Engine Operation - Toro TC 1000 Service Manual

SECTION 6 ENGINE
Engine
-
Operation
The TC1000 engine is based upon a two-stroke,
port to port design. The term "two-stroke" refers
to the number of operations the piston goes
through in order to complete a single com-
bustion cycle. Those two operations are called
an intake stroke (where an air/fuel mix is drawn
into the combustion chamber), and an exhaust
stroke (where the exhaust gases are purged from
the combustion chamber).
The term port to port refers to the way in which
the intake and exhaust gases enter and exit the
engine. The TC1000 engine uses no valves, but
rather, relies on the piston passing by the intake
and exhaust ports to control the flow of gases.
Hence the term: port to port.
There are four major components that are in-
volved in the combustion cycle:
- Piston
-
Intake Port
- Exhaust Port
- Scavenger Ports
Their relative locations can be seen in Figure 76.
EXHAUST PO SCAVENGER
INTAKE PORT
Figure 76
Proper operation of the TC1000 engine relies on
nine separate phases. Beginning with the piston
at a midway point of its upward stroke, those
nine phases are described below.
1. The piston closes the scavenger ports. This
prevents prevents equalization of pressures
between the lower crankcase and the com-
bustion chamber. See Fig. 77.
32
SCAVENGER
Figure 77
2. As the piston continues its upward stroke,
vacuum begins to build within the lower
crankcase. That vacuum will later be used to
draw the intake mixture. See Fig. 78.
VACUUM
Figure 78
3. The piston covers the exhaust port which
completely seals the combustion chamber.
See Fig. 79.