Overhauling the Class 57 for the 21st Century

Keeping older locomotives in passenger service comes down to one simple idea: age matters less than condition. If a fleet still suits the job, the route, and the operator, a heavy overhaul can turn what looks like yesterday’s traction into a reliable asset for today’s railway. That is exactly what the Class 57 G exam programme is about. Rather than treating older locomotives as a short-term stopgap, it shows how they can be renewed, improved, and sent back out ready for another spell of useful service. At a time when replacement often seems like the only answer, this programme is a good reminder that overhaul can still make solid technical and operational sense, especially when dealing with a small fleet. Keeping ageing fleets Great Western Railway’s (GWR) Class 57 fleet has a very specific role: hauling the Night Riviera Sleeper between London Paddington and Penzance. That is not the sort of work that leaves much room for unreliability. Sleeper services need steady performance, dependable electric train supply, and the resilience to handle long overnight runs in all seasons. There are six locomotives in the fleet, with four Class 57/6s and two Class 57/3s, all leased from Porterbrook, and one of the 57/3s sub-leased through GBRf. When numbers are that tight, every locomotive matters, especially once operational changes increase the need for availability and rescue cover in the west, having withdrawn the HSTs which could carry out a rescue. For the Class 57s, the G exam is comprehensive. Due at around 1,000,000 miles or every 10 years, it is far more than a routine inspection; it is the point at which the locomotive is restored to a state of good repair for continued front-line use. By 2024, the 57/6 fleet G exam was almost due. Although the work could theoretically have been carried out separately for bogies, engine, and the rest of the locomotive, GWR chose to tackle all three together. That meant a true heavy overhaul, giving the team the best chance to deal properly with wear, corrosion, ageing wiring, fatigue, and the sort of hidden defects that build up over time. The programme did not start with the assumption that the heaviest possible intervention was needed. An early study looked at whether parts of the exam could be reduced. But previous G and F exams had already been descoped, and there was not much left to cut without leaving bigger problems for later. Planning the overhaul Procuring the overhaul was unexpectedly difficult. Few approved suppliers were out there and they were busy with other work, and none could offer the full turnkey package required. That meant the locomotives needed extension work just to stay in traffic while a workable plan was put together, all while failures elsewhere in the fleet pushed up mileage and made the overhaul more urgent. The answer came from a useful overlap between operational need and engineering capability. At Laira depot in Plymouth, the earlier-than-planned withdrawal of the CrossCountry HST fleet left behind a skilled team and facilities that could have gone underused. Crucially, Laira already knew its way around heavy maintenance, with experience of F and G exams on HST power cars and major coach work. It also had the right kit for a job like this: jacks, lifting equipment, high-level access, and space that could be adapted for major strip-down and rebuild work. What started as a struggle to find a contractor ended up becoming a strong in-house opportunity. That said, not everything could sensibly be done at one depot. Bogie overhauls needed specialist tooling, frame measurement facilities, and undercover space beyond what was realistically available. Electrical machine overhauls for traction motors, alternators, compressors, and blower motors also went to outside specialists, along with brake work and repainting. The depot handled inspection, cleaning, repair, wiring checks, and final assembly, while selected components were sent out to keep the programme moving. It was a practical and sensible split of responsibility, led by GWR. Challenges emerge The biggest engineering question centred on the engine. Class 57s are rebuilt from Class 47s (which date from the mid-1960s) but use reconditioned EMD 12-645 series engines and Class 56 alternators as part of the rebuild concept that originally improved reliability. At first, the original equipment manufacturer looked interested in taking on the overhaul work. In the end, timescales and supplier workload got in the way, and other options were not available when needed. So, GWR made a bold call to overhaul the engines in-house. That was a major step: this level of work means a full strip and rebuild to zero-hours standard, with the sort of cleanliness, measurement, tooling, and process control usually associated with specialist overhaul shops. Making that possible took a lot of groundwork. Engine stands and bespoke tooling had to be designed and built, and a tented clean area was set up for precision reassembly. The paperwork was another challenge. Drawings, manuals, and technical references were often old, complex, and not always specific to the exact engine configuration in the fleet. That meant engineering judgement and careful cross-checking were just as important as hands-on work. It is a good reminder that in heavy overhaul, the prep matters every bit as much as the rebuild itself. As work progressed, the locomotives confirmed why a full overhaul had been the right call. Corrosion varied from one locomotive machine to another and demanded a serious amount of welding and structural repair. Some engines also needed deeper intervention than expected, and one had already suffered a catastrophic failure before entering the programme. Delays to bogie overhauls from external suppliers have affected progress too, underlining how even a well-planned hybrid model can be exposed to supply-chain bottlenecks. Then there was obsolescence: many parts were no longer easy to source, forcing the team to find workarounds and recover knowledge that in some cases had not been actively used for years. Once the locomotives had been stripped, assessed, and repaired, the job shifted from dismantling to renewal. Reassembly is where good planning starts to pay off: overhauled components come back in, wiring is re-established, repaired structures are integrated, and the locomotive starts to look like a railway asset again rather than a workshop project. But finishing the rebuild is only part of the story. Testing is what really turns engineering confidence into service confidence. On the Class 57 programme, that takes several weeks and includes load-bank testing to prove the rebuilt power unit and its associated systems before the locomotive returns to traffic. Progress is being made. One locomotive has completed its G exam and returned to service with good reliability, while another is back in traffic with some restrictions pending final rectification and repainting. Others remain at different stages of completion, with engine repairs, corrosion work, bogie fitment, and reassembly still under way. That is fairly typical of a big overhaul programme on older locomotives – each one turns up with its own mix of wear, defects, and surprises. The important point is that the work is delivering locomotives back into service and building resilience for the fleet as a whole. Lessons learned The wider lessons go well beyond one fleet. Older locomotives nearly always reveal more complexity than the early plan suggests, so preparation time matters. Float material helps protect both budget and timescales. Skills in areas such as welding and specialist electrical work need to be kept alive because they are not easy to rebuild once lost. Documentation also needs to be gathered early and treated as a project. Above all, the Class 57 G exam programme shows that modern railway engineering is not just about bringing in new traction. It is also about knowing when existing assets are worth backing. In the right service, and with the right overhaul behind them, older locomotives can still more than earn their keep. This article is based on a presentation to the IMechE Railway Division Rolling Stock Lifecycle Conference in May 2026 by Karl Atkinson, Class 57 Fleet Engineer GWR. Image credit: James Gregory