GENERAL INFORMATION
Two-cycle
Engine Theory
of
Operation
Two-cycle engines are used on TORO Trimmers
because of their:
1.
Light weight.
2.
Excellent power-to-weight ratio
3.
Ability to operate
in
any position
4. Easy maintenance
5. Simple construction
The
TORO
Two-cycle Engine used on the TC-1500,
TC-300 and TC-400 Trimmers is a third-port, loop-
scavenged design. This design name describes the
path
of
the fuel/air mixture into the crankcase and
combustion chamber, and the exhausting of spent
gases (Fig.
1
st Port
\
transfer
(Both
Cylinder)
Figure
1
In
a loop-scavenged engine
with
a third-port, the
flow of the fuel/air mixture can be described as
follows: (See Fig.
1).
1.
The fresh fuel/air mixture enters the crankcase
through the third-port on
the
side of the cylinder.
The oil
in
the fuel/air mixture lubricates the
moving parts
within
the crankcase.
2.
The fuel/air mixture is transported through the
fuel transfer ports to the combustion chamber
where
it
is compressed, ignited, and then expelled
from the engine through the exhaust port.
Engine Operation
,
The piston closes all engine ports as
it
moves toward
the combustion chamber (Fig.
2).
The moving piston
creates high pressure
in
the combustion chamber
and partial vacuum
in
the crankcase.
Figure
2
Compression Stroke
At a point slightly before top dead center (BTDC) of
the piston travel, the spark from the plug ignites the
fuel air mixture (Fig.
3).
Also, at this time, the third-
port opens allowing the fresh fuel/air mixture to
rush into the crankcase to equalize the partial
vacuum.
Spark
Ignites
Fuel/Air Mixture
I
Piston
at or
Near
T.D
C.
Exhaust
Port
Closed
Open
Fresh Fuel/Air Mixture
Lubricates
Moving
Parts
Figure
3
Ignition
1
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