CYLINDER BLOCK AND METHOD OF MANUFACTURING THE SAME

PROBLEM TO BE SOLVED: To provide a cylinder block having a lower manufacturing cost for allowing easy molding of a semifinished product of which spiracle machining sites are made thinner by an ordinary casting and molding machine and still greatly reducing a machine working time to form spiracles passing through the molded product, and to provide a method of manufacturing the same.SOLUTION: The cylinder block includes a cylinder forming part 12 and a crank chamber forming part 13, the crank chamber forming part 13 having partition wall portions 18 for partitioning a plurality of crank chambers 14, and spiracle forming portions 20 in which spiracles 41 communicating the adjacent crank chambers 14 with each other are formed by machine work, each of the spiracle forming portions 20 being formed thinner than each of the partition wall portions 18. 【課題】通常の鋳造成形機で呼吸孔加工部位を薄肉化した半製品を容易に成形でき、しかも、その成形品に呼吸孔を貫通形成する機械加工時間を大幅に短縮できる低製造コストのシリンダブロックおよびその製造方法を提供する。【解決手段】気筒形成部１２とクランク室形成部１３を備えたシリンダブロックであり、クランク室形成部１３が、複数のクランク室１４を区画する隔壁部１８と、隣り合うクランク室１４を互いに連通させる呼吸孔４１が機械加工により形成される呼吸孔形成部２０とを有し、呼吸孔形成部２０の厚さが隔壁部１８の厚さよりも薄く形成されている。【選択図】図１