Introduction

NOTE: For Specifications with illustrations, make reference to Specifications, 3408C Engine For Caterpillar Built Machines, SENR6475. If the Specifications in SENR6475 are not the same as in the Systems Operation and the Testing And Adjusting, look at the printing date on the front cover of each book. Use the Specifications given in the book with the latest date.

Engine Design

Cylinder, Valve And Injection Pump Location

Bore ... 137.2 mm (5.40 in)

Stroke ... 152.4 mm (6.00 in)

Number and Arrangement of Cylinders ... V-8

Firing Order (Injection Sequence) ... 1,8,4,3,6,5,7,2

Rotation of Crankshaft (when seen from flywheel end) ... counterclockwise

Rotation of Fuel Pump Camshaft (when seen from pump drive end) ... counterclockwise

NOTE: Front end of engine is opposite to flywheel end.

Left side and right side of engine are as seen from flywheel end.

No. 1 cylinder is the front cylinder on the left side.

No. 2 cylinder is the front cylinder on the right side.

Fuel System

Fuel System Schematic
(1) Fuel tank. (2) Tank shutoff valve. (3) Fuel injection nozzle. (4) Fuel manifolds. (5) Fuel injection pump housing. (6) Bleed orifice. (7) Fuel inlet line from secondary filters. (8) Fuel inlet line from primary filter. (9) Check valve. (10) Fuel transfer pump. (11) Secondary fuel filter. (12) Primary fuel filter. (13) Fuel priming pump. (14) Fuel transfer pump relief valve.

There is one fuel injection pump and one fuel injection valve for each cylinder. The fuel injection pumps are located in the fuel injection pump housing. The fuel injection valves are located in direct injection adapter (3).

When the engine is running, fuel is pulled from the fuel tank through the fuel supply line and primary fuel filter (12) by fuel transfer pump (10). The fuel is then pushed to secondary fuel filters (11), and into the fuel filter housing. A bleed orifice (6) in the fuel filter housing cover vents air in the system through a line back to fuel tank (1). Fuel from the fuel filter housing goes through inlet line (7) to fuel manifolds (4) in fuel injection pump housing (5). The fuel manifolds supply fuel to each fuel injection pump.

Individual fuel injection lines carry fuel from the fuel injection pumps to each cylinder. One section of line connects between the fuel injection pump and an adapter on the valve cover base. Another section of line on the inside of the valve cover base connects between the adapter and the fuel injection valve in direct injection adapter (3).

The fuel filters and priming pump are located in a compartment at the front of the fuel tank. The fuel transfer pump is mounted on a drive adapter on the fuel injection pump housing, and is driven by a shaft connected to the fuel injection pump camshaft. Fuel transfer pump relief valve (14) is located in the cover of the pump.

Fuel priming pump (13) is used before the engine is started to put pressure in the fuel system and to vent air from the system. A check valve (9) located in the fuel transfer pump adapter housing will let fuel go around the fuel transfer pump when the priming pump is in use.

There is no bleed orifice or valve installed on the fuel injection pump housing to vent air from this part of the fuel system. Air trapped in the fuel injection lines can be vented by loosening all of the fuel injection line nuts where they connect to the adapters in the valve cover base. Move the governor lever to the low idle position. Crank the engine with the starter motor until fuel without air comes from the fuel line connections. Tighten the fuel line nuts. This procedure is necessary because the fuel priming pump will not give enough pressure to push fuel through the reverse flow check valves in the fuel injection pumps of a direct injection system.

Location Of Fuel System Components (Typical Illustration)
(4) Fuel manifolds. (5) Fuel injection pump housing. (7) Fuel inlet line from secondary filters. (8) Fuel inlet line from primary filter. (10) Fuel transfer pump.

Location Of Fuel System Components (Typical Illustration)
(1) Fuel tank. (6) Bleed orifice in cover. (11) Secondary fuel filters. (12) Primary fuel filter. (13) Fuel priming pump.

An automatic timing advance unit is mounted on the front of the fuel injection pump camshaft. It is driven by the engine camshaft gear inside the front timing gear housing. The automatic timing advance unit gives easier starting and smooth low speed operation. It will also advance timing as engine speed increases to give correct engine operation efficiency.

Fuel Injection Pump

Cross Section Of The Fuel Injection Pump Housing
(1) Fuel manifold. (2) Inlet passage. (3) Check valve. (4) Pressure relief passage. (5) Pump plunger. (6) Spring. (7) Gear. (8) Fuel rack (left). (9) Lifter. (10) Link. (11) Lever. (12) Camshaft.

The rotation of the lobes on the camshaft (12) cause lifters (9) and pump plungers (5) to move up and down. The stroke of each pump plunger is always the same. The force of springs (6) hold lifters (9) against the cams of the camshaft.

The pump housing is a "V" shape (similar to the engine cylinder block), with four pumps on each side.

When the pump plunger is down, fuel from fuel manifold (1) goes through inlet passage (2) and fills the chamber above pump plunger (5). As the plunger moves up it closes the inlet passage.

The pressure of the fuel in the chamber above the plunger increases until it is high enough to cause check valve (3) to open. Fuel under high pressure flows out of the check valve, through the fuel line to the injection valve, until the inlet passage opens into pressure relief passage (4) in the plunger. The pressure in the chamber decreases and check valve (3) closes.

The longer inlet passage (2) is closed, the larger the amount of fuel which will be forced through check valve (3). The period for which the inlet passage is closed is controlled by pressure relief passage (4). The design of the passage makes it possible to change the inlet passage closed time by rotation of the plunger. When the governor moves fuel racks (8), they move gears (7) that are fastened to plungers (5). This causes a rotation of the plungers.

The governor is connected to the left rack. The spring load on lever (11) removes the play between the racks and link (10). The fuel racks are connected by link (10). They move in opposite directions (when one rack moves in, the other rack moves out).

Fuel Injection Nozzles

The fuel injection nozzle is installed in an adapter in the cylinder head and is extended into the combustion chamber. The fuel injection pump sends fuel with high pressure to the fuel injection nozzle where the fuel is made into a fine spray for good combustion.

Fuel Injection Nozzle
(1) Carbon dam. (2) Seal. (3) Passage. (4) Filter screen. (5) Inlet passage. (6) Orifice. (7) Valve. (8) Diameter. (9) Spring.

Seal (2) goes against the nozzle adapter and prevents leakage of compression from the cylinder. Carbon dam (1) keeps carbon out of the bore in the nozzle adapter.

Fuel with high pressure from the fuel injection pump goes into inlet passage (5). Fuel then goes through filter screen (4) and into passage (3) to the area below diameter (8) of valve (7). When the pressure of the fuel that pushes against diameter (8) becomes greater than the force of spring (9), valve (7) lifts up. This occurs when the fuel pressure goes above the Valve Opening Pressure of the fuel injection nozzle. When valve (7) lifts, the tip of the valve comes off of the nozzle seat and the fuel will go through the six small orifices (6) into the combustion chamber.

The injection of fuel continues until the pressure of fuel against diameter (8) becomes less than the force of spring (9). With less pressure against diameter (8), spring (9) pushes valve (7) against the nozzle seat and stops the flow of fuel to the combustion chamber.

The fuel injection nozzle can not be disassembled and no adjustments can be made.

Hydra-Mechanical Governor

The throttle lever, or governor control, is connected to the control lever on the engine governor. The governor then controls the amount of fuel needed to keep the desired engine rpm at the throttle lever setting.

The governor has governor weights (5) driven by the engine through the drive assembly (15). The governor has a governor spring (6), valve (9) and piston (11). The valve and piston are connected to one fuel rack through pin (17) and lever (18). The pressure oil for the governor comes from the governor oil pump, on top of the injection pump housing. The oil used is from the engine lubrication system. Pressure oil goes through passage (14) and around sleeve (13). The throttle lever, or governor control, controls only the compression of governor spring (6). Compression of the spring always pushes down to give more fuel to the engine. The centrifugal force of governor weights (5) always pulls to get a reduction of fuel to the engine. When these two forces are in balance, the engine runs at the desired rpm (governed rpm).

The governor valve (9) is shown in the position when the force of the governor weights and the force of the governor spring are in balance.

When the engine load increases, the engine rpm decreases and the rotation of governor weights (5) will get slower. (The governor weights will move toward each other). Governor spring (6) moves valve (9) down. This lets the oil flow from the lower passage (12) around the valve (9) and through the upper passage (10) to fill the chamber behind piston (11). This pressure oil pushes the piston (11) and pin (17) down to give more fuel to the engine. (The upper end of the valve stops the oil flow through the top of the piston, around the valve). Engine rpm goes up until the rotation of the governor weights is fast enough to be in balance with the force of the governor spring.

Hydra-Mechanical Governor
(1) Collar. (2) Bolt. (3) Lever assembly. (4) Upper spring seat. (5) Weights. (6) Governor spring. (7) Lower spring seat. (8) Thrust bearing. (9) Valve. (10) Upper oil passage in piston. (11) Piston. (12) Lower oil passage in piston. (13) Sleeve. (14) Oil passage in cylinder. (15) Drive assembly. (16) Cylinder. (17) Pin. (18) Lever.

When there is a reduction in engine load, there will be an increase in engine rpm and the rotation of governor weights (5) will get faster. This will move valve (9) up. This stops oil flow from the lower passage (12), and oil pressure above piston (11) goes out through the top, around valve (9). Now, the pressure between the sleeve (13) and piston (11) pushes the piston and pin (17) up. This causes a reduction in the amount of fuel to the engine. Engine rpm goes down until the centrifugal force (rotation) of the governor weights is in balance with the force of the governor spring. When these two forces are in balance, the engine will run at the desired rpm (governed rpm).

When engine rpm is at Low Idle, a spring-loaded plunger in lever assembly (3) comes in contact with a shoulder on the adjustment screw for low idle. To stop the engine, push throttle lever to vertical position. This will let the spring-loaded plunger move over the shoulder on the low idle adjustment screw and move the fuel rack to the fuel closed position. With no fuel to the engine cylinders, the engine will stop.

The governor oil pump supplies oil to the valve (9) to increase governor power and response. Oil from the governor oil pump gives lubrication to the governor weight support (with gear), thrust bearing (8), and drive gear bearing. The other parts of the governor get lubrication from "splash-lubrication" (oil thrown by other parts). Oil from the governor runs down into the housing for the fuel injection pumps.

Fuel Ratio Control

Fuel Ratio Control (Engine Stopped)
(1) Inlet air chamber. (2) Valve. (3) Diaphragm assembly. (4) Oil drains. (5) Pressure oil chamber. (6) Large oil passages. (7) Oil inlet. (8) Small oil passages. (9) Oil outlet. (10) Fuel rack linkage. (11) Valve.

With the engine stopped, valve (11) is in the fully extended position. The movement of fuel rack linkage (10) is not limited by valve (11).

When the engine is started, oil flows through oil inlet (7) into pressure oil chamber (5). From chamber (5) the oil flows through large oil passages (6), inside valve (11), and out small oil passages (8) to oil outlet (9).

A hose assembly connects inlet air chamber (1) to the inlet air system. As the inlet air pressure increases, it causes diaphragm assembly (3) to move down. Valve (2), that is part of the diaphragm assembly, closes large and small oil passages (6 and 8). When these passages are closed, oil pressure increases in chamber (5). This increase in oil pressure moves valve (11) up. The control is now ready for operation.

When the governor control is moved to increase fuel to the engine, valve (11) limits the movement of fuel rack linkage (10) in the "Fuel On" direction. The oil in chamber (5) acts as a restriction to the movement of valve (11) until inlet air pressure increases.

Fuel Ratio Control (Ready For Operation)
(1) Inlet air chamber. (2) Valve. (5) Pressure oil chamber. (6) Large oil passages. (8) Small oil passages. (11) Valve.

As the inlet air pressure increases, valve (2) moves down and lets oil from chamber (5) drain through large oil passages (6) and out through oil drains (4). This lets valve (11) move down so fuel rack linkage (10) can move gradually to increase fuel to the engine. The control is designed not to let the fuel increase until the air pressure in the inlet manifold is high enough for complete combustion. It prevents large amounts of exhaust smoke caused by an air/fuel mixture with too much fuel.

The control movements take a very short time. No change in engine acceleration (rate at which speed increases) can be felt.

Fuel Ratio Control (Increase In Inlet Air Pressure)
(2) Valve. (4) Oil drains. (5) Pressure oil chamber. (10) Fuel rack linkage. 11) Valve.

Automatic Timing Advance Unit

Automatic Timing Advance Unit
(1) Flange. (2) Weight. (3) Springs. (4) Slide. (5) Drive gear. (6) Camshaft.

The automatic timing advance unit is installed on the front of the camshaft (6) for the fuel injection pump and is gear driven through the timing gears. The drive gear (5) for the fuel injection pump is connected to camshaft (6) through a system of weights (2), springs (3), slides (4) and flange (1). Each one of the two slides (4) is held on gear (5) by a pin. The two weights (2) can move in guides inside flange (1) and over slides (4), but the notch for the slide in each weight is at an angle with the guides for the weight in the flange. As centrifugal force (rotation) moves the weights away from the center, against springs (3), the guides in the flange and the slides on the gear make the flange turn a small amount in relation to the gear. Since the flange is connected to the camshaft for the fuel injection pump, the fuel injection timing is also changed. No adjustment can be made in the timing advance unit.

Air Inlet And Exhaust System

The air inlet and exhaust system components are: air cleaner, turbocharger, inlet manifold (passages inside the cylinder block), cylinder head, valves and valve system components, and exhaust manifold.

Air Inlet And Exhaust System
(1) Exhaust manifold. (2) Pipe to inlet manifold. (3) Engine cylinders. (4) Air inlet. (5) Turbocharger compressor wheel. (6) Turbocharger turbine wheel. (7) Exhaust outlet.

Air Inlet And Exhaust System
(1) To exhaust manifold. (2) Pipe to inlet manifold. (4) Air inlet. (7) Exhaust outlet. (8) Turbocharger. (9) Cross pipe.

Clean inlet air from the air cleaner is pulled through air inlet (4) of the turbocharger by the turning of compressor wheel (5). The compressor wheel causes a compression of the air. The air then goes through pipe to inlet manifold (2) of the engine. When the intake valves open, the air goes into engine cylinders (3) and is mixed with the fuel for combustion. When the exhaust valves open, the exhaust gases go out of the engine cylinders and into exhaust manifold (1). From exhaust manifold, the exhaust gases go through the blades of turbine wheel (6). This causes the turbine wheel and compressor wheel to turn. The exhaust gases then go out exhaust outlet (7) of the turbocharger.

Air Flow Schematic
(1) Exhaust manifold. (2) Pipe to inlet manifold. (4) Air inlet. (7) Exhaust outlet. (8) Turbocharger.

Aftercooler

The aftercooler cools the air coming out of the turbocharger before it goes into the inlet manifold. The purpose of this is to make the air going into the combustion chambers more dense. The more dense the air is, the more fuel the engine can burn efficiently. This gives the engine more power.

Turbocharger

The turbocharger is installed at the top, rear of the engine on a cross pipe for the two exhaust manifolds. All the exhaust gases from the engine go through the turbocharger.

The exhaust gases go through the blades of turbine wheel (6). This causes the turbine wheel and compressor wheel (5) to turn, which causes a compression of the inlet air.

When the load on the engine is increased, more fuel is put into the engine. This makes more exhaust gases and will cause the turbine and compressor wheels of the turbocharger to turn faster. As the turbocharger turns faster, it gives more inlet air and makes it possible for the engine to burn more fuel and will give the engine more power.

Turbocharger
(1) Turbocharger. (2) Cross pipes. (3) To exhaust manifold.

Turbocharger
(4) Air inlet. (5) Compressor wheel. (6) Turbine wheel. (7) Exhaust outlet. (8) Compressor housing. (9) Oil inlet port. (10) Thrust collar. (11) Thrust bearing. (12) Turbine housing. (13) Spacer. (14) Air outlet. (15) Oil outlet port. (16) Bearing. (17) Coolant passages. (18) Bearing. (19) Exhaust inlet.

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.

Bearings (16 and 18) for the turbocharger use engine oil under pressure for lubrication. The oil comes in through the oil inlet port (9) and goes through passages in the center section for lubrication of the bearings. Oil from the turbocharger goes out through the oil outlet port (15) in the bottom of the center section and goes back to the engine lubrication system.

This type turbocharger has coolant passages (17) around the bearings to cool the oil in these areas. Engine coolant is taken from the top, rear of the engine and sent into the rear of the turbocharger (center section). The coolant flows through the passages around the bearings, and out the front of the turbocharger (center section) back to the radiator top tank.

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.

Valve System Components

The valve system components control the flow of inlet air and exhaust gases into and out of the cylinders during engine operation.

The crankshaft gear drives the camshaft gear. The camshaft gear must be timed to the crankshaft gear to get the correct relation between piston and valve movement.

The camshaft has two cams for each cylinder. One cam controls the exhaust valves, the other controls the intake valves.

Valve System Components
(1) Intake bridge. (2) Intake rocker arm. (3) Push rod. (4) R Rotocoil. (5) Valve spring. (6) Valve guide. (7) Intake valves. (8) Lifter. (9) Camshaft.

As the camshaft turns, the lobes of camshaft (9) cause lifters (8) to go up and down. This movement makes push rods (3) move rocker arms (2). Movement of the rocker arms makes the bridges move up and down on dowels mounted in the cylinder head. The bridges let one rocker arm open and close two valves (intake or exhaust). There are two intake and two exhaust valves for each cylinder.

Rotocoils (4) cause the valves to turn while the engine is running. The rotation of the valves keeps the deposit of carbon on the valves to a minimum and gives the valves longer service life.

Valve springs (5) cause the valves to close when the lifters move down.

Valve System Components (Typical Illustration)
(1) Intake bridge. (2) Intake rocker arm. (7) Intake valves. (10) Exhaust rocker arm. (11) Exhaust bridge. (12) Exhaust valves.

Lubrication System

Engine Oil Flow During Normal Operation
(1) To rocker arm shaft. (2) To gear bearings in flywheel housing. (3) To fuel injection pump housing, governor and fuel ratio control. (4) Rocker arm shaft. (5) To valve lifters. (6) Camshaft bearings. (7) Piston cooling tubes. (8) Left oil manifold. (9) To timing gear housing. (10) To idler gear shaft. (11) Right oil manifold. (12) Main bearings. (13) Oil supply line to filters on left side of block. (14) Oil filters. (15) Oil supply line to turbocharger. (16) Oil bypass line to right manifold in cylinder block. (17) Filter bypass valve. (18) Cooler bypass line. (19) Cooler bypass valve. (20) Turbocharger. (21) Engine oil cooler. (22) Oil return line from turbocharger. (23) Suction line for scavenge oil pump. (24) Scavenge oil pump. (25) Oil pan. (26) Oil pump suction line. (27) Oil pump.

Oil Flow Through The Oil Cooler, Oil Filters And The Engine

Lubrication System Components (Right Side Of Engine)
(13) Oil supply line to filters. (21) Engine oil cooler. (25) Oil pan. (28) Transmission oil cooler.

Lubrication System Components (Left Side of Engine)
(14) Oil filters. (25) Oil pan.

With the engine warm (normal operation), oil comes from oil pan (25) through a suction bell on suction line (26) to oil pump (27). The oil pump sends warm oil, under pressure, to engine oil cooler (21), through an outside oil supply line (13) that connects to the oil pan, and through a line inside the oil pan to the other side of the cylinder block. The oil now flows through oil passage in the filter base, through the oil filters and back to oil manifold (8) on left side of engine.

From oil manifold (8) in left side of the cylinder block, oil is sent to right oil manifold (11) through drilled passages in the cylinder block that connect main bearings (12) and camshaft bearings (6). Oil goes through drilled holes in the crankshaft to give lubrication to the connecting rod bearings. A small amount of oil is sent through tubes (7) to make the pistons cooler. Oil goes through grooves in the bores for the front and rear camshaft bearings and then into passages (5) that connect the valve lifter bores. These passages give oil under pressure for the lubrication of the valve lifters.

Oil is sent through passages (1), on front and rear, to rocker arm shafts (4) on both cylinder heads. Holes in the rocker arm shafts let the oil give lubrication to the valve system components in the cylinder head.

The fuel injection pump and governor gets oil from passage (3) in the cylinder block. There is a small gear pump between the injection pump housing and the governor. This pump sends oil under pressure for the hydraulic operation of the hydra-mechanical governor. The automatic timing advance unit gets oil from the injection pump housing, through the camshaft for the fuel injection pumps.

The idler gear bores get oil from passages (10) in the cylinder block, oil then goes through the shaft for the bearings of the idler gears installed on the front and rear of the cylinder block.

The rear gear bearings get oil from an external line (2) that connects to the flywheel housing.

Pressure oil is sent to the turbocharger bearings through external supply line (15). The oil goes out of turbocharger (20) back to the top of flywheel housing through oil return line (22). This oil flows over the gears in flywheel housing to give them lubrication and then goes back to oil pan (25).

There is a bypass valve in the oil pump. This bypass valve controls the maximum pressure of the oil from the oil pump. The oil pump can put more oil into the system than is needed. When there is more oil than needed, the oil pressure goes up and the bypass valve will open. This allows the oil that is not needed to go back to the inlet oil passage of the oil pump.

After the oil for lubrication has done its work, it goes back to the engine oil pan.

This lubrication system also has a scavenge oil pump. Scavenge oil pump (24) is connected to and is driven by main oil pump (27). Oil is taken from the small reservoir at the rear of the oil pan through suction line (23) and is pumped into main reservoir at front of oil pan (25).

When the front of vehicle is tilted up on a long slope, the oil that returns to oil pan (after engine lubrication) will accumulate at the rear of the oil pan. This can let the main reservoir level decrease enough to cause oil pump (27) to not have any output.

Scavenge oil pump (24) is in operation all the time that the engine is in operation. The only purpose of the scavenge oil pump is to take the extra oil from the rear of the oil pan and put it back into the main reservoir at the front of the oil pan.

Flow Of Oil (Engine Cold)
(11) Right oil manifold. (13) Oil supply line to filters. (14) Oil filters. (15) Oil supply line to turbocharger. (16) Oil bypass line to right manifold in cylinder block. (17) Filter bypass valve. (18) Cooler bypass line. (19) Cooler bypass valve. (20) Turbocharger. (21) Engine oil cooler. (22) Oil return line from turbocharger. (23) Suction line for scavenge oil pump. (24) Scavenge oil pump. (25) Oil pan. (26) Oil pump suction line. (27) Oil pump.

When the engine is cold (starting condition), bypass valves (17 and 19) open because cold oil with high viscosity causes a restriction to the oil flow through oil cooler (21) and oil filters (14). With the bypass valves open, oil flows directly from the oil pump to right oil manifold (11) through bypass lines (16 and 18). This will give immediate lubrication to all components until engine becomes warm.

When the oil gets warm, the pressure difference in the bypass valves decreases and the bypass valves close. Now there is a normal flow through oil cooler (21) and oil filters (14).

The bypass valves will also open when there is a restriction in the oil cooler or oil filter. This action does not let an oil cooler or oil filter with a restriction prevent the lubrication of the engine.

Cooling System

Radiator Cooled System Schematic
(1) Radiator. (2) Coolant outlet line from turbocharger. (3) Outlet from temperature regulator housing to radiator top (one on each side at front of engine). (4) Temperature regulator housing (both sides). (5) Cylinder heads. (6) Turbocharger. (7) Cylinder block. (8) Coolant outlet line from turbocharger to radiator. (9) Water pump. (10) Engine oil cooler. (11) Transmission oil cooler. (12) Hydraulic oil cooler.

This engine has a pressure type cooling system. A pressure type cooling system gives two advantages. The first advantage is that the cooling system can have safe operation at a temperature that is higher than the normal boiling (steam) point of water. The second advantage is that this type system prevents cavitation (the sudden making of low pressure bubbles in liquids by mechanical forces) in the water pump. With this type system, it is more difficult for an air or steam pocket to be made in the cooling system.

In normal operation (engine warm), water pump (9) sends coolant through engine oil cooler (10), transmission oil cooler (11) and hydraulic oil cooler (12). Water from the engine oil cooler flows into the block while water from the other two oil coolers flows into the inlet of the water pump. Coolant moves through cylinder block (7) to both cylinder heads (5), and then goes to the housings for the temperature regulators (4). The temperature regulators are open and most of the coolant goes through the outlets to radiator (1). The coolant is made cooler as it moves through the radiator. When the coolant gets to the bottom of the radiator, it goes to water pump (9).

NOTE: The water temperature regulator is an important part of the cooling system. It divides coolant flow between radiator (6) and radiator bypass lines (15) as necessary to maintain the correct temperature. If the water temperature regulator is not installed in the system, there is no mechanical control, and most of the coolant will take the path of least resistance through the bypass. This will cause the engine to overheat in hot weather. In cold weather, even the small amount of coolant that goes through the radiator is too much, and the engine will not get to normal operation temperatures.

When the engine is cold, the water temperature regulator is closed, and the coolant is stopped from going to the radiator. The coolant goes from the temperature regulator housing (5) back to the water pump (13) through radiator bypass lines (15).

A small amount of coolant also moves constantly through line (1) that connects from the water pump outlet to the center section of turbocharger (2). The coolant flows through passages around the turbocharger bearings and then out the front of the center section. The coolant then flows through line (3) back to the top center of the cylinder block.

Coolant Conditioner

Some conditions of operation have been found to cause pitting (small holes in the metal surface) from corrosion or cavitation erosion (wear caused by air bubbles in the coolant) on the outer surface of the cylinder liners and the inner surface of the cylinder block next to the liners. The addition of a corrosion inhibitor (a chemical that gives a reduction of pitting) is required to keep this type of damage to a minimum.

Coolant Conditioner
(1) Base (part of regulator housing). (2) Element. (3) Valve

The "spin-on" coolant conditioner element (2), similar to the fuel filter and oil filter elements, fastens to a base (1) that is part of the regulator housing on the left front of the engine. Coolant flows from the water pump through the cylinder head to the base, through the element and back through bypass line to water pump inlet. There is a constant flow of coolant through the element when valve (3) is in the ON position.

The element has a specific amount of inhibitor for acceptable cooling system protection. As coolant flows through the element, the corrosion inhibitor, which is a dry material, dissolves (goes into solution) and mixes to the correct concentration. Two basic types of elements are used for the cooling system, and they are called the "Precharge" and the "Maintenance" elements. Each type of element has a specific use and must be used correctly to get the necessary concentration for cooling system protection. The elements also contain a filter and should be left in the system so coolant flows through it after the conditioner material is dissolved.

The "Precharge" element has more than the normal amount of inhibitor, and is used when a system is first filled with new coolant. This element has to add enough inhibitor to bring the complete cooling system up to the correct concentration.

The "Maintenance" elements have a normal amount of inhibitor and are installed at the first change interval and provide enough inhibitor to keep the corrosion protection at an acceptable level. After the first change period, only "Maintenance" elements are installed at specified intervals to give protection to the cooling system.

Basic Block

Cylinder Block, Liners And Heads

The cylinders in the left side of the block make an angle of 65 degrees with the cylinders in the right side of the block. The main bearing caps are fastened to the block with two bolts per cap.

The cylinder liners can be removed for replacement. The top surface of the block is the seat for the cylinder liner flange. Engine coolant flows around the liners to keep them cool. Three O-ring seals around the bottom of the liner make a seal between the liner and the block.

The engine has a single, cast head on each side. Four vertical valves (two intake and two exhaust), controlled by a pushrod valve system, are used per each cylinder. The opening for the fuel nozzles is located between the four valves. Series ports (passages) are used for both intake and exhaust valves.

A steel spacer plate is used between the cylinder head and block. A thin gasket is used between the (plate and liners) and the block to seal water and oil. A thick gasket of metal and asbestos is used between the plate and the head to seal combustion gases, water and oil.

The size of the pushrod openings through the head permits the removal of the valve lifters with the head installed.

Valve guides without shoulders are pressed into the cylinder head.

Pistons, Rings And Connecting Rods

The aluminum pistons have three rings; two compression rings and one oil ring. All rings are located above the piston pin bore. The two compression rings are of the Keystone type, which have a tapered shape. The seat for the rings is an iron band that is cast into the piston. The action of the rings in the piston groove, which is also tapered, helps prevent seizure of the rings caused by too much carbon deposits. The oil ring is a standard (conventional) type. Oil returns to the crankcase through openings in the oil ring groove.

The piston pin is held in place by two snap rings that fit in grooves in the pin bore of the piston. The connecting rod has a taper on the pin bore end. This gives the rod and piston more strength in the areas with the most load.

Oil spray tubes, located on the cylinder block main webs, direct oil to cool and give lubrication to the piston components and cylinder walls.

Crankshaft

The crankshaft changes the combustion forces in the cylinder into usable rotating torque which powers the machine. Vibration, caused by combustion impacts along the crankshaft, is kept small by a vibration damper on the front of the crankshaft.

There is a gear at the front of the crankshaft to drive the timing gears and the oil pump. Seals and wear sleeves are used at both ends of the crankshaft for easy replacement and a reduction of maintenance cost. Pressure oil is supplied to all bearing surfaces through drilled holes in the crankshaft. The crankshaft is supported by five main bearings. A thrust plate at either side of the center main bearing controls the end play of the crankshaft.

Camshaft

The engine has a single camshaft that is driven at the front end. It is supported by five bearings. As the camshaft turns, each cam (lobe) (through the action of valve systems components) moves either two exhaust valves or two intake valves for each cylinder. The camshaft gear must be timed to the crankshaft gear. The relation of the cam (lobes) to the camshaft gear cause the valves in each cylinder to open and close at the correct time.

Vibration Damper

Cross Section Of A Vibration Damper
(1) Flywheel ring. (2) Rubber ring. (3) Inner hub.

The twisting of the crankshaft, due to the regular power impacts along its length, is called twisting (torsional) vibration. The vibration damper is installed on the front end of the crankshaft. It is used for reduction of torsional vibrations and stops the vibration from building up to amounts that cause damage.

The damper is made of a flywheel ring (1) connected to an inner hub (3) by a rubber ring (2). The rubber makes a flexible coupling between the flywheel ring and the inner hub.

Electrical System

The electrical system can have three separate circuits: the charging circuit, the starting circuit and the low amperage circuit. Some of the electrical system components are used in more than one circuit. The battery (batteries), circuit breaker, ammeter, cables and wires from the battery are all common in each of the circuits.

The charging circuit is in operation when the engine is running. An alternator makes electricity for the charging circuit. A voltage regulator in the circuit controls the electrical output to keep the battery at full charge.

The starting circuit is in operation only when the start switch is activated.

The electrical systems include a Diagnostic Connector which is used when testing the charging and starting circuits.

The low amperage circuit and the charging circuit are both connected to the same side of the ammeter. The starting circuit connects to the opposite side of the ammeter.

Charging System Components

Alternator (3T6352, 4N3986 And 3E7577)

The alternator is driven by V-belts from the crankshaft pulley. This alternator is a three phase, self-rectifying charging unit, and the regulator is part of the alternator. There is a 3T6352 Alternator with 35 amp output, 4N3986 Alternator with a 60 amp output and a 3E7577 Alternator with a 75 amp output.

This alternator design has no need for slip rings or brushes, and the only part that has movement is the rotor assembly. All conductors that carry current are stationary. The conductors are the field winding, stator windings, six rectifying diodes and the regulator circuit components.

The rotor assembly has many magnetic poles like fingers with air space between each opposite pole. The poles have residual magnetism (like permanent magnets) that produce a small amount of magnet-like lines of force (magnetic field) between the poles. As the rotor assembly begins to turn between the field winding and the stator windings, a small amount of alternating current (AC) is produced in the stator windings from the small magnetic lines of force made by the residual magnetism of the poles. This AC current is changed to direct current (DC) when it passes through the diodes of the rectifier bridge. Most of this current goes to charge the battery and to supply the low amperage circuit, and the remainder is sent on to the field windings. The DC current flow through the field windings (wires around an iron core) now increases the strength of the magnetic lines of force. These stronger lines of force now increase the amount of AC current produced in the stator windings. The increased speed of the rotor assembly also increases the current and voltage output of the alternator.

Alternator
(1) Regulator. (2) Roller bearing. (3) Stator winding. (4) Ball bearing. (5) Rectifier bridge. (6) Field winding. (7) Rotor assembly. (8) Fan.

Alternator (7N9720 And 100-5046)

The alternator is driven by two V-belts. It has a three phase full wave rectified output. The alternator is brushless.

Alternator
(1) Winding. (2) Stator. (3) Rectifier. (4) Rotor. (5) Non-magnetic ring.

The rotor (4) and the bearings are the only moving parts. There is a 7N9720 Alternator with a 35 amp output and a 100-5046 Alternator with a 50 amp output.

The main parts of the alternator are the stator (2) which has three phase windings, the rectifier (3) which changes the three phase AC to DC and provides excitation current.

The field winding (1) is a stationary coil assembly that provides the magnetic field.

The rotor provides the north and south poles which cut the magnetic field between the stationary field winding and the stator (2). North and south poles are separated magnetically by a non-magnetic ring (5).

Alternator (9G4574 And 100-5045)

This alternator has three-phase, full-wave rectified output. It is brushless. The rotor and bearings are the only moving parts. There is a 9G4574 Alternator with 35 amp output and a 100-5045 Alternator with a 50 amp output.

Alternator
(1) Fan. (2) Front frame assembly. (3) Stator assembly. (4) Rotor assembly. (5) Field winding (coil assembly). (6) Regulator assembly. (7) Condenser (suppression capacitor). (8) Rectifier assembly. (9) Rear frame assembly.

When the engine is started and the rotor turns inside the stator windings, three-phase alternating current (AC) and rapidly rising voltage is generated.

A small amount of alternating current (AC) is changed (rectified) to pulsating direct current (DC) by the exciter diodes on the rectifier assembly. Output current from these diodes adds to the initial current which flows through the rotor field windings from residual magnetism. This will make the rotor a stronger magnet and cause the alternator to become activated automatically. As rotor speed, current and voltages increase, the rotor field current increases enough until the alternator becomes fully activated.

The main battery charging current is charged (rectified) from AC to DC by the other positive and negative diodes in the rectifier and pack (main output diodes) which operate in a full wave linkage recitifer circuit.

Alternator output is controlled by a regulator, which is inside the alternator rear frame.

Alternator Regulator (3T6354)

The voltage regulator is a solid state (transistor, stationary parts) electronic switch. It feels the voltage in the system and switches on and off many times a second to control the field current (DC current to the field windings) for the alternator to make the needed voltage output.

Alternator Regulator (9G7567)

The voltage regulator is an electronic switch. It feels the voltage in the system and gives the necessary field current (current to the field windings of the alternator) for the alternator to make the needed voltage. The voltage regulator controls the field current to the alternator by switching on and off many times a second.

Alternator Regulator (7T2798)

The regulator is fastened to the alternator by two different methods. One method fastens the regulator to the top, rear of alternator. With the other method the regulator is fastened separately by use of a wire and a connector that goes into the alternator.

The voltage regulator is a solid state (transistor, no moving parts) electronic switch. It feels the voltage in the system and gives the necessary field current (current to the field windings of the alternator) for the alternator to make the needed voltage. The voltage regulator controls the field current to the alternator by switching on and off many times a second. There is no voltage adjustment for this regulator.

Starting System Components

Solenoid

A solenoid is an electromagnetic switch that does two basic operations:

a. Closes the high current starter motor circuit with a low current start switch circuit.

b. Engages the starter motor pinion with the ring gear.

Typical Solenoid Schematic

The solenoid has windings (one or two sets) around a hollow cylinder. There is a plunger (core) with a spring load inside the cylinder that can move forward and backward. When the start switch is closed and electricity is sent through the windings, a magnetic field is made that pulls the plunger forward in the cylinder. This moves the shift lever (connected to the rear of the plunger) to engage the pinion drive gear with the ring gear. The front end of the plunger then makes contact across the battery and motor terminals of the solenoid, and the starter motor begins to turn the flywheel of the engine.

When the start switch is opened, current no longer flows through the windings. The spring now pushes the plunger back to the original position, and, at the same time, moves the pinion gear away from the flywheel.

When two sets of windings in the solenoid are used, they are called the hold-in winding and the pull-in winding. Both have the same number of turns around the cylinder, but the pull-in winding uses a larger diameter wire to produce a greater magnetic field. When the start switch is closed, part of the current flows from the battery through the hold-in windings, and the rest flows through the pull-in windings to motor terminal, then through the motor to ground. When the solenoid is fully activated (connection across battery and motor terminal is complete), current is shut off through the pull-in windings. Now only the smaller hold-in windings are in operation for the extended period of time it takes to start the engine. The solenoid will now take less current from the battery, and heat made by the solenoid will be kept at an acceptable level.

Starter Motor

The starter motor is used to turn the engine flywheel fast enough to get the engine running.

Starter Motor
(1) Field. (2) Solenoid. (3) Clutch. (4) Pinion. (5) Commutator. (6) Brush assembly. (7) Armature.

The starter motor has a solenoid. When the start switch is turned to the START position, the solenoid will be activated electrically. The solenoid core will now move to push the starter pinion, by a mechanical linkage, to engage with the ring gear on the flywheel of the engine. The starter pinion will engage with the ring gear before the electric contacts in the solenoid close the circuit between the battery and the starter motor. When the circuit between the battery and the starter motor is complete, the pinion will turn the engine flywheel. A clutch gives protection for the starter motor so that the engine, when it starts to run, can not turn the starter motor too fast. When the start switch is released, the starter pinion will move away from the flywheel ring gear.

Magnetic Switch

A magnetic switch (relay) is used sometimes for the starter solenoid circuit. Its operation electrically is the same as the solenoid. Its function is to reduce the current load on the start switch and control current to the starter solenoid.

Rack Shutoff Solenoid

A shutoff solenoid changes electrical input into mechanical output. The shutoff solenoid is used to move the fuel rack to a no fuel position. This stops the engine. The shutoff solenoid is activated by a remote manual control switch.

Rack Shutoff Solenoid (Typical Example)

Other Components

Circuit Breaker

The circuit breaker is a switch that opens the battery circuit if the current in the electrical system goes higher than the rating of the circuit breaker.

A heat activated metal disc with a contact point completes the electric circuit through the circuit breaker. If the current in the electrical system gets too high, it causes the metal disc to get hot. This heat causes a distortion of the metal disc which opens the contacts and breaks the circuit. A circuit breaker that is open can be reset after it cools. Push the reset button to close the contacts and reset the circuit breaker.

Circuit Breaker Schematic
(1) Reset button. (2) Disc in open position. (3) Contacts. (4) Disc. (5) Battery circuit terminals.