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TM 10-4320-343-14
1.14.2.5 Engine Assembly. The engine assembly (Figure 1-7) provides the drive for the 350 GPM pumping assembly.
When the engine is started, starter motor B1 turns the crankshaft. When the crankshaft is turned, the pistons , and
valves move up and down. While one of the pistons is moving upward, fuel is injected into the combustion chamber and
mixed with air at a controlled rate. The temperature inside the combustion chamber causes the fuel and air to burn
(combustion). This combustion forces the piston downward, which causes the crankshaft to rotate and the engine to start.
The starter motor B1 is then disengaged. The up and down movement of the pistons continues with fuel being injected
into selected cylinders. The rotation of the crankshaft also turns the camshaft and timing gears. The timing gears turn the
oil pump and the fuel pump. Oil is pumped through the lubrication system and fuel is pumped to the fuel injectors. In
addition, the drive pulley rotates and drives the V-belts. The V-belts operate the cooling fan and alternator. The cooling
fan keeps the oil and engine cool to prevent overheating. The alternator provides 14 V dc. The following paragraphs
provide a more detailed description of diesel engine operation.
1.14.2.5.1 Engine Operation Overview. The 350 GPM pumping assembly uses a four-stroke diesel engine with three
cylinders. The complete cycle for a four-stroke engine occurs in four events for each piston. Two revolutions of the
crankshaft are required to complete one cycle. The four events are as follows:
Intake stroke
Compression stroke
Power stroke
Exhaust stroke
When the intake stroke begins, the piston is pulled down into the cylinder by the crankshaft and connecting rod. When
the piston is at the lowest point possible, it is at bottom dead center (BDC). During this time the intake valve is held open
by the camshaft. Since the piston has moved down in the cylinder to BDC, a vacuum is created and air is forced past the
intake valve into the cylinder's combustion chamber.
Change 1 1-16
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