3306C Truck 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 172 ± 28 kPa (25 ± 4 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.

Scroll (9) changes the distance that the pump plunger pushes the fuel between closed bypass port (5) and spill port (10). The longer the distance from the top of the pump plunger to the point of scroll (9) uncovering spill port (10), the more fuel will 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 injector 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) Filter screen (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 filter screen (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	g00318863
Fuel injection pump and governor (1) Servo (2) Fuel injection pump housing (3) Cover (4) Oil supply from cylinder block (5) Oil drain into cylinder block (6) Dashpot (7) Governor rear housing (8) Governor center housing

Lubrication oil from the side of the cylinder block flows into the side of the fuel injection pump housing at location (4). The oil then flows to a passage between fuel injection pump housing (2) and governor center housing (8). Here, the lubrication oil flows to three different locations.

Some of the oil flows back into the main oil passage in fuel injection pump housing (2). This oil provides lubrication for the three camshaft bearings in the fuel injection pump. Oil flows into drilled passages in the camshaft 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 the fuel injection pump housing. A drain hole in the fuel injection pump housing keeps the fuel injection pump housing's oil level even with the center of the camshaft. Oil drains from the fuel injection pump housing, through oil drain (5), and back to the engine block.

Oil also flows through a different passage back to the fuel injection pump housing. This passage is connected to governor servo (1). The governor servo provides hydraulics for assisting the mechanical governor in moving the fuel rack.

The remainder of the oil flows through a passage in governor center housing (8) and governor rear housing (7). The oil flows to cover (3) or to the fuel air 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 dashpot (6).

The internal parts of the governor are also lubricated by oil leakage from governor servo (1). This leaked oil has been left behind by the parts in rotation. An opening between the lower part of the governor and the fuel injection pump housing allows oil out of the governor. The fuel injection pump housing has an oil drain port (5) that is connected to the engine block.

Governor

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 "FUEL OFF", the fuel rack moves toward the front of the fuel pump housing. In Illustration 7, the direction of this movement is to the right.

Illustration 7	g00318866
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

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 speed 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 speed 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 with the engine at high idle, engine speed 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 on 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 with the engine at high idle, engine speed 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 on 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 speed will decrease. This decrease in speed 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 consists of the following components: cylinder (3), cylinder sleeve (4), piston (2) and valve (1) .

When the governor moves in the FUEL ON direction, 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 speed 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 in the FUEL OFF direction, 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 vehicle speed changes and there are sudden load changes, the dashpot helps the governor with better speed control. 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 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 direction, 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.

Governor Control Group and the Regulation of Low Speed

Some engine applications use the engine in two ways:

• As power for the mobile truck

• As a stationary engine

For applications of these dual purpose engines, a control group is installed on the rear of the standard governor for stationary operation. The control group is not used when the truck is operating, but the control group can be engaged by air pressure for use as a stationary application. The governor control group sets the engine at 1600 rpm without any load. When the lever assembly is connected with the standard governor spring, the governor control group regulates engine speed within 5%.

Operation

Illustration 14	g00322246
Governor control group during normal operation (1) Spring (2) Piston assembly (3) Lever (4) Low speed governor spring

During normal operation, spring (1) holds piston assembly (2) forward far enough so that lever (3) does not contact low speed governor spring (4). This allows the normal operation of the governor.

Illustration 15	g00322254
Governor control group during stationary operation (2) Piston assembly (3) Lever (4) Low speed governor spring (5) Governor control group (6) Adjusting screw (7) Governor spring

When the engine is used as a stationary engine, air pressure engages governor control group (5). The air pressure affects two operations:

• Air pressure moves piston assembly (2) to the rear.

• Air pressure holds the piston assembly against adjusting screw (6) .

The movement of the piston to the rear causes low speed governor spring (4) to contact lever (3). This moves governor spring (7) in the direction toward maximum fuel. When the engine speed reaches 1600 rpm, the governor springs are in balance. This balance allows the governor springs to hold the engine at that speed.

When a load is applied to the engine, the engine speed slows to 1500 rpm. Then, the engine can supply the horsepower necessary to operate the load.

When the load is removed, the low speed governor spring reacts against the governor spring. This holds the engine overspeed at 1600 rpm, and the engine will remain at this speed until one of two conditions exist:

• The load is applied again.

• The governor control group is disengaged.

Fuel Air Ratio Control

Illustration 16	g00322257
Fuel ratio control (engine started) (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 speed. 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" direction only.

When the engine is stopped, there is no engine oil pressure. Stem (6) is fully extended as seen in Illustration 16. 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 a way that restricts the fuel rack and lever (11) 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). A 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 speed

• Governor spring force

• High idle speed

Illustration 17	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 group is moved and this control group increases the fuel to the engine, stem (6) limits the movement of lever (11) in the "Fuel On" direction. 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.