Cylinder head structure in four-cycle engine

A cylinder head structure in a four-cycle engine, comprising:

• a cylinder block having a cylinder bore in which a piston can be slidably fitted;
• a cylinder head connected to the cylinder block, the cylinder head forming a combustion chamber that faces a top of the piston in a space defined by the cylinder head and the cylinder block;
• a camshaft disposed on an extension of an open/close operation axis of an intake valve, the camshaft forming part of a valve actuating system driving to open and close the intake valve and an exhaust valve openably disposed in the cylinder head;
• an intake port disposed in a first side wall extending along an axis of the camshaft so as to be disposed in the cylinder head;
• an exhaust port disposed in a second side wall disposed in the cylinder head so as to oppose the first side wall;
• and
• a head cover forming a valve train chamber that accommodates therein the valve actuating system in a space defined by the head cover and the cylinder head, a connection surface formed in the cylinder head for connecting the head cover being extended to follow along a plane that is inclined so as to be spaced further away from the cylinder block toward the first side wall relative to the second side wall, wherein:
• camshaft holders having semi-circular bearing portions that generally receive a half portion of the camshaft to be integrally connected to the first side wall are integrated with the cylinder head and the semi-circular bearing portions protrude above the entire connection surface as viewed from an axial direction of the camshaft;
• cam caps are respectively fastened to the camshaft holders and receive a remainder substantially half portion of the camshaft;
• bolts pass through the head cover and are respectively threaded into the cam caps such that the head cover is in direct contact with the cam caps, and at least one of the bolts extends along a plane that obliquely crosses a cylinder axis;
• the intake port is disposed in the first side wall;
• and
• a stem end of the exhaust valve is disposed at a position protruding above the connection surface as viewed in a direction along the axis of the camshaft,
• wherein the intake port has an upper end disposed upward of a lower end of the camshaft, and
• wherein a stem of the intake valve driven to open or close by valve lifters is longer in length than the stem of the exhaust valve.