A rotor seizure can be due to a loss of clearance between the hydraulic head and rotor during the transient (or
warm-up) condition. Heat generated by shearing the oil film at the hydraulic head to rotor interface causes heating
of the hydraulic head and rotor. Because the mass of the rotor is less than that of the hydraulic head, it heats and
expands at a faster rate. The clearance at the interface of the hydraulic head and rotor is thereby reduced and the
possibility of rotor seizure is introduced.
The rotor seizures in a test series occurred at the midpoint of the rotor length indicating that the maximum rotor
heating and expansion occurred at the midpoint. Therefore, a relief groove was added to the diameter of the rotor,
as shown in Figure 4-77 to minimize the potential for rotor seizure following a cold, high speed acceleration.
The final component that we will examine is the heart of the diesel injection pump; the rotor. (Figure 4-77). Due to the extremely close tolerances of the rotor and head assemblies, a thermal relief groove has been incorporated into the rotor design. Thermal shock can cause a head assembly to contract, resulting in the seizure of the head and rotor. To lessen the possibility of this happening, a reduction in the rotor diameter at the area between the ports has been added.
The rotor in 1980 through 1984 pumps incorporates residual pressure balancing ports. These small vent ports operate by simultaneously registering with the head discharge outlets shortly after each injection. This operation allows a balance of the residual pressures between injection lines and helps smooth out the operation and the sound of the engine.
See Figure 4-76. The 6.2L uses a ball-pivot governor arm which has a slot below the bi-metal strip. This prevents interference with the ball pivot conical extrusion. All governor arms of this style now have a tab at the bottom of the conical extrusion, for better retention. The bi-metal strip is covered by a .012″ thick back-up leaf for wear resistance.
When idle speed drops due to hot fuel, a bi-metal strip on the governor arm deflects. This creates a “ spring load” on the governor arm causing it to rotate slightly, thus repositioning the metering valve to pass more fuel and increase speed slightly. (Figure 4-75).
The 1984 and later 6.2L California applications use an internal idle spring, which controls the gap between the sleeve and the washer. (Figure 4-74). The close tolerance will result in a more accurate input to the engine throttle position sensor, which regulates the exhaust gas recirculation and exhaust pressure regulator functions.
Now for a look at the operation of the assembly that controls the engine speed at low idle and high speed. The Min-Max governor.
Illustrated here (Figure 4-70) are the main components of the governor. They are the governor weights, the governor arm, the low idle spring, the idle spring guide, the main governor spring, the main governor spring guide and the guide stud.
Figure 4-71 shows the relationship of the parts when the pump is running at low idle. The low force developed by the governor weights is balanced by the low idle spring. Thus, only a small amount of fuel is delivered by the metering valve.
In Figure 4-72, the throttle is in a mid-range position. The idle spring is fully collapsed, and the governor weights have moved out partially. The main governor spring is designed such that the governor weight force cannot overcome the spring’s preload until the engine reaches the maximum rated speed. Thus, at partial throttle, the assembly acts as a solid link against the governor arm. This permits the driver to control the metering valve position with the throttle over the entire mid-range speed.
With the throttle in the full load position, the engine speed and the pump speed increase until the governor weights have generated enough force to deflect the main governor spring. This movement turns the metering valve to the shut-off position, thereby preventing an engine overspeed condition. (Figure 4-73).
All pumps are equipped with a Housing Pressure Cold Advance solenoid. (Figure 4-67).
This component has been designed to allow more advance during engine warm-up. It consists of a solenoid assembly and a ball check return connector, both in a redesigned governor cover. The electrical signal which controls the operation of the solenoid is generated by a sensing unit mounted on the rear of the right cylinder head.
1984 and later H.P.C.A. is controlled by a cold advance circuit (C.A.C.) relay.
The switch is calibrated to open the circuit at 95°F for 83 and later (115° on 1982). Below the switching point, housing pressure is decreased from 8-12 psi to zero which advances the timing 3°. Above, the switch opens deenergizing the solenoid and the housing pressure is returned to 8-12 psi. The fast idle solenoid is energized by the same switch. The switch again closes when the temperature falls below 85°F (95°F on 1982).
1. Emission Control device.
2. Better cold starts.
3. Improves idle, reduces white smoke and noise when cold.
During cold warm-up conditions, the plunger moves up and the rod contacts the return connector ball. (Figure 4-68). When the ball is moved off of its seat, the housing pressure is reduced due to an increased flow through the connector. Because of lowered housing pressure, the resistance to the advance piston movement is less, and thus the piston can move further in the advance direction.
When the engine reaches normal operating temperature the electrical signal to the solenoid ceases, and the plunger is returned to its initial position. (Figure 4-69).
1984 H.P.C.A. Terminal will be changed (24669) because of 84 California System.
A new head locating screw (#24566) with nylon filter has been introduced to prevent contaminants from reaching the advance piston area. See Figure 4-66. The filter is installed into the body of the screw, the end of which is crimped over. The screw is only available as an assembly, as shown on the right, and is identified by a groove around the head of the screw. Suitable for use in all mechanical light load advance-type pumps.
See Figure 4-65. The advance piston orifice screw has been eliminated, and the orifice is now machined into the piston. The orifice size in 1984 and later is .030 in. 1982-83 orifice size was a .040 in. orifice screw. Stanadyne part #24433 (2443405).
As with the previous advance system, the rotor’s force is transferred to the cam ring during injection. This force continually urges the piston toward the retard position. However, an opposing force is supplied by transfer pump pressure acting on one end of the servo advance piston. (Figure 4-62).
The position of the servo valve in the advance piston bore regulates this force, and determines the degree of advance achieved at any throttle setting or load. (Figure 4-63).
Additional advance at low throttle settings is provided by the face cam to rocker lever action which changes the reference point of the spring. (Figure 4-64).
This allows the servo-advance valve to open further and provide a greater degree of advance at low throttle settings. The end result of both of these advance mechanisms is a vast improvement in the driveability of diesel equipped vehicles.