In the automotive world, there are two basic types of engines.  There are two-stroke and four-stroke engines.  Almost every car or truck on the road today contains a four-stroke reciprocating internal combustion engine.  This classifies both gasoline and diesel automotive engines, whereas two-stroke engines are more commonly found in lower power appliances, such as chain saws, mopeds, jet skis, and more.

            Two-stroke engines have two important advantages over four-stroke engines: 1. They do not have valves, which simplifies their construction. 2. Its spark plug fires once every revolution (as compared to four-stroke engines which fire once every other revolution) giving it a considerable power boost.  Because there are twice as many power strokes per revolution, it can pack twice the power in the same space as a four-stroke engine.  These advantages make the engine not as heavy and less expensive to manufacture, which is why you will find it in most small devices.

With two-stroke engines, you need to use special two-stroke oil with the gasoline.  In a four-stroke engine, the crankcase is totally disconnected from the combustion chamber, so the crankcase can be filled with heavy oil to lubricate the bearings.  In a two-stroke engine, the crankcase is performing as a pressurization compartment to force air and fuel into the cylinder, so it can?t hold a thick oil.

However, you will practically never find a two-stroke engine in any automobile.  Despite the fact that two-stroke engines are simpler, lighter, and produce twice as much power as a four-stroke engine, there are four important disadvantages that they have.  First of all, their lifespan is not nearly as long as that of a four-stroke engine.  The parts of the engine wear down a lot faster due to the lack of a good lubrication system that is found in most four-stroke engines.  Two-stroke oil is very expensive and is used quite often.  It needs about four ounces for every gallon of gas.  On the environmental side, they produce a lot of pollution.  It would only be that much more if they were used in cars, considering the large amount of cars and trucks out on the road today.  Because of the pollution they are already creating from small devices that use them, they may not be around for too much longer.