| 摘要 |
PURPOSE:To make thermal expansion around the circumference of a sleeve during running approximately uniform, and to restrict the gap between a piston and the sleeve in order to prevent the shortcircuiting of gas and the waste of oil by using a cast-iron sleeve heated and provided with a radially expanding force in a specific casting stage and boring it thereafter. CONSTITUTION:The deformation of each sleeve 3 caused by the filling pressure of a molten aluminum alloy is prevented by previously providing a radially expanding force to each sleeve 3. Further, when each sleeve 3 is preheated up to 150-700 deg.C, each sleeve 3 is heated by the molten metal approximately to the same temperature as that of the metal during casting to lower the rigidity of sleeve 3. By this operation, when the radially expanding force of each sleeve 3 is removed after solidifying the molten metal, each sleeve 3 lowered in its rigidity deforms so as to follow the cross-sectional shapes of cylinder barrels 11-14 after their shrinkages. The cross-sectional shape of each sleeve 3 is changed into a slightly elliptic shape parallel to the arranged direction of cylinder barrels 11-14. Accordingly, the residual casting stress is made approximately uniform around the circumference. Each sleeve 3 is subjected to boring work in this state, and the thermal expansion around the circumference of each sleeve 3 is made approximately uniform when an engine is driven after assembling.
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