Introduction

Reference: For Specifications with illustrations, make reference to Specifications for G3408 & G3412 Engines, SENR6407. If the Specifications in SENR6407 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

G3408

Cylinder And Valve Location

Bore ... 137.2 mm (5.40 in)

Stroke ... 152.4 mm (6.00 in)

Displacement ... 18 liter (1099 cu in)

Number of Cylinders ... V-8

Arrangement of Cylinders ... 65 degrees

Valves per Cylinder ... 4

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

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

Firing Order ... 1,8,4,3,6,5,7,2

Combustion ... spark ignited

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.

G3412

Cylinder And Valve Location

Bore ... 137.2 mm (5.40 in)

Stroke ... 152.4 mm (6.00 in)

Displacement ... 27 liter (1649 cu in)

Number of Cylinders ... V-12

Arrangement of Cylinders ... 65 degrees

Valves per Cylinder ... 4

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

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

Firing Order ... 1,4,9,8,5,2,11,10,3,6,7,12

Combustion ... spark ignited

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.

Ignition System

Solid State Magneto

Solid State Magneto
(1) Alternator section. (2) Electronic firing section.

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

Cross Section Of Solid State Magneto (Altronic)
(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.

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 wiring harness to the ignition coils where it is transformed to the high voltage needed to fire the spark plugs.

Spark Plug Adapter

Spark Plug Adapter
(1) Adapter. (2) Seal. (3) Cylinder head.

The spark plug adapter (1) is mounted in the cylinder head (3). Seal (2) stops any type of leakage between the adapter and the cylinder head. The adapter extends upward through a hole in the valve cover.

Spark Plug And Transformer

Spark Plug And Transformer
(1) Transformer (Red). (2) Wire assembly. (3) Rubber boot (part of wire assembly). (4) Spark plug. (5) Seal.

Transformer (1) is mounted on the valve cover. Wire assembly (2) is the high tension lead to ignite the spark plug (4). Rubber boot (3) is part of wire assembly (2). The boot forms a seal between the adapter and valve cover to keep dirt, water or other foreign material out of the adapter. Seal (5) prevents crankcase vapors and oil from entering the adapter.

NOTE: Wire assembly should not be painted.

Ignition Transformer

The ignition transformer causes an increase of the magneto voltage. This is needed to send a spark (impulse) across the electrodes of the spark plugs. For good operation, the connections (terminals) must be clean and tight. The negative transformer terminals, with (-) mark, for each transformer are connected together and to ground. The wiring diagrams show how all wires are to be connected to the plug connection at the magneto.

Wiring Diagrams

G3408 Engine
(1) Spark plug. (2) Transformer. (3) Magneto plug connector.

G3412 Engine
(1) Spark plug. (2) Transformer. (3) Magneto plug connector.

Gas, Air Inlet And Exhaust System

Gas, Air Inlet And Exhaust System With Turbocharger
(AA) Exhaust Gas. (BB) Air & Gas To Cylinders. (CC) Gas Supply. (DD) Low Pressure Gas. (EE) Air Inlet. (1) Gas pressure regulator. (2) Balance line. (3) Carburetor. (4) Air cleaner. (5) Turbocharger. (6) Gas supply. (7) Governor. (8) Aftercooler. (9) Air inlet manifold. (10) Cylinder. (11) Differential pressure regulator. (12) Exhaust manifold.

In addition to components shown in the diagram, some installations have a shutoff valve attachment in the supply line for the gas. 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 setting is needed to start the engine.

Engine installations using dual fuel have system components the same as illustrated above. In addition, dual fuel engines have a vacuum regulator and a load adjusting valve. These additional components permit an adjustment to be made for differences in BTU content of the gas being used. Dual fuel engines will switch from one fuel to another automatically, but engine timing must be adjusted manually at the time of switcher.

Changes in engine load and fuel burnt cause changes in rpm of the turbine wheels and impellers of the turbocharger (5).

When the turbocharger gives a pressure boost to the inlet air, the temperature of the air goes up. A water cooled aftercooler (8), is installed between the carburetor (3) and the air inlet manifold (9) to cylinders. The aftercooler causes a reduction of air temperature from the turbocharger.

Aftercooler

The aftercooler is installed on the top of the inlet manifold. Water flow through the aftercooler, lowers the temperature of the inlet air from the turbocharger. With cooler air, an increase in weight of air will permit more fuel to burn. This gives an increase in power. The aftercooler can be changed to use sea water as the coolant.

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) Rotocoil. (5) Valve spring. (6) Valve guide. (7) Intake valves. (8) Liter. (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 bridge (1) 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.

Turbocharger

The turbochargers are installed at the rear of the exhaust manifolds. All the exhaust gases from the engine go through the turbocharger.

Cross Section Of Turbocharger
(Typical Example) (1) Air inlet. (2) Compressor wheel. (3) Compressor outlet. (4) Lubrication inlet port. (5) Turbine wheel. (6) Thrust bearing. (7) Shaft bearings. (8) Exhaust outlet.

The exhaust gases go through the blades of turbine wheel (5). This causes the turbine wheel and compressor wheel (2) to turn.

Clean inlet air from the air cleaners is pulled through air inlet (1) of the compressor housing by the compressor wheel (2). The compressor wheel causes a compression of the air. The air goes to the inlet manifold of the engine.

The turbocharger bearings use engine oil under pressure for lubrication. The oil comes in through port (4) and goes through passages for lubrication of the thrust bearing (6), the rings and bearings (7). Oil from the turbocharger goes through an opening in the bottom of the center section and to the engine sump.

Exhaust Bypass Group (Engines With Turbocharger)

Exhaust Bypass System
(1) Air inlet pipe. (2) Turbocharger. (3) Exhaust manifold housing. (4) Differential pressure regulator. (5) Regulator control line.

Exhaust Bypass Group
(6) Regulator control line connection. (7) Diaphragm. (8) Spring. (9) Bypass valve. (10) Breather location.

The exhaust bypass group (4) is installed on the exhaust manifold housing (3). It controls the amount of exhaust gases to the turbine wheel. The exhaust bypass valve (9) is activated directly by a pressure differential between the air pressure (atmosphere) and turbocharger compressor outlet pressure to the carburetor.

One side of the diaphragm (7) in the regulator feels atmospheric pressure through a breather (10) 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 (5) connected at (6). When outlet pressure to the carburetor gets to the correct value, the force of the air pressure on the diaphragm moves the diaphragm which overcomes the force of the spring (8) and atmospheric pressure. This opens the valve, and stops exhaust gases from going to the turbine wheel.

The location of the bypass passage is inside the exhaust manifold housing. Under constant load conditions, the valve will take a set position, permitting just enough exhaust gas to go to the turbine wheel to give the correct air pressure to the carburetor.

Lubrication System

Oil Flow Through The Oil Cooler And Oil Filters

Lubrication System Components (G3408 Shown)
(2) Filter bypass valve. (3) Engine oil cooler. (4) Cooler bypass valve. (6) Oil pan. (7) Oil filters.

Schematic Of Oil Flow
(1) To oil manifold. (2) Filter bypass valve. (3) Engine oil cooler. (4) Cooler bypass valve. (5) Oil pump. (6) Oil pan. (7) Oil filters.

With the engine warm (normal operation), oil is pulled from oil pan (6) through a bell assembly and pipe to oil pump (5). The oil pump sends oil through a pipe to a passage in the cylinder block. The oil then goes through oil cooler bypass valve (4) into oil cooler (3). The oil goes out of the oil cooler through oil filters (7). The clean oil then goes through oil filter bypass valve (2), then into the oil manifold on the right side of the cylinder block.

When the engine is cold (starting condition), bypass valves (2 and 4) open because cold oil with high viscosity causes a restriction to the oil flow through oil cooler (3) and filters (7). When the bypass valves are open, oil flows directly through passages in the valve body to the oil manifold.

When the oil gets warm, the pressure difference at the bypass valves decreases and the bypass valves close. This gives normal oil flow through oil cooler (3) and oil filters (7).

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

There is also a bypass valve in engine oil pump (5). This bypass valve controls the 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 lets the oil that is not needed to go back to the inlet oil passage of the oil pump.

Oil Flow In The Engine

Schematic Of Oil Flow In The G3408 Engine
(1) Passage is plugged. (2) To rear idler gear. (3) To rocker arm shaft. (4) To turbocharger. (5) To magneto and governor drive housing. (6) Rocker arm shaft. (7) To rocker arm shaft and valve lifters. (8) To valve lifters. (9) Bore for camshaft bearings. (10) Piston cooling jets. (11) To SCAC water pump. (12) Oil manifold (left side). (13) To timing gear housing. (14) To front idler gear. (15) Oil supply line to manifold in cylinder block. (16) Oil manifold (right side). (17) Main bearing bores.

The oil manifolds are cast into the sides of the cylinder block. Oil goes into manifold (16) from the bypass valve body. From manifold (16) oil is sent to manifold (12) through drilled passages in the cylinder block that connect main bearing bores (17) and camshaft bearing bores (9). Oil goes through holes in the bearings and gives them lubrication. Oil from the main bearings goes through holes drilled in the crankshaft to give lubrication to the connecting rod bearings. A small amount of oil from the oil manifolds goes through tubes (10) to make the pistons cooler.

Oil goes through grooves in the outside of the front and rear camshaft bearings to passages (7 and 8). The oil in these passages gives lubrication to the valve lifters and rocker arm shafts. Holes in the rocker arm shafts let the oil give lubrication to the valve system components in the cylinder head.

The magneto and governor drive housing and governor get oil from passage (5) in the cylinder block. Oil for the hydraulic operation of the hydra/mechanical governor comes from a small gear pump inside the governor.

The bearing of the idler gear on the front of the engine gets oil through a passage in the idler gear shaft that is connected to passage (14).

The bearing for the balancer gear at the rear of the engine (G3408 only) gets oil through a passage in the balancer gear shaft that is connected to passage (2).

Turbocharger Lubrication (G3408 Shown)
(18) Oil supply line to turbocharger. (19) Oil drain line from turbocharger.

Tube assembly (18) gives oil to the turbocharger impeller shaft bearings. The oil goes out of the turbocharger through tube assembly (19) to the flywheel housing.

Oil that gives pressure lubrication to gear shafts and bearings then flows free to give lubrication to the gear teeth. After the oil for lubrication has done its work it flows free back to the oil pan.

Schematic Of Oil Flow In The G3412 Engine
(1) Passage is plugged. (3) To rocker arm shaft. (4) To turbocharger. (5) To magneto and governor drive housing. (6) Rocker arm shaft. (7) To rocker arm shaft and valve lifters. (8) To valve lifters. (9) Bore for camshaft bearings. (10) Piston cooling jets. (11) to SCAC water pump. (12) Oil manifold (left side). (13) To timing gear housing. (14) To front idler gear. (15) Oil supply line to manifold in cylinder block. (16) Oil manifold (right side). (17) Main bearing bores.

Cooling System

Cooling System Schematic (G3408 Shown)
(1) Water inlet connection. (2) Water pump. (3) Bypass lines. (4) Temperature regulator housings. (5) Water outlet connections. (6) Water to turbocharger. (7) Water cooled turbocharger. (8) Water from turbocharger. (9) Aftercooler. (10) Separate circuit water pump. (11) Water cooled exhaust manifold. (12) Oil cooler bypass. (13) Engine oil cooler.

Jacketwater System

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.

This engine can be cooled by a radiator or heat exchanger. The following explanation covers only the cooling circulation of the engine.

In normal operation (engine warm), water pump (2) receives coolant through inlet connection (1) and sends the coolant to engine oil cooler (13) and oil cooler bypass (12). The oil cooler outlet sends the coolant from the cooler and bypass to the water cooled turbocharger (7) and to the engine cylinder block. Coolant to the turbocharger flows through line (6) through the turbocharger and returns to the water cooled exhaust manifold (11) and on to the block. The coolant to the cylinder block circulates through the block up through the cylinder heads, on to the water temperature regulator housings (4). Part of the coolant in housing (4) flows into water cooled exhaust manifolds (11), and part of the coolant passes through open temperature regulators through outlet connections (5) to be cooled. The coolant in the exhaust manifold flows into the cylinder block through the head and back to housing (4). The water pump (2) will pump the cooled coolant through the engine to keep the cycle going.

NOTE: The water temperature regulator is an important part of the cooling system. It divides coolant flow between the radiator and bypass lines (3) 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 or heat exchanger is too much, and the engine will not get to normal operation temperatures.

When the engine is cold, the water temperature regulators are closed. The coolant in the temperature regulator housings (4) flows through bypass lines (3) to water pump (2). The coolant continues to flow through system as described above except the coolant does not flow out to be cooled.

Total system coolant capacity will depend on the size of the radiator or heat exchanger. Use the correct amount of permanent antifreeze and pure water to provide freeze protection to the lowest expected outside temperature. Add a concentration of three to six percent corrosion inhibitor.

Separate Circuit Aftercooler (SCAC) System

The aftercooler (9) is cooled by a separate water circuit. The separate water circuit is used to maintain a specific and constant water temperature. Water is pumped from the separate water supply by pump (10) through the aftercooler and back to the water supply.

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. A filler band at the top of each liner forms a seal between the liner and the cylinder block.

A steel spacer plate is used between the cylinder head and block. A thin gasket is used between the plate 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 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 spark plug adapter is located between the four valves. Series ports (passages) are used for both intake and exhaust valves.

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 piston has three rings; two compression rings (top and intermediate) and one oil ring. All the rings are located above the piston pin bore. The compression ring seats in an iron band which is cast in the piston. The oil ring is spring loaded. External cast notches in the oil ring groove return oil to the crankcase.

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

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

Gallery cooled pistons have two cooling jets, per cylinder. One cools the under crown of the piston and the other directs oil into a cast gallery behind the piston rings.

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. 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 bearing surfaces through drilled holes in the crankshaft. The crankshaft is supported by five main bearings in G3408 engines and by seven main bearings in the G3412 engines. 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. Five bearings for the G3408 and seven bearings for the G3412 support the camshaft. As the camshaft turns, each cam (lobe) (through the action of valve system 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 cams (lobes) to the camshaft gear cause the valves in each cylinder to open and close at the correct time.

A gear on the rear of the camshaft is used to drive the balancer gear on G3408 engines.

Vibration Damper

The twisting of the crankshaft, due to the regular power impacts along its length, is called twisting (torsional) vibration. The fluid type 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.

Electrical System

Engine 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 low amperage circuit and the charging circuit are both connected through the ammeter. The starting circuit is not connected through the ammeter.

Grounding Practices

Proper grounding for vehicle and engine electrical systems is necessary for proper vehicle performance and reliability. Improper grounding will result in uncontrolled and unreliable electrical circuit paths which can result in damage to main bearings and crankshaft journal surfaces. Uncontrolled electrical circuit paths can also cause electrical noise which may degrade vehicle and radio performance.

To insure proper functioning of the vehicle and engine electrical systems, and engine-to-frame ground strap with a direct path to the battery must be use. This may be provided by way of a starting motor, a frame to starting motor ground, or a direct frame to engine ground.

Ground wires/straps should be combined at ground studs dedicated for ground use only. The engine alternator must be battery (-) grounded with a wire size adequate to handle full alternator charging current.

Starting System Components

Solenoid

Typical Solenoid Schematic

A solenoid is a magnetic 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.

The solenoid switch is made of an electromagnet (one to two sets of windings) 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 winding, 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 to start running.

The starter motor has a solenoid. When the start switch is activated, the solenoid will move the starter pinion to engage it 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 can not turn the starter motor too fast. When the start switch is released, the starter pinion will move away from the ring gear.

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

Other Components

Circuit Breaker

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

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 makes complete the electric current 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 (an adjustment to make the circuit complete again) after is becomes cool. Push the reset button to close the contacts and reset the circuit breaker.

Water Temperature Sending Unit (WTSU)

Sending Unit for Water Temperature
(1) Connection (2) Bushing (3) Bulb

The sending unit for water temperature is an electrical resistance. It changes the value of its resistance according to the temperature which the bulb (3) feels.

The sending unit is in a series circuit with the electrical gauge. When the temperature is high, the resistance is high. This makes the gauge have a high reading.

The sending unit must be in contact with the coolant. If the coolant level is too low because of a sudden loss of coolant while the engine is running or because the level is too low before starting the engine, the sending unit will not work correctly.

This sending unit requires 24VDC electrical input, therefore, it is only used with the energized-to-run protection systems.

Electric Service Meter

The electric service meter group is self-powered. A magnetic pickup mounted on the flywheel housing provides voltage (starting at 200 engine rpm) to power the electric service meter which records clock hours with quartz accuracy. A separate magnetic pickup must be used for each service meter; it cannot be shared with the digital tachometer, electronic speed switch, or electronic governor magnetic pickup.

Magnetic Pickup (MPU)

Magnetic Pickup
(1) Clearance dimension (2) Magnetic pickup (3) Wires (4) Locknut (5) Gear tooth (6) Housing

The magnetic pickup is a single pole, permanent magnet generator made of wire coils around a permanent magnet pole piece. As the teeth of the flywheel ring gear go through the magnetic lines of force around the pickup, an AC voltage is made. A positive voltage is made when each tooth goes by the pole piece. Each time the space between the teeth goes by the pole piece, a negative voltage is made. Engine speed is then determined by the frequency of these signals.

Overspeed Contactor Switch (MOS)

The overspeed contactor is used in a self powered protection system to protect the engine from damage due to overspeeding. It contains a micro switch that is activated by high engine speed. The overspeed switch is mounted on the tachometer drive. If the engine overspeeds, the switch contacts close and connect the magneto to ground to shut down the engine. When the engine shuts down because of overspeeding, the overspeed contactor switch must be reset by pushing reset button (1). The overspeed contactor switch is adjustable.

Overspeed Contactor
(1) Reset button

Oil Pressure Switch (OPS)

Oil Pressure Switch

The oil pressure switch uses a spring loaded piston to activate a micro switch for a specific pressure rating. This type of switch has better accuracy over the operating temperature range and uses a much higher electrical contact rating to improve reliability.

Slave Relay (SR)

This is a standard type relay that, when energized, has contacts that open across one circuit and close across another circuit. The circuits are wired so that voltage from the magneto goes to the spark plugs when the relay is energized. When not energized, the relay causes magneto voltage to go to ground. This relay is not used on the self-powered protection system.

Electronic Speed Switch (ESS)

Electronic Speed Switch (ESS)
(1) Verify button (2) Reset button (3) "LED" overspeed light (4) Seal screw plug (overspeed) (5) Seal screw plug (crank terminate)

The Electronic Speed Switch (ESS) is designed with controls built into a single unit to monitor several functions at the same time. The functions that the ESS monitors are:

Engine Overspeed (OS)

This is an adjustable engine speed setting (normally 118% of rated speed) that prevents the engine from running at a speed that could cause damage. This condition will cause a switch to close that shuts off the fuel to the engine and connects the magneto to ground to stop current flow to the spark plugs.

Crank Termination (CT)

This is an adjustable engine speed setting that signals the starter motor that the engine is firing and cranking must be terminated. When the speed setting is reached, a switch will open to stop current flow to the starter motor circuit. The starter motor pinion gear will now disengage from the engine flywheel ring gear.

Junction Box

Junction Box (Box for Self Powered Engine Shown)
(1) Terminal strips (TS) (2) Location for electric speed switch (ESS) (3) Emergency stop switch (ES) (4) Location for slave relay (SR) (5) Stop-by pass switch (SBS) [(also location for start-stop switch (SSS)] (6) Location for circuit breakers (CB)

The junction box contains the terminal strips (TS) and emergency stop switch (ES). An oil pressure switch (OPS) is located at the back of the junction box. Depending on the protection system used, the J box may also contain the electric speed switch (ESS), slave relay (SR), circuit breakers (CB), and start-bypass switch (SBS) or start-stop switch (SSS).

NOTE: The start-bypass switch is always located on the J box cover. A start-bypass switch may also be located on the bracket below the instrument panel on the right side of the engine to accommodate RH mounted starting controls.

Wiring Diagrams

Engine Protection Systems, Starting, Charging, and Tachometer Circuits

This section contains point-to-point wiring diagrams for the engine protection systems and starting, charging, and tachometer circuits.

These diagrams can be helpful for the user who is not familiar with the electrical schematic-type format, or who is interested in the component position layout for replacement purposes.

Refer to the notes and abbreviations on this page when using the wiring diagrams in this section. See the chart on the following page for the battery cable size.

NOTES

NOTE A: Cable to be grounded at tachometer only when used without electric speed switch. Ground cable at speed switch when available.

NOTE B: Grounded system required for proper operation of shutoff system.

NOTE C: If 2301 Governor is used, only one magnetic pick-up is required. Use magnetic pick-up from speed switch. Connect magnetic pick-up to speed switch and then to 2301 Governor Control. Do not use multiple grounds on any particular length of shielded cable.

NOTE D: If electric starting motor is not used, connect battery cables to power input studs on bottom of power distribution box. If neither electric starting motor nor charging alternator is used, connect positive lead of 24 VDC power source to TS-1 on junction box terminal strip and negative to TS-28.

NOTE E: Diagrams and schematics for junction box wiring shipped inside junction box.

NOTE F: Attach ground wire to ground strap bolt on junction box mounting bracket.

NOTE G: Jumper on junction box terminal strip between points TS-30 and TS-31 must be removed when right-hand mounted start-stop switch is used on engine. (No external power source).

NOTE H: When starting engine, stop-bypass switch must be held in up position until oil pressure is achieved. Failure to do so will result in engine shutdown.

NOTE J: Attach ground wire to start-stop switch mounting bracket bolt.

NOTE L: Start-stop switch required with oil pressure, water temperature, overspeed protection system only when used in a non-auto-start-stop application.

NOTE M: Jumper on terminal strip between points TS-4 and TS-5 must be removed when a remote normal stop switch is used.

NOTE N: Magneto shutoff contacts ... G

NOTE P: Remove jumper between terminal points TS-31 and TS-32 when gas shutoff valve is used.

Wiring Diagram
Starting, Charging, Tachometer Circuits (Engine With Self-Powered Protection)

Wiring Diagram
Oil Pressure, Water Temperature Mechanical Overspeed Protection (Self-Powered Protection)

Wiring Diagram - ETR, Independent, Full Protection Wiring Diagram - ETR, Auto-Start-Stop, Full Protection

Junction Box Wiring Diagrams

This section contains point-to-point wiring diagrams for the junction boxes used with the engine protection systems. These diagrams can be helpful for the user who is not familiar with the electrical schematic-type format, or who is interested in the component position layout for replacement purposes.

NOTE: The junction boxes for the ETR independent and ETR auto-start-stop protection systems are used for other engines in addition to the G3408 and G3412. Therefore, some components shown in the junction box wiring diagrams for the ETR protection systems will not apply to the G3408 and G3412.

Refer to the abbreviations on this page when using the wiring diagrams in this section.

Junction Box Wiring Diagram
Self-Powered Protection

Junction Box Wiring Diagram
ETR, Independent, Full Protection

Junction Box Wiring Diagram
ETR, Auto-Start-Stop, Full Protection