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Engine Systems


Engine Systems ... Charging Ignition ... piece Two piece Projection-tip Valve hardfacing Valve stem surface treatments Valve head design Interference interface angle ... – PowerPoint PPT presentation

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Title: Engine Systems

Engine Systems
Five (5) Engine Systems
  • All engine parts and functions can be divided
    into five (5) systems.
  • Compression
  • Fuel
  • Electrical
  • Cooling
  • Lubrication

Compression System
  • The compression system includes all of the parts
    that create, contain and manage the engine

Valves Valve springs Connecting
rod Crankshaft Gaskets
Block Piston Piston rings Cylinder head Cylinder
Adiabatic Process
  • A process in which heat is derived from the
    process itself.
  • During compression heat is produced from the work
    applied by the piston.
  • The greater the work, higher compression, the
    greater the heat produced.
  • Changes in the charge
  • As the air-fuel mixture is compressed the
    molecular forces produce heat.
  • As the temperature increases gasoline molecules
    become more active. This results in additional
    heat to the air-fuel charge.
  • Results of heating
  • Small droplets of gasoline are vaporized.
  • Larger droplets are broken apart.
  • Reduced energy required to maintain combustion.

Compression Problems
  • Two possible problems
  • Inadequate compression
  • Excessive compression
  • Inadequate compression
  • Commonly caused by leaks
  • Maverick air undesirable air entering the engine
    through leaks.
  • Excessive compression
  • Harder starting
  • Engine performance problems
  • Detonation
  • Preignition

  • An undesirable engine condition in which pockets
    of fuel start to burn at about the same time as
    the spark plug fires.
  • Multiple pressure fronts collide
  • Sometimes called knocking, spark knock or
  • Causes large pressure differentials in the
    combustion chamber.
  • Can cause engine damage.
  • Causes
  • Increased compression
  • High temperatures
  • Lean fuel/air mixture
  • Advanced ignition timing
  • Lower octane fuels

Prevention Remove any cause
  • Fuel starts to burn before the spark plug fires.
  • Decreases engine performance and produces and
    audible pinging or knocking sound in the engine.
  • Increases the peak combustion pressure in the
  • Increases internal temperature.
  • Will cause engine parts like pistons, connecting
    rods and crankshafts to fail.
  • Causes
  • An overheated spark plug
  • Glowing carbon deposits
  • Over heated exhaust valve
  • A sharp edge in the combustion chamber or on top
    of a piston
  • Sharp edges on valves that were reground
  • A lean fuel mixture.

  • Control flow of air-fuel into and exhaust gases
    out of the cylinder.
  • Types
  • One piece
  • Two piece
  • Projection-tip
  • Valve hardfacing
  • Valve stem surface treatments
  • Valve head design
  • Interference interface angle
  • Face can be resurfaced
  • Valve dynamics
  • Most valves rotate slightly each time they open
    and close.
  • Rotation improves temperature distribution
  • Rotation helps clean valve interface.

-- Rotation can be enhanced through use of
valve rotators
Valve Guide
  • Controls the position of the valves
  • Subject to fluctuations in temperature, chemical
    corrosion, ingestion of foreign material and for
    the exhaust valve, high temperatures.
  • Must provide a predictable and consistent
    clearance between itself and the valve stem.
  • Can be aluminum, brass or sintered iron.

Valve Seats
  • Mate with valve face to seal combustion chamber.
  • Metal to metal seal
  • Usually insert
  • Can be resurfaced

  • Acts as moveable end of the combustion chamber
    and must withstand pressure fluctuations, thermal
    stress, and mechanical loads.
  • May use elliptical shape
  • Elliptical when cold
  • Diameter at piston pin bore expands more that
    thin edge of piston.
  • Round when hot

  • Some piston pins are offset
  • Piston must be orientated correctly in bore.
  • Windows are used in oil ring groove to allow
    excess oil to return to crankcase.

Ring Grooves
  • Ring grooves are machined grooves in the piston
    designed to hold the rings.
  • Ring lands are the areas of the piston between
    the ring grooves.
  • The clearance between the rings and the ring
    lands is critical.
  • During overhaul the grooves should be cleaned
    with a ring groove cleaner.

Piston Rings
  • The job of the rings is to fill the space between
    the piston and the cylinder walls.
  • The combustion chamber is sealed by a thin film
    of oil between the rings and the piston and
    between the rings and the cylinder wall.
  • Usually constructed of cast iron.
  • The total number of rings per piston can vary,
    but there are three types of rings on each piston.

Piston Rings--cont.
  • Compression
  • Subject to to greatest amount of chemical
    corrosion and highest temperatures.
  • Transfers 70 of combustion heat from piston to
    cylinder walls.

Compression Ring
Wiper Ring
Oil Ring
  • Wiper ring
  • Meters oil film on cylinder walls
  • Must be installed correctly.
  • Oil ring
  • Constructed of two thin rails with holes or slots
    cut inbetween.
  • Has the highest pressure against the cylinder
    wall of the three rings.

Cylinder Bore
  • Three types
  • Cast aluminum
  • Cast aluminum with cast iron sleeve
  • Cast iron
  • Usually use a cross-hatch finish to improves ring

Crankcase Breather
  • Maintains pressure in the crankcase at less than
    ambient pressure to assist in the control of oil
  • Excessive blow by renders the breather useless.
  • Old engines vent to the atmosphere.
  • New engines vent to the carburetor.

Compression Release
  • Compression release systems are used to decrease
    effort required to start engine.
  • Holds the exhaust or intake valve slightly open
    during starting, and then allows it to fully
    close once engine starts.
  • May be designed into camshaft and hold the valve
    open for a short period of time on every
    compression stoke.
  • May be mechanical. Engages during starting and
    disengages after the engine reaches operating

Compression release pin
Fuel System
  • The function of the fuel system is to store,
    meter, atomize, vaporize and start the mixing
    with the air.
  • Fuel system parts
  • Supply (tank)
  • Lines
  • Valves
  • Filter
  • Pump
  • Carburetor
  • Common Small Engine Fuels include
  • Gasoline
  • Diesel
  • LPG
  • LNG

Combustion Chemistry
  • Combustion the rapid oxidizing chemical reaction
    in which fuel chemically combines with oxygen in
    the atmosphere and releases energy in the form of
  • Stoichiometric ratio
  • Ratio of air to fuel, by weight, where the most
    efficient combustion occurs.
  • Does not produce maximum horsepower.
  • Lambda (?) excess air factor
  • A numerical value assigned to represent the
    stoichiometric ration of atmospheric air to any
    hydrocarbon fuel.
  • A ? of 1.0 is theoretically perfect ratio.
  • Small engines use a ? of 0.6 to 0.8

  • Volatility is the propensity of a liquid to
    become a vapor.
  • The volatility of gasoline changes with the

Low Volatility High Volatility
Poor cold weather operation Poor hot weather operation
Spark plug deposit buildup Vapor lock
Combustion chamber deposit buildup Poor fuel economy
Poor cold starting Excessive fuel evaporation
  • Vapor lock the stoppage of fuel flow caused by
    internal pressure of fuel vapor bubbles.

  • Vaporization is the process converting a liquid
    to a vapor.
  • Requires heat
  • The rate and efficiency of vaporization is
    improved when the liquid is reduced to small
    droplets (atomized).

Oxygenated Gasoline
  • Clean Air Act 1990 requires gasoline to be
    modified with oxygen additives in nonattainment
  • Nonattainment zone areas of the country that
    exceed ozone levels.
  • Two common additives
  • Alcohol
  • Methyl Tertiary Butyl Ether (MTBE)
  • Alcohol
  • Two types
  • Ethanol distilled from grains and sugar
    containing plants
  • Methanol distilled form natural gas
  • The addition of alcohol to gasoline increases the
    available oxygen during the combustion process.
  • Up to 10 ethanol acceptable for Briggs
    Stratton engines.
  • Methanol should not be used in Briggs Stratton
  • MTBE
  • Removed from marked because of health concerns.

Engine Emissions
  • An engine with a ? of 1.0 exhausts 12 water
    vapor and 14 carbon dioxide.
  • Emissions are changed because additional
    chemicals are added to improve the performance of
    the gasoline.

Additive Function
Anti-icers Prevent fuel from freezing in lines
Anti-oxidants Reduce hum formation in stored gasoline
Corrosion inhibitors Minimize corrosion in fuel system
Detergents Reduce/remove fuel system deposits
Fluidizer oils Control intake valve deposits
Lead replacement additives Minimize exhaust valve seat wear
Metal deactivators Minimize effects of metals present in gasoline
Engine Emissions--cont.
  • Carbon Monoxide
  • Product of incomplete combustion
  • The richer the air-fuel ration, the more CO is
  • Hydrocarbon emissions
  • Product of incomplete combustion
  • Contains gasses not readily oxidized at normal
    engine operating temperature. Methane, ethane,
    acetylene, etc.
  • Oxides of Nitrogen
  • Nitric oxide (CO)
  • Nitrogen dioxide (CO2)
  • Dinitrogen monoxide (N2O)

  • Octane the ability of a fuel sample to resist
    engine knock and/or ping.
  • The octane rating required for an engine is based
    on the compression ratio.
  • Higher compression ratio requires higher octane.
  • Higher compression ratios increase compression
    temperatures--increases chance of autoignition or
    the fuel.

  • Antiknock Index (AKI)
  • The number assigned to gasoline that indicates
    the ability to eliminate knocking and/or pinging.
  • Research octane number (RON)
  • Market octane number (MON)
  • RON the octane number that affects engine knock
    at low to medium speed
  • MON the octane number that affects engine knock
    at high speed, performance in severe operating
    conditions and under load.

  • The AKI is posted on the gasoline pump.
  • The AKI can be raised or lowered by the use of
  • Tetraethyl Lead
  • Alcohol
  • Methyl Tertiary Butyl Ether (MTBE)

Fuel System--Carburetor
  • Carburetor the engine component that provides
    the required air-fuel mixture to the combustion
    chamber based on engine speed and load.

Carburetors achieve this result using four common
principles of fluids.
Four Fluid Principles
  • Fluids flow from areas of high pressure to areas
    of low pressure.
  • When there is no pressure difference--there is no
    fluid flow.
  • Fluids exert pressure of the same value
    throughout a system.
  • Fluid flow in a carburetor utilizes Bernoullis
  • Air flowing through a narrowed portion of a tube
    increases in velocity and decreases in pressure.

Carburetor Operating Principles
  • A carburetor is a tube attached to the intake
    port of the engine and open to the atmosphere.
  • On the intake stroke a volume with little to no
    pressure develops in the combustion chamber.
  • Atmospheric pressure outside the engine--14.7 psi
  • Low pressure in the combustion chamber--0 to
    slight vacuum.
  • Result air flows from outside to inside the

Carburetor Operating Principles
  • As the air flows through the carburetor, the fuel
    is metered, atomized and vaporized.
  • To have available fuel, the carburetor must have
    a source of fuel.
  • In the float type carburetor this source is the
    fuel bowel.

  • A pressure difference is also needed to cause the
    fuel to flow from the fuel bowel into the air
  • This is accomplished using a venturi, Bernoullis
    principle and a tube connecting the mouth of the
    venture to the fuel bowel.
  • This is a functioning carburetor and it will
    operate an engine as long as it has a constant
    load and constant speed.

  • Very few engines operate at a constant load and
    constant speed.
  • To adjust the rate of fuel flow a throttle is
  • When the throttle is in the closed position there
    is minimum air flow through the carburetor.

Less air flow less pressure difference in
venturi Less pressure difference less fuel
flow Less fuel flow less speed.
  • When the throttle is in the wide open position,
    there is maximum air flow through the carburetor.
  • To provide a means to adjust maximum fuel flow, a
    needle valve was added to the orifice in the
    emulsion tube.

Maximum air flow maximum pressure
difference Maximum pressure difference maximum
fuel flow Maximum fuel flow maximum speed
  • A carburetor with this design would function well
    under varying loads and speeds,
  • Starting is a different condition
  • For starting an engine needs a richer fuel-air
  • This was accomplished by adding a choke.

  • Closing the choke increases the pressure
    difference between the fuel bowel and the
  • Increased pressure difference increased fuel
  • Once engine starts the choke must be opened to
    prevent the engine from running too rich.
  • A primer bulb has replaced the choke on most
    modern engines.

Carburetor-Idle Circuit
  • The addition of a choke/primer improved engine
    starting, but this carburetor still has a problem
    if the engine needs to idle.
  • When the throttle is in the idle position, almost
    closed, the area with greatest restriction, and
    greatest pressure difference, moves from the
    venturi to the area between the throttle plate
    and the wall of the tube.
  • This problem was solved with the addition of an
    idle circuit and idle needle valve.

  • To have constant fuel flow with constant pressure
    difference the lift, distance from the top of the
    fuel to the top of the main nozzle, must remain
  • A constant level of fuel is maintained in the
    fuel bowel by the float, float needle valve and
    float needle valve seat.

Complete Carburetor - Old Style
Carburetor-Additional Features
  • Several additional features have been tried/added
    to improve carburetor performance.
  • Air bleeds
  • Fixed jets
  • Transition ports
  • Pilot jets

Carburetor Designs
  • All carburetors have the same basic components.
    The design of any individual carburetor is
    determined by the operating conditions of the
  • The more variable the load and speed the more
    complex the required carburetor design.
  • Carburetors are also classified by the direction
    of the air flow.
  • Updraft
  • Downdraft
  • Sidedraft
  • Some carburetors also use multiple barrels,

Three Types of Briggs Stratton Carburetors
  • Carburetor attached to top of fuel tank.
  • A single pickup tube is used between the
    carburetor and the tank.
  • Must use shallow fuel tank because the main jet
    extends from the venturi to the bottom of the
    fuel tank.
  • As the level of fuel in the tank changes, the
    fuel-air ratio changes.
  • Not included in latest B S repair manual.

Three Types of Briggs Stratton
  • Carburetor is attached to the top of fuel the
    fuel tank.
  • Two tubes are used.
  • Primary is attached to fuel pump to pump fuel
    from the main tank to the secondary tank.
  • Secondary tube draws fuel from secondary tank to
    the venturi.
  • The fuel pump is designed with excessive
    capacity, and the secondary tank has a drain
  • The fuel in the secondary tank stays at a
    constant level.
  • Not included in latest B S repair manual.

Pulsa Jet Parts
  1. Fuel pump
  2. Primary fuel tube
  3. Primary fuel tank
  4. Primary fuel tube check valve
  5. Fuel screens
  6. Secondary fuel tube check valve
  1. Secondary fuel tank
  2. Secondary fuel tube
  3. Secondary tank drain
  4. Choke
  5. High speed needle valve
  6. Air horn (inlet)

Three Types of Briggs Stratton
  • Different types and sizes are used.
  • Most popular on modern engines.
  • All use a fuel bowel and float system to maintain
    a consistent supply of fuel.

Fuel Injection
  • Fuel injection is the preferred method of
    metering the fuel in modern engines.
  • Cost has limited use for small gas engines.
  • BOSH has developed a system.

Fuel System---Governor
  • The function of the governor system is to
    maintain the desired engine speed regardless of
    engine load.
  • The governor is attached to the throttle on the
    carburetor and supplies a force that attempts to
    close the throttle.
  • The governor spring is attached to the governor
    linkage and applies a force that attempts to open
    the throttle.
  • A constant engine speed means these two forces
    are balanced.
  • Small engines use two types of governors.
  • Pneumatic
  • Mechanical

Pneumatic Governor Operation--Engine Not Operating
  1. When preparing to start an engine the throttle
    will be set to the run (choke) position.
  2. The engine is stopped--there is no air flow.
  3. No air flow means the governor will not be
    producing any force.
  4. In the choke position the the governor spring
    produces the maximum force.
  5. The throttle is wide open.

Pneumatic Governor Operation--Top No Load Speed
  • Once the engine starts, the throttle is moved to
    the run position.
  • This sets the engine to operate at top--no load
  • When the flywheel starts to rotate, air starts
    flowing pass the the governor arm.
  • Air movement produces a force on the governor
    vane which is then applied to the linkage.
  • The force on the governor linkage stretches the
    governor spring and attempts to close the

When the force on the governor linkage equals the
force produced by the spring, the throttle is
held in a constant position and the engine runs
at a constant speed.
Pneumatic Governor Operation--Engine Under Load
  • When the engine load increases the engine speed
    is reduced.
  • Less speed Less air flow
  • Less air flow less force
  • When the force produced by the governor
    decreases, the force produced by governor spring
    is greater and the spring opens the throttle.
  • Opened throttle more fuel
  • More fuel more speed
  • More speed more air flow.
  • More air flow more force
  • The governor and throttle spring are constantly
    wrestling for control of the throttle.

When the forces are balanced, the engine speed is
Mechanical Governor
  • The mechanical governor operates on the same
    principles as the pneumatic governor.
  • The difference is that the force to balance the
    governor spring is produced by rotating weights
    not a pneumatic arm.
  • The weights are rotated by the governor gear
    which meshes with the crankshaft gear.
  • As the governor spins the governor weights move
    out from the center shaft.
  • The weights are mounted on a lever arm that
    pushes the governor shaft up as the weights move
  • The higher the speed the greater the force

Mechanical Governor--cont
Electrical System
  • Electricity is a predictable force, yet it is
    often challenging to service electrical systems
    because it can not been seen and there is the
    concern of electrical shock.
  • Because almost all small engine electrical
    systems operate on 12 volts, the danger of severe
    electrical shock is reduced.

Electrical Terms
  • Before attempting to understand small engine
    electrical systems, it is important to know the
    terms and parts associated with electricity and
    the electrical systems.
  • Electricity
  • Conductor
  • Electron
  • Free Electron
  • Voltage
  • Load
  • Current
  • Direct Current
  • Alternating Current
  • Polarity
  • Amperes
  • Resistance
  • Short circuit
  • Series Circuits
  • Parallel Circuits
  • Ohms Law
  • Magnetism
  • Induction
  • Solenoid
  • Diodes
  • Voltage Regulator
  • Battery
  • Primary winding
  • Secondary winding
  • Condenser

  • Electricity is energy created by the flow of
    electrons in a conductor.
  • Conductor a material that allows the free flow
    of electrons.
  • Electron one of three parts of atoms. Electrons
    have negative charge and rotate in orbits around
    the nucleus of the atom.
  • Free Electron an electron that is capable of
    jumping in or out of an orbit.
  • Voltage the amount of electrical pressure in a
  • Voltage is measured in volts (V).
  • A voltage exists when there is an excess number
    of electrons at one terminal of a voltage source
    and deficiency of electrons at the other terminal.

  • Circuit A complete path that controls the rate
    and direction of electron flow. The parts of a
    circuit include
  • Voltage source
  • Pathway for electrons
  • Load or loads
  • Controls
  • Current the flow of electrons past a point in
    the circuit. It may be alternating or direct.
  • Alternating current the flow of electrons
    reverses direction at regular intervals.
  • Direct current the flow of electrons is in one
  • Polarity the state of an object as negative or
  • Amperes the unit of measure for current flow.

Alternating Current
  • The voltage builds to a maximum value in one
    direction (polarity), decreases to zero and then
    builds to a maximum direction in the other
  • Alternating current is supplied by generators and
  • How often this occurs is called the frequency.

Direct Current
  • In direct current the polarity and the voltage
    stay constant.
  • Direct current is supplied by batteries or

  • Resistance is opposition to the flow of
  • All circuit components have some resistance.
  • Forcing electricity through a resistance uses
    energy. The energy is lost as heat.
  • Resistance is measured in units of Ohms (?).
  • The amount of current flow and resistance in a
    circuit determines the wire size for the circuit.

Wire Size and Resistance
AWG Number Diameter ?/1000 ft (68 oF)
12 80.8 1.6
14 64.1 2.5
16 50.8 4.0
18 40.3 6.4
20 32 10.2
22 25.35 16.2
  • A complete path that controls the rate and
    direction of electron flow.
  • Four terms are used to describe the different
    types of circuits
  • Series circuit
  • Parallel Circuit
  • Series-Parallel
  • Short Circuit

  • In a series circuit the electricity has no
    alternative paths.
  • All of the electricity must go through all of the
    loads in the circuit.
  • In the illustration the switch is in series with
    two loads that are also in series.
  • All types of small engine electrical systems may
    have components in series.

  • In parallel circuits the electricity has
    alternative paths through the loads in the
  • The amount of electricity that flows down either
    path is determined by the voltage and resistance
    of that path.
  • In the illustration, a switch is in series with
    two loads that are in parallel.

  • Circuits that have loads in both series and
  • Not vary common in small gas engines.
  • In the illustration load one is in series with
    loads two and three--which are parallel with each

Circuit--Short Circuit
  • A short circuit occurs when a low resistance
    circuit to ground develops.
  • Low resistance means high current flow.
  • Excessive current flow will damage electrical
    components if it is not stopped.
  • Over current protection devices are used to
    protect the circuit when a short occurs.

Ohms Law
  • Ohms Law explains the relationship between
    voltage, amperage and resistance.
  • Law

  • Magnetism is an atomic level force derived from
    the atomic structure and motion of certain
    orbiting electrons.
  • A Magnet field is an area of magnetic force
    created and defined by lines of magnetic flux
    surrounding a material in three dimensions.
  • Magnetic flux invisible lines of force in a
    magnetic field.
  • Magnet a material that attracts iron, cobalt or
    nickel and produces a magnetic field.
  • Permanent
  • Temporary

  • Induction the production of voltage and current
    by the proximity and motion of a magnetic field
    or electric charge.
  • With a conductor, either current, a magnetic
    field or motion can be produced as long as the
    other two are present.
  • Magnetic field When electricity passes through a
    conductor it forms a magnetic field around the
  • Current When a conductor passes through a
    magnetic field or when magnetic field moves
    and/or varies in strength around a conductor,
    electrons are made to flow. A current is induced
    in the conductor.

Five Small Gas Engine Electrical Systems
  • Small engines may have one or more of five (5)
    electrical systems.
  • Charging
  • Ignition
  • Starting
  • Accessories
  • Safety

1. Charging System
  • Charging systems produces electrical to operate
    accessories and the replace electrical energy
    taken from a battery.
  • Two different systems can be used.
  • Generator
  • Alternator
  • Generator produces DC.
  • Alternator produces AC. When DC is needed the
    current is converted, rectified.
  • Some small engines use a stationary coil close to
    the flywheel. When the flywheel magnets pass by
    the coil they induce a current in the coil.
  • Other systems use stationary magnets and a
    rotating coil.
  • Conductors are sized for circuits with low
    current flow.

Charging System--cont.
  • The components of a charging system may include
  • Coil
  • Magnets
  • Voltage regulator
  • Rectifier
  • Switches
  • Conductors

2. Ignition System
  • The ignition system provides a high voltage spark
    in the combustion chamber at the proper time.
  • Two types of ignition systems
  • Battery
  • Magneto
  • Battery
  • Battery systems transforms the battery voltage
    and fires the spark plug at the correct time.
  • Magneto
  • Magneto systems must produce the current,
    transform the voltage and time the spark plug.
  • Most small engines use the magneto system
  • Two types of magneto systems
  • Breaker point ignition
  • Solid state (electronic) ignition

2. Ignition System-cont.
  • Breaker point ignition
  • Older system. Most manufacturers have replaced
    them with solid state.
  • Uses a set of points to break the primary
  • Solid state ignition
  • Uses a transistor to break the primary circuit.

Ignition system--Magneto Ignition
  • Magnets
  • Points (Breaker point only)
  • Trigger coil
  • Conductors
  • Spark plug
  • Condenser (Breaker point only)
  • Lamination stack
  • Primary winding
  • Secondary winding

Magneto Ignition System--Points
Spark plug
  • As magnets in flywheel rotate past the magneto,
    the points close.
  • The magnetic flux of the magnets in the flywheel
    induces a current in the primary coil.

Secondary Winding
Primary Winding
Lamination stack
Magnetic field
Flywheel magnets
  • With current flowing in the primary circuit, a
    magnetic field develops around the primary coil.
  • This magnetic field also surrounds the secondary
  • As the flywheel continues to rotate the breaker
    points open.

Magneto Ignition System- Firing Spark Plug
  • When the breaker points open the magnetic field
    produced by the current in the primary winding
  • The collapsing magnetic field flows across the
    secondary coil which induces a current in the
    secondary coil.
  • Because there is a 601 ratio of windings in the
    two coils, the voltage is transformed to the
    10,000 and 15,000 volts needed to fire the spark

Magneto Ignition system
  • As long as the flywheel is rotating and the
    ignition switch is on, the spark plug fires every
    time the magnets move past the magneto.

Differences Between Breaker Point and Solid State
Ignition System
  • The solid state (electronic) ignition system
    replaces the mechanical points (switch) with an
    electronic switch.
  • A trigger coil senses the presence of the magnets
    and opens the primary circuit.

3. Starting System
  • The purpose of the starting system is to use
    energy to turn the engine until it starts.
  • System components may include
  • Electrical source
  • Starting motor
  • Conductors
  • Ignition switch
  • Solenoid switch
  • Two primary electrical systems.
  • Single switch
  • Solenoid

Staring Systems--cont.
  • Single Switch
  • For systems with a single switch the switch must
    be able to switch the current for the starting
  • Requires a heavy duty switch because starter
    motors drawn a lot of current.
  • Solenoid
  • In this system the ignition switch only switches
    the current that powers the solenoid.
  • The solenoid has heavy duty contacts for
    switching the current to the starting motor.

4. Accessories
  • Small engines are used on machines that may
    require electricity to operate accessories.
  • Accessories may include
  • Lights
  • Electrical clutches
  • Electrical lift systems
  • Radio, etc.
  • The conductors must be sized for the electrical
  • Each separate circuit should have overload

5. Safety
  • It is common for small engines to be used on
    machines that may have one or more electrical
    safety systems.
  • These systems are usually designed to stop the
    engine when activated.
  • The electrical system is used because that is the
    easiest way to automate an engine stopping
  • Safety systems can include
  • Low oil switch
  • Seat switch
  • Anti after fire solenoid
  • Deck switch
  • Transmission switch
  • Tilt switch

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