Abstract: A cooling water passage structure in a cylinder head of an internal combustion engine includes a first exhaust-side cooling water passage and a second exhaust-side cooling water passage arranged to sandwich an exhaust collecting portion and extending in a lengthwise direction of the cylinder head. An exhaust pipe is fastened to a exhaust-side lateral surface of the cylinder head via a fastening member. A shunt passage is formed in at least one of the first exhaust-side cooling water passage and the second exhaust-side cooling water passage to cool the fastening member and is formed along a water flow in the first exhaust-side cooling water passage or the second exhaust-side cooling water passage by partly expanding the first exhaust-side cooling water passage or the second exhaust-side cooling water passage to increase a passage cross-sectional area of the first exhaust-side cooling water passage or the second exhaust-side cooling water passage.

Abstract: A cooling water passage structure in a cylinder head of an internal combustion engine includes a main cooling water passage extending in the lengthwise direction above combustion chambers. An exhaust-side communication passage communicates the main cooling water passage with a first exhaust-side cooling water passage and with a second exhaust-side cooling water passage. A ridge extends in the lengthwise direction to adjust a flow speed of cooling water to flow through the main cooling water passage and is provided on a first wall surface of a main passage defining portion on a side away from the combustion chambers. An exhaust-side throttle portion extends in a direction substantially perpendicular to the lengthwise direction to reduce a passage cross-sectional area of the exhaust-side communication passage and is provided on a second wall surface of an exhaust-side communication passage defining portion on a side away from the combustion chambers.

Abstract: A cooling water passage structure in a cylinder head of an internal combustion engine includes a first exhaust-side cooling water passage and a second exhaust-side cooling water passage arranged to sandwich an exhaust collecting portion and extending in a lengthwise direction of the cylinder head. An exhaust pipe is fastened to a exhaust-side lateral surface of the cylinder head via a fastening member. A shunt passage is formed in at least one of the first exhaust-side cooling water passage and the second exhaust-side cooling water passage to cool the fastening member and is formed along a water flow in the first exhaust-side cooling water passage or the second exhaust-side cooling water passage by partly expanding the first exhaust-side cooling water passage or the second exhaust-side cooling water passage to increase a passage cross-sectional area of the first exhaust-side cooling water passage or the second exhaust-side cooling water passage.

Abstract: A cooling water passage structure in a cylinder head of an internal combustion engine includes a main cooling water passage extending in the lengthwise direction above combustion chambers. An exhaust-side communication passage communicates the main cooling water passage with a first exhaust-side cooling water passage and with a second exhaust-side cooling water passage. A ridge extends in the lengthwise direction to adjust a flow speed of cooling water to flow through the main cooling water passage and is provided on a first wall surface of a main passage defining portion on a side away from the combustion chambers. An exhaust-side throttle portion extends in a direction substantially perpendicular to the lengthwise direction to reduce a passage cross-sectional area of the exhaust-side communication passage and is provided on a second wall surface of an exhaust-side communication passage defining portion on a side away from the combustion chambers.