Engine Systems

1
Engine Systems
2
Five (5) Engine Systems

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

3
Compression System

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

Parts
Valves Valve springs Connecting
rod Crankshaft Gaskets
Block Piston Piston rings Cylinder head Cylinder
bore
4
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.

5
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

6
Detonation

• 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
  pinging.
• 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
7
Preignition

• 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
  cylinder.
• 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
  improperly
• A lean fuel mixture.

8
Valves

• 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
9
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.

10
Valve Seats

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

11
Pistons

• 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

12
Piston--cont.

• 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.

13
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.

14
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.

Compression
Oil
Wiper
15
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.

16
Cylinder Bore

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

17
Crankcase Breather

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

18
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
  speed.

Compression release pin
19
Fuel System
20
Introduction

• 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

21
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
  heat.
• 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

22
Volatility

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

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.

23
Vaporization

• 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).

24
Oxygenated Gasoline

• Clean Air Act 1990 requires gasoline to be
  modified with oxygen additives in nonattainment
  zones.
• 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
  engines.
• MTBE
• Removed from marked because of health concerns.

25
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
26
Engine Emissions--cont.

• Carbon Monoxide
• Product of incomplete combustion
• The richer the air-fuel ration, the more CO is
  produced.
• 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)

27
Octane

• 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.

28
Octane--cont.

• 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.

29
Octane--cont.

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

30
Fuel System--Carburetor
31
Introduction

• 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.
32
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
  principle.
• Air flowing through a narrowed portion of a tube
  increases in velocity and decreases in pressure.

33
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
  engine.

34
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.

35
Carburetor--Venturi

• A pressure difference is also needed to cause the
  fuel to flow from the fuel bowel into the air
  stream.
• 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.

36
Carburetor-Throttle

• Very few engines operate at a constant load and
  constant speed.
• To adjust the rate of fuel flow a throttle is
  used.
• 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.
37
Throttle--cont.

• 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
power
38
Carburetor-Choke

• 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
  mixture.
• This was accomplished by adding a choke.

39
Carburetor-Choke--cont.

• Closing the choke increases the pressure
  difference between the fuel bowel and the
  venturi.
• Increased pressure difference increased fuel
  flow
• 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.

40
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.

41
Carburetor-Float

• 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
  constant.
• A constant level of fuel is maintained in the
  fuel bowel by the float, float needle valve and
  float needle valve seat.

42
Complete Carburetor - Old Style
43
Carburetor-Additional Features

• Several additional features have been tried/added
  to improve carburetor performance.
• Air bleeds
• Fixed jets
• Transition ports
• Pilot jets

44
Carburetor Designs

• All carburetors have the same basic components.
  The design of any individual carburetor is
  determined by the operating conditions of the
  engine.
• 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,
  venturi.

45
Three Types of Briggs Stratton Carburetors
Vacu-jet

• 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.

46
Three Types of Briggs Stratton
Carburetors--cont.
Pulsa-jet

• 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.

47
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)

48
Three Types of Briggs Stratton
Carburetors--cont.
Flow-jet

• 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.

49
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.

50
Fuel System---Governor
51
Introduction

• 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

52
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.

53
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
  speed.
• 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
  throttle.

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.
54
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
constant.
55
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
  out.
• The higher the speed the greater the force
  produced.

56
Mechanical Governor--cont
57
Electrical System
58
Introduction

• 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.

59
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

60
Terms

• 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
  circuit.
• 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.

61
Terms-cont.

• 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
  direction.
• Polarity the state of an object as negative or
  positive.
• Amperes the unit of measure for current flow.

62
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
  direction.
• Alternating current is supplied by generators and
  alternators.
• How often this occurs is called the frequency.

63
Direct Current

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

64
Resistance

• Resistance is opposition to the flow of
  electrons.
• 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
65
Circuits

• 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

66
Circuits--Series

• 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.

67
Circuits--Parallel

• In parallel circuits the electricity has
  alternative paths through the loads in the
  circuit.
• 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.

68
Circuits--Series-Parallel

• Circuits that have loads in both series and
  parallel.
• 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
  other.

69
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.

70
Ohms Law

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

71
Magnetism

• 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

72
Induction

• 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
  conductor.
• 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.

73
Five Small Gas Engine Electrical Systems

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

74
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.

75
Charging System--cont.

• The components of a charging system may include
• Coil
• Magnets
• Voltage regulator
• Rectifier
• Switches
• Conductors

76
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

77
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
  circuit.
• Solid state ignition
• Uses a transistor to break the primary circuit.

78
Ignition system--Magneto Ignition

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

79
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.

Condenser
Secondary Winding
Primary Winding
Lamination stack
Points
Magnetic field
Armature
Flywheel magnets

• With current flowing in the primary circuit, a
  magnetic field develops around the primary coil.
• This magnetic field also surrounds the secondary
  coil.
• As the flywheel continues to rotate the breaker
  points open.

80
Magneto Ignition System- Firing Spark Plug

• When the breaker points open the magnetic field
  produced by the current in the primary winding
  collapses.

• 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
  plug.

81
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.

82
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.

83
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

84
Staring Systems--cont.

• Single Switch
• For systems with a single switch the switch must
  be able to switch the current for the starting
  motor.
• 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.

85
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
  load.
• Each separate circuit should have overload
  protection.

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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
  system.
• Safety systems can include
• Low oil switch
• Seat switch
• Anti after fire solenoid
• Deck switch
• Transmission switch
• Tilt switch

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Questions