Engine

An engine comprising:

• a crankshaft extending in a widthwise direction of the engine and converting reciprocal motions of pistons to produce rotary motion;
• a crankcase supporting the crankshaft;
• a plurality of cylinders extending from the crankcase so as to protrude in a reciprocating direction of the pistons, the cylinders being arranged along the widthwise direction of the engine;
• a cylinder head coupled to protruding ends of the cylinders, the cylinders and the cylinder head defining combustion chambers therein;
• air intake ports which introduce intake air to the combustion chambers;
• air intake valves which open and close the air intake ports;
• exhaust ports which discharge exhaust gas from the combustion chambers;
• exhaust valves which open and close the exhaust ports;
• a valve operation control mechanism which opens and closes the air intake valves and the exhaust valves in a synchronous manner with the rotary motion of the crankshaft;
• a power transmission member which transfers the rotary motion of the crankshaft to the valve operation control mechanism;
• a transmission member housing space defined by the cylinders and the cylinder head, extending in the reciprocating direction, and having the power transmission member disposed therein;
• and
• ignition plugs which ignite an air-fuel mixture in the combustion chambers, the ignition plugs including first and second ignition plugs for each of the combustion chambers, the first ignition plug being located on the cylinder axis, and the second plug being arranged offset relative to the first ignition plug so as to be away from the transmission member housing space in the widthwise direction of the engine.