Motion is created by an arrangement of crankshafts and connecting rods acting on the wheels. Visitors can see the detailed inner workings of a steam engine in the sectioned Merchant Navy Class locomotive Ellerman Lines and in a sectioned replica of Rocket in the Great Hall. Former LNER Class V2 Green Arrow 1936 is in full working order and is occasionally used to haul steam charter trains on Britain's mainlines. For a steam locomotive to run on the mainline in Britain it needs a full mechanical overhaul, boiler insurance, a spark arrestor test, and ultrasonic testing of wheels, all of which are very costly. For example, Flying Scotsman has recently cost in the region of 750,000 to restore to mainline condition.
Boiler certificates last ten years and are valid for seven years on the mainline.
A number of BR diesel-electric locomotives are also in working order. Agenoria and Sans Pareil which were both built in 1829. The newest steam locomotive is Class 9F Evening Star 1960, the last steam engine built by British Railways. August 1968 for mainline steam. The narrow gauge Vale of Rheidol railway in Wales was owned by British Rail and steam hauled until privatisation in 1989.