ARMY TM 9-611-6012
NAVY NAVFAC P-8-633-12
Compression Stroke. Both intake and exhaust valves are closed, and upward movement of the piston
compresses the air to a mechanical ratio of 14.5'1 at the top of the compression stroke. This high compression
raises the temperature of the air above the ignition point of the fuel. At engine operating speeds, the effective
compression ratio is even higher due to the increased cylinder filling efficiency derived from turbocharging.
Power Stroke. Both Intake and exhaust valves are closed. During the last part of the compression stroke, before
the piston reaches TDC (top dead center), fuel is injected into the cylinder In a metered amount. Because of the
small orifice in the injector nozzle and the high pressure created by the injector, the fuel is finely atomized. The
high temperature compressed air rapidly ignites the incoming atomized fuel and, as the piston passes TDC, the
rapidly burning air and fuel mixture forces the piston downward on the power stroke. This lineal movement of the
piston on the power stroke is converted to rotary motion by the connecting rod and crankshaft, and is used to
power the generator Because the 12 cylinders fire In sequence, the power impulses are close together, and the
rotary motion Imparted to the generator is smooth and even.
Exhaust Stroke. The Intake valves are closed, the exhaust valves are open and the piston is moving up in the
cylinder. This upward movement of the piston forces the burned gasses out of the cylinder and through the
exhaust valves, turbocharger, exhaust system, and into the atmosphere. Near the end of the exhaust stroke, the
Intake valves open and the cycle is repeated through the four strokes as outlined above. The valve and injector
timing during the sequence of the Intake, compression, power, and exhaust strokes is controlled by the camshaft.
The camshaft is geared to the crankshaft, and turns at 1/2 engine speed (rpm). Lobes on the camshaft time the
opening and closing of the valves and injectors in accordance with piston position In the cylinder. Proper engine
operation depends on two main factors.
Compression The compression must be high enough to ignite the fuel Burned, improperly adjusted valves,
or worn piston rings will prevent the high compression and heat needed to Ignite the fuel.
Timing. The fuel must be Injected In the correct amount and at the correct time for proper Ignition and
burning during the power stroke Therefore wear or Improper functioning of any components that affect
compression injection, or timing will result In Improper engine operation, or failure of the engine to start.
4-75. ENGINE TEST. An operational performance test of the engine is conducted as follows:
Start and warm-up engine in accordance with Chapter 2.
During engine warm-up, observe the following:
Oil pressure. If oil pressure falls below 45 psi (310 kPa), stop engine and troubleshoot lubrication system in
accordance with Table 4-3.
Oil temperature Normal oil temperature should be between 180 and 225°F (82 and 107C). If oil temperature
is not within the normal range, troubleshoot in accordance with Table 4-3.
Coolant temperature. After thermostat opening, coolant temperature should remain In the range of 175 to 1
95°F (79 to 91 °C). If coolant does not remain within normal range, troubleshoot in accordance with Table 4-
If engine does not run smoothly after normal operating temperature is reached, or exhaust smoke is excessive,
troubleshoot In accordance with Table 4-3.
During operation and shut down, observe engine for unusual noise or vibration If unusual noise or vibration occurs,
shut down engine and refer to the next higher level of maintenance.
Shut down engine immediately If any of the following conditions are noted.
Low oil pressure Minimum oil pressure should be 40 psi (276 kPa) at rated load of 750 kW at 60 Hz and at 50
High oil temperature Maximum oil temperature should be 235°F (113C).
High coolant temperature Maximum coolant temperature should be 219°F (104C).
Any unusual noise or vibration.
If engine does not accelerate smoothly to rated load, or exhaust smoke Is excessive, troubleshoot In accordance
with Table 4-3