BR Class 31 Brush Type 2

The Mirrlees engined type 2 locomotives built by Brush of Loughborough initially proved to be among the more reliable of the pilot scheme diesels, despite their weight having to be spread over an idler axle and series production was ordered. 263 had been built, including examples with uprated engines before stress crack problems began to afflict the Mirrlees engine blocks. Despite the builder attempting remedies BR faced both operational and political issues if a significant number of the new diesels were sidelined and an alternative known-reliable engine was tried.
The Brush class 31 body proved able to accommodate the English Electric 12SVT engine, as fitted to the class 37s. To keep the engine output matched to the designed capacity of the Brush electrical machinery the non-intercooled engine was used, delivering 1,470bhp. The entire class was re-engined through the late 1960s, being given class number 31 under the TOPS system, split into sub-classes 31/0 for the pilot scheme locomotives with their own multiple-working system and 31/1 for the main production batch which were equipped with the BRs' standard 'blue star' multiple working system. Later sub-class 31/4 was added for locomtoives equipped with Electric Train Supply (ETS) generators for train heating.
Class 31 locomotives have continued in service on the national network until recent years with 5 examples still registered in 2018, though all listed as stored, and 26 examples on heritage railways.