Patent ID: 8051819
Filing Date: 2011-11-08
Classification: F01L,F02B,F02F

Abstract:
1. A crankcase structure for an overhead-camshaft internal combustion engine having an endless loop member which operatively connects a loop drive sprocket integral with a crankshaft having an intake and exhaust valve-driving sprocket thereon for driving intake and exhaust valves, said crankcase structure comprising: a crankcase having a bearing member mounted thereon for rotatably supporting said crankshaft, said crankcase having a crankcase wall with a wall opening formed therein thereof for receiving an end portion of said crankshaft, an outer surface of said wall of said crankcase, proximate an extension of a center line of said crankshaft, having a loop guide-engaging recess formed thereon; said loop guide-engaging recess supporting a base end portion of a loop guide for guiding movement of said endless chain; and a loop-retaining member located on a lower side of said loop drive sprocket and operable to help retain said endless loop member on said sprocket; wherein: when viewed in a side view, an inner peripheral surface of said wall opening is formed as a spiral surface, such that a diameter of the opening increases along a direction reverse to a rotational direction of said crankshaft; said spiral surface having a starting end between a vertical plane and a horizontal plane; said vertical plane passing through a center of said crankshaft and directed downwards; and said horizontal plane passing through the center of said crankshaft and being on a rotational direction side of said crankshaft, wherein a maximum-radial end of said spiral surface is terminated by a surface which intersects a surface passing through the center of said crankshaft and through said starting end; said loop-retaining member is integrally provided projecting outwardly from said outer surface of said wall along a circumferential direction of said loop drive sprocket; and said loop guide-engaging recess is formed on a plane which is substantially orthogonal to the extension of a cylinder center line, and which passes through the center of said crankshaft.