Operation; Engine Operation - Toro GTS 150 Service Manual

SECTION 5 ENGINE
Engine
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Operation
Intake Stroke
The GTS 150 is a four stoke cycle, over head valve engine.
The running engine begins with the first of four strokes
being the intake stroke. The piston moves from Top Dead
Center (TDC) to Bottom Dead Center (BDC) with the
intake valve opening as the piston leaves TDC and closing
as the piston reaches BDC. While the piston is moving
toward BDC with the intake valve open, a partial vacuum
is created in the cylinder. Air and fuel will enter the cylinder
under atmospheric pressure as long as the intake valve is
open and the piston is moving toward BDC. See Figure 32.
Figure
32
Compression Stroke
The second stroke (compression) begins as the piston
leaves BDC and moves toward TDC. Both the intake and
exhaust valves are closed at this time. As the piston
moves, the air/fuel mixture is compressed in the cylinder.
See Figure 33.
Figure 33
GTS 150 29
Power Stroke
When the piston comes close to TDC the mixture is ignite
by the spark plug and the third stroke begins. The
ing combustion gases push the piston down in the cylinder
creating the power stroke, both the intake and exhaust
valves are still closed a t this time. See Figure 34.
Figure
34
Exhaust Stroke
The fourth stroke (exhaust) begins as the piston reached
BDC and the exhaust valve opens. As the piston moves
toward TDC the piston forces the exhaust gases from
engine. See Figure 35.
Figure
35
Engine