2 Stroke, 4 stroke wut?

[Guest]

Ok so im a newb, looking to be on a 125 after winter. Whats all this business about strokes. I gather 2 strokes are faster/more powerful, but what does it actually mean? Im not a enginehead so laymans terms please

[argentum40]

2 strokes are much simpler engines than 4 strokes.... 2strokes are faster size for size than a 4 stroke but 2 strokes tend to need a rebuild of the top end every so many miles whereas 4 strokes as long as they are maintained well need very little maintainence.... i love 2 stroke bikes myself but in all honesty they wont be around much longer so 4 stroke is the way to go really

[BigShot]

If you were after an answer about what happens differently in the engine as opposed to what it means in terms of actual riding/maintenance...

4-stroke:

http://auto.howstuffworks.com/engine1.htm

2-stroke:

http://science.howstuffworks.com/transp ... troke2.htm

Put simply, in a 4 stroke engine for the 4 "strokes" of the piston (a stroke is the piston moving up or down) there's one ignition of fuel (down, up, ignition, down, up) The first down draws in fuel and air, the first up compresses the air and fuel mix, then the fuel is ignited and drives the piston down as it burns, and on the final up the exhaust gases are expelled.

In a 2 stroke engine the ignition and exhaust strokes are combined into the "down" stroke of the piston and the intake and compression are combined into the up stroke (that's a crude explanation, but it's fit for purpose).

The 2 stroke has an ignition of fuel every 2 strokes, the 4 stroke has an ignition of fuel every 4 strokes.

That's why argentum40 says "2 strokes are faster size for size than a 4 strokes". For a given size of engine, the 2 stroke burns twice as much fuel and so gives more power/speed... of course, it's a bit more complicated than that. Some 2 stroke 125s have fewer horsepower than some 4 stroke 125s (and vise versa) and either way you're limited to 14.6hp as a learner anyway.

I dunno if that helps, it's dead easy to understand once you can visualise what's happening, but I have a feeling it might not be so clear otherwise. Hopefully the links above will help you understand.

[Guest]

Thanks Bigshot i can just about visualise that. So a 4 stroke would actually be more economical and for a newb with no tinkering skills probs the best idea?

[argentum40]

Thanks Bigshot i can just about visualise that. So a 4 stroke would actually be more economical and for a newb with no tinkering skills probs the best idea?

 

you pretty much have it yeah... a 4t 125 will give you good mpg as long as u dont hammer it in all gears...

[Stu]

4 stroke

http://upload.wikimedia.org/wikipedia/commons/archive/a/a6/20080815230450!4-Stroke-Engine.gif

2 stroke

http://upload.wikimedia.org/wikipedia/commons/3/33/Two-Stroke_Engine.gif

hope that paints a better pic