Books.

2 stroke and 4 stroke:

The engines are called the above because of the amount of “strokes” the piston makes per cycle, a stroke being the upwards or downwards movement of the piston.
The strokes are intake, compression, combustion and exhaust, each achieved in the following way for a 4 stroke:
Intake- The valve opens allowing in a mixture of fuel and air as the piston travels down the cylinder.
Compression- The piston travels back up the cylinder, and compresses the mixture. The valve is closed.
Combustion- The compressed mixture is ignited by the spark plug. The explosion sends the piston back down the cylinder.
Exhuast- The valve is opened and the piston goes back up the cylinder. The gases are pushed out and the whole process can start again.

2 stroke:
Stroke 1: The piston travels up the barrel, opening the inlet and sucking fuel/air into the engine, precisely the crankcase. At the same time, the fuel/air mix at the top of the engine is compressed.
Stroke 2: The compressed mix is ignited, sending the piston back down the barrel, exposing the exhaust port and the transfer port. This sucks the fresh mix up to the cylinder and displaces the gases.

I now understand why a 2 stroke makes twice as much power compared to a 4 stroke- the 2 stroke ignites once every revolution, whereas the 4 stroke ignites every other revolution.

Thanks tim

And to both Tims, please teach me all you will

[timwilky]

Ok, based on what you now know. A 4 stroke has valves to control inlet/outlet and a 2 stroke uses ports. how are a 4 strokes valves opened, What simple mechanism controls all the timings of what to open when

A 4 strokes valves are opened and closed by a cam shaft, which I believe rotates at half the speed of the crankshaft. I'd imagine that when and how much the valve opens is dictated by the shape of the cam itself.

What is meant by a high lift camshaft?

And what is meant by a long duration camshaft (i.e 290 deg)?

High lift camshaft- more air and fuel into the engine. Better air flow.
Long duration- how long the valve is held open for?

After some more reading..

Long duration cams are conducive to making better high end power, whereas shorter duration cams are better for making low spped torque and throttle response.


Please note I'm not just reading this and posting this, I'm learning and remembering it too

[yorkie_chris]

OK then, get a bit more involved about cam duration.

Why?

At work so I can't do much. Why? Err.. Why have different durations? So you can controll the duration the valves are open, how far they're open. Going from standard cams to race cams.. Do it for a performance increase- it'd make more power, probably more power higher up the rev range.

I can't research until I get home

Oh, also, you can get the opening and closing of the valves (inlet and exhaust) to overlap.