A rocker shaft assembly configured to support a rocker arm and deliver oil to the rocker arm and related method of making is provided. The rocker shaft assembly includes a core shaft and a sleeve. The core shaft has a core body including a main oil supply channel formed thereon. The sleeve has passages formed thereon. The sleeve is disposed around the core shaft. The main oil supply channel aligns with at least one of the passages on the sleeve. The main oil supply is milled into the core shaft.

An axis line of a cylinder and a cylinder head of a four-stroke engine is disposed inclining to one side in a lateral direction with respect to a center line extending in a front-rear direction of the outboard motor from a top view, and a fuel tank is disposed on a side portion of the cylinder and the cylinder head in another side in the lateral direction with respect to the center line.

The oil filter device is disposed on a side portion of one side of a cylinder body in a width direction in a cylinder head side with respect to an engine case in a space between center lines of main lubricating oil passages and a cylinder axis line of the cylinder body, and includes an oil pump disposed on the engine case and further lubricating oil passages that connect to the main lubricating oil passage.

An engine case includes bearings, an oil pump, lubricating oil passages, and a relief device. The bearings rotatably support a crankshaft and a camshaft. The oil pump and the lubricating oil passages are configured to pressure-feed lubricating oil to the bearings. The relief device is configured to adjust a pressure of the lubricating oil. The lubricating oil passages include main lubricating oil passages. The main lubricating oil passages include communication portions linearly formed with extending portions. The communication portions communicate between the respective bearings of the crankshaft and the camshaft from outside the engine case. The extending portions extend from outside the engine case to the bearing of the camshaft. The relief device is disposed having a relief valve and a relief hole at the extending portions.

A valvetrain for translating force and oil between a valve and intermediate member of an engine, including a rocker, a shaft, and a recess. The rocker has an inner surface, a pad for engaging the valve, a socket for engaging the intermediate member, a socket port defined in the surface, and a socket channel extending from the socket port to the socket. The shaft has a bearing surface for supporting the rocker, a channel spaced from the bearing surface, a feed port in the bearing surface, and a feed channel extending from the feed port to the channel. The rocker rotates between: closed, with the socket port and feed port aligned; and open, with the socket port spaced from the feed port. A recess is disposed in the bearing surface adjacent to the feed port and extends to a base aligned with the socket port when the rocker is open.

A rocker shaft assembly configured to support a rocker arm and deliver oil to the rocker arm and related method of making is provided. The rocker shaft assembly includes a core shaft and a sleeve. The core shaft has a core body including a main oil supply channel formed thereon. The sleeve has passages formed thereon. The sleeve is disposed around the core shaft. The main oil supply channel aligns with at least one of the passages on the sleeve. The main oil supply is milled into the core shaft.