Introduction

NOTE: For Specifications with illustrations, make reference to SPECIFICATIONS for 3500 NATURAL GAS ENGINES, Form No. SENR3103. If the Specifications in Form SENR3103 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 given in the book with the latest date.

Engine Design

Bore ... 170 mm (6.7 in.)

Stroke ... 190 mm (7.5 in.)

Displacement:

3512 ... 51.8 liter (3158 cu.in.)

3516 ... 69.1 liter (4210 cu.in.)

Number and Arrangement of Cylinders:

3512 ... 60° V-12

3516 ... 60° V-16

Valves per Cylinder ... 4

Valve Setting:

Intake ... 0.51 mm (.020 in.)

Exhaust ... 1.02 mm (.040 in.)

Compresstion Ratio ... 10:1

Type of Combustion ... Spark Ignited

Firing Order:

3512 ... 1-12-9-4-5-8-11-2-3-10-7-6

3516 ... 1-2-5-6-3-4-9-10-15-16-11-12-13-14-7-8

Direction of Crankshaft Rotation (when seen from flywheel end):

SAE Standard Rotation ... 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 right side. No. 2 cylinder is the front cylinder on the left side.

Ignition System

The ignition system has five basic components: a magneto, ignition transformers for each cylinder, wiring harness, spark plugs and instrument panel.

COMPONENT LOCATION
1. Ignition transformer. 2. Wiring harness. 3. Magneto.

Fairbanks Morse Magneto

Ignition power is generated in the alternator section (1) of the magneto. This section consists of an eight pole permanent magnet rotor in combination with a four pole stator. The output from the alternator section is three phase full wave rectified and flows into the main storage capacitor (3) on each power pulse. A zener diode located in the end cap with the capacitor is the regulator of the capacitor voltage for proper ignition.

The trigger rotor (5) is timed to the distributor rotor (2) which is timed to the engine. The rotation of the trigger rotor (5) in the pulser coil (4) generates properly timed pulses in two series connected trigger coils. The coils energize the ignition triggering circuit by discharging an auxiliary supply capacitor through an auxiliary trigger silicon controlled rectifier (SCR) switch.

The voltage generated by both the alternator section and the trigger coil combine and feed into a single triggering circuit that ignites all cylinders. Distribution of the voltage to the proper cylinder is accomplished by the rotation of the distributor rotor which operates as a rotating transformer. It performs no ignition timing, but by mechanical position selects the proper cylinder to which the ignition triggering signal is coupled. The distributor rotor and shaft rotating at engine camshaft speed is positioned so that pulsed triggering energy is transferred from a single coil surrounding the distributor and shaft to a selected coil on a multicoil stator assembly. By this selection, the proper SCR switch ignites the correct cylinder spark plug.

CUTAWAY VIEW OF SOLID STATE MAGNETO (FAIRBANKS MORSE)
1. Alternator section. 2. Distributor rotor. 3. Capacitor. 4. Pulser coil. 5. Pulser (trigger) rotor.

Altronic Magneto

ALTRONIC MAGNETO
1. Alternator section. 2. Electronic firing section.

The Altronic magneto is made of a permanent magnet alternator section (1) and brakerless electronic firing circuit (2). There are no brushes or distributor contacts.

The engine turns magneto drive tang (7). The drive tang turns alternator (3), speed reduction gears (5) and rotating timer arm (9). As the alternator is turned it provides power to charge energy storage capacitor (8). There are separate pick-up coils (6) and SCR (silicon controlled rectifier) solid state switches (10) for each engine cylinder. The timer arm passes over pick-up coils (6) in sequence. The pick-up coils turn on solid state switches (10) which release the energy stored in capacitor (8). This energy leaves the magneto through output connector (11). The energy travels through the engine wiring harness to the ignition coils where it is transformed to the high voltage needed to fire the spark plugs.

CROSS SECTION OF ALTRONIC MAGNETO
3. Alternator. 4. Vent. 5. Speed reduction gears. 6. Pick-up coil. 7. Drive tang. 8. Energy storage capacitor. 9. Rotating timer arm. 10. SCR solid state switch. 11. Output connector.

Wiring Diagrams

3512 ENGINES WITH FAIRBANKS MORSE MAGNETO
Firing Order 1-12-9-4-5-8-11-2-3-10-7-6
Pin Order A-B-C-D-E-F-J-N-P-R-S-T

3516 ENGINES WITH FAIRBANKS MORSE MAGNETO
Firing Order 1-2-5-6-3-4-9-10-15-16-11-12-13-14-7-8
Pin Order A-B-C-D-E-F-J-N-P-R-S-T-G-K-L-M

3512 ENGINES WITH ALTRONIC MAGNETO
Firing Order 1-12-9-4-5-8-11-2-3-10-7-6
Pin Order A-M-L-K-J-I-H-F-E-D-C-B

3516 ENGINES WITH ALTRONIC MAGNETO
Firing Order 1-2-5-6-3-4-9-10-15-16-11-12-13-14-7-8
Pin Order A-T-S-R-P-N-M-L-K-J-H-F-E-D-C-B

Fuel, Air Inlet And Exhaust Systems

FUEL, AIR INLET AND EXHAUST SYSTEM COMPONENTS (3516 Shown)
1. Carburetor. 2. Aftercooler. 3. Air cleaners. 4. Turbocharger. 5. Balance line between carburetor and gas pressure regulator. 6. Inlet line to carburetor. 7. Exhaust elbow. 8. Exhaust bypass valve. 9. Gas pressure regulator.

The components of the fuel, air inlet and exhaust system control the quality, temperature and amount of fuel/air mixture available for combustion. These components are the air cleaner, turbochargers, aftercooler (air or watercooled) gas pressure regulator, carburetor, turbulence chamber, distribution channel, an inlet manifold and the intake and exhaust valve mechanisms. Two camshafts one on each side of the block, control the movement of the valve system components.

The inlet manifold is a series of elbows that connect the distribution channel (located in the middle of the engine) to the inlet ports (passages) of the cylinder heads.

There is a separate air cleaner, turbocharger and watercooled exhaust manifold on each side of the engine. The watercooled exhaust manifolds provide a "gas tight" connection from the cylinder heads to the turbochargers. The manifolds also serve as a water manifold by collecting coolant from each cylinder head and directing it to the regulator housing.

Some installations have a shutoff valve in the gas supply line. The valve is electrically operated from the ignition system and can also be manually operated to stop the engine. After the engine is stopped, manual resetting is needed to start the engine.

Engine installations using Propane gas have the same system components. In addition, a Thermac valve for reduction of pressure, and a load adjusting valve between the gas pressure regulator and carburetor are used.

Fuel System

FUEL SYSTEM
1. Carburetor. 2. Gas supply line to carburetor. 3. Balance line from gas pressure regulator vent to inlet air pressure at carburetor. 4. Gas pressure regulator.

From the main gas supply, fuel enters gas pressure regulator (4) and then goes to the carburetor. The carburetor controls the amount and quality of air-fuel mixture that the engine is allowed to use.

Turbocharged engines have a balance line (3) connected between the carburetor air inlet and the atmospheric vent of gas pressure regulator (4). Balance line (3) directs carburetor inlet air pressure to the upper side of the regulator diaphragm to control gas pressure at the carburetor. The inlet air pressure added to the spring force on the diaphragm, makes sure that gas pressure to the carburetor will always be greater than inlet air pressure, regardless of load conditions. For example, under engine acceleration, the air pressure increases. A small amount of the increased air pressure is directed to gas pressure regulator (4) and moves the control to increase supply gas pressure to the carburetor. By this method, the correct differential pressure between the gas pressure regulator and the carburetor air inlet is controlled. A turbocharged engine will not develop full power with the balance line disconnected.

Gas Pressure Regulator

REGULATOR OPERATION
1. Spring side chamber. 2. Adjustment screw. 3. Spring. 4. Outlet. 5. Valve disc. 6. Main orifice. 7. Main diagphragm. 8. Lever side chamber. 9. Lever. 10. Pin. 11. Valve stem. 12. Inlet.

Gas goes through the inlet (12), main orifice (6), valve disc (5), and the outlet (4). Outlet pressure is felt in the chamber (8) on the lever side of diaphragm (7).

As gas pressure in chamber (8) becomes higher than the force of the diaphragm spring (3) and air pressure in the spring side chamber (1) (atmosphere on naturally aspirated engines; turbocharger boost on turbocharged engines), the diaphragm is pushed against the spring. This turns the lever (9) at pin (10) and causes the valve stem (11) to move the valve disc to close the inlet orifice.

With the inlet orifice closed, gas is pulled from the lever side of chamber (8) through the outlet. This gives a reduction of pressure in the chamber (8). As a result the pressure becomes less than pressure in the spring side chamber. Force of spring and air pressure in the chamber on the spring side moves the diaphragm toward the lever. This turns (pivots) the lever and opens the valve disc, permitting additional gas flow to the carburetor.

When the pressure on either side of the diaphragm is the same, the regulator sends gas to the carburetor at a set amount.

Carburetor

NOTE: Operation of a carburetor with a single air valve is described. Operation of carburetors with dual air valves is the same.

Atmospheric air goes through the air cleaners to the air horn of the carburetor on naturally aspirated engines. On turbocharged engines, the air is pulled through the air cleaners to the turbochargers and then pushed through an aftercooler core to the carburetor air horn. In the air horn, air goes around air valve body (5) and pushes on diaphragm (2) and then goes down through the center of air valve (4), around gas inlet body (6), by throttle plate (10) into the engine.

CARBURETOR OPERATION (3512 Carburetor Shown)
1. Cover. 2. Diaphragm. 3. Spring. 4. Air valve. 5. Air valve body. 6. Gas inlet body. 7. Gas valve. 8. Power screw. 9. Plate. 10. Throttle plate.

Fuel goes into the carburetor at the center, through gas inlet body (6). The fuel flows out the top of gas inlet body (6) to mix with the air and then flows around gas inlet body (6), by throttle plate (10) into the engine. Gas valve (7) is connected to air valve (4) and is designed to let the correct amount of fuel into the carburetor at any opening of the air valve between idle and full load. Thus, at low idle, gas valve (7) keeps fuel flow to a minimum and gives a lean air fuel mixture. As the engine speed and load is increased, gas valve (7) lets more fuel flow to give a richer air fuel mixture. When the engine is stopped, spring (3) holds gas valve (7) down against the valve seat in the closed position and no fuel can enter the carburetor. Power screw (8) and plate (9) control fuel inlet at full load conditions when gas valve (7) is at a maximum distance off its seat.

As the engine is started, the intake strokes of the pistons cause a vacuum in the cylinders which causes a low pressure condition below the carburetor. Passages in air valve body (5) connect the low pressure to the upper side of diaphragm (2). At this point, atmospheric pressure pushes up on diaphragm (2) and lifts it against the downward force of spring (3). Air valve (4) is connected to and pulled up by diaphragm (2). At this point, air can push upward against the outside of air valve (4) to help lift it. Gas valve (7) is connected to air valve (4) and is also lifted off its seat to let fuel enter the carburetor. The air pushes up on diaphragm (2) and at the same time goes around the outside and inside of air valve (4) and around gas inlet body (6). As the air passes around gas inlet body (6), it mixes with the fuel. The air fuel mixture then goes down by throttle plate (10), into the distribution channels, to the inlet manifolds and then into the cylinders for combustion.

Air Inlet And Exhaust Systems

Air flow is the same on both sides of the engine. Clean inlet air from the air cleaners is pulled through the turbocharger compressor housing by a compressor wheel. Rotation of the compressor wheel causes compression of the air and forces it through lines to the aftercooler. The aftercooler lowers the compressed air temperature and provides air at a constant temperature to the carburetor for maximum air/fuel ratio control independent of load on engine. The aftercooler can be watercooled or an air to air type.

From the aftercooler the air goes through the carburetor (where it mixes with gas) and then into a turbulence chamber which keeps the air and fuel properly mixed. A distribution channel is located below the turbulence chamber and has holes in it to direct an equal temperature air/fuel mixture to each cylinder head inlet port. Air flow from the inlet ports into the cylinder combustion chamber is controlled by the intake valves.

There are two intake and two exhaust valves for each cylinder. Make reference to Valve System Components. The intake valves open when the piston moves down on the inlet stroke. Cooled, compressed air from the inlet port is pulled into the cylinder. The intake valves close and the piston starts to move up on the compression stroke. When the piston is near the top of the compression stroke, the magneto sends voltage through a transformer to the spark plug. The spark plug is ignited and combustion starts. The force of combustion pushes the piston down on the power stroke. When the piston moves up again it is on the exhaust stroke. The exhaust valves open and the exhaust gases are pushed through the exhaust port into the exhaust manifolds. After the piston completes the exhaust stroke, the exhaust valves close and the cycle (inlet, compression, power, exhaust) starts again.

Exhaust gases from the exhaust manifolds go into the turbine side of each turbocharger and cause a turbine wheel to turn. The turbine wheel is connected to the shaft that drives the compressor wheel. The exhaust gases then go out the exhaust outlet through the exhaust elbow. Changes in engine load and fuel burnt cause changes in rpm of the turbine and compressor wheels. As the turbocharger air pressure boost increases, the air-fuel ratio can change. To increase air and gas densities equally during increased boost, a balance line is connected between the carburetor air inlet and the atmospheric vent of the gas pressure regulator.

AIR INLET SYSTEM
1. Turbochargers. 2. Aftercooler. 3. Carburetor. 4. Turbulence chamber. 5. Distribution channel. 6. Cylinder head.

EXHAUST SYSTEM
7. Exhaust elbow. 8. Exhaust manifold.

Aftercoolers

ENGINE WITH WATERCOOLED AFTERCOOLER
1. Aftercooler. 2. Coolant return line. 3. Water pump.

The aftercooler is located in the air lines between the turbochargers and the carburetor. The aftercooler can be an air to air type or it can be watercooled.

Watercooled aftercoolers have a separate circuit cooling system, from the engine jacket water cooling system. Coolant is supplied to water pump (3). The water pump sends coolant through a water line into the bottom of the aftercooler. It then flows through the core assembly and back out of the aftercooler through line (2) to the water pump. A thermostatic valve is installed in line (2) to keep coolant in the aftercooler core assembly at the correct temperature.

Air flow through both cooling systems is as follows. Inlet air from the compressor side of the turbochargers flows into the aftercooler through pipes. This air then passes through the aftercooler core assembly which lowers the temperature. The cooler air goes out of the aftercooler into the carburetor, where fuel is mixed, through the turbulence chamber and distribution channel and up through the elbows to the inlet ports (passages) in the cylinder heads by the intake valves into the combustion chambers.

DISTRIBUTION CHANNEL AND AIR CHAMBER DRAIN
4. Drain plug.

All engines have two drain plugs (4) installed. One drain plug is located between the No. 1 and No. 3 cylinder heads, and another plug is located between the last two cylinder heads on the left side of the engine. These plugs can be removed to check for water or coolant in the cylinder block air chamber.

SCHEMATIC OF AN AIR TO AIR AFTERCOOLED ENGINE
5. Actuator with valve positioner. 6. Air cleaner. 7. Carburetor. 8. Turbocharger. 9. Cooling unit.

Air to air aftercooled systems contain a temperature controller that is pressurized to keep dirt and moisture out of it and a bypass valve which consists of an actuator and valve positioner. The temperature controller monitors inlet air temperature and is adjusted to keep it at 43°C (110°F). If the air temperature is too cold, the temperature controller signals an actuator (with pneumatic or gas pressure) to bypass the aftercooler core so air flows from the turbochargers directly into the carburetor.

TYPICAL AIR TO AIR AFTERCOOLED SYSTEM
5. Actuator with valve positioner. 6. Air cleaner. 7. Carburetor. 10. Vent cap for temperature controller. 11. Sensing element for temperature controller. 12. Temperature controller.

TEMPERATURE CONTROLLER INSTALLATION
10. Vent cap. 12. Temperature controller. 13. Pressure relief valve. 14. Pressure reducing valve. 15. Filter.

SCHEMATIC OF INSTRUMENT INSTALLATION FOR AIR TO AIR AFTERCOOLED SYSTEMS

Turbochargers

There are two turbochargers, on the rear of the engine. The turbine side of the turbochargers is fastened to the exhaust manifolds. The compressor side of the turbocharger is connected to the aftercooler.

TURBOCHARGERS
1. Turbocharger. 2. Oil drain line. 3. Oil supply line.

The exhaust gases go into turbine housing (8) and push the blades of turbine wheel (9). This causes the turbine wheel and compressor wheel to turn at up to 70,000 rpm.

TURBOCHARGER (3512 SHOWN)
4. Compressor wheel. 5. Bearing. 6. Oil inlet. 7. Bearing. 8. Turbine housing. 9. Turbine wheel. 10. Air inlet. 11. Oil outlet.

Clean air from the air cleaners is pulled through the compressor housing air inlet (10) by rotation of compressor wheel (4). The action of the compressor wheel blades causes a compression of the inlet air. This compression gives the engine more power because it makes it possible for the engine to burn additional fuel with greater efficiency.

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

The bearings (5 and 7) in the turbocharger use engine oil under pressure for lubrication. The oil comes in through oil inlet port (6) and goes through passages in the center section for lubrication of the bearings. Then the oil goes out oil outlet port (11) and back to the oil pan.

Exhaust Bypass Valve (Engines With Turbochargers)

EXHAUST BYPASS VALVE LOCATION
1. Exhaust elbow. 2. Exhaust bypass valve. 3. Air line from carburetor inlet. 4. Turbocharger.

Exhaust bypass valve (2) is installed in adapter (12) which is connected to exhaust elbow (1). This valve controls the amount of exhaust gases that go through the turbocharger turbine housing and drive the turbine wheel.

Valve (9) is activated directly by a pressure differential between the air pressure (atmosphere) and turbocharger compressor outlet pressure to the carburetor.

AIR LINE CONNECTION
3. Air line. 5. Carburetor.

One side of the diaphragm (13) in the regulator feels atmospheric pressure through a breather in the top of the regulator. The other side of the diaphragm feels air pressure from the outlet side of the turbocharger compressor through a control line connected to inlet side of the aftercooler. When outlet pressure to the carburetor gets to the correct value, the force of the air pressure on the diaphragm moves the diaphragm which over comes the force of the spring (8) and atmospheric pressure. This opens the valve, and stops exhaust gases from going to the turbine wheel.

EXHAUST BYPASS VALVE OPERATION (TYPICAL EXAMPLE)
6. Air line connection. 7. Spacers. 8. Spring. 9. Valve. 10. Breather location. 11. Bypass passage. 12. Adapter housing. 13. Diaphragm. 14. Shims.

Under constant load conditions, the valve will take a set position, permitting just enough gas to go to the turbine wheel to give the correct air pressure to the carburetor.

Valve System Components

VALVE SYSTEM COMPONENTS
1. Rocker arm. 2. Bridge. 3. Rotocoil. 4. Valve spring. 5. Push rod. 6. Lifter.

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 gears through idlers. Both camshafts must be timed to the crankshaft to get the correct relation between piston and valve movement.

The camshafts have two cam lobes for each cylinder. The lobes operate the valves.

As each camshaft turns the lobes on the camshafts cause lifters (6) to go up and down. This movement makes push rods (5) move rocker arms (1). Movement of the rocker arms makes bridges (2) move up and down on dowels 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 (3) 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 (4) cause the valves to close when the lifters move down.

Lubrication System

LUBRICATION SYSTEM SCHEMATIC
1. Main oil gallery. 2. Left camshaft oil gallery. 3. Piston cooling jet oil gallery. 4. Piston cooling jet oil gallery. 5. Right camshaft oil gallery. 6. Turbocharger oil supply. 7. Sequence valve. 8. Sequence valve. 9. Adapter. 10. Oil filter bypass valve. 11. Oil cooler. 12. Oil cooler bypass valve. 13. Oil pump relief valve. 14. Engine oil pump. 15. Elbow. 16. Suction bell. 17. Oil filter housing.

This system uses an oil pump (14) with three pump gears that are driven by the front gear train. Oil is pulled from the pan through suction bell (16) and elbow (15) by the oil pump. The suction bell has a screen to clean the oil.

The oil pump pushes oil through oil cooler (11) and the oil filters to oil galleries (1 and 2) in the block. The fin and tube type oil cooler lowers the temperature of the oil before the oil is sent on to the filters.

Bypass valve (12) lets oil flow directly to the filters if the oil cooler becomes plugged or if the oil becomes thick enough (cold start) to increase the oil pressure differential (cooler inlet to outlet) by an amount of 180 ± 20 kPa (26 ± 3 psi).

Cartridge type filters are located in oil filter housing (17) at the front of the engine. A single bypass valve is located in the oil filter housing.

Clean oil from the filters goes into the block through adapter (9). Part of the oil goes to the left camshaft oil gallery (2) and part goes to the main oil gallery (1).

The camshaft oil galleries are connected to each camshaft bearing by a drilled hole. The oil goes around each camshaft journal, through the cylinder head and rocker arm housing, to the rocker arm shaft. A drilled hole connects the bores for the valve lifters to the oil hole for the rocker arm shaft. The valve lifters get lubrication each time they go to the top of their stroke.

Main oil gallery (1) is connected to the main bearings by drilled holes. Drilled holes in the crankshaft connect the main bearing oil supply to the rod bearings. Oil from the rear of the main oil gallery goes to the rear of right camshaft gallery (5).

Sequence valves (7 and 8) let oil from main oil gallery (1) go to piston cooling jet oil galleries (3 and 4). The sequence valves open at 140 kPa (20 psi). The sequence valves will not let oil into the piston cooling jet oil galleries until there is pressure in the main oil gallery. This decreases the amount of time necessary for pressure build-up when the engine is started. It also helps hold pressure at idle speed.

PISTON COOLING AND LUBRICATION
18. Cooling jet.

There is a piston cooling jet (18) below each piston. Each cooling jet has two openings directed at the center of the piston. This helps cool the piston and gives lubrication to the piston pin.

TURBOCHARGERS
6. Oil supply lines. 19. Oil drain for left turbocharger. 20. Oil drain for right turbocharger.

Oil lines (6) give oil to the turbochargers. The turbocharger drain lines (19 and 20) are connected to the flywheel housing on each side of the engine.

Oil is sent to the front and rear gear groups through drilled passages in the front and rear housings and cylinder block faces. These passages are connected to camshaft oil galleries (2 and 5).

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

RIGHT FRONT SIDE OF ENGINE
10. Oil filter bypass valve. 17. Oil filter housing. 21. Oil line to filter housing.

LEFT FRONT OF ENGINE
9. Adapter. 17. Oil filter housing. 22. Oil outlet line from oil filter housing.

Cooling System

RIGHT FRONT OF ENGINE
1. Water line to front of engine cylinder block. 2. Bypass line. 3. Oil cooler. 4. Water pump.

This system uses a water pump (4) that is driven by the lower front right gear group. Coolant from a radiator or other heat exchanger is pulled into the center of the water pump housing by the rotation of the water pump impeller. The coolant flow is then divided at the water pump outlet. Part of the coolant flow is sent to the front of the cylinder block and part is sent through the engine oil cooler.

NOTE: There is one opening on the pump outlet so that a remote pump can be connected to the system. The remote pump can be used if there is a failure of the water pump on engine.

Coolant sent to the front of the cylinder block goes through a main distribution manifold to each cylinder water jacket. The main distribution manifold is located just above the main bearing oil gallery in the center of the cylinder block. Some of the coolant goes out the back of the cylinder block and into the adapter housing for the exhaust bypass valve. Flow from the exhaust bypass valve adapter housing is divided. Part of the coolant goes up through the exhaust elbow and part goes up through the turbocharger turbine housings. All coolant flow is then directed into the water cooled exhaust manifolds.

The coolant sent to the oil cooler goes through the oil cooler and flows into the water jacket of the block at the right rear cylinder. The cooler coolant mixes with the hotter coolant and goes to both sides of the block through the distribution manifolds connected to the water jacket of all the cylinders.

The coolant flows up through the water jackets and around the cylinder liners from the bottom to the top. Near the top of the cylinder liners, where the temperature is the hottest, the water jacket is made smaller. This shelf (smaller area) causes the coolant to flow faster for better liner cooling. Coolant from the top of the liners goes into the cylinder head which sends the coolant around the parts where the temperature is the hottest. Coolant then goes to the top of the cylinder head and out through an elbow one at each cylinder head, into watercooled exhaust manifolds (13) at each bank of cylinders. Coolant goes through the manifolds to the temperature regulator (thermostat) housing.

COOLANT FLOW FROM REAR OF ENGINE
5. Exhaust elbow. 6. Water line between exhaust elbow and exhaust manifold. 7. Water line from left turbocharger to exhaust manifold. 8. Water line from right turbocharger to exhaust manifold. 9. Left turbocharger. 10. Right turbocharger. 11. Water line to left turbocharger. 12. Water line to right turbocharger.

WATER TEMPERATURE REGULATOR HOUSINGS
2. Bypass line. 13. Watercooled exhaust manifolds. 14. Regulator housing. 15. Water outlet. 16. Housing.

Regulator housing (14) has an upper and lower flow section, and uses four temperature regulators. The sensing bulbs of the four temperature regulators are in the coolant in the lower section of the housing. Before the regulators open, cold coolant is sent through the lower section of the housing and through the bypass line back to the inlet of the water pump. As the temperature of the coolant increases enough to make the regulators start to open, coolant flow in the bypass line is stopped and coolant is sent through the outlets to the radiator or heat exchanger.

Total system coolant capacity will depend on the size of the heat exchanger. Use a coolant mixture of 50 percent pure water and 50 percent permanent anti-freeze, then add a concentration of 3 to 6 percent corrosion inhibitor.

Separate Circuit Aftercooler (SCAC) System

LEFT SIDE OF ENGINE
1. Aftercooler. 2. Coolant return line. 3. Coolant inlet line to the aftercooler. 4. Water pump. 5. Thermostatic valve.

Engines with a water cooled aftercooler use a separate circuit aftercooler (SCAC) coolant system, instead of the normal engine jacket water circuit, to cool the air in the aftercooler. With the SCAC system, coolant is supplied from a separate radiator or heat exchanger.

With the engine running and not at operating temperature, the aftercooler coolant circuit is closed. Auxiliary water pump (4) sends coolant through line (3) to aftercooler (1) at approximately 570 liter/m (150 U.S. gpm). Coolant flows up through the core assembly and out of the aftercooler through line (2), thermostatic valve (5) and back to auxiliary water pump (4). As the coolant temperature increases, thermostatic valve (5) opens and coolant flow from the aftercooler core assembly is directed to a radiator or heat exchanger and then back to auxiliary water pump (4). Thermostatic valve (5) will be fully open when the coolant temperature is 32°C (90°F) or 54°C (130°F) depending on the thermostat installed in the valve housing.

Total system coolant capacity will depend on the size of the heat exchanger. Use a coolant mixture of 50 percent pure water and 50 percent permanent anti-freeze, then add a concentration of 3 to 6 percent corrosion inhibitor.

Basic Block

Cylinder Block, Liners And Heads

The cylinders in the left side of the block make an angle of 60° with the cylinders in the right side of the block. The main bearing caps are fastened to the block with four 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 cylinder block. A filler band goes under the liner flange and makes a seal between the top of the liner and the cylinder block.

The engine has a separate cylinder head for each cylinder. Four valves (two intake and two exhaust), controlled by a push rod valve system, are used for each cylinder. Valve guides without shoulders are pressed into the cylinder heads. The opening for the spark plug is located between the four valves.

There is an aluminum spacer plate between each cylinder head and the block. Coolant goes out of the block through the spacer plate and into the head through eight openings in each cylinder head face. Grommets the width of the spacer plate prevent coolant leakage. Gaskets seal the oil drain passages between the head, spacer plate and block.

LEFT SIDE OF 3512 ENGINE
1. Covers for camshaft and valve lifter inspection. 2. Covers for crankshaft main and rod bearing inspection.

Covers (1) allow access to the camshafts and valve lifters.

Covers (2) allow access to the crankshaft connecting rods, main bearings and piston cooling jets. With covers removed, all the openings can be used for inspection and service.

Pistons, Rings And Connecting Rods

The aluminum pistons have an iron band for the top two rings. This helps reduce wear on the compression ring grooves. The pistons have three rings; two compression rings and one oil ring. All the rings are located above the piston pin bore. The oil ring is a standard (conventional) type. Oil returns to the crankcase through holes in the oil ring groove. The top two rings are the KEYSTONE type, which are tapered. The action of the ring in the piston groove, which is also tapered, helps prevent seizure of the rings caused by too much carbon deposit.

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. Four bolts set at a small angle hold the rod cap to the rod. This design keeps the rod width and weight to a minimum, so that the largest possible rod bearing (and crank journal) can be used and the rod can still be removed through the top of the liner bore.

Crankshaft

The crankshaft changes the combustion forces in the cylinder into usable rotating torque which powers the machine. A vibration damper of the fluid type is used at the front of the crankshaft to reduce torsional vibrations (twist on the crankshaft) that can cause damage to the engine.

The crankshaft is symmetrical. This makes it possible to turn the crankshaft end for end when opposite engine rotation is desired.

The crankshaft drives a group of gears on the front and rear of the engine. The gear group on the front of the engine drives the oil pump, water pump, fuel transfer pump, governor or governor actuator and two accessory drives. The gear group on the rear of the engine drives the camshafts.

Lip 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 main bearings through drilled holes in the webs of the cylinder block. The oil then flows through drilled holes in the crankshaft to provide oil to the connecting rod bearings. The crankshaft is held in place by seven main bearings on the 3512, and nine main bearings on the 3516. A thrust plate at either side of the center main bearing controls the end play of the crankshaft.

Camshafts

The engine has a camshaft or camshaft group for each side of the engine, driven at the rear of the engine. Seven bearings for the 3512, and nine bearings on the 3516 support each camshaft or camshaft group. The 3512 and 3516 each use two camshafts per side that are doweled and bolted together to make a camshaft group. As the camshaft turns, each lobe moves a lifter assembly. There are two lifter assemblies for each cylinder. Each lifter assembly moves a push rod and two valves (either intake or exhaust). The camshafts must be in time with the crankshaft. The relation of the cam lobes to the crankshaft position cause the valves in each cylinder to operate at the correct time.

Air Starting System

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

TYPICAL AIR STARTING SYSTEM
1. Air starting motor. 2. Relay valve. 3. Oiler.

The air starting motor can be mounted on either side of the engine. Air is normally contained in a storage tank and the volume of the tank will determine the length of time the engine flywheel can be turned. The storage tank must hold this volume of air at 1720 kPa (250 psi) when filled.

For engines which do not have heavy loads when starting, the regulator setting is approximately 690 kPa (100 psi). This setting gives a good relationship between cranking speeds fast enough for easy starting and the length of time the air starting motor can turn the engine flywheel before the air supply is gone.

If the engine has a heavy load which can not be disconnected during starting, the setting of the air pressure regulating valve needs to be higher in order to get high enough speed for easy starting.

The air consumption is directly related to speed; the air pressure is related to the effort necessary to turn the engine flywheel. The setting of the air pressure regulator can be up to 1030 kPa (150 psi) if necessary to get the correct cranking speed for a heavily loaded engine. With the correct setting, the air starting motor can turn the heavily loaded engine as fast and as long as it can turn a lightly loaded engine.

Other air supplies can be used if they have the correct pressure and volume. For good life of the air starting motor, the supply should be free of dirt and water. A lubricator with SAE 10 nondetergent oil [for temperatures above 0°C (32°F)], or diesel fuel [for temperatures below 0°C (32°F)] should be used with the starting system. The maximum pressure for use in the air starting motor is 1030 kPa (150 psi). Higher pressures can cause safety problems.

TYPICAL AIR START INSTALLATION
4. Air start control valve.

The air from the supply goes to relay valve (2). The starter control valve (4) is connected to the line before the relay valve (2). The flow of air is stopped by the relay valve (2) until starter control valve (4) is activated. The air from starter control valve (4) goes to piston (10) behind pinion (8) for the starter. The air pressure on piston (10) puts spring (11) in compression and puts pinion (8) in engagement with the flywheel gear. When the pinion is in engagement, air can go out through another line to relay valve (2). The air activates relay valve (2) which opens the supply line to the air starting motor.

AIR STARTING MOTOR
5. Air inlet. 6. Vanes. 7. Rotor. 8. Pinion. 9. Gears. 10. Piston. 11. Piston spring.

The flow of air goes through oiler (3) where it picks up lubrication oil for the air starting motor.

The air with lubrication oil goes into the air motor through air inlet (5). The pressure of the air pushes against vanes (6) in rotor (7), and then exhausts through the outlet. This turns the rotor which is connected by gears (9) and a drive shaft to starter pinion (8) which turns the engine flywheel.

When the engine starts running the flywheel will start to turn faster than starter pinion (8). Pinion (8) retracts under this condition. This prevents damage to the motor, pinion (8) or flywheel gear.

When starter control valve (4) is released, the air pressure and flow to piston (10) behind starter pinion (8) is stopped, piston spring (11) retracts pinion (8). Relay valve (2) stops the flow of air to the air starting motor.

Electrical System

The electrical system has 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 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

The alternator is driven by V-type belts from the crankshaft pulley. This alternator is a three phase, self-rectifying charging unit, and the regulator is part of the alternator.

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 with an 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

The voltage regulator is a solid state 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) to the alternator. The output voltage from the alternator will now supply the needs of the battery and the other components in the electrical system.

Starter System Components

Starter Motor

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

The starter motor has a solenoid. When the start switch is activated, electricity will flow through the windings of the solenoid. 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, cannot turn the starter motor too fast. When the start switch is released, the starter pinion will move away from the flywheel ring gear.

STARTER MOTOR
1. Field. 2. Solenoid. 3. Clutch. 4. Pinion. 5. Commutator. 6. Brush assembly. 7. Armature.

Starter Solenoid

SCHEMATIC OF A SOLENOID
1. Coil. 2. Switch terminal. 3. Battery terminal. 4. Contacts. 5. Spring. 6. Core. 7. Component terminal.

A solenoid is a magnetic switch that causes low current to close a high current circuit. The solenoid has an electromagnet with a core (6) which moves.

There are contacts (4) on the end of core (6). The contacts are held in the open position by spring (5) that pushes core (6) from the magnetic center of coil (1). Low current will energize coil (1) and make a magnetic field. The magnetic field pulls core (6) to the center of coil (1) and the contacts close.

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 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.

Water Temperature Contactor Switch

The contactor switch for water temperature is installed in the regulator housing. No adjustment to the temperature range of the contactor can be made. The element feels the temperature of the coolant and then operates the micro switch inside the contactor when the coolant temperature is too high. The element must be in contact with the coolant to operate correctly. If the reason for the engine being too hot is caused by low coolant or no coolant, the contactor switch will not operate.

WATER TEMPERATURE CONTACTOR SWITCH