The 2 stroke is more complex in
happening at the same time. The Intake stroke is the same as the
power stroke and exhaust stroke. Confused yet? Let me explain.A stroke is one pass of the piston through the cylinder. So one revolution of this crankshaft will produce two strokes of the piston in the cylinder.
valve. When the piston is on the way towards the ignition source,
air/fuel is being pulled into the crank case or the bottom side of
the piston. This flow into the crankcase can either be
timed/controlled with a rotary valve or piston port, or it can be
controlled by a reed valve. On the top side of the piston air/fuel
is being compressed for an upcoming power stroke.
the top of the compression stroke and the piston starts its travel on
the power stroke.
The expanding gases produce power
until the exhaust port is revealed, by the piston and the expanding gases from the ignition leak out through the exhaust port. All this
time the air/fuel in the crankcase is gaining positive pressure
because the volume in the crankcase is shrinking due to the piston
moving closer to the crankshaft.
of the ignition chamber air/fuel mixture in the crankcase continues
to get compressed. When the top of the piston uncovers the intake
ports, the pressurized mixture in the crankcase is forced into the
ignition chamber, charging the cylinder with fresh air/fuel to burn,
and purging the remaining exhaust gases. Some of the air fuel
mixture is pulled into the exhaust port as well, due to inertia of
By this time the Piston has hit BDC (bottom dead center) and the piston is starting to go back to the ignition source. This creates negative pressure in the crank case causing air fuel to be pulled in to the crank case..
The exhaust pipe or expansion chamber (if designed
correctly), will push some of this unspent fuel/air that traveled into the exhaust pipe back into the
ignition chamber (a pressure wave in the exhaust causes this). By
this time the piston is finishing covering the exhaust port and is on its way back to the ignition source, and
the process starts all over again.
Hope this explains the operation of a 2 cycle or 2 stroke engine.