With ever higher passenger numbers, the Bure Valley Railway's class of ZB locomotives were increasingly found to be underpowered and heavy on fuel and water. The decision to rebuild two of the locomotives provided the opportunity to solve these problems by radically redesigning the front end to incorporate new cylinders, modified valve gear and a Lempor exhaust system.
Steam Loco Design's Ian Gaylor carried out the design work for the modifications and tells the full story of the ZBs' transformation in this six part article. The article covers the background to the decision to rebuild the locomotives, details of the modifications and the results of comprehensive dynamometer testing before going on to consider possible future developments including the design of an even more powerful 2-8-0T locomotive.
This article was written in 2005 and first appeared, in an altered and abridged form, in Steam Railway nos. 324 and 325 in 2006.