an internal combustion engine comprises a cylinder block including cylinder barrels , and main bearing bulkheads each having a bearing section ; main bearing cap sections respectively secured to the bearing bulkheads so that each main bearing cap section and the corresponding cylinder block bearing section associate to constitute a main bearing for rotatably supporting a crankshaft ; and a bearing beam structure detachably secured to the main bearing cap sections to connect the main bearing cap sections with each other as a single unit , the bearing beam structure including a plurality of beam sections which are disposed parallel with each other and extend along the row of the main bearing cap sections , the beam sections being connected with each other , thereby effectively decreasing engine noise while facilitating the handling of the engine parts before assembly .