General Information; Two-Cycle Engine -Theory Of Operation; Engine Operation - Toro 51603 Maintenance And Repair Manual

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
F u e l / A i r M i x t u r e
I
Piston at or
Near T.D C.
Exhaust
Port
Closed
Open
Fresh Fuel/Air Mixture
Lubricates Moving Parts
Figure 3
Ignition
1