BLOWBY GAS PROCESSING STRUCTURE IN CRANKCASE VENTILATION SYSTEM FOR INTERNAL COMBUSTION ENGINE

A cylinder block 2 includes: a first boss 62 surrounding a first opening 61 of a communication passage 23; a second boss 64 connected to a lower portion of the first boss 62 and surrounding a second opening 63 of an oil passage 26, and a first outer wall 66, which, in cooperation with a timing chain case 21, seals a timing chain chamber 22. The timing chain case 21 includes: a third boss 91 covering the second opening 63; a second outer wall 92 joined to the first outer wall 66, and a protection wall 94, which interconnects the third boss 91 and the second outer wall 92, joined to the first boss 62. On the cylinder block 2, an upper portion of the first boss 62 is connected to the first outer wall 66 at a point located between the adjacent on of fastener holes 65 formed through the first outer wall 66 and the second boss 64. With the cylinder block 2 and the timing chain case 21 being joined, a blowby gas passage 60 is formed.