Engine valve operation mechanism

An engine valve operation mechanism comprising a timing transmission that is linked to a crankshaft and a cam system that has a cam linked to the driven side of the timing transmission and transmits the rotational force of the cam as opening and closing forces to intake and exhaust valves, the engine valve operation mechanism being provided in a valve operation chamber that is defined between a cylinder head and a head cover that is joined in an oil tight manner to the upper end of the cylinder head,

• wherein opposite ends of a support shaft that supports the cam in a rotatable manner are supported in a first support hole of a first support wall formed in the cylinder head and a second support hole of a second support wall placed inwardly from the first support wall relative to the cylinder head, the first support hole is made as a through hole to allow the support shaft to be inserted into the first support hole and the second support hole from outside the cylinder head, and the inner face of the head cover prevents the support shaft from becoming detached from the first support hole.