Mark Selway, chief executive of the engineering group Weir, is to leave the company to take up a position with Australian building materials supplier Boral.He will be replaced by Keith Cochrane, currently finance director of Weir. Cochrane, who joined Weir in 2006, is a former finance boss of energy group Scottish Power and former chief executive of the rail and bus operator Stagecoach.'Choosing to leave Weir has been one of the toughest decisions of my life but the time is now right to handover to a successor to continue the Group's future development,' said Selway.Weir, which operates in the mining, oil and gas and energy generation markets, is now searching for a new finance director.