By David Shepardson, Valerie Insinna and Tim Hepher WASHINGTON (Reuters) -The U.S. Federal Aviation Administration late on Wednesday tightened pressure on Boeing by barring the troubled planemaker from expanding production of its best-selling 737 MAX narrowbody planes, following “unacceptable” quality issues. The unprecedented decision looked set to deepen turmoil at Boeing even as the FAA also agreed to allow the 737 MAX 9, which was grounded after a mid-air blowout on an Alaska Airlines jet on Jan. 5, to resume flying once inspections were completed. The ability to resume flying was a relief…