British Rail Class 23

"Baby Deltic" D5902 at King's Cross, July 1966.

The British Railways Class 23 were a class of ten Bo-Bo diesel-electric locomotives built by the English Electric Company (EE) in 1959. The power unit used was a Napier Deltic T9-29 9-cylinder engine of 1,100 bhp (820 kW) driving an EE generator, which powered the four traction motors. They were numbered from D5900 to D5909.

The T9-29 diesel engine was a single, half-sized version of those used in the more powerful Class 55 "Deltic" locomotives, and the overall design and external appearance of the Class 23 was also similar to the Class 55, but much shorter, leading to their nickname of Baby Deltics.

History

On initial completion, the first locomotives were found to weigh 3 long tons (3.05 t; 3.36 short tons) over the specification weight of 72 long tons (73.2 t; 80.6 short tons). A programme of lightening was begun: some of this involved cutting circular lightening holes into the bogie frames, and replacing steel buffer beams or roof panels with aluminium. Much of the over-weight was due to ancillary components, particularly the train-heating steam generators, being supplied over weight. To avoid waste, these components were replaced by lighter versions from other makers, but the heavier originals were then used in the D20/3 and D20/1 locomotives. The lightened locomotives eventually met British Rail's approval, but only after a painstaking weighing that involved specifying the amount of sand in the sandboxes and other precise details.

Technical designs and reliability problems

Initial problems with the locomotives were minor and varied, although a problem with cracking in the cylinder liner around the injector hole required the engine to be changed. By November 1959, seven engines had been changed and this reduced availability first raised comparisons with the better reliability of the D11/3 Type 2. The Type 2s were averaging 30-40,000 miles per failure, the Baby Deltic less than a quarter of this. Although they suffered problems with the cylinder liners that were not dissimilar to those of the Class 55 Deltics, most of the Class 23's early problems were a variety of failures with the engine ancillaries. The auxiliary gearbox used to drive the compressor and cooling fans was a particular problem, suffering from vibration in its geartrain and a resonant whirling in the long drive shaft to it at particular rpm. Many engines seized because this shaft driving the auxiliaries snapped and then whipped round, rupturing coolant hoses and causing overheating. By October 1960 the emphasis of failures had shifted from the ancillaries to the engine itself. Locomotive mileages had only reached 40-60,000 miles each, including stoppages, whilst in this 18 months there had been 44 engine changes across only 10 locomotives. Despite a generous availability of spare engines, four of the ten locomotives were out of service at the time. Four main engine problems had been identified: Fractured cylinder liners from the injector hole, caused by assembly stresses Fractured cylinder liners from the injector hole, caused by electrolytic corrosion. Turbocharger bearing failures, caused by exhaust gases leaking through the labyrinth seals. Seized pistons, due to poor cooling caused by chemical erosion from incorrect lubricants. In July 1961 BR suggested replacing the Napier engine with an English Electric 8SVT V8. This would however have added eight tons in extra weight, and so was rejected. EE also pointed out that the locomotives were now highly reliable in general, except when a major failure required the considerable downtime for an engine change. By around 1963 all the locomotives had gradually been moved to Stratford Depot as they failed and were added to the line in store, pending a decision on their future. By this time the locos were based at the new diesel maintenance depot at Finsbury Park.

Withdrawal

By the late 1960s BR had drawn up a "National Traction Plan", whose aim was to rationalise the number and types of diesel locomotives in traffic (and thus reduce operating costs). The 'Baby Deltics' were an obvious target, being only a ten-strong class, and still beset with operational problems. The locos were withdrawn between 1968 and 1971. The last two locos in traffic on revenue-earning service were D5905 and D5909. Several of the class received full yellow ends whilst still in two-tone green. These were D5900/3/4/8; D5908 also carried the new double-arrow BR symbol. D5909 was the only locomotive to receive the full "rail blue" livery. D5901 was transferred to the departmental fleet of the Railway Technical Centre in 1969. It worked test trains to and from the RTC until 1975, when it was replaced by a Class 24. The loco was cut up in 1977, still carrying two-tone green livery with a grey roof and small yellow warning panel.

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