Four Stroke Gas Scooter Engines
They are quieter, run cooler and are more likely than not, made in the USA. So how come we don't see more four stroke gas scooters?
When purchasing a scooter you have many options and the choice of engine is one of them. Electric, two stroke, four stroke and let's not forget sheer gravity. I will speculate that only 1% of the gas scooters on the market today (I only know of one) are powered by four stroke engines, and of all the scooters featured on this site only several are powered by a four stroke engine. Why is that? Let's take a look at the differences between four stroke and two stroke gas scooter engines in this article and the reasons will be more obvious.
Two stroke gas scooter engines complete a power cycle with every revolution of the drive shaft which arguably allows them to produce the twice the power for the same cylinder displacement of a four stroke engine. (Displacement, or the size of the cylinder where the gas vapor is exploded is measured in cubic centimeters or "cc's". Hence a 50cc engine has the ability to hold 50cc's of gas vapor and will produce more power than a 35cc engine). For an excellent treatment on exactly how a two or four stroke engine works, I highly recommend you visit www.howstuffworks.com; they have animated graphics that are outstanding!
Gas scooters admittedly have a small platform to mount an engine, so if you can get the same power in a smaller package, two stroke gas scooter engines are the way to go. Four stroke gas scooter engines also require an oil sump (a reservoir) that is typically housed in the cast iron base of the engine. Both the sump and the oil itself add weight, which for a light weight scooter would degrade from it's performance. Four stroke engines also use a system of valves and cam shafts to regulate the inlet of gas vapor and the outlet of exhaust. These valves degrade with time, lowering the compression of the engine resulting in the loss of power.
So what's good about a four stroke gas scooter engine? They are quiet! Compared to the staccato bark of a revving two stroke engine, four strokes are very quiet by comparison. That's why they are used for generators near residential areas or as stand by power for hospitals. Most auto's use four stroke engines. Another big advantage is that they do not require that you mix the gas with the oil. Like your car, you can fill a four stroke engine direct from the pump. Some two strokes now come with an oil injector, that feeds the right ratio of oil in which is a big plus, but would still require that you carry oil with you to refill the injector when gassing up.
The last and most likely reason you see two stroke engines on gas scooters is that they are used widely for other applications. Chainsaws, portable hedge trimmers, portable sprayers all use these engines. Subsequently parts are widely available, and maintenance costs are greatly reduced. Personally I wish more four stroke gas scooters were available. I like the technology behind them and have fond memories of maintaining a home made go-kart that had a four stroke unit on it as a child. However, for competition, power and performance it's hard to beat a well tuned two stroke engine.
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