Before coming to the WHR, Glaslyn and Kinnerley both worked at Blockleys Ltd, Hadley (in Telford, Shropshire). Both are type 40DL, although the original Ruston 3VRH engine in Glaslyn was replaced by a Perkins 6.354.
For use on the WHR it has been fitted with air brakes (powered by a compressor added at the side of the engine) and a cab. Some years after entering service a starter motor was fitted.
Glaslyn is the main passenger diesel, but occasionally one of the LYd2 Polish diesels replaces it.