It was the mid 1980s before any effort was made to obtain a diesel locomotive that could work trains up the line. Between 1986 and 1992, four diesel locomotives were bought from the Hunslet Engine Company of Leeds, to a design and specification jointly developed with the railway. These became Nos. 9 to 12. During the period between the building of No. 9 and No. 12 both the locomotive manufacturer and the diesel engine manufacturer changed their names, Hunslet becoming Hunslet-Barclay and Rolls-Royce diesel engines being sold to Perkins.