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. 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. Modification It was decided by BR and EE to carry out a programme to refurbish the class and modify the engines with new parts designed by the engine manufacturer. The locos also had modifications to their nose ends, losing the gangway