THR was able to make money by supplying parts for YEC locomotives and carrying out repairs and maintenance work. The THR service department now had two full-time representatives on the road selling parts and service agreements. The sudden addition of around 700 locomotives to the potential market in the UK provided a great boost, although frustrated for some years by a policy laid down by Rolls-Royce that THR must supply diesel engine spares only for Sentinel and Vanguard locos and refer all Yorkshire locomotive users to Cripps (the Rolls-Royce main distributor) for engine parts.