster was used in classes 71 & 74 unlike the two of class 70). Thus, these locomotives could operate either from a third rail supply at 650V DC (Eastern & Central sections), 750V DC (Western section) or from their Paxman 6YJXL diesel engine, which produced 650 hp.

Complications arise with the build of E6102

In August 1966, after initial stripdown and examination of E5016, engineers were forced to re-assess the build when it became apparent the planned equipment changes could not be accommodated. It was even mooted that the body shell would have to be divided and lengthened. One might think putting a diesel engine into an electric locomotive with a booster set is simply a matter of coupling the crankshaft of the engine to the main shaft of the existing booster through some clutch/gearbox arrangement, but this was not so. When working on diesel power, the engine drove generator EE843/1C (615V output) direct to the booster power input (so simulating the third rail power). It must not, however, be thought that the 615V input was a direct replacement of the conventional electric supply - the configuration of the booster set did not work simply by utilizing the line voltage. See the article on Boosters for clarification. The equipment train of Engine+Generator+Booster proved too long with the existing equipment layout. Modifications were made - very little of the progenitor locomotive layout remained - and all was well with production back on track.

Operations

The Paxman engine of class 74 was marginally more powerful than class 73's English Electric engine but it was nowhere near as reliable. The Paxman was also difficult to start on occasion - rather negating the novel change-over whilst in motion and subsequent flexibility off the third rail. Excessive engine noise in the cab was also a problem. The class's general unreliability often led to electric to diesel changeovers when on the move, regular passengers on Class 74-hauled passenger trains became quite used to this. Until four additional '4-REP' units were built in 1973/74, class 74 had regular daytime passenger turns including the 15:30 Waterloo-Weymouth. Subsequently their only regular passenger runs were the night mail and newspaper runs to/from Bournemouth, and boat trains (which were not available to regular ticket holders).
In practice class 74 was a rare visitor to Weymouth and was usually replaced at Bournemouth by class 33 for the final leg of the journey. This was almost directly attributable to their problems when running on diesel power and totally negated their ''raison d'être''. As a result, they offered none of the expected advantages of a higher power (than class 73) electro-diesel. Services to Southampton Ocean terminal did use them over non-electrified lines, but this required only a few miles of diesel haulage rather than 60+ on the trip to Weymouth and back. The steep ascent from Weymouth would also have taxed their power output to the utmost, as the 'Channel Islands Boat Train' usually loaded to 11 cars.
Class 73 had a simpler electrical system arrangement for control of the dual power sources - even to the point of two separate power controllers on the driver's desk; one for diesel and one for electric. The complex control system of class 74 (with one dual-purpose controller) was problematic, and the class was dogged with electrical system failures up to their last days. Together, the three complaints of poor reliability, difficult engine starting and excessive noise made class 74 unpopular with crew and fitters alike.
When in good order they were sprightly performers and running on third rail with the full 2552 hp (the original class 71 traction equipment having been down-rated slightly from 2700 hp to extend service intervals), many 100+ mph runs were noted despite a stated maximum of 90 mph - though nothing approaching this was achievable on diesel power.
They were regular visitors to the London area, often running on Midland and Western Region tracks. In the early half of the 1970s, milk trains for the Southern Region were a staple for the class as far as Acton Yard, requiring diesel power from Clapham Junction through Kensington and onto the Western Region mainline (class 52 or occasionally 47 were used for the major haul west of Acton to & from Cornwall and Devon). This would often produce two trains per weekday and usually two different examples of the class.
The entire class was allocated to Eastleigh depot for their operational life, and 74003 was the last locomotive to enter Eastleigh works for repairs. In common with class 73, class 74 were sent to Crewe for heavy maintenance up until 1972, when Eastleigh took over all treatment of both classes.

The end

In 1976 the first example was withdrawn: this was 74006 which was damaged by fire. The other nine remained operational till 1977, when they were all taken out of service as a result of a motive power rationalisation scheme.

Departmental use

In 1978 one example, 74010, was sent to Derby for Departmental use at the Railway Technical Centre. It remained there for a short while before being scrapped.

Type HB	Previous Type HA	TOPS	Disposition
E6101	E5015	74001	Scrapped
E6102	E5016	74002	Scrapped
E6103	E5006	74003	Scrapped
E6104	E5024	74004	Scrapped
E6105	E5019	74005	Scrapped
E6106	E5023	74006	Scrapped
E6107	E5003	74007	Scrapped
E6108	E5005	74008	Scrapped
E6109	E5017	74009	Scrapped
E6110	E5021	74010	Departmental then scrapped

External links

★ SEMG site