What is 4 stroke and 2 stroke? difference

Question

Pl..........

Answer 1

2 stroke you have to mix oil and gas together, 4 stroke is just like your car no mixing required.

Answer 2

As said earlier, 4 stroke engines have 4 piston motions. Intake, Compression, Combustion, exhaust, so every other up-down action is a power stroke. 2 stroke engines combine these actions and fire on every downward stroke of the piston.

As a result, 2-stroke engines are very simple. They don't have an oil sump, or overhead valves. They are powerful for their size, and are lighter weight than an equivilent 4 stroke motor. They are lubricated by mixing oil in the gas, either by injection or pre-mixing in older models. This is why they smoke a little when running. They can be a little less reliable, but it they fail, it is usually cheap to fix.

4-strokes are cleaner running and use less fuel. By seperating the 4 cycles of the engine, they run smoother, cleaner, and quieter. They do not smoke.They have an oil sump, like a car that needs to be changed once in a while. They are much more complex, and heavier than the same hp 2 stroke engine. They are also more expensive. They are very reliable, but if they fail it costs big bucks to repair.

Answer 3

Instead of valves, the two-stroke has holes ("ports") on either side of the cylinder walls, one for intake the other for exhaust.

Half-way through the power stroke (when the plug fires), the piston uncovers the ports (exhaust first), so the exhaust gasses are expelled by remaining pressure, then pushed out the exhaust port by the incoming fresh charge.  The piston covers the ports as it begins the compression stroke.

The intake manifold is separated from the crankcase by "reeds", just a flat piece of metal covering a hole.  When the piston moves up into the cylinder it creates a vacuum in the crankcase that opens the reeds and pulls in a fresh charge.  When the piston moves back out, it pressurizes teh crankcase closing off the reeds and forcing the air/fuel charge through the intake port.

So, all four stages are accomplished in two strokes and all the spark plugs fire on every crankshaft rotation.  There is no oil pan or pump;  lubricating oil is mixed with the fuel.

As a result, the 2-stroke is lighter and less complex, therefore faster and less expensive to buy and repair than a 4-stroke of the same HP.

However it is considerably less fuel efficient and more polluting.

Answer 4

Good information so far, the other consideration is that Four Stroke engines have a crankcase oil system so they need to have the oil changed periodically.  Two Stroke engines do not because the lubricating oil is mixed with the fuel either manually or automatically.

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Answer 5

The strokes are the different motions that the engine takes to complete the combustion's cycle.

A four stroke engine for example.

The cycle begins when the piston is going down. The admission valve opens and the air/fuel mix enters, being sucked into the chamber by the vacuum produced.

The second stroke happens when the piston goes back up again and compresses the gas mix.

The third one is almost immediate. The spark plug does what it was meant to do (a spark) and the mix explodes.

The forth and final stroke happens only when the piston makes a full turn and pushes the post-combustion gases out through the exhaust valve.

Two stroke engines aren't really my cup of tea. All i know is that only have two turns. The difference in the process makes them usually noisier and with higher engine oil comsuption, ence highly polluting.

Two stroke engines stop being used in cars long ago. the last model i've heard of that used a 2 stroke was the East German Trabant.

Answer 6

Two stroke engines fire each time the piston reaches top dead center. Instead of having convential valves as a four stroke motor does they work this way: At the moment if ignition the piston moves down where the exhaust gasses pass through the exhaust port through the side of the cylinder. When the cylinder is on it's way down during the fireing stroke pressure in the crankcase forces the air fuel that's in the crankshaft area to pass through ports directly beside the cylinder to an opening through the cylinder into the upper combustion chamber. It gets a little confusing here as some two strokes are intake port (air fuel) timed and others are reed valved timed.

Let's go back to the bottom of the compression stroke for a moment as two stroke motors actually are doing two functions at the same instant. In port timed 2 stroke motors as the piston starts to raise during the compression stroke the lower skirt of the piston uncovers the intake port. As the piston raises during the compression stroke vacuum is created in the lower crankshaft case. When the shirt of the piston uncovers the lower intake port the air /fuel is sucked in the crankcase from the carburetor. As soon as the sparkplug fires the previous mixture the piston skirt covers the intake port sealing it off. As the piston continues down it forces the mixture up the intake "transfer ports" through the cylinder into the upper combustion chamber. Reed valved timed 2 stroke engines rely on thin metal reed valves to open in the lower crankcase allowing fuel in when they sense any vacuum.

A four stroke motor fires on every other stroke of the piston: When the spark plug fires the burning fuel and air drives the piston down to nearly the bottom of the stroke when the exhaust valve opens. When the piston raises the exhaust gasses excape underneath the exhaust valve through the exhaust port. Just before the piston is at the top of the exhaust stroke the intake valve opens and the exhaust valve closes. When this happens, the air fuel mixture starts entering the combustion chamber. As the piston continues down during the intake stroke vacuum is created in the cylinder and more fuel and air enter the cylinder. At the bottom of the intake stroke the intake valve closes. The piston raises compressing the fuel air mixture. A few degrees of crankshaft rotation before the piston reaches top dead center the spark plug fires driving the piston back down the cylinder and the four stroke cycle starts all over again.

I would suggest you open the Wikipedia Encyclopedia and look at the four and two stroke cycle motors to get a better feel of what happens through their very good explinations and pictures throughout each of their cycles.

As another person said you are required to mix 2 stroke oil and gasoline as the oil takes the place of crankcase oil in a four stroke motor. I would argue that today expensive two stroke chainsaws and line weed trimmers have tamper proof carbureters which run on the lean side for emission purposes. Pound for pound two stroke motors make a lot of horsepower and engine RPM for their displacement size. These qualities are necessary for these two applications. For instance: The professional line of Husqvarna chainsaw's are made in Sweden and they reach 14,000 revolutions per minute.