cams 5a and 5b relative to the helical gear 7 the closer the location of the exhaust cams 5a and 5b relative to the helical gear 7 is the harder it is to twist the exhaust overhead camshaft 3 because of this decreasing the distance of the cams 5a and 5b of the exhaust overhead camshaft 3 from helical gear 7 causes a decrease in absorbing torque change and hence an increase in thrust thrust produced by the cams 5 a and 5b adjacent to the helical gear 7 is greater than that produced by any of the other cams of the exhaust overhead camshaft 3 for this reason the radial oil passage 20 formed in the thrust collar 14 is determined in direction so as to minimize a decrease in rigidity caused in the thrust collar 14 relative to the maximum thrust which depends upon the axial location of the cams 5a and 5b adjacent to the helical gear 7 the radial oil passage 20 thus directed is prevented from being brought into parallel with the fitting surface 21 of the plain split thrust bearing 16 upon the build up of a maximum thrust by any of the remaining cams 5a and 5b other than the cams 5a and 5b adjacent to the helical gear 7 the other end of the exhaust overhead camshaft 3 opposite to the one end where the sprocket wheel is to be mounted is formed with a mounting bore for mounting a distributor 22 thereon denoted by a reference numeral 35 in fig3 and.