Camshaft structure for double overhead camshaft engine

An overhead camshaft structure for a double overhead camshaft engine having at least three in-line cylinders and two camshafts which are formed with series of pairs of cam lobes and series of camshaft journals, respectively, and are operatively connected with each other by helical gears comprises a thrust collar formed on each camshaft, a thrust bearing formed with a thrust restrictive groove consisting of an upper half and a lower half, narrower than the upper half, for receiving therein the thrust collar, and an oil passage consisting of a radial passage portion penetrating through the thrust collar and an axial passage portion formed in each camshaft for allowing oil to pass up to each cam lobe and camshaft journal for lubrication. The radial passage is directed in parallel with a straight line connecting an axial centerline of rotation of each said camshaft and a juncture of a valve opening ramp of said cam lobe adjacent to said thrust collar.