Spark-ignited internal combustion engine

摘要

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.