Abstract: A process for manufacturing a siamese-type clyinder block which is disclosed herein comprises a blank making step of providing a cylinder block blank in which a sleeve made of a cast iron is cast in each cylinder barrel of a siamese-type barrel made of an aluminum alloy and consisting of a plurality of cylinder barrels connected in series, and a mechanically working or machining step of forming the inner peripheral surface of each sleeve of the cylinder block blank into a true circle. The process is characterized in that the blank making step includes placing highly rigid sleeves each having a thickness set as large as 10% or more of the inner diameter thereof into a siamese-type cylinder barrel molding cavity in a mold and then pouring a molten metal of aluminum alloy under a pressure into the cavity to effect a casting. The sleeve is cast-in as it is at an ambient temperature or in a heated state.

Abstract: A body frame for a motor bicycle includes a main frame, a head tube provided at a front end of the main frame and down tubes extending rearward from the main frame. The main frame, head tube and down tubes are cast with a light alloy into an integral form of a hollow and thin-wall structure. A production process of the body frame, wherein an integrally-formed core, which is formed into a shape similar to that of the body frame, is hollow and has good permeability. A molten metal is charged into the mold and a vacuum is applied to the interior of the core.

Abstract: A body frame for a motor bicycle includes a main frame, a head tube provided at a front end of the main frame and down tubes extending rearward from the main frame. The main frame, head tube and down tubes are cast with a light alloy into an integral form of a hollow and thin-wall structure. A production process of the body frame, wherein an integrally-formed core, which is formed into a shape similar to that of the body frame, is hollow and has good permability. A molten metal is charged into the mold and a vacuum is applied to the interior of the core. The molten metal is charged into a cavity defined between the core and the molding surface of the mold by a low-pressure casting method, and the molten metal is solidified so as to cast the body frame.

Abstract: A siamese-type cylinder block blank which is composed so that upon the pouring a molten metal under a pressure, a sleeve of cast iron is cast in each cylinder barrel of a siamese-type cylinder barrel made of an aluminum alloy and consisting of a plurality of cylinder barrels connected in series. The cylinder block blank is characterized in that each sleeve cast presents a substantially oval configuration in section with the lengthwise axis parallel to the direction of cylinder barrels arranged, as a result of the reception of the solidification shrinkage force of each cylinder barrel.

Abstract: A method for manufacturing a siamese-type cylinder block, which comprises the steps of pouring under pressure a molten metal of aluminum alloy into a siamese-type cylinder barrel molding cavity with an expansion force applied to the sleeve placed in such cavity, and then removing the expansion force after the completion of solidification of the molten metal to cast a cylinder block blank, and subjecting the resulting blank to a working operation for forming the peripheral inner surface of the sleeve into a true circle.

Abstract: A process for casting a cylinder block blank made of light alloy provided with a cylinder barrel reinforced around its cylinder bore with a reinforcing tubular body and a crankcase provided continuous to the cylinder bore, which includes placing the reinforcing tubular body in a first cavity formed for shaping a cylinder barrel at the lower portion of a mold which is formed at its upper portion with a second cavity for shaping a crankcase communicating with the first cavity, and pouring a light alloy molten metal from the lower portion of the first cavity into the first and second cavities while simultaneously venting gas from the first and second cavities.