rajnish

Two-stroke engines have two important advantages over four-stroke engines:

Two-stroke engines do not have valves, which simplifies their construction.
Two-stroke engines fire once every revolution (four-stroke engines fire once every other revolution) -- this gives two-stroke engines a significant power boost.
These two advantages make two-stroke engines lighter, simpler and less expensive to manufacture. They also have the potential to pack about twice the power into the same space because there are twice as many power strokes per revolution. The combination gives two-stroke engines a great power-to-weight ratio.

The Two-stroke Cycle

The biggest difference to notice when comparing to a Four Stroke engine is that it fires once every revolution in a two-stroke engine.


You can understand a two-stroke engine by watching each part of the cycle. It isn't clear to see in any of the below diagrams but most model two stroke engines have a hollow crankshaft that connects the carburettor to the inside of the crankcase. As the crankshaft revolves it acts as a valve only allowing air/fuel from the carburettor into the crankcase at the correct times.

It's called a two-stoke engine because there is a compression stroke and then a power stroke. In a four-stroke engine, there are separate intake, compression, combustion and exhaust strokes.

You can see that the piston is really doing three different things in a two-stroke engine:

On one side of the piston is the combustion chamber, where the piston is compressing the air/fuel mixture and capturing the energy released by the ignition of the fuel.
On the other side of the piston is the crankcase, where the piston is creating a vacuum to suck in air/fuel from the carburetor through the crankshaft and then pressurizing the crankcase so that air/fuel is forced into the combustion chamber.
Meanwhile, the sides of the piston are acting like valves, covering and uncovering the intake and exhaust ports drilled into the side of the cylinder wall.
The more asstute among you will of realised that it is possible for some of the fresh charge to get sucked out along with the spent charge, this means that some power is getting wasted. What we need is a method to keep all the fresh charge in the cylinder, so we can have as big an explosion as possible. To do this you use a tuned pipe. I tuned pipe fits on the exhaust of the engine much like a silencer. What a tuned pipe does is restrict the exhaust gases so they create a back pressure standing wave, that stops then fresh charge from getting out. Tuned pipes are great for giving you engine a power boost.

Finally here is an exploded picture of an actual model two stroke engine.


the animated two stroke cycle.the green denotes the fresh charge and black shows the burnt gasses.red indicates the power stroke.

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\'87 High Torque RD 350B
in first gear,6000 rpm,whack the throttle.

rohit_180

Gr8 stuff rajnish. Please tell us about the 7 port RD engine man. And also how the torque induction works.

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\'84 RD350 2 stroke forever.
A sound clip of my RD: http://rapidshare.de/files-en/481080/15/Rohit1.wav

rajnish

thanks.the torque induction refers to the reed valve setup.helps in low and mid range.i'll put some info on rd and it's port maps shortly.

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\'87 High Torque RD 350B
in first gear,6000 rpm,whack the throttle.

vikas_l

http://science.howstuffworks.com//two-stroke.htm
Chk out this link , more detailed info on how 2 stroke engines work . enjoy!

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Vikaz...

rajnish

thanks pal.any links helping us know better or any thoughts r most appriciated.

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\'87 High Torque RD 350B
in first gear,6000 rpm,whack the throttle.

rajnish

this is for guys having 2st engines-do a exhaust port cleanup done.get the barrels up at the mech.look into the ports,get any carbon removed from them taking care not to scbeat metal.then feel the port walls for any sharp edges and use emery paper to smoothen them,wash the liners using petrol and a scotchbrite (Ron's recipie).i did it once on a much used rx and believe me there is a good difference in power.any other ideas r welcome.

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\'87 High Torque RD 350B
in first gear,6000 rpm,whack the throttle.

rajnish

btw this is good for a bajaj scooter to a shogun to a RD.

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\'87 High Torque RD 350B
in first gear,6000 rpm,whack the throttle.

ascent11in

thanks for kind info

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