From the main oil gallery oil reaches the main and big-end bearings through the crank shaft holes. From the big-end bearings the oil passes through connecting rod and reaches gudgeon pin, . Automobile Engineering piston and the walls of the cylinder. From the main bearing there …is a passage from which the oil passes on to cam shaft bushes. From the forward bush of the cam shaft oil passes on to the timing gears. If there are overhead valves then a separate pipe is provided for delivering oil to the rocker etc. from the oil gallery.