Engineering group Weir was the best performing FTSE 250 stock on Monday morning after trading in the nine weeks to 4 June exceeded expectation.Broker KBC Peel Hunt has reiterated its "buy" recommendation on the stock, saying: "Aftermarket demand remains strong and continues while original equipment orders are beginning to improve."Weir said first half pre-tax profit is now expected to be around £140m, while over the full year it should be somewhere in the range of £250m to £260m. KBC Peel Hunt had originally been forecasting pre-tax profit of £220m for the current year.