Figure 5. Helix and Charging Port Metering Positions

Figure 7. Cut-Away View of Governor Assembly

TM-5-3820-256-24-5 Drilling System Well Rotary Truck Mounted Air Transportable 600 Feet Capacity Model LP-12 NSN 3820-01-246-4276 Manual
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SERVICE MANUAL GENERAL Section 1 METERING Metering (providing proper amount of fuel to meet engine requirements at various loads and speeds) is accomplished by rotating the plunger in its barrel to change the effective pumping stroke. The effective stroke is the distance traveled upward by the plunger from the time the charging port is covered until it is again uncovered by the lower helix. A short effective stroke means a small amount of fuel is injected. As effective stroke increases, the amount of fuel injected increases. The metering function can be described by observing the relationship of plunger helix to barrel charging port under various metering positions as shown in Figure 5. Figure 5. Helix and Charging Port Metering Positions 1. Start Position (Charging Port Closed) 2. Idle Position (Charging Port Closed) 3. Full Load Position (Charging Port Closed) 4. Stop Position (Charging Port Open) 5. Effective Stroke 6. Charging Port Position Starting (Excess Fuel) For starting, plunger is rotated by control rack to a point where the maximum effective stroke (port closing to port opening) is obtained. When engine starts, release accelerator pedal. This rotates plunger out of start fuel position to decrease fuel delivery. Engine Operating (Metered Delivery) At engine operating speeds from idle through maximum governed speed, the quantity of fuel delivered is determined by effective stroke (port closing to port opening) as controlled by the position of the throttle lever and governor. Engine Stop (No Delivery) To stop the engine, plungers are rotated so that vertical slots (stop slots) are in line with barrel ports. As plunger moves up and down fuel is transferred back and forth from top of plunger through vertical slots and into charging gallery. The ports do not close - thus, no delivery. Plungers are rotated to the various metering positions by the control rack. Rack movement is controlled by the throttle lever and governor speed. PUMP FEATURES Mounting Adapter A mounting adapter (9, Figure 1) incorporating four studs attaches to the injection pump housing. Capscrews through the injection pump drive gear cover secure the mounting adapter to the engine front plate. Removal of the timing pointer plug (7, Figure 1) in the adapter is necessary when verifying or adjusting pump to engine timing. The mounting adapter is an integral part of the injection pump because it contains the timing pointer. During injection pump calibration, a port closure mark is stamped on the injection pump hub directly in line with the pointer. Because the timing pointer is located on the mounting adapter and the mounting adapter is fastened to the injection pump housing by the four studs and nuts, these four nuts should not be loosened. Loosening the nuts and rotating the pump housing in relationship to the mounting adapter will change the relationship of the timing pointer/hub mark which was established during injection pump calibration. CGES-375 Printed in United States of America Page 4

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