Cylinder head structure of an internal combustion engine

A cylinder head arrangement for an internal combustion engine having a crankshaft defining a crankshaft axis, said cylinder head arrangement comprising:

• a cylinder head and a cylinder block together defining at least one combustion chamber, said cylinder head having a longitudinal axis generally parallel with a longitudinal axis of the crankshaft and dividing said cylinder head into an intake side and an exhaust side;
• a plurality of intake and exhaust ports disposed in said cylinder head at said intake side and said exhaust side, respectively, and communicating with said combustion chamber, said intake ports opening at an upper surface of said cylinder head and said exhaust ports opening at a side surface of said cylinder head;
• a plurality of intake valves mounted in said cylinder head to open and close said intake ports, and a plurality of exhaust valves mounted in said cylinder head to open and close said exhaust ports, each said intake valve and exhaust valve having a tappet portion disposed at one end thereof;
• a plurality of intake tappet boss portions disposed in said cylinder head at said intake side and configured for axially movably supporting said tappet portions of said intake valves, and a plurality of exhaust tappet boss portions disposed in said cylinder head at said exhaust side and configured for axially movably supporting said tappet portions of said exhaust valves;
• a plurality of intake bolt boss portions and exhaust bolt boss portions disposed in said cylinder head at said intake side and said exhaust side, respectively, and configured for receiving a bolt for fixing said cylinder head to said cylinder block;
• said intake tappet boss portions being disposed a first distance from the cylinder head axis, said intake bolt boss portions being disposed a second distance from the cylinder head axis, said second distance being less than said first distance;
• and
• said exhaust tappet boss portions being disposed a third distance from the cylinder head axis, said exhaust bolt boss portions being disposed a fourth distance from the cylinder head axis, said fourth distance being greater than said third distance.