The British Rail 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 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 British Rail 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.
Introduction and service history
On initial completion, the first locomotives were found to weigh over the specification weight of . 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 Class 20 and Class 40 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.
After acceptance trials at Doncaster, they entered service between April and June 1959. They were based at Hornsey, although at weekends were usually located at Hitchin engine shed. It had been British Rail's original intention to work the locos across London on the Widened Lines but the locomotives were found to be too heavy. The first of the class was held at Vulcan Foundry whilst EE tried to reduce the weight but this could not be completed to a satisfactory standard.
Operation
The locomotives were put to work on King's Cross outer suburban duties such as the Cambridge Buffet Express as well as services from Kings Cross to Moorgate sub-surface platforms via the 'widened lines' (more recently, part of Thameslink). The locomotives were later banned from Moorgate because of excessive exhaust smoke in the tunnels.
Other services entrusted to the class were race specials run from King's Cross to race meetings at Newmarket.
Technical, design 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 British Rail Class 24 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.