Engine Assembly
51
Theory of operation
The P25 series of engines are piston ported engines.
As the piston travels upward:
• The exhaust port is covered.
• The fuel/air mixture above the piston is com-
pressed. See Figure 8.1.
• Fuel/air mix is drawn into the crankcase.
• The spark plug will fire just before the piston
reaches top dead center, igniting the fuel/air mix-
ture.
As the piston travels downward:
• The exhaust post is uncovered, allowing the burn
gases to escape.
• The piston compresses the fuel/air mix in the
crankcase, forcing the mixture up through trans-
fer ports in the side of the cylinder.
• The fuel/air mixture enters the combustion camber,
flowing towards the intake side of the cylinder.
NOTE: This flow pattern helps to push the exhaust gases
out of the cylinder.
Figure 8.1
Exhaust port
Intake port
Figure 8.2
Exhaust
CHAPTER 8: ENGINE ASSEMBLY
For Parts Call 606-678-9623 or 606-561-4983
www.mymowerparts.com
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