The A4 class had previously had problems with the big end bearing for the middle cylinder, so the big end was fitted with a "stink bomb" of aniseed oil which would be released if the bearing overheated. Shortly after attaining the record speed, the middle big end did overheat and "Mallard" reduced speed, running at 70–75 miles an hour onwards to Peterborough. It then travelled to Doncaster Works for repair. This had been foreseen by the publicity department, who had many pictures taken for the press, in case "Mallard" did not make it back to Kings Cross. The (Edwardian period) Ivatt Atlantic that replaced "Mallard" at Peterborough was only just in sight when the head of publicity started handing out the pictures.