3306B Industrial Engine Caterpillar

Illustration 1	g00319028
Fuel System Schematic (1) Fuel tank (2) Fuel return line (3) Priming pump (4) Fuel injection nozzle (5) Fuel injection line (6) Fuel injection pump (7) Primary fuel filter (8) Check valves (9) Fuel transfer pump (10) Secondary fuel filter (11) Constant purge valve (12) Fuel injection pump housing

Fuel transfer pump (9) pulls fuel from fuel tank (1) through both primary fuel filter (7) and check valves (8). From the fuel transfer pump, the fuel is pushed through secondary fuel filter (10) and to the fuel manifold in fuel injection pump housing (12). A bypass valve in the fuel transfer pump keeps the fuel pressure in the fuel system at 170 kPa (25 psi) to 280 kPa (41 psi).

Constant purge valve (11) allows a constant fuel flow through fuel return line (2) and back to fuel tank (1). The constant bleed valve returns approximately 34 L (9 US gal) per hour of fuel and air to the fuel tank. This helps keep the fuel cool and free of air. Fuel injection pump (6) receives fuel from the fuel manifold.

Fuel injection pump (6) pushes fuel at a very high pressure through fuel line (5) to fuel injection nozzle (4). The fuel injection nozzle contains very small holes in the tip. The small holes change the flow of fuel to a very fine spray. This fine spray improves the fuel combustion in the cylinder.

Fuel Injection Pump

Illustration 2	g00352392
Fuel Injection Pump (1) Check valve. (2) Inlet passage. (3) Fuel manifold. (4) Pump barrel. (5) Closed bypass port. (6) Pump plunger. (7) Slot. (8) Spring. (9) Scroll. (10) Spill port. (11) Lifter. (12) Fuel rack. (13) Gear. (14) Cam.

There is one fuel injection pump for each cylinder in the engine. A fuel injection pump functions in two ways:

• A fuel injection pump increases the pressure of the fuel.

• A fuel injection pump sends a precise amount of fuel to the fuel injection nozzle.

The fuel injection pump is moved by cam (14) of the fuel pump camshaft. When the camshaft turns, the cam raises the following components to the top of the stroke:

• Pump plunger (6)

• Lifter (11)

The pump plunger always makes a full stroke. As the camshaft turns farther, spring (8) returns the same components to the bottom of the stroke.

When the pump plunger is at the bottom of the stroke, any fuel at transfer pump pressure flows into inlet passage (2). This fuel flows around pump barrel (4) and to bypass port (5) .

Fuel fills the area above the pump plunger.

After the pump plunger begins the upstroke, fuel pushes out of the bypass port. Fuel pushes out until the top pump plunger closes the port. As the pump plunger continues to move up, the pressure of the fuel increases. At approximately 690 kPa (100 psi), check valve (1) opens. This allows fuel to flow through the fuel injection line to the fuel injection nozzle.

As the pump plunger continues to move up, scroll (9) uncovers spill port (10). The fuel above the pump plunger flows through slot (7) and along the edge of scroll (9). Then, the fuel flows out of spill port (10) and back to fuel manifold (3). This is the end of the injection stroke. The pump plunger can continue to travel upward, but more fuel will NOT flow to the fuel injection nozzle.

When the pump plunger travels downward, this plunger uncovers closed bypass port (5). The fuel begins to fill the area above the pump plunger again, and the pump is ready to begin another stroke.

The rotation of the fuel pump changes the amount of fuel that is sent from the fuel injection pump to the fuel injection nozzle. Gear (13) is attached to the pump plunger. This gear meshes with fuel rack (12). The governor moves the fuel rack according to the engine's need for fuel.

The pump plunger uses scroll (9) in order to control the amount of fuel that is pushed between closed bypass port (5) and spill port (10). A longer distance from the top of the pump plunger to the point of scroll (9) that uncovers spill port (10) will cause more fuel to be injected.

To stop the engine, the pump plunger is rotated so that slot (7) on the pump plunger is in line with spill port (10). The fuel will now flow out of the spill port, and the fuel will NOT flow to the fuel injection nozzle.

Fuel Injection Nozzle

The fuel injection nozzle is installed through the cylinder head into the combustion chamber. The fuel injection pump sends fuel with high pressure to the fuel injection nozzle. Then, the fuel is made into a fine spray for good combustion.

Illustration 3	g00318823
Fuel Injection Nozzle (1) Carbon dam. (2) Seal. (3) Passage. (4) Edge filter. (5) Orifice. (6) Valve. (7) Diameter. (8) Spring.

Seal (2) is positioned against the cylinder head. This prevents leakage of compression from the cylinder. Carbon dam (1) keeps carbon out of the bore in the cylinder head's nozzle.

Fuel with high pressure from the fuel injection pump flows into the inlet passage. Fuel then flows through edge filter (4) and into passage (3). The fuel continues to the area below diameter (7) of valve (6). When the fuel pressure against diameter (7) becomes greater than the force of spring (8), valve (6) lifts up.

Valves (6) lift up when the fuel pressure rises above the Valve Opening Pressure of the fuel injection nozzle. When valve (6) lifts up, the tip of the valve comes off the nozzle seat, and the fuel will flow through orifice (5) into the combustion chamber.

The injection of fuel continues until the pressure of fuel against diameter (7) becomes less than the force of spring (8). With less pressure against diameter (7), spring (8) pushes valve (6) against the nozzle seat. This stops the flow of fuel to the combustion chamber. The fuel injection nozzle cannot be disassembled, and no adjustments can be performed.

Fuel Transfer Pump

The fuel transfer pump is a piston pump that is moved by an eccentric cam on the camshaft for the fuel injection pump. The transfer pump is on the bottom side of the fuel injection pump housing.

Illustration 4	g00318826
Fuel Transfer Pump at Start of Down Stroke (Arrows for Fuel Flow Direction) (1) Pushrod. (2) Piston. (3) Outlet check valve. (4) Pump check valve. (5) Pumping spring. (6) Pump inlet port. (7) Inlet check valve. (8) Pump outlet port.

When the fuel injection pump camshaft turns, the cam drives pushrod (1) and piston (2) downward. As the piston moves downward, inlet check valve (7) and outlet check valve (3) close, and pump check valve (4) opens. This allows the fuel below the piston to move into the area above the piston. Pumping spring (5) is compressed as the piston is pushed down by pushrod (1).

As the camshaft continues to turn, the cam stops applying force on pushrod (1). Pump spring (5) moves piston (2) upward. This causes pumping check valve (4) to close while inlet check valve (7) and outlet check valve (3) open.

Illustration 5	g00318827
Fuel Transfer Pump in Start of Up Stroke (Arrows for Fuel Flow Direction) (1) Pushrod. (2) Piston. (3) Outlet check valve. (4) Pump check valve. (5) Pumping spring. (6) Pump inlet port. (7) Inlet check valve. (8) Pump outlet port.

As the piston moves upward, the fuel in the area above the piston is pushed through the outlet check valve (3) and out pump outlet port (8). Fuel also moves through pump inlet port (6) and inlet check valve (7). The fuel fills the area below piston (2). The pump is now ready to start a new cycle.

Oil Flow for Fuel Injection Pump and Governor

Illustration 6	g00491661
Fuel Injection Pump and Governor (1) Cover (2) Governor servo (3) Rear governor housing (4) Front governor housing (5) Fuel injection pump housing (6) Drain (7) Camshaft (8) Drain (9) Support

Lubrication oil from the side of the cylinder block flows into support (9). The oil then flows into the bottom of front governor housing (4). Here, the lubrication oil flows to three different locations.

Some of the oil flows into the rear camshaft bearing in fuel injection pump housing (5). This oil provides lubrication for three camshaft bearings in the fuel injection pump. Oil flows into drilled passages in camshaft (7) in order to provide lubrication to the flyweight carrier thrust bearing. This oil enters through drilled passages at the camshaft bearing next to the governor.

Oil drains from the camshaft bearings into fuel injection pump housing (5). Drain (6) in fuel injection pump housing (5) keeps the fuel injection pump housing's oil level even with the center of camshaft (7). The oil returns to the oil pan through the timing gear housing.

Oil also flows through a different passage back to fuel injection pump housing (5). This passage is connected to governor servo (2). Governor servo (2) provides hydraulics for assisting the mechanical governor in moving the fuel rack.

The remainder of the oil flows through a passage in rear governor housing (3) and back into another passage in rear governor housing (3). The oil flows into cover (1) or into the fuel ratio control. Then, the oil drains from these components. This oil drains into the governor housing. This drained oil serves two functions:

• Drained oil lubricates the governor control components.

• Drained oil supplies the oil for the dashpot.

The internal parts of the governor are also lubricated by oil leakage from governor servo (2). This oil that has leaked has been left behind by parts in rotation. Oil from the governor returns to the oil pan through a hole in the bottom of front governor housing (4). Oil also returns to the oil pan through passages in support (9) and the cylinder block.

Governor

Illustration 7	g00491665
Governor (1) Governor spring. (2) Sleeve. (3) Valve. (4) Piston. (5) Governor servo. (6) Fuel rack. (7) Lever. (8) Flyweights. (9) Riser. (10) Spring seat. (11) Stop bolt. (12) Stop collar. (13) Torque rise setting screw. (14) Power setting screw. (15) Torque spring. (16) Load stop bar. (17) Stop bar.

The governor controls the amount of fuel that is needed by the engine to maintain a desired rpm. The governor flyweights (8) are driven directly by the fuel pump camshaft. Riser (9) is moved by flyweights (8) and governor spring (1). Lever (7) connects the riser with sleeve (2) which is fastened to valve (3). Valve (3) is a part of governor servo (5). This valve moves piston (4) and fuel rack (6). When the governor servo is changed to the "FUEL-OFF" position, the fuel rack moves toward the front of the fuel pump housing. In Illustration 7, the direction of this movement is to the right.

Governor spring (1) always applies pressure so the governor can supply more fuel to the engine. The centrifugal force (rotating force) from flyweights (8) applies opposing pressure. This reduces the amount of fuel to the engine. When these two forces are in balance (equivalent), the engine runs at a constant rpm.

When the governor control lever is moved to the HIGH IDLE position, governor spring (1) is compressed. This pushes riser (9) toward the flyweights. When the riser moves forward, lever (7) moves sleeve (2) and valve (3) toward the rear. Valve (3) stops oil flow through governor servo (5), and the oil pressure moves piston (4) and the fuel rack to the rear. This increases the amount of fuel to the engine. As engine rpm increases, the flyweight force increases. This moves the riser toward the governor spring.

When the riser moves to the rear, lever (7) moves sleeve (2) and valve (3) forward. Valve (3) now directs oil pressure to the rear of piston (4). This moves the following components forward:

• Piston

• Fuel rack

This movement decreases the amount of fuel to the engine. When the flyweight force and the governor spring force become equal, the engine rpm is constant and the engine runs at high idle rpm. High idle rpm is adjusted by the high idle adjustment screw. The adjustment screw limits the governor spring's compression.

Engines with Stop Bar

When the load is increased and the engine is at high idle, engine rpm will decrease. Flyweights (8) move in, and governor spring (1) pushes riser (9) forward. This increases the amount of fuel to the engine.

As the load is increased, governor spring (1) continues to push riser (9) forward. Spring seat (10) pulls stop bolt (11). Stop collar (12) on the opposite end has power setting screw (14) that controls the maximum amount of fuel rack travel. The power setting screw moves forward until the screw contacts load stop bar (16). This is the full load balance point.

Engines with Torque Spring

When the load is increased and the engine is at high idle, engine rpm will decrease. Flyweights (8) move in, and governor spring (1) pushes riser (9) forward. This increases the amount of fuel to the engine. As the load is increased, governor spring (1) continues to push riser (9) forward. Spring seat (10) pulls stop bolt (11) .

Stop collar (12) on the opposite end has power setting screw (14). This screw and torque rise setting screw (13) control the maximum amount of fuel rack travel. The power setting screw moves forward until the screw contacts torque spring (15). This is the full load balance point.

If more load is added to the engine, engine rpm will decrease. This decrease in rpm continues to push riser (9) forward. The forward movement causes power setting screw (13) to bend torque spring (15) until torque rise setting screw contacts stop bar (17). This is the full load balance point.

Governor Servo

Illustration 8	g00319003
Governor Servo (FUEL-ON Position) (1) Valve. (2) Piston. (3) Cylinder. (4) Cylinder sleeve. (5) Fuel rack. (A) Oil inlet. (B) Oil outlet. (C) Oil passage. (D) Oil passage.

The governor servo provides hydraulics for assisting the mechanical governor in moving the fuel rack. The governor servo has cylinder (3), cylinder sleeve (4), piston (2), and valve (1) .

When the governor moves toward the FUEL-ON position, valve (1) moves to the left. The valve simultaneously opens oil outlet (B), and the valve closes oil passage (D). Pressure oil from oil inlet (A) pushes piston (2) and fuel rack (5) to the left. Oil behind the piston flows through oil passage (C) and along valve (1). Finally, this oil flows out of oil outlet (B).

Illustration 9	g00319027
Governor Servo (Balanced Position) (1) Valve. (2) Piston. (3) Cylinder. (4) Cylinder sleeve. (5) Fuel rack. (A) Oil inlet. (B) Oil outlet. (C) Oil passage. (D) Oil passage.

When the governor spring and flyweight forces are balanced and the engine rpm is constant, valve (1) stops moving. Pressure oil from oil inlet (A) pushes piston (2) until oil passages (C) and (D) are opened. Oil now flows through oil passage (D) along valve (1) and out through oil outlet (B). With no oil pressure on the piston, the piston and fuel rack (5) stop moving.

Illustration 10	g00319024
Governor Servo (FUEL-OFF Position) (1) Valve. (2) Piston. (3) Cylinder. (4) Cylinder sleeve. (5) Fuel rack. (A) Oil inlet. (B) Oil outlet. (C) Oil passage. (D) Oil passage.

When the governor moves toward the FUEL-OFF position, valve (1) moves to the right. The valve closes oil outlet (B) and opens oil passage (D). Pressure oil from oil inlet (A) is now on both sides of piston (2). The area on the left side of the piston is larger. The area on the right side of the piston is smaller. Similarly, the force of the oil is greater on the left side of the piston. This moves the piston and fuel rack (5) to the right.

Dashpot

Illustration 11	g00319031
Dashpot (FUEL-ON Position) (1) Cylinder. (2) Piston. (3) Dashpot spring. (4) Spring seat. (5) Needle valve. (6) Check valve. (7) Oil reservoir.

When there are sudden speed changes and there are sudden load changes, the dashpot helps the governor with better control of the rpm. The dashpot contains the following components:

• Cylinder (1)

• Piston (2)

• Dashpot spring (3)

• Needle valve (5)

• Check valve (6)

When the governor moves toward the FUEL-ON position, spring seat (4) and piston (2) move to the right. This movement pulls oil from oil reservoir (7) through check valve (6) and into cylinder (1) .

Piston (2) and spring seat (4) are fastened to dashpot spring (3).

Illustration 12	g00319123
Dashpot (FUEL-OFF Position) (1) Cylinder. (2) Piston. (3) Dashpot spring. (4) Spring seat. (5) Needle valve. (6) Check valve. (7) Oil reservoir.

When the governor moves toward the FUEL-OFF position, spring seat (4) and piston (2) move to the left. This movement pushes oil out of cylinder (1), through needle valve (5), and into oil reservoir (7) .

If the governor movement is slow, the oil provides no restriction to the movement of the piston and spring seat.

If the governor movement is fast and the governor movement is in the FUEL-OFF position, the needle valve gives a restriction to the oil. The piston and the spring seat will move slowly.

Automatic Timing Advance Unit

Illustration 13	g00322244
Automatic Timing Advance Unit (1) Weights. (2) Springs. (3) Slides. (4) Dowels. (5) Automatic timing advance unit.

The automatic timing advance unit (5) is installed on the front of the fuel pump drive shaft. Weights (1) in the timing advance are driven by two slides (3). These slides (3) fit into notches that are made on an angle in the weights (1). The slides (3) are driven by two dowels (4) in the hub assembly of the gear assembly in automatic timing advance unit (5) .

When the centrifugal force (rotation) moves weights (1) outward against the force of springs (2), a movement of the notches in the weights occurs. This movement (1) causes slides (3) to change the angle between the timing advance gear and the two dowels (4) in the hub assembly.

Since automatic timing advance unit (5) drives the fuel pump drive shaft, which is connected to the fuel injection pump camshaft, the fuel injection timing is also changed.

Fuel Air Ratio Control

Illustration 14	g00322257
Fuel Ratio Control (Engine Starting and Steady State Operation) (1) Inlet air chamber (2) Diaphragm assembly (3) Internal valve (4) Oil drain passage (5) Oil inlet (6) Stem (7) Spring (8) Piston (9) Oil passage (10) Oil chamber (11) Lever

The fuel air ratio control limits the amount of fuel to the cylinders during an increase of engine rpm. This reduces the amount of exhaust smoke. With the proper adjustment, the fuel air ratio control also minimizes the amount of soot in the engine.

Stem (6) moves lever (11) which will restrict the movement of the fuel rack in the FUEL-ON position only.

When the engine is stopped, there is no engine oil pressure. Stem (6) is fully extended. This is shown in Illustration 14. Therefore, the movements of both the fuel rack and lever (11) are not restricted by stem (6). This provides maximum fuel to the engine for easier starts.

When oil pressure arrives at the fuel air ratio control, pressurized oil flows through oil inlet (5) and into oil chamber (10). Piston (8) and stem (6) move in order to restrict lever (11) and the fuel rack to the fuel rack setting for limiting smoke.

Stem (6) will not move from the fuel rack setting for limiting smoke until inlet manifold air pressure increases. This increase must be enough to move internal valve (3). An air line connects the inlet manifold with inlet air chamber (1) of the fuel air ratio control.

The fuel air ratio control always limits the fuel rack's travel unless inlet manifold air pressure moves stem (6) out of the way. The fuel rack setting for limiting smoke is affected by the following conditions:

• Engine rpm

• Governor spring force

• High idle rpm

Illustration 15	g00322283
Fuel Ratio Control (Engine Acceleration) (1) Inlet air chamber (2) Diaphragm assembly (3) Internal valve (4) Oil drain passage (5) Oil inlet (6) Stem (7) Spring (8) Piston (9) Oil passage (10) Oil chamber (11) Lever

When the governor control is moved in order to increase fuel to the engine, stem (6) limits the movement of lever (11) in the FUEL-ON position. The oil in oil chamber (10) acts as a restriction to the movement of stem (6) until inlet air pressure increases.

As the inlet air pressure increases, diaphragm assembly (2) and internal valve (3) move to the right. The internal valve opens oil passage (9), and oil in oil chamber (10) flows to oil drain passage (4). When the oil pressure is reduced behind piston (8), spring (7) moves the piston and stem (6) to the right.

Piston (8) and stem (6) will move until oil passage (9) is closed by internal valve (3). Lever (11) can now move. This movement allows the fuel rack to attain the FUEL-ON position completely. The fuel air ratio control is designed to restrict the fuel until the air pressure in the inlet manifold is high enough for complete combustion. The fuel air ratio control prevents large amounts of exhaust smoke that are caused by an fuel air mixture with too much fuel.