Abstract: The object of the present invention is to concentrate the intake air flowing into a combustion chamber of an internal combustion engine near the ignition point of a spark plug, and to form a strong swirl effect in this area.A projection 16 is formed on an end surface 5a of a piston 5. Projection 16 is positioned near an intake port disposed on one side of the upper surface of a combustion chamber. A cavity 17 is formed at a position closer to an exhaust port than projection 16. An ignition point of a spark plug is disposed above cavity 17. The intake port points toward the outer perimeter of the combustion chamber. The portion of projection 16 on piston end surface 5a that lies in the direction of the intake port is cut away. An intake flow passage 19 is formed on end surface 5a of piston 5, extending from a cut-away section 18 toward the exhaust port via the outer perimeter of piston end surface 5a.

Abstract: A lubricating oil passage structure for a cylinder block having a plurality of cylinders separated from each other by journal walls and arranged in a row, bearing bores formed in the journal walls for rotatably supporting a pair of rotary shafts in parallel with the crankshaft of the engine on either side of the cylinder row, comprising: a hollow gallery member internally defining three galleries extending in parallel with the crankshaft in the hollow gallery member, and mechanically connecting the bearing caps with each other. Lubricating oil passages extend from these oil galleries to the bearings for the crankshaft and the rotary shaft linearly and in parallel with the bolts for securing bearing caps for the crankshaft bearings to the journal walls. Thus, the lubricating oil passages can be formed in a single manner, and the lengths of the passages are minimized. Furthermore, the gallery member can effectively reinforce the journal walls.

Abstract: A water-cooled multi-cylinder internal combustion engine comprises a water jacket which extends deeper towards the crank case than conventional water jackets without increasing the width of the water jacket. As a result, the lubricating oil in the crank case is effectively cooled by the cooling water. Further, the narrower and deeper water jacket improves the overall cooling efficiency of the cylinder block and the reduced volume of the water jacket speeds up the warm-up of the engine. Casting of this cylinder block is made possible by providing projections at the bottom ends of the water jacket intermediate between adjacent cylinders. These projections facilitates the process of pulling out the core for defining the water jacket during the casting process from the water jacket of the cylinder block without causing any undue stress either to the core or to the cylinder block.

Abstract: A piston for an internal combustion engine in which the skirt portion of the piston is slightly oval rather than cylindrical and the size of the oval is varied along the skirt to produce contact surfaces of a particular shape engaging the cylinder. Specifically, the smallest diameter of the oval continuously increases from the piston rings downwardly and the largest diameter increases for a portion thereof. The contact surface shape has sloping sides to enhance the flow of lubricating oil away from the rings.