Introduction

NOTE: For Specifications with illustrations, make reference to Specifications For G3306 Truck Engine. If the Specifications are not the same as in the Systems Operation, 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.

General Description

Right Side View
(1) Transformer. (2) Governor actuator. (3) Deceleration Fuel Cutoff Valve (DFCV). (4) Air/Fuel control. (5) Carburetor. (6) Deceleration Fuel Cutoff Solenoid (DFCS). (7) DIS magnetic pick-up sensor. (8) Governor speed magnetic pick-up sensor. (9) Pre-catalyst. (10) Oxygen sensor.

Left Side View
(2) Governor actuator. (3) Deceleration Fuel Cutoff (DFCV). (4) Air/Fuel control. (5) Carburetor. (6) Deceleration Fuel Cutoff Solenoid (DFCS). (11) Caterpillar Interface Module (CIM). (12) Air temperature sensor. (13) Manifold air pressure sensor.

The G3306 Truck Engines are in-line six cylinder arrangements, with a firing order of 1, 5, 3, 6, 2, and 4. The engine rotation is counterclockwise as viewed from the flywheel. The engines are turbocharged and air-to-air aftercooled. The G3306 Truck Engines have a bore size of 120.7 mm (4.75 in) and a stroke of 152.4 mm (6.00 in).

Engine Control System

The G3306 Truck Engines has been designed with an electronically controlled ignition and governor systems in combination with an electronic air fuel ratio control module (ECM). The ignition system controls the timing of the transformers which send a spark (impulse) across the electrodes of the spark plug. The governor system controls engine speed by controlling the amount of flow into the combustion chamber with the use of a governor actuator connected to a throttle plate under the carburater. The ECM uses the following inputs:

* Manifold Air Pressure Sensor (MAPS)

* Inlet Manifold Temperature Sensor (IMTS)

* Throttle Position Sensor (TPS)

* Oxygen Sensor

With these measured parameters the ECM is capable of controlling the air/fuel mixture to provide the best engine performance at all engine speeds. The software maps are set to adjust the mixture flow into the carburetor based on temperature, pressure, the amount of oxygen in the exhaust gases, etc.

Ignition System

Ignition System Schematic

The Digital Ignition System (DIS) is designed to replace the traditional magneto ignition system. The Digital Ignition System eliminates the magneto and other components that were subject to mechanical wear.

The DIS system has no wearing parts and monitors engine operation and distributes power to the cylinder transformer. The DIS system releases stored energy in response to process signals from the speed sensor to provide precision timed sparks for maximum engine performance. The DIS system allows improved operation, economy and lower emission levels. The system consists of three basic groups: The DIS control module, ignition coils and sensors.

Spark Plug Adapter

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

The spark plug adapter (1) is mounted on a bracket located on the top of the engine. 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 Ignition Transformer

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

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. The rubber boot (3) 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 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 DIS.

Governor System

Governor System Schematic

The governor control system provides precise engine speed control over a broad range of driving conditions. The control is programmed through a lap top computer. The control system has the following OEM features: transmission neutral contact, neutral fuel limit, door interlock contact, PTO contact, speed switch/throttle position switch output, idle validation contact, and transmission signal output.

The governor control system is programmed with both minimum and maximum engine speed governor set points. The minimum governor set point controls both the speed of the engine and the position of the governor actuator under idle conditions when the throttle pedal is resting at its minimum position. The maximum governor set point controls engine speed and actuator position if the maximum speed set point is reached. Between these two set points, the position of the governor actuator is directly proportional to the position of the throttle pedal.

Fuel System

Fuel, Air Inlet And Exhaust System With Turbocharger

The fuel system consists of a gas regulator(s), an idle enrichment line, a Deceleration Fuel Cutoff Valve (DFCV), and air/fuel control valve and a carburetor/throttle. In addition to components shown in the diagram, typical installations have an OEM supplied Gas Shut Off Valve (GSOV) in the supply line for the gas. The valve is electrically operated from the ECM or by oil pressure.

The gas is supplied to thee gas regulators which regulate the flow of fuel through the DFCV to the air/fuel control valve. The air/fuel control valve supplies the correct amount of fuel to the carburetor based on an input signal from the ECM. The carburetor mixes the gas with inlet air and delivers it to the combustion chamber. The throttle body which is controlled by the governor actuator.

The idle enrichment line is used to improve the low idle air fuel ratioo and startibility. The DFCV is an air operated valve that is used to shut-off the fuel supply during deceleration to save fuel and reduce exhaust emissions. When engine deceleration condition is recognized by the ECM, the Deceleration Fuel Cutoff Solenoid (DFCS) receives an input signal and provides air to the DFCV. The balance line maintains the correct differential pressure between the gas pressure regulator(s) and carburetor inlet.

Gas Pressure Regulator

Regulator Operation (Typical Example)
(1) Spring side chamber. (2) Adjustment screw. (3) Spring. (4) Outlet. (5) Valve disc. (6) Orifice. (7) Main diaphragm. (8) Lever side chamber. (9) Lever. (10) Pivot pin. (11) Valve stem. (12) Inlet.

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

As gas pressure in lever side chamber (8) becomes higher than the force of spring (3) and turbocharger boost, the diaphragm is pushed against the spring. This turns the lever (9) at pivot pin (10) and causes the valve stem (11) to move the valve disc (5) to close the orifice (6).

With the orifice (6) closed, gas is pulled from lever side 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 (1). Force of spring and turbocharger boost 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 flow.

Carburetor Group

(1) Carburetor. (2) Air/Fuel Control Valve. (3) Deceleration Fuel Cutoff Solenoid (DFCS). (4) Throttle Assembly. (5) Deceleration Fuel Cutoff Valve (DFCV).

The carburetor group consists of a Deceleration Fuel Cutoff Solenoid (DFCS) (3), Deceleratioon Fuel Cutoff Valve (DFCV) (5), air/fuel control valve (2), carburetor (1), and a throttle assembly (4). The fuel flows from the gas pressure regulator to inlet side of the Deceleration Fuel Cutoff valve (DFCV) (5) which is controlled by the Deceleration Fuel Cutoff solenoid (3). After the fuel is set to a pre-determined pressure then the fuel flows into the carburetor (1) and the throttle assembly (4) for proper air/fuel mixing. The mixture then passes by the throttle assembly (4) and into the engine. During idle the fuel then enters the air/fuel control valve (2) from the fuel enrichment port on the gas pressure regulator.

Deceleration Fuel Cutoff Valve (DFCV)

The DFCV is used with the DFCS to shut off the fuel flow when all the following conditions are met:

* Foot pedal signal is in the idle position

* Negative inlet manifold pressure

* Engine speed is at a pre-determined setting

When the above conditions are met the DFCS provides air pressure to the DFCV which in turn closes the valve. The DFCV is a normally closed when the key is in the ON position. The DFCS is shipped loose and should be mounted off the engine within 1.2 m (4 ft) from the left hand side of the engine

Air/Fuel Control Valve

The air/fuel control valve is used to maintain a desired fuel pressure to the carburetor. The control valve maintains this pressure with the use of a stepper motor. The stepper motor is controlled by the ECM. The ECM takes input signals from the oxygen sensor, the manifold air pressure sensor, and the inlet manifold temperature sensor and sends a signal to the stepper motor which will compensate for different conditions and maintain the desired fuel pressure.

Carburetor

(1) Fuel Metering Holes. (2) Carburetor.

Air from the gas pressure regulator's balance line passes through the carburetor's venturi. The pressure decreases in the throat of the carburetor (2) is proportional to the speed of the incoming air. This pressure drop is used to "draw" the fuel into the venturi. The fuel enters through the fuel metering holes (1) on the cross and through holes on in the wall off the venturi's throat. The air/fuel control valve maintains a fuel pressure that is equal to that of the air entering the carburetor (2). The desired air/fuel mixture can be achieved by varying the setting of the main adjusting screw. Once the proper air/fuel mixture is satisfied then the mixture passes through the throttle assembly and into the engine.

Balance Line

The balance line controls the correct pressure differential between the line pressure regulator and the carburetor inlet.

When the load on the engine changes, the boost pressure from the turbocharger changes in the inlet manifold. The balance line sends a signal of this change through the vent valve to the spring side chamber of the line pressure regulator. This pressure change causes the regulator diaphragm to move the line regulator valve to correct the gas pressure to the carburetor.

Air Inlet And Exhaust System

Air Flow Schematic
(1) Air line. (2) Aftercooler core. (3) Inlet manifold. (4) Exhaust outlet from turbocharger. (5) Turbine side of turbocharger. (6) Compressor side of turbocharger.

The components of the air inlet and exhaust system control the quality and the amount of air available for combustion. These components are the air cleaner, turbocharger, aftercooler, cylinder head, valves and valve system components, piston and cylinder, and exhaust manifold.

Inlet air is pulled through the air cleaner, compressed and heated by the compressor wheel in compressor side of turbocharger (6) to about 150°C (300°F), then pushed through the air-to-air aftercooler core (2) and moved to the air inlet manifold (3) at about 43°C (110°F). Cooling of the inlet air increases combustion efficiency, which helps to lower fuel consumption and increase horsepower output. Aftercooler core (2) is a separate cooler core installed in front of the standard engine radiator core of the truck. Ambient temperature air is moved across the aftercooler core by the engine fan and by the ram effect of the vehicles forward motion, this cools the turbocharged inlet air.

From the aftercooler core (2) the air is forced into the cylinder head to fill the inlet ports. Air flow from the inlet port into the cylinder is controlled by the intake valves.

Air Inlet And Exhaust System
(2) Aftercooler core. (4) Exhaust outlet. (5) Turbine side of turbocharger. (6) Compressor side of turbocharger. (7) Exhaust manifold. (8) Exhaust valve. (9) Intake valve. (10) Air inlet.

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. The cooled, compressed air/fuel mixture 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 Digital Ignition System (DIS) sends a signal through a transformer to the spark plug. The transformer increases the voltage until a spark is created across the spark plug gap. The spark ignites the air/fuel mixture 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 competes the exhaust stroke, the exhaust valves close and the cycle (inlet, compression, power, exhaust) starts again.

Exhaust gases from exhaust manifold (7) enter turbine side of the turbocharger (5) and cause the turbine wheel to turn. The turbine wheel is connected to the shaft which drives the compressor wheel. Exhaust gases from the turbocharger pass through the exhaust outlet pipe, the muffler and the exhaust stack.

Turbocharger

Turbocharger
(1) Air inlet. (2) Compressor housing. (3) Compressor wheel. (4) Bearing. (5) Oil inlet port. (6) Bearing. (7) Turbine housing. (8) Turbine wheel. (9) Exhaust outlet. (10) Oil outlet port. (11) Exhaust inlet.

The exhaust gases go into turbine housing (7) through exhaust inlet (11) and push the blades of turbine wheel (8). The turbine wheel is connected by a shaft to compressor wheel (3).

Clean air from the air cleaner is pulled through the compressor housing air inlet (1) by the rotation of compressor wheel (3). 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 more air and fuel during combustion.

When the load on the engine increases, more fuel is injected into the cylinders. This makes more exhaust gases, and will cause the turbine and compressor wheels of the turbocharger to turn faster. As the compressor wheel turns faster, more air is forced into the engine. The increased flow of air gives the engine more power because it makes it possible for the engine to burn additional fuel with greater efficiency.

Bearings (4 and 6) for the turbocharger use engine oil under pressure for lubrication. The oil comes in through the oil inlet port (5) and goes through passages in the center section for lubrication of the bearings. Oil from the turbocharger goes out through the oil outlet port (10) in the bottom of the center section and goes back to the engine lubrication system.

Exhaust Bypass

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

One side of the diaphragm 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 at the regulator control line connection. When outlet pressure gets to the correct value, the force of the air pressure on the diaphragm moves the diaphragm which overcomes the force of the spring and atmospheric pressure. This opens the valve, and allows exhaust gases to bypass the turbine wheel.

Cylinder Head And Valves

There is one cylinder head for all cylinders. Each cylinder has one intake and one exhaust valve. Each intake and exhaust valve has a valve rotator. The valve rotator causes the valve to turn a small amount each time the valve opens and closes. This action helps keep carbon deposits off of the valve face and valve seat.

The cylinder head has valve seats installed and they can be replaced.

The valve guides can be replaced. There are threads on the inside diameter of the valve guides to hold oil that lubricates the valve stem.

Valve Mechanism

The valve mechanism controls the flow of inlet air and exhaust gases in and out of the cylinders. The valve mechanism consists of rocker arms, push rods, valve lifters and camshaft.

The camshaft is driven by and timed to the crankshaft. When the camshaft turns, the camshaft lobes move the valve lifters up and down. The valve lifters move the push rods which move the rocker arms. Movement of the rocker arms make the intake and exhaust valves open according to the firing order (injection sequence) of the engine. A valve spring for each valve makes the valve go back to the closed position and holds it there.

Lubrication System

System Oil Flow

Lubrication System Schematic (Engine Warm)
(1) Oil passage (to front idler gear). (2) Oil passage (to turbocharger and fuel injection pump). (3) Rocker arm shaft. (4) Oil pressure connection. (5) Oil manifold. (6) Piston cooling orifices. (7) Camshaft bearing bore. (8) Oil cooler bypass valve. (9) Oil filter bypass valve. (10) Engine oil cooler. (11) Oil filter. (12) Turbocharger. (13) Oil pump. (14) Oil pan.

Oil pump (13) pulls oil from oil pan (14) and then pushes the oil to oil cooler (10). From the oil cooler the oil goes to oil filter (11) and then to oil manifold (5). From the oil manifold, oil goes to all main bearings, and piston cooling orifices (6). Oil passages in the crankshaft send oil to the connecting rod bearings. Oil from the front main bearing goes through oil passage (1) to the bearing for the fuel injection pump idler gear.

Oil from the front main bearing also goes to camshaft bearing bore (7). The front camshaft bearing is the only bearing to get pressure lubrication.

Oil passage (2) from No. 4 main bearing sends oil to the fuel injection pump housing on the right side of the engine. Oil from the oil filter base feeds oil to the turbocharger.

An oil passage from the rear of the cylinder block goes below the head bolt hole and connects with a drilled passage that goes up next to the head bolt hole. A hollow dowel connects the vertical oil passage in the cylinder block to the oil passage in the head. The spacer plate has a hole with a counterbore on each side that the hollow dowel goes through. An O-ring is in each counterbore to prevent oil leakage around the hollow dowel. Oil flows through the hollow dowel into a vertical passage in the cylinder head to the rocker arm shaft bracket. The rocker arm shaft has an orifice to restrict the oil flow to the rocker arms. The rear rocker arm bracket also has an O-ring that seals against the head bolt. This seal prevents oil from going down around the head bolt and leaking past the head gasket or spacer plate gasket. The O-ring must be replaced each time the head bolt is removed from the rear rocker arm bracket.

Rocker Arm Oil Supply

Holes in the rocker arm shafts let the oil give lubrication to the valve system components in the cylinder head.

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

There is a bypass valve in the oil pump. This bypass valve controls the pressure of the oil coming 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 increases and the bypass valve will open. This allows the oil that is not needed to go back to the engine oil pan.

With the engine cold (starting conditions), bypass valves (8 and 9) will open and give immediate lubrication to all components when cold oil with high viscosity causes a restriction to the oil flow through oil cooler (10) and oil filter (11). Oil pump (13) sends the cold oil through the bypass valves around the oil cooler and oil filter to oil manifold (5) in the cylinder block.

When the oil gets warm, the pressure difference in the bypass valves decreases and the bypass valves close. Now there is a normal flow of oil through the oil cooler and oil filter.

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 lubrication of the engine.

Flow Of Oil (Engine Cold)
(8) Oil cooler bypass. (9) Oil filter bypass. (10) Engine oil cooler. (11) Oil filter. (12) Turbocharger. (13) Oil pump. (14) Oil pan.

Cooling System

This engine has a pressure type cooling system equipped with a shunt line.

The pressure type cooling system has 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.

NOTE: In air to air aftercooled systems, a coolant mixture with a minimum of 30 percent ethylene glycol base antifreeze must be used for efficient water pump performance. This mixture keeps the cavitation temperature range of the coolant high enough for efficient performance.

Cooling System (Engine Warm)
(1) Cylinder head. (2) Water temperature regulator. (3) Outlet hose. (4) Vent tube. (5) Shunt line. (6) Water elbow. (7) Water pump. (8) Cylinder block. (9) Oil cooler. (10) Inlet hose. (11) Radiator.

In operation water pump (7) sends most of the coolant from radiator (11) to oil cooler (9).

The coolant from oil cooler (9) goes through a bonnet and elbow into cylinder block (8). Inside the cylinder block, the coolant goes around the cylinder liners and up through the water directors into the cylinder head. The water directors send the flow of coolant around the valves and the passages for exhaust gases in the cylinder head. The coolant then goes to the front of the cylinder head. At this point, water temperature regulator (2) controls the direction of coolant flow.

If the coolant temperature is less than normal for engine operation, water temperature regulator (2) is closed. The coolant flows through the regulator housing and elbow (6) back to water pump (7).

If the coolant is at normal operating temperature (engine warm) water temperature regulator (2) is open and the coolant flows to radiator (11) through outlet hose (3). The coolant is made cooler as it moves through the radiator. When the coolant gets to the bottom of the radiator, it goes through inlet hose (10) and into the water pump.

NOTE: Water temperature regulator (2) is an important part of the cooling system. It divides coolant flow between radiator (11) and bypass [water elbow (6)] 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 operating temperatures.

Shunt line (5) gives several advantages to the cooling system.

1. The shunt line gives a positive coolant pressure at the water pump inlet to prevent pump cavitation.

2. A small flow of coolant constantly goes through shunt line (5) to the inlet of water pump (7). This causes a small amount of coolant to move constantly through vent tube (4) between the lower and upper compartment in the radiator top tank. Since the flow through the vent tube is small and the volume of the upper compartment is large, air in the coolant comes out of the coolant as it goes into the upper compartment.

3. The shunt line is a fill line when the cooling system is first filled with coolant. This lets the cooling system fill from the bottom to push any air in the system out the top.

Coolant For Air Compressor

Coolant Flow In Air Compressor
(1) Outlet hose. (2) Inlet hose. (3) Air compressor.

The coolant for the air compressor (3) comes from the cylinder block through hose (2) and into the air compressor. The coolant goes from the air compressor through hose (1) back into the front of the cylinder head.

Cooling System Components

Water Pump

The water pump is located on the left front side of the engine. It is gear driven by the timing gears at a 1:1 ratio.

The centrifugal-type water pump has two seals, one prevents leakage of water and the other prevents leakage of lubricant.

An opening in the bottom of the pump housing allows any leakage at the water seal or the rear bearing oil seal to escape.

Fan

The fan is driven by two V-belts, from a pulley on the crankshaft and the fan drive. Belt tension is adjusted by moving the alternator.

Basic Block

Cylinder Block And Liners

A steel spacer plate is used between the cylinder head and the block to eliminate liner counterbore and to provide maximum liner flange support area (the liner flange sits directly on the cylinder block).

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

Pistons, Rings And Connecting Rods

The piston has three rings; two compression and one oil ring. All rings are located above the piston pin bore. The two compression rings seat in an iron band which is cast into the piston. The pistons use compression rings which are of the KEYSTONE type. KEYSTONE rings have a tapered shape and the movement of the rings in the piston groove (also of tapered shape) results in a constantly changing clearance (scrubbing action) between the ring and the groove. This action results in a reduction of carbon deposit and possible sticking of rings.

The oil ring is a standard (conventional) type and is spring loaded. Holes in the oil ring groove provide for the return of oil to the crankcase.

The piston pin bore in the piston is offset (moved away) from the center of the piston 0.76 mm (.030 in). The full floating piston pin is held in the piston by two snap rings which fit into grooves in the piston pin bore.

The piston pin end of the connecting rod is tapered to give more bearing surface at the area of highest load. The connecting rod is installed on the piston with the bearing tab slots on the same side as the "V" mark on the piston.

Crankshaft

The crankshaft changes the combustion forces in the cylinder into usable rotating torque which powers the machine. There is a gear at the front of the crankshaft that drives the timing gears and the engine oil pump. The connecting rod bearing surfaces get oil for lubrication through passages drilled in the crankshaft. A lip type seal and wear sleeve is used to control oil leakage in the front crankshaft seal. A hydrodynamic grooved seal assembly is used to control rear crankshaft oil leakage. The hydrodynamic grooves in the seal lip move lubrication oil back into the crankcase as the crankshaft turns.

Vibration Damper

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

Cross Section Of A Vibration Damper
(1) Weight. (2) Case.

The vibration damper is installed on the front of the crankshaft. The damper has a weight in a metal housing. The space between the weight and the housing is filled with a thick fluid. The weight moves in the housing to limit the torsional vibration.

Electrical System

The engine 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), disconnect switch, 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.

If the machine has a disconnect switch, the starting circuit can operate only after the disconnect switch is put in the ON position.

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.

Starting System Components

Solenoid

A solenoid is a magnetic switch that does two basic operations.

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

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

Typical Solenoid Schematic

The solenoid switch is made of an electromagnet (one or 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 starting 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 windings and the pull-in windings. Both have the same number of turns around the cylinder, but the pull-in windings 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.

Starting Motor

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

The starting motor has a solenoid. When the start switch is activated, the solenoid will move the starting motor pinion to engage it with the ring gear on the flywheel of the engine. The starting motor pinion will engage with the ring gear before the electric contacts in the solenoid close the circuit between the battery and the starting motor. When the circuit between the battery and the starting motor is complete, the pinion will turn the engine flywheel. A clutch gives protection for the starting motor so that the engine cannot turn the starting motor too fast. When the start switch is released, the starting motor pinion will move away from the ring gear.

Starting 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 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 (an adjustment to make the circuit complete again) after it becomes cool. Push the reset button to close the contacts and reset the circuit breaker.