a method of assembling a valve driving mechanism , having a variable valve timing unit incorporated in a cylindrical mounting base , to a dual overhead camshaft engine . the engine has camshafts which are rotatably connected by camshaft gears . the method includes the initial step of mounting one camshaft gear , maintained at a predetermined angular position relative to the other camshaft gear attached to the other camshaft , and a lock nut on the one camshaft . subsequent steps include first adjusting the angular position of the mounting base relative to the one camshaft gear and then the angular position of the variable valve timing unit relative to the one camshaft , and fastening the one camshaft gear to the mounting base by the lock nut and , simultaneously , the variable valve timing unit to the one camshaft .