Patent ID: 8376795

Claim:
An engine for an outboard motor, comprising: an oil pan disposed underneath a crank chamber; an oil pump for pumping up oil in the oil pan; an oil filter for filtering the oil that has been pumped up; and a vertically extending oil passage for leading the filtered oil to parts required by the engine, wherein the oil passage has a communication duct disposed lower than the oil filter and communicating with the crank chamber, the communication duct has a valve seat and a threaded portion downstream of the seat, and a drain valve inserted into the communication duct, the drain valve being configured for selectively opening and fully closing the communication duct; the oil passage has an air inlet duct positioned higher than the oil filter and designed to let air in from an exterior, the air inlet duct being closed by an air vent bolt capable of manual opening and closing; the drain valve has a threaded, tapered part at a distal end thereof engaging the threaded portion of the communication duct for bringing the valve face into engagement with the valve seat closing off the communication duct; and the drain valve has a small-sectional-area part located farther distally outward than the tapered part and having less sectional surface area than a flow passage surface area of the communication duct, the small-sectional-area part being inserted through the communication duct.