
03-21
SECTION 03 - ENGINE PREPARATION
Ignition and Combustion
1. Fresh charge
As the piston nears the top of the cylinder (TDC),
the compressed air/fuel mixture in the combus-
tion chamber is ignited by the spark plug. The
burning gases expand and push the piston down-
ward, thus causing a power stroke.
Exhaust and Primary Compression
1. Fresh charge for the other cylinder
2. Intake port covered
As the piston descends, the intake port is blocked
by the rotary valve and pressure begins to build
inside the crankcase (primary compression). The
exhaust port is uncovered as the piston continues
its course downward, and burnt gases are al-
lowed to escape.
Transfer
1. Fresh charge for the other cylinder
2. Fresh charge
3. Intake port covered
Near the bottom of the downward stroke, the
transfer ports are uncovered by the piston, and
the compressed air/fuel mixture in the crankcase
rushes into the combustion chamber via the
transfer ports. Piston dome and combustion
chamber configuration and exhaust back pres-
sures prevent fresh charge (air/fuel mixture) from
escaping through the exhaust port. This also as-
sists in clearing the combustion chamber of all
burnt gases.
Rotary Valve Drive Gears
Located in crankcase halves between the 2 cylin-
der bases. These gears transmit crankshaft rota-
tion to the 90° angled rotary valve shaft.
The helical gear mounted on the rotary valve shaft
uses the crankshaft as a power source. To pre-
vent overheating and provide lubrication, the
gears operate in an oil bath.
To prevent pressurization of the system, a vent
tube from the top of the gear chamber returns to
the oil reservoir which is vented to the atmo-
sphere.
F01D6UA
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F01D6VA
F01D6WA
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Содержание Bombardier
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