Please help me, how does a 4 stroke motor work?

 

Ok, you know the piston goes up and down in the cylinder, so let's start with the piston at the top. The intake valve opens, so that as the piston travels down to the bottom of the cylinder, it can suck air/fuel from the carburetor in through the intake valve (this is the intake stroke). Then the intake valve is closed, and the piston travels back up to the top. Since the cylinder is sealed (no valves open), the air/fuel gets compressed to about 1/10th it's original volume (this is the compression stroke). Once the piston gets all the way to the top, the spark plug fires, which ignites the compressed air/fuel. The explosion forces the piston back down to the bottom (this is the power stroke). Then the exhaust valve opens, and as the piston travels back to the top, the burnt air/fuel is pushed out the exhaust valve and out your tailpipe (the exhaust stroke). Then it all starts over. This is over simplified though.. the valves don't open exactly at the top and bottom of the stroke, the exact timing depends on your camshaft, which has lobes on it that push the valves open as it rotates. There are a ton of articles with cool animations and stuff out on the internet that can explain it better than I just did.

 

Sorry to switch topics a little, but how does a 2 stroke work...i know it doesn't have the type of valvles a 4 stroke does so how does it allow air in and exhause out? Also, why is it called a 2 stroke?

 

a 4 stroke has needs 2 crank revolutions to complete a cycle (described above), whereas the 2 stroke needs only one.
How does a 2 stroe work? I'll try to be as explicit as Motorhead did (very nice post BTW).
There are no valves, but holes in the cylinder walls. To simplify, there's one hole for intake, and one for exhaust. By definition they are always open, though we consider them "closed" when the piston is in front of them.
Let's start when the spark plug fires and pushes the piston down, from its highest position.
It goes down, because of the consumed gasses and explosion, it "opens" the exhaust hole (or the upper part of the hole), so the burnt gasses will rush out (they need more space than unburnt gasses). At that moment (the piston still going down) the intake "opens" (the piston has got low enough to "open" the hole). The fresh gasses will keep "pushing" the burnt ones out of the cylinder Meanwhile, the piston has reached its lowest point and is starting to come back up. That's what reeds are for, they allow flow only in one way (from outside to inside), allowing the gasses already inside not to go out by the wrong exit (intake instead of exhaust). The piston still coming up closes the intake hole and right after the exhaust one. It will continue to go up (compressing the mixture), and BANG, we start all over again.
If you got everything here, you'll understand why 2 strokes aren't fuel efficient. exhaust and intake are open in the same time, which allows unburnt mixture to get out...these are no good.
Talking about reeds, Rotax has replaced reeds by a rotative disc (now you get where their name comes from)that allows mixture inside when it's supposed. It's much more precise, but more complicated.

Did you got it? Did I make it?

 

Check out howstuffworks.com there is a great description on how 2 stroke and 4 strokes work.

 

Greetings,

May I say, excellant work here gentleman.

Also, one of the best ways to learn about this stuff is to get one of those "visible engine" model kits. My father had each of us build one of those as we approached driving age and the experience has been invaluable. [Ought to be part of a standard school curriculum since cars are part of a standard life.] Anyway, I'm not sure if they make a motorcycle type kit, but any type would illustrate the principles at work.

 

Good basic rundown Zorro!

Please note: Reeds are not essential for 2-stroke operation; in the dim past, all 2-stroke engines had straight garden-variety carburetors without reed valves at all.

Diogenes