Lesson 4/Learning Event 1
A variation of the splash system is used in the two-stroke-cycle engine. Here the lubricating oil is mixed with
the gasoline in the fuel tank. During the compression stroke of the piston, the reed valve opens and a fresh
charge of oil, fuel, and air enters the crankcase. The fuel, air, and oil moves through the intake port into the
cylinder when the piston moves down on its power stroke. The oil in the fuel lubricates the moving parts.
This method of lubricating the engine is very common on small two-stroke-cycle engines, especially those used
on motorcycles and motorboats. This system is known as the vapor lubrication system.
The amount of oil mixed with the fuel in the two-stroke-cycle engine must be carefully controlled. Too little
oil will cause rapid wear of the engine parts. Too much oil will cause carbon to form in the combustion
chamber, foul up the spark plugs, and clog the exhaust ports. Spark plug fouling is a very common problem
with this type of engine.
An advantage of this type of lubrication system is that the engine can be tilted or operated in any position. If
the engine was operated on its side or in an upside down position, it would not last long. This is because the
oil in the crankcase would flow away from the dipper and could not be splashed over all of the moving parts.