PURPOSE:To prevent mutual interference between a beam member and a crank locus in a condition that the total height of a bearing cap is suppressed by providing a dome member on the tip end of a part extending in a lower direction from both sides of the cap. CONSTITUTION:Both ends 6a of a bearing cap positioned outside rather than right and left gap bolt seats 15 are extended downwardly, and made to be extending parts 7. The tip ends 7a of these parts 7 are arranged outside rather than the locus of a crank. In six bearings 6 arranged with specified spaces in the direction of a crank shaft, the tip ends 7 are interconnected monolithically by means of a pair of beam members 8 extending in the crank shaft direction, and are made to be bearing cap assembly 20 shaped like a ladder. Further, a pair of skirt parts 23 are mutually connected by means of a spacer 10 between the tip ends and reinforcing members 9 arranged on the outside thereof, so vibration can be restrained.
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