Handheld type four-cycle engine

A handheld type four-cycle engine including

• an engine main body, the engine main body including a crankcase having a crank chamber, a cylinder block having a cylinder bore and a cylinder head having an intake port and an exhaust port;
• a crankshaft supported in the crankcase and housed inside the crank chamber;
• a piston fitted inside the cylinder bore and connected to the crankshaft;
• an intake valve and an exhaust valve for opening and closing the intake port and exhaust port, the intake valve and the exhaust valve being mounted in the cylinder head;
• a valve operation mechanism operable in association with the rotation of the crankshaft so as to open and close the intake valve and the exhaust valve;
• and
• a power output mechanism provided on one end of the crankshaft projecting out of the engine main body;
• wherein the valve operation mechanism includes
• a camshaft rotatably supported in the cylinder head so as to open and close the intake valve and the exhaust valve;
• and
• a timing transmission placed outside the engine main body on the side opposite to the power output mechanism and operated for providing association between the crankshaft and the camshaft, and
• wherein a flywheel is mounted on the crankshaft between the engine main body and the power output mechanism, the flywheel including cooling vanes for sending cooling air to the engine main body and having a diameter larger than that of the power output mechanism.