Systems Operation



NOTE: For Specifications with illustrations, make reference to ENGINE SPECIFICATIONS FOR D349 VEHICULAR ENGINE, Form No. SENR7174. If the Specifications in Form SENR7174 are not the same as in the Systems Operation and the Testing and Adjusting, look at the printing date on the back cover of each book. Use the Specifications in the book with the latest date.

Fuel System

1. Fuel priming pump. 2. Pressure relief valve. 3. Fuel return line to fuel tank. 4. Bleed valve for the fuel injection pump. 5. Fuel injection pump bleed passage. 6. Check valve. 7. Check valve. 8. Bleed valve for the fuel filter housing. 9. Fuel supply line to priming pump. 10. Fuel supply line. 11. Fuel transfer pump. 12. Check valve. 13. Fuel filter housing. 14. Fuel injection pump housing.

Fuel from the fuel tank goes through fuel line (10) to fuel transfer pump (11). From the fuel transfer pump, fuel goes directly to filter housing (13), through the filter elements and into the fuel manifold in injection pump housing (14). Pressure relief valve (2) is in the fuel system to control fuel pressure. When fuel pressure gets too high, pressure relief valve (2) will open and allow some fuel to return to the fuel tank. Pump housing (14) has a separate fuel injection pump for each cylinder of the engine.

Air bleed valve (4) is used to remove air from fuel pump housing (14). Use air bleed valve (8) to remove air from the fuel filter housing.

Fuel priming pump (1) is used to prime the fuel system. When the fuel priming pump is operated, fuel goes from fuel supply line (10) through inlet and outlet check valves (6 and 7), then to fuel filter (13) and fuel pump housing (14). Check valve (12) is in the system to stop fuel from going back to the priming pump inlet when the priming pump is being operated.

Fuel Injection Pump

Fuel enters the fuel injection pump housing through passage (6) and enters the fuel injection pump body through the inlet port (2). The injection pump plungers (5) and the lifters (11) are lifted by the cam lobes (12) on the camshaft and always make a full stroke. The lifters are held against the cam lobes by the springs (3). Each pump measures the amount of fuel to be injected into its respective cylinder and forces it out the fuel injection nozzle.

The amount of fuel pumped each stroke is varied by turning the plunger in the barrel. The plunger is turned by the governor action through the fuel rack (8) which turns the gear segment (10) on the bottom of the pump plunger. Passage (4) provides fuel to lubricate the pump plunger and passage (7) allows air to be bled from the system through the valve on top of the fuel filter case.

1. Check valve. 2. Inlet port. 3. Spring. 4. Lubrication passage (fuel). 5. Pump plunger. 6. Fuel passage. 7. Bleed passage. 8. Fuel rack. 9. Lubrication passage (oil). 10. Gear segment. 11. Pump Lifter. 12. Camshaft lobe.

Fuel Injection Pump

Fuel, under high pressure from the injection pumps, is transferred through the injection lines to the injection valves. As high pressure fuel enters the nozzle assembly, the check valve within the nozzle opens and permits the fuel to enter the precombustion chamber. The injection valve provides the proper spary pattern.

1. Fuel line assembly. 2. Seal. 3. Body. 4. Nut. 5. Seal. 6. Nozzle assembly. 7. Glow plug. 8. Precombustion chamber.

Speed Sensing, Variable Timing Unit

The variable timing unit, couples the fuel injection pump camshaft to the engine rear timing gears. The variable timing unit advances the timing as engine rpm increases.

On earlier engines the timing advances from 11° BTC at low idle to 19° BTC at high idle. On later engines the timing advances from 8° BTC at low idle to 19° BTC at high idle.

1. Power piston. 2. Power piston cavity. 3. Control valve spring. 4. Power piston return spring. 5. Oil inlet passage. 6. Drain port. 7. Control valve. 8. Flyweights. 9. Shaft assembly.

During engine low rpm operation, the flyweight (8) force is not sufficient to overcome the force of control valve spring (3) and move control valve (7) to the closed position. Oil merely flows through the power piston cavity (2).

As the engine rpm increases, flyweights (8) overcome the force of control valve spring (3) and move control valve (7) to the closed position, blocking the oil drain port (6). Pressurized oil, trapped in power piston cavity (2), overcomes the force of spring (4) and moves power piston (1) outward. This causes the fuel injection pump camshaft to index slightly ahead of the shaft portion (9) of the variable timing unit. Any outward movement of the power piston increases the force on the control valve spring. This tends to reopen the control valve, letting oil escape from the power piston cavity. As oil begins flowing from the cavity again, return spring (4) moves the power piston inward.

1. Power piston. 2. Power piston cavity. 3. Control valve spring. 4. Power piston return spring. 5. Oil inlet passage. 6. Drain port. 7. Control valve. 8. Flyweights. 9. Shaft assembly.

At any given rpm, a balance is reached between the flyweight force and the control valve spring force. The resultant position of control valve (7) will tend to maintain proper pressure behind the power piston. The greater the rpm, the smaller the drain port opening, and the further outward the power piston is forced.

As the power piston is moved outward, the angular relationship of the ends of the drive unit change. As the power piston moves forward in the internal helical spline, the fuel injection pump timing advances.

The gear teeth on shaft assembly (9) drive the governor drive pinion.

Hydra-Mechanical Governor

The governor controls engine speed by balancing governor spring force with governor weight centrifugal force. The compressed governor spring force is applied to increase the supply of fuel to the engine, while the centrifugal force of the engine driven governor weights is applied to decrease fuel to the engine.

Oil pump gear (15), driven by shaft (19), provides immediate pressure oil for the servo portion of the governor. A sump in governor drive housing (16) provides an immediate oil supply for governor operation. A bypass valve in the governor drive housing maintains correct oil pressure.

When the engine is operating, the balance between the centrifugal force of revolving weights (9) and the force of spring (7) controls valve (8). The valve directs pressure oil to either side of rack-positioning piston (13). Depending on the position of the valve (8), piston (13) will move the rack to increase or decrease fuel to the engine to compensate for load variation.

1. Shutoff shaft. 2. Collar. 3. Adjusting screw. 4. Stop bar. 5. Lever assembly. 6. Seat assembly. 7. Governor spring. 8. Valve. 9. Weight assembly. 10. Seat. 11. Oil passage. 12. Cylinder. 13. Piston. 14. Sleeve. 15. Oil pump gear. 16. Governor drive housing. 17. Oil pump cover. 18. Pin assembly. 19. Shaft assembly. 20. Lever. 21. Fuel rack. 22. Drive pinion.

Pressurized lubrication oil, directed through passages in governor drive housing (16) and oil pump cover (17) enters a passage in governor cylinder (12). The oil encircles sleeve (14) within the cylinder. Oil is then directed through passage (11) in piston (13) where it contacts valve (8).

When engine load increases, engine rpm decreases and revolving weights (9) slow down. The weights move toward each other and allow governor spring (7) to move valve (8) down. As valve (8) moves, an oil passage around valve (8) opens to pressure oil. Oil then flows through passage (11) and fills the chamber behind piston (13). The pressure forces the piston and rack down, increasing the amount of fuel to the engine. Engine rpm increases until the revolving weights rotate fast enough to balance the force of the governor spring.

When engine load decreases, engine rpm increases, revolving weights (9) speed-up, and the toes on the weights move valve (8) up, allowing the oil behind piston (13) to flow through a drain passage opened at the rear of the piston. At the same time, the pressure oil between sleeve (14) and piston (13) forces the piston and rack up, decreasing the amount of fuel to the engine. Engine rpm decreases until the revolving weights balance the force of the governor spring.

When the engine is started, a speed limiter plunger located in the governor housing, restricts the movement of the governor control linkage. When operating oil pressure is reached, the plunger in the speed limiter retracts and the governor control can be moved to the HIGH IDLE position.

Fuel Ratio Control

The fuel ratio control coordinates the movement of the fuel rack with the amount of air available in the inlet manifold. The control keeps the fuel to air ratio more efficient, thus minimizing exhaust smoke.

A manually operated override lever (1) is provided to allow unrestricted rack movement during cold starts. After the engine starts, the override automatically resets in the RUN position.

Bolt and collar (8) mechanically connect to the fuel rack. The head of bolt assembly (7) latches through a slot in hook (6) attached to bolt and collar (8). An air line joins the chamber above diaphragm (5), with the air in the engine inlet manifold.

1. Lever. 2. Housing. 3. Spring. 4. Spring. 5. Diaphragm. 6. Hook. 7. Bolt assembly. 8. Bolt and collar.

When the operator moves the governor control to increase engine rpm, the fuel rack moves bolt and collar (8) down until hook (6) contacts the head of bolt assembly (7). The bolt assembly restricts the movement of the bolt and collar until spring (3) and a boost of air pressure in housing (2) forces diaphragm (5), spring (4) and bolt assembly (7) to relieve the restriction to bolt and collar (8). This allows the fuel rack to move to increase the fuel as turbocharger air pressure (boost) increases with the increase in engine rpm.

Fuel Ratio Control (Hydraulic Activated)

The hydraulic activated fuel ratio control automatically causes a restriction to the amount of travel of the rack in the "fuel on" direction, until the air pressure in the inlet manifold is high enough to give complete combustion. The fuel ratio control keeps engine performance high so that black exhaust gases are not seen.

1. Valve. 2. Oil inlet passage. 3. Passage for inlet air pressure. 4. Oil outlet passage. 5. Large oil passage. 6. Oil drain. 7. Spring. 8. Diaphragm. 9. Valve.

The hydraulic activated fuel ratio control has two valves (1) and (9). Engine oil pressure works against valve (1) to control the movement of the fuel rack. Air pressure from the inlet manifold works against diaphragm (8) to move valve (9) to control oil pressure against valve (1).

When the engine is stopped, there is no pressure on either valve. Spring (7) moves both valves to the ends of their travel. In this position, the fuel rack travel is not restricted. Also in this position, an oil outlet passage (4) is open to let oil away from valve (1).

When the engine is started, the open oil outlet passage (4) prevents oil pressure against valve (1) until air pressure from the inlet manifold is high enough to move valve (9) to close the large oil passage (5). Engine oil pressure then works against valve (1) to move this valve into its operating position. The control will operate until the engine is stopped.

When the governor control is moved toward the full load position with the engine running, the head on the stem of valve (1) will cause a restriction to the travel of the fuel rack, until the air pressure in the inlet manifold has an increase. As there is an increase in the air pressure in the inlet manifold, this pressure works against diaphragm (8) to cause valve (9) to move to the left. The large oil passage (5) becomes open to let oil pressure away from valve (1), toward spring (7), and out to drain (6). As there is a decrease in oil pressure, valve (1) moves to the left to let the fuel rack open at a rate equal to (the same as) the air available for combustion.

Air Induction And Exhaust

1. Left side exhaust manifold. 2. Aftercoolers. 3. Right side exhaust manifold. 4. Equalizer tube. 5. Left side air cleaner. 6. Turbocharger. 7. Exhaust outlet. 8. Turbocharger. 9. Right side air cleaner.

The air induction and exhaust system includes two turbochargers (6 and 8) located at the rear of the engine.

Each turbocharger is driven from, and charges, its own cylinder bank. Balanced inlet manifold pressures between banks are assured through an equalizer tube (4) connecting the two aftercooler housings.

Exhaust manifolds (1 and 3) have one section to a cylinder. These are interchangeable between banks. High-temperature studs and nuts are used to secure the manifold sections to the cylinder heads.

The aftercooler housings (2) are located directly on top of the "V" side of the cylinder heads. The aftercooler housings contain the aftercooler cores, with provision for either jacket water or separate circuit water as a cooling medium for the inlet air. The air inlet section of the aftercooler housing is connected to the turbochargers (6 and 8).

Inlet air for the engine is drawn through air cleaners (5 and 9) and directed to the turbochargers. From turbochargers (6 and 8), air is forced directly through the cores of aftercoolers (2) and into the combustion area.

There are four in-head valves (two intake and two exhaust) for each cylinder. The valves are actuated by overhead camshafts and forked rocker arm assemblies, located in the housing on top of the cylinder heads.

Exhaust gases leave each cylinder through two exhaust valve ports. After passing through the turbine side of the turbochargers, the exhaust exits through exhaust outlet (7) located between the turbochargers.


The turbochargers are supported by brackets mounted to the engine cylinder block. All the exhaust gases from the diesel engine pass through the turbochargers.

TURBOCHARGER (Typical Illustration)
1. Air inlet. 2. Compressor housing. 3. Nut. 4. Compressor wheel. 5. Thrust plate. 6. Center housing. 7. Lubrication inlet port. 8. Shroud. 9. Turbine wheel and shaft. 10. Turbine housing. 11. Exhaust outlet. 12. Spacer. 13. Ring. 14. Seal. 15. Collar. 16. Lubrication outlet port. 17. Ring. 18. Bearing. 19. Ring.

The exhaust gases enter the turbine housing (10) and are directed through the blades of a turbine wheel (9), causing the turbine wheel and a compressor wheel (4) to rotate.

Filtered air from the air cleaners is drawn through the compressor housing air inlet (1) by the rotating compressor wheel. The air is compressed by action of the compressor wheel and forced to the inlet manifold of the engine.

When engine load increases, more fuel is injected into the engine cylinders. The volume of exhaust gas increases causing the turbocharger turbine wheel and compressor impeller to rotate faster. The increased rpm of the impeller increases the quantity of inlet air. As the turbocharger provides additional inlet air, more fuel can be burned; hence more horsepower derived from the engine.

Maximum rpm of the turbocharger is controlled by the rack setting, the high idle speed setting and the height above sea level at which the engine is operated.

------ WARNING! ------

If the high idle rpm or the rack setting is higher than given in the book RACK SETTING INFORMATION (for the height above sea level at which the engine is operated), there can be damage to engine or turbocharger parts.


The bearings for the turbocharger use engine oil under pressure for lubrication. The oil comes in through the oil inlet port (7) and goes through passages in the center section for lubrication of the bearings. Oil from the turbocharger goes out through the oil outlet port (16) in the bottom of the center section and goes back to the engine lubricating system.

The fuel rack adjustment is done at the factory for a specific engine application. The governor housing and turbocharger are sealed to prevent changes in the adjustment of the rack and the high idle speed setting.

Cylinder Heads, Valves And Camshafts

Cylinder Heads and Valves

This is a four stroke cycle engine; i.e., four separate piston strokes are required to complete the firing of one cylinder.

There are four in-head valves for each cylinder; two intake valves and two exhaust valves.

The in-head valves are perpendicular to the bottom face of the cylinder head. The exhaust valves and ports are located toward the outside of the engine. The intake valves are on the inside, toward the vee.

A primary feature of the cylinder head is parallel porting. This provides individual porting for each of the two exhaust valves and the two intake valves. This permits unrestricted flow of air and exhaust gasses; resulting in maximum breathing capability and efficiency.

Valves, valve seats, seating springs and rotators are all part of the cylinder head assembly. The valve seats are pressed into the cylinder head and are replaceable.

Valve rotators add much to valve life. Each valve is rotated three degrees on every lift; thus minimizing pitting of the valve faces and valve seats. The rotation also causes a wiping action to remove carbon deposits from the valve seat.

Rocker Arms

Valve action is accomplished through a roller-rocker arm arrangement. The forked rocker arm (2), located in the camshaft housing, pivots on a shaft (4) at one end and depresses two valves at the other end through adjusting screws. A roller (5), supported by a pin near the center of the rocker arm, rides on the camshaft (1) lobe. Thus, one camshaft lobe actuates the forked rocker arm and opens two valves simultaneously.

1. Camshaft. 2. Rocker arm. 3. Adjusting screw. 4. Pivot shaft. 5. Roller. 6. Spring. 7. Valve.

Valve adjustment can be quickly and accurately accomplished with a screwdriver. No thickness gauge is required. Turn the adjusting screw (3) down to remove all clearance, then back off to the required setting.


This engine uses two overhead camshafts in each cylinder bank. The inner camshaft in each bank actuates all the intake valves and the other camshaft actuates all the exhaust valves.

The camshafts are driven from both ends of the engine. The right bank camshafts are driven by the rear gear train. On the left bank, the inlet camshaft drives the exhaust camshaft. On the right bank, the exhaust camshaft (F) drives the inlet camshaft (E).

A. Flywheel end. B. Left side. C. Front end. D. Right side. E. Inlet camshaft. F. Exhaust camshaft.

The camshaft journals are supported in integrally cast webs of the camshaft housings. Pressure lubrication to the camshaft journals is supplied from the cylinder block through the cylinder head, and into drilled passages in the camshaft housing.

A crankcase breather is mounted on the front of the right bank camshaft cover. The element is removable for cleaning. A fumes disposal tube carries the crankcase fumes to a level below the engine.

Lubrication System

1. Turbocharger oil drain line. 2. Turbocharger lubrication oil supply line. 3. Oil supply to left rear valve train. 4. Left bank oil manifold. 5. Oil supply to left front valve train. 6. Oil supply to front timing gears. 7. Turbocharger lubrication valve. 8. Oil supply to governor. 9. Main oil manifold. 10. Oil supply to rear timing gears. 11. Oil supply to right rear valve train. 12. Oil supply to right front valve train. 13. Oil cooler bypass valve. 14. Right bank oil manifold. 15. Oil pump pressure relief valve. 16. Engine oil cooler. 17. Engine oil pump. 18. Oil filter housing. 19. Oil filter bypass valve.

The lubrication system has a two-section gear driven oil pump (17) located at the bottom of the cylinder block, within the oil pan.

This pump is gear driven through an idler off the rear timing gears. The drive gear is baffled to reduce aeration of the oil in the oil pan.

Oil from the pump is directed to oil cooler (16). An oil cooler bypass valve (13) is provided to bypass cool oil around the cooler. The increased pressure of cool oil causes the bypass valve to open and permit oil to flow directly from the pump to the filters. When oil temperature increases, the pressure returns to normal and the bypass valve closes, allowing the oil to flow through the cooler before going to the filters.

Oil flow then goes to the oil filter housing (18), located at the right side of the engine. A bypass valve (19) allows oil to bypass the oil filter elements if they become restricted.

From the oil filters, oil is directed to main oil manifold (9). This manifold is a passage extending the entire length of the cylinder block just below the "V". From this manifold, branch passages supply lubricating oil to the front and rear timing gears, right and left bank valve mechanisms, main and connecting rod bearings, piston cooling jets, and the governor and fuel injection pump housing.

The governor and fuel injection pump lubrication system includes an oil pump within the governor. Oil that drains from the speed limiter collects in the governor housing. This reservoir supplies oil to the governor oil pump located in the governor drive housing. The governor oil pump also supplies pressure oil to the servo to obtain immediate governor response during starting.

The fuel injection pump housing contains an oil manifold that supplies oil to the camshaft bearings and the lifter rollers. The lifter rollers and camshaft lobes are lubricated each time the individual lifters move up and uncover an oil hole. Lubricant drains from the fuel injection pump housing back to the cylinder block.

Cooling Systems

1. Aftercooler water radiator. 2. Engine water radiator. 3. Return line. 4. Return line. 5. Aftercoolers. 6. Fan. 7. Bypass line. 8. Aftercooler water pump. 9. Engine water pump. 10. Supply line for engine water pump. 11. Supply line for aftercooler water pump. 12. Engine oil cooler. 13. Supply line to aftercoolers.

Coolant for the aftercooling circuit is supplied from aftercooler radiator through line (11) to the gear driven aftercooler water pump, located on the left rear of the front timing gear housing. Coolant from the pump is directed through line (13), located on the left side of the cylinder block, to a tee connection at the rear of the engine where the coolant flow is divided equally and directed to the rear of each aftercooler. Coolant flows through the aftercoolers, combines into one line (4) and is directed to the top of the aftercooler radiator.

1. Radiator. 2. Return line. 3. Bypass line. 4. Aftercooler outlet line. 5. Aftercoolers. 6. Water pump supply line. 7. Water pump. 8. Supply line from water pump to engine oil cooler. 9. Engine oil cooler. 10. Aftercooler supply line from water pump.

Coolant flows from radiator (1) through line (6) to the water pump (7). Coolant flow is divided when leaving the water pump. Part of the coolant is directed through line (10) to the rear of the aftercoolers. Coolant from each aftercooler enters line (4) and is directed to the cylinder block.

The other stream of coolant from the water pump is directed through line (8) to the engine oil cooler and then into the cylinder block. The two streams of coolant join in the cylinder block. Coolant is then directed through the cylinder block and up through the cylinder head to the water temperature regulators, located at the front of the engine.

Until the coolant reaches the temperature required to open the temperature regulators, it is bypassed through line (3) back to the water pump. When the temperature regulators are open, coolant is directed to the radiator through line (2).

Basic Engine Components

Cylinder Block

A. Flywheel end. B. Left side. C. Front end. D. Right side.

The cylinder block is a 60° vee. One bank of cylinders is offset from the other bank of cylinders. This offset provides space at each end of the cylinder block for the camshaft drives. The offset also allows two connecting rods to be secured to each connecting rod journal of the crankshaft.

Cylinder Liners

The cylinder liner sits directly on the cylinder block. Engine coolant flows around the liners to cool them. Three O-ring seals at the bottom and a filler band at the top of each cylinder liner form a seal between the cylinder liner and the cylinder block.

Pistons, Rings And Connecting Rods

The piston has three rings; two compression rings and one oil ring. All rings are located above the piston pin bore. The two compression rings seat in an iron band which is cast integrally in the piston. The oil ring is spring loaded. Holes in the oil ring groove provide for the return of oil to the crankcase.

The full-floating piston pin is retained by two snap rings which fit in grooves in the pin bore.

A steel heat plug, in the crater of the piston, protects the top of the piston from erosion and burning at the point of highest heat concentration.

Oil spray jets, located on the cylinder block main bearing webs, direct oil to cool and lubricate the piston components and cylinder walls.

The connecting rods have diagonally cut serrated joints which allow removal of the piston and connecting rod assembly upward through the cylinder liner. Earlier engines use the same part number connecting rod for both odd and even numbered cylinders. This connecting rod uses a locating tab to position the connecting rod bearing.

Connecting rod bearings in later engines do not have locating tabs but are positioned by dowels in the connecting rods. The rods with dowel located bearings are marked " Even Cyl Only..." or " Odd Cyl Only...". These rods must be installed in the correct bank. They may be installed in earlier engines if the correct piston cooling jets are installed. Refer to Special Instruction (GEG02495) for complete instructions.


The crankshaft transforms the combustion forces in the cylinders into usable rotating torque which powers the machine. There is a timing gear at each end of the crankshaft which drives the respective timing gears.

Interconnecting drilled passages supply pressurized lubricating oil to all bearing surfaces on the crankshaft.

Electrical System

The charging circuit is in operation when the diesel engine is operating. The electricity producing (charging) unit is an alternator. A regulator in the circuit senses the state of charge in the battery and regulates the charging unit output to keep the battery fully charged.

The diesel engine starting circuit includes a glow plug for each diesel engine cylinder. Glow plugs are small heating elements in the precombustion chambers which promote fuel ignition when the engine is started in low temperatures.


The alternator is a belt driven, three phase, self-rectifying, brushless charging unit with a built in voltage regulator.

The only moving part in the alternator is the rotor, which is mounted on a ball bearing at the drive end, and a roller bearing at the rectifier end.

The regulator is enclosed in a sealed compartment. It senses the charge condition of the battery, the electrical system power demands and controls the alternator output accordingly.


Safety Devices - (Engine Mounted Controls)

Water Temperature Contactor Switch

A water temperature sending unit is located in the cooling system. The unit is nonadjustable. Thermal expansion of the element operates a micro-switch that signals the shutoff solenoid which causes engine shutdown. The water temperature element must be in contact with the coolant. If overheating occurs due to low coolant level or no coolant, the sending unit will not function.

The water temperature sending unit can also be wired into an alarm system or light to signal high water temperature. After an overheated engine is allowed to cool, the contactor automatically resets itself.


Shut-Off Solenoid


The shutoff solenoid, when energized moves to over-ride the governor action, which in turn moves the governor and fuel rack to the shutoff position. The solenoid can be energized by any one of several sources. The most usual are: water temperature contactor switch, oil pressure contactor switch, overspeed contactor switch and remote manual control switch.

Oil Pressure Switch

An oil pressure switch is provided in the lubrication system. The switch turns on the alarm system when engine oil pressure falls below 15 psi (1.05 kg/cm2).


Fuel Pressure Switch

A fuel pressure switch is provided in the fuel system. The switch turns on the alarm system when engine fuel pressure is 5 psi (0.4 kg/cm2) or less.


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