The present invention relates to a cooling means for the squish part of an air cooling over head valve engine, comprising a fan disposed in front of said engine for generating cooling wind. A fan case is provided which covers the front side of the fan and engine. A wind tunnel is formed through the cylinder head of said engine near the squish area and is aligned so as to pass a cooling wind, generated by the fan, above the squish area. The engine is provided with an intake and exhaust ports opening at the front and rear surfaces of said cylinder head, respectively. In the lateral side of the wind tunnel, an intake or exhaust pipe is disposed laterally over the front space of the tunnel, so as to guide cooling wind blown up from the fan to the tunnel along its lower peripheral surface thereof.

A spark plug guard can be switched between a spark-plug covering position to protect a spark plug and a spark-plug opening position. An operator displaces the spark plug guard from the spark-plug covering position to the spark-plug opening position, thereby obtaining a wide working space to perform the maintenance and inspection of the spark plug efficiently. The spark plug guard has a function of fixing a predetermined part in the spark-plug covering position. Consequently, the need for a part fixing member which was conventionally required for fixing the predetermined part to the engine body is eliminated, thus contributing to a decrease in the weight of the whole internal combustion engine and to cost reduction.

A cooling system which comprises one or more cooling jackets secured to or otherwise formed with the head plate of an internal combustion engine and in close proximity to the cylinder heads of the engine. Each jacket is closely adjacent to and surrounds a spark plug associated with a cylinder. Furthermore, each of the jackets is connected to a heat exchanger, such as a radiator, through coolant delivery and return lines. A metal composition which is in a solid state at non-operating temperatures of the engine and is changed to a liquified state by the heat of the engine, when operating, serves as the coolant, and during operation is continually circulated through the jackets surrounding each of the spark plugs to cool the portions of the engine adjacent thereto. By virtue of cooling the immediate areas of the engine in proximity to the spark plugs, the heat of combustion can be rapidly dissipated which allows the engine to be operated at optimum temperatures, thereby increasing the operating efficiency, without the attendant problems incident to the presence of localized excess temperature conditions normally produced at or adjacent to the cylinder heads. Moreover, as a result of higher operating efficiency, the exhaust gases from engines equipped with the present cooling system contain a relatively low amount of the pollutants normally produced by internal combustion engines.

A ventilation system for an encapsulated internal combustion engine providing a reduction in short-circuit air flow from the pressure side to the suction side of the ventilation radial fan.

In a spark-ignited engine in which a spark plug is supported so that its igniting tip is centrally located in the combustion chamber, a bore for forming a coolant passage is provided in the wall of the cylinder head defining the combustion chamber to extend between an exhaust port and a threaded bore into which the spark plug is screwed. The bore is formed to extend from a cooland inlet formed in the lower side of the cylinder head through which coolant from the cylinder block enters the cylinder head to the water jacket formed in the cylinder head so that the coolant from the cylinder block flows through the bore under the pressure difference between the coolant inlet and the water jacket.