A cylinder head for an overhead camshaft engine comprises an end wall to which an idler is rotatably mounted, and two side walls which extend in generally parallel from the end wall. Upper and lower beams interconnect and extend between the two side walls. The side walls, and the upper and lower beams cooperate with each other to define a mounting site extending to surround a window opening. A cover is detachably mounted on the mounting site to conceal the window opening.