What is the difference between a two cycle and four cycle engine?

Answer 1

In a 2-cycle engine, the fuel/air mixture is ignited with every upstroke of the piston resulting in a power stroke when the piston gets pushed down by the expanding gases. At the end of the power stroke, spent gases are exhausted and a new fuel/air mixture is drawn into the cylinder for another round.
In a 4-cycle engine, the fuel air mixture is drawn into the cylinder on the down-stroke, compressed on the up stroke and ignited. The piston travels down on a power stroke and exhausts the spent gases on the upstroke. Suck, squeeze, bang, blow.
The 4-stroke results in more complete combustion and cleaner exhaust.

Answer 2

A two cycle engine fires every time the piston approaches the top of the cylinder. A four cycle fires every other time. A two cycle engine produces more power for its size than a four cycle of the same size. A two cycle engine is less efficient, pollutes more and makes more noise.
I suggest looking up the engines on Wikipedia as there is more knowledge to be garnered than that I can put here.

Answer 3

The two-stroke cycle of an internal combustion engine differs from the more common four-stroke cycle by having only two strokes (linear movements of the piston) instead of four, although the same four operations (intake, compression, power, exhaust) still occur. Thus, there is a power stroke per piston for every engine revolution, instead of every second revolution. Two-stroke engines can be arranged to start and run in either direction.

Answer 4

From Wikipedia:

The two-stroke cycle of an internal combustion engine differs from the more common four-stroke cycle by having only two strokes (linear movements of the piston) instead of four, although the same four operations (intake, compression, power, exhaust) still occur. Thus, there is a power stroke per piston for every engine revolution, instead of every second revolution. Two-stroke engines can be arranged to start and run in either direction.

The four-stroke cycle is more fuel efficient and clean burning than the two-stroke cycle, but requires considerably more moving parts and manufacturing expertise. Moreover, it is more easily manufactured in multi-cylinder configurations than the two-stroke, making it especially useful in high-output applications such as cars. The later-invented Wankel engine has four similar phases but is a rotary combustion engine rather than the much more usual, reciprocating engine of the four-stroke cycle.

Lots of wonderful moving graphics!!!

Answer 5

Technically, I'm not qualified to answer this one but I will try anyway. On a four cycle engine, air and gas are introduced into the combustion chamber, while the piston is down. Next, the piston comes up and compresses the fuel mixture. Next, a spark is introduced into the cumbustion chamber, sending the piston down. Next, the piston comes up and sends the spent gases out the exhaust valve. On a two cycle engine, there is no compression of the fuel mixture. So, not as much power.

Answer 6

4-2=2

Answer 7

two...

Actually you get a power stroke at every upward motion of the piston. Generally there are no (or one set of exhuast) valves - ports are used to do the camber filling. Also the incoming air-fuel charge pushes the exhaust out and that means you lose some and fuel economy suffers in the process.