Several embodiments of outboard motors embodying four-cycle engines and improved lubricating systems therefor. In all of the embodiments, an oil reservoir is provided in the drive shaft housing and a combined screen and drain plug assembly filters the oil flowing from the oil reservoir to the engine lubricating system and for facilitating servicing of the screen by removal of the drain plug. In one embodiment, the oil reservoir is formed integrally with the drive shaft housing. A pressure relief valve depends into the oil reservoir and is carried by a plate that connects the engine to the drive shaft housing for facilitating servicing and reducing the likelihood of leakage back of oil to the engine when the outboard motor is tilted up. An improved relief valve screen assembly is also illustrated in one embodiment where in the screen may be bypassed if it becomes clogged.