Engines Teaching Manual

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INTERNAL COMBUSTION ENGINESTEACHING MANUAL

Agricultural Education ProgramWashington State University

Pullman, Washington


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Internal Combustion Engines

Teaching Manual

By

Dr. Michael K. Swan

Project Manager

Agricultural Education Program

Washington State University

This manual should be used with

Internal Combustion EnginesLaboratory Manual


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In cooperation with

Biological Systems Engineering Department

Washington State University

Pullman, Washington 99164-6120

TABLE OF CONTENTS

Page

Objectives 3

Suggested activities 7

References 8

Suggested Materials 9

General Information sheet 11

General information transparency masters 18

Ignition system information sheets 22

Ignition system transparency masters 44

Lubrication system information sheets 76

Lubrication system transparency masters 81

Cooling system information sheets 86

Cooling system transparency masters 89

Fuel system information sheets 90

Fuel system transparency masters 98


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Compression system information sheets 112

Compression system transparency masters 121

Trouble shooting information sheets 127


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UNIT OBJECTIVE

After completion of this unit, the student should be able to perform the duties assigned in the

small engines unit. Competencies will be demonstrated by correctly performing the procedures

outlined in the work sheets and lab activities.

SPECIFIC OBJECTIVES

After completion of this unit the student should be able to:

1. Identify the uses of small engines.

2. Identify the advantages of small engines.

3. Identify the disadvantages of small engines.

4. Explain the function of an engine.

5. Understand the four strokes that take place in a small engine.

6. Match all engine measurement terms with the correct definition.

7. Figure out horsepower when given a problem.

8. Figure out bore and stroke when given a problem.

9. Figure out piston displacement when given a problem.

10. Figure out compression ratio when given a problem.

11. Figure out mechanical efficiency when given a problem.

12. Match ignition system terms with the correct definitions.

13. Understand the basic concepts of electricity.


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14. Figure out problems in electricity using ohms law.

15. Define the purpose of the ignition system.

16. Understand the similarities and differences between the different ignition systems.

17. Explain magnetism and its relation to small engines.

18. Explain the function of the ignition coil.

19. Explain the function of the spark plug.

20. Identify the components of a mechanical breaker point ignition system.

21. Explain the function of a mechanical breaker point ignition system.

22. Identify the components of a solid state ignition system.

23. Explain the function of a solid state ignition system.

24. Identify the components of a battery ignition system.

25. Explain the function of a battery ignition system.

26. Match lubrication terms with the correct definitions.

27. Define the purpose of the lubrication system.

28. Identify the various types of lubricating systems.

29. Identify the differences between oil types.

30. Explain the SAE viscosity rating.

31. Analyze the differences between the API engine service motor oil types.

32. List oil contaminants found in oil.

33. Identify and explain the additives found in oil.


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34. Demonstrate the proper selection of oil.

35. Match cooling system terms with the correct definitions.

36. Define the purpose of the cooling system.

37. List the effects of an engine overheating.

38. Identify the causes of overheating.

39. List the features of an air-cooled system.

40. Label the components of an air-cooled system.

41. Match fuel system terms with the correct definitions.

42. Define the purpose of the fuel system.

43. Explain how fuel quality is determined.

44. List the problems with low fuel quality.

45. Identify ways to protect fuel quality.

46. Identify similarities and differences between fuel system types.

47. Explain the components of the fuel system.

48. Identify the types of fuel filters.

49. Identify the types of air cleaners.

50. Define the function of the carburetor.

51. Identify and explain the types of carburetors.

52. Explain the results of lean and rich fuel mixtures.


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53. Identify the types of governors.

54. Define the purpose of the governor.

55. Define the function of the fuel pump.

56. Explain the operation of the fuel pump.

57. Explain the use of the fuel pump hand primer.

58. Match compression system terms with the correct definitions.

59. Explain the operating conditions of a valve.

60. Label the parts of a valve.

61. Explain the relationship between the camshaft lobe and the four power strokes.

62. List the operating conditions of a piston.

63. Label and explain the parts of the piston.

64. Discuss the advantages of various materials used in piston construction.

65. Discuss the disadvantages of various materials used in piston construction.

66. Define the function of the piston rings.

67. Identify the different types of piston rings.

68. Explain the design of the different types of piston rings.

69. Label and explain the parts of the connecting rod.

70. Label the parts of the crankshaft.

71. Explain the ways of balancing the crankshaft.

72. Explain the use of sleeves.


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73. Demonstrate the troubleshooting technique for ignition.

74. Demonstrate the troubleshooting technique for Carburetion.

75. Demonstrate the troubleshooting technique for compression.


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SMALL ENGINES

SUGGESTED ACTIVITIES

A. Obtain additional materials and/or invite resource people to class to

supplement/reinforce information provided in this unit of instruction.

(NOTE: This activity should be completed prior to the teaching of this unit.)

B. Make transparencies from transparency masters included in this unit.

C. Provide students with objectives sheet.

D. Discuss unit and specific objectives.

E. Discuss information sheets.

(NOTE: Use the transparencies to enhance the information as needed.)

F. Provide students with laboratory activities.

REFERENCES USED IN DEVELOPING THIS UNIT

Briggs and Stratton Corporation. (1989). Service and repair instruction: For single cylinder 4-

cycle engines. Milwaukee, WI: Author.

Goering, C. E. (1989). Engine and tractor power. St. Joseph, MI: American Society of

Agricultural Engineers.

Hires, B., Taylor M., & Bundy, M. (1977). Comprehensive small engine repair. Stillwater, OK:

Mid. American Vocational Curriculum Consortium, Inc.

Hoerner, H. J., Bear, W. F., & Ahrens, D. L. (1973). Small gasoline engines: Operation, repair

& maintenance. St. Paul, MN: Hobar Publications.


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Roth, A. C. (1987). Small gas engines fundamentals, service, troubleshooting, & repairs.

South Holland, IL: The Goodheart - Willcox Company, Inc.


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SUGGESTED SUPPLEMENTAL MATERIALS

A. Publications

1. Briggs and Stratton Corporation. (1989). Service and repair instruction:For single cylinder 4-cycle engines. Milwaukee, WI: Author.

2. Goering, C. E. (1989). Engine and tractor power. St. Joseph, MI: American

Society of Agricultural Engineers.

3. Hoerner, H. J., Bear, W. F., & Ahrens, D. L. (1973). Small gasoline engines:

Operation, repair and maintenance. St. Paul, MN: Hobar Publications.

4. Roth, A. C. (1987). Small gas engines fundamentals, service, troubleshooting, andrepairs. South Holland, IL: The Goodheart - Willcox Company, Inc.

5. Care and Operation of Small Gasoline Engines. St. Paul, MN: Hobar Publications.

6. Mechanics Handbooks from Tecumseh. St. Paul, MN: Hobar Publications.

7. Small Engine Repair Series. St. Paul, MN: Hobar Publications.

8. Small Air-Cooled Engines Service Manual. St. Paul, MN: Hobar Publications.


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SUGGESTED SUPPLEMENTAL MATERIALS

B. Audio-visuals

1. John Deere Compact Equipment. St. Paul, MN: Hobar Publications.

2. FOS Compact Equipment Series. St. Paul, MN: Hobar Publications

3. Tecumseh Training Aids.

Tecumseh Products Company

Engine and Transmission Group Service Division

Grafton, WI 53024

(414) 377-2700

4. Briggs & Stratton Vocational Education Program and Teaching Aids.

Briggs & Stratton Corporation

P.O. Box 702

Milwaukee, WI 53201

Attention: Education Department

(414) 445-2800

C. Computer software

1. Small Engine Trouble Shooter. St. Paul, MN: Hobar Publications.


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SMALL ENGINES/GENERAL INFORMATION AND MEASUREMENTS

I. Small Engines in Use.

A. There at least 100 million small engines now being used in the United States.

B. There are 6 million purchased each year.

C. Uses

1. Lawn mowers

2. Snowblowers

3. Chainsaws

4. Air compressors

5. Others

D. Small gasoline engine sizes range from 1/2 to 15 horsepower.

E. Major manufactures.

1. Briggs and Stratton

2. Tecumseh

3. Clinton

4. Kohler

5. Lawn Boy

F. Advantages of small gasoline engines

1. Inexpensive to purchase

2. Inexpensive to operate

3. Portable

4. Compact

5. Light in weight

6. Air cooled

7. Self-contained

8. Easy to service


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G. Disadvantages of small gas engines

1. Hard to start

2. Wear out fast

3. Not very sophisticated (low efficiency)

H. What does an engine do?

1. Convert fossil fuel energy into mechanical energy.

a. Fossil fuel (chemical energy) - mix gas and air (a process called

atomization).

b. Burn gas (heat energy released) - expansion pressure from burning causes

pressure in combustion chamber.

c. Piston is forced down (mechanical energy minus reciprocating action).

d. Crankshaft transfers reciprocating action to rotating action, in which form it can be used.

Chemical energy minus heat energy minus mechanical energy.

I. Events necessary in an internal combustion engine.

1. Intake - air and fuel

2. Compression

3. Ignition

4. Combustion

5. Power

6. Exhaust

J. These six events take place in four strokes in a four stroke engine.

1. Intake stroke - The piston goes down, creating a vacuum in the cylinder which

draws gas through open intake valve into the space above the piston (TM 1-1).

2. Compression stroke - The piston comes up with both valves closed, highly

compressing the gas into the space left between the top of the piston and


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cylinder head (TM 1-2).

3. Power stroke - At this point the magneto sends high tension current to the spark

plug, firing or exploding the compressed gas and driving the piston down (TM

1-3).

4. Exhaust stroke - The exhaust valve opens and the upward stroke of the piston

forces out all of the burnt gases, thus completing the power cycle (TM 1-4).

II. Engine Measurements

A. Work - Moving an object against an opposing force either by a push, pull, or lift. It is

measured in terms of distance and force.

Example: A 5 pound weight lifted 2 feet would equal 10 foot-pounds.

B. Energy - The ability or capacity to do work. When work is done on an object, energy

is stored in that object.

C. Power - Rate at which work is done (rapidly or slowly).

D. Torque - A twisting or turning effort. Turning a lid on a jar or turning a steering

wheel.

Example: Pushing on a 1 1/2 foot crank with 20 lbs. of force equals 30 pound feet of

torque.

E. Horsepower (hp) - The power of one horse.

hp = ft. lbs. per minute = L X W

33,000 33,000 X t

hp = torque X RPM

5252

L = Length in feet

W = Force in pounds

t = Time in minutes

RPM = Revolutions per minute

Example: You have a heavy box loaded with sand that you must


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drag across a level lot for 500 feet in 2 minutes. A pull of 2000

lbs. is required to move the box. What is the horsepower?

hp = 500 X 2000 = 15.15 horse power

33,000 X 2

F. Inertia - The property of all material objects that causes them to resist any change in

speed or direction of travel.

G. Friction - Resistance to motion between two objects in contact with each other.

H. Bore and Stroke - Indicates the size of an engine cylinder.

1. Bore - Diameter of the cylinder.

2. Stroke - Distance the piston travels from BDC (Bottom Dead Center) to TDC(Top Dead Center).

Example: A cylinder 3 by 2 1/2 has a 3 inch bore and a 2 1/2 inch stroke.

I. Piston displacement - Volume that the piston displaces, or sweeps out, as it moves

from BDC to TDC.

Example: You have a cylinder 3 X 2.

Formula: 1/4 (3.14) X D2 X L

D = Diameter of bore

L = Length of stroke

so 0.785 X 9 X 2 = 14.13 Cubic inches

If an engine has 4 cylinders, the total displacement is 56.52 cubic inches (one cubic

in. = 16.39 cubic centimeters) or 927 cc.

J. Compression ratio - The measure of how much the air/fuel mixture is compressed in

an engine cylinder. It is calculated by dividing the air volume in one cylinder with

the piston at BDC by the air volume in the piston at TDC (also refereed to as

clearance volume) to 1.

Example: Volume at BDC is 42.35 the volume at TDC is 4.45. 42.35/4.45 = 9.5:1


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K. Engine performance measurement.

1. Volumetric efficiency - The amount of air/fuel mixture taken into the cylinder

on the intake stroke. The ratio is determined by the amount of air/fuel mixture

that actually enters the cylinder to the amount that could possibly enter.

Example: A cylinder can hold 0.034 ounces of air. The engine is running at a high

speed and 0.027 ounces get in so the volumetric efficiency is 0.027/0.034 or 80%.

The volumetric efficiency should be at least 50% at high speeds.

2. Ways to increase volumetric efficiency

a. Widen intake ports and passages and keep ports and passages as straight

as possible.

b. Smooth the inside surfaces of the intake ports.

c. Use more carburetors or carburetors with a larger air passages.

L. Brake horsepower (bhp) - Horsepower output or power delivered in the engine.

M. Indicated horsepower (ihp) - The power that develops inside the combustion chamber

of the engine during the combustion process.

N. Friction horsepower (fhp) - The power required by the engine to overcome the

friction of the moving parts in the engine (the greatest loss occurs when the rings

scrape on the cylinder walls).

The relationship is bhp = ihp - fhp.

O. Engine efficiency - The relationship between power delivered and power that could

be obtained.

1. Mechanical efficiency - The relationship between bhp and ihp.

Mechanical efficiency = bhp / ihp


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Example: At a certain speed the bhp of an engine is 116 and the ihp is 135.

The mechanical efficiency is 116 = .86 or 86%.

135

The remaining 14% is loss due to fhp.

2. Thermal efficiency - The relationship between power output and the energy of

the fuel burned.

a. Losses due to:

1) Combustion carried away by the cooling system.

2) Exhaust gases.

b. May be as low as 20%.

c. Seldom higher than 25%.


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4-CYCLE SPARK IGNITION ENGINE

INTAKE STROKE


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Transparency Master 1-1


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COMPRESSION STROKE


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POWER STROKE


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EXHAUST STROKE


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SMALL ENGINES/IGNITION SYSTEMS

INFORMATION SHEET

I. Terms and Definitions

A. Ampere -- Unit of measure for electrical current.

B. Armature -- The device to "pick-up" a magnetic field from a moving magnet and toassist the coil in "building-up" a stronger magnetic field within the coil.

C. Battery -- A device that stores chemical energy in reserve for later use; may be a wettype or a dry type.

D. Breaker Points -- Two contact surfaces that are mechanically opened and closed tocontrol flow of electricity; essentially an electrical switch.

E. Capacitor (Condenser) -- Device for temporarily collecting and storing a surge ofelectrical current for later discharge.

F. Circuit -- The path of electrical current, fluids, or gas.

G. Coil -- Essentially a transformer which through the action of induction converts lowvoltage to high voltage.

H. Conductor -- Substance or body through which an electrical current readily flows.(Example: Copper, aluminum and silver.)

I. Current -- Flow of electrons through a conductor.

J. Flashover -- The tendency for current to travel down the outside of the spark plugrather than through the center electrode.

K. Ignition System -- The group of component parts that delivers the spark to the sparkplug at the precise moment to fire the compressed air-fuel at the beginning of thepower stroke.

L. Insulator -- Material that does not readily permit current flow.


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(Example: Rubber, glass, plastic, porcelain, air, and plastic.)

M. Laminations -- In the ignition system it's the layer that is compressed under heat.

N. Magnetic Induction -- Inducing voltage in a conductor that moves across a magnetic

field.

O. Ohm (Resistance) -- Standard unit of measuring resistance to flow of an electricalcurrent.

P. Ohm's Law -- Summarizes the relationship between electrical current, voltage, andresistance.

Q. Spark -- An electrical current possessing sufficient pressure to jump through the airfrom one electrode to another.

R. Spark Advance -- When used with reference to an ignition distributor, means to causethe spark to occur at an earlier time in the timing circle.

S. Spark Gap -- The space between the electrodes of a spark plug through which thespark jumps.

T. Spark Plug -- A device inserted into the combustion chamber of an engine containingan insulated control electrode for conducting current. It delivers the spark needed forcombustion.

U. Solid State -- When used in the context of ignition systems, this term applies to anyignition system which uses electronic semi-conductors (diodes, transistors, silicon

controlled rectifiers, etc.) in place of one or more standard ignition components.

V. Voltage -- Electromotive force or pressure that causes current to flow in an electricalcircuit.


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II. Basic Electricity

A. Electron theory

1. Atoms

a. All matter is composed of atoms.

b. It is the smallest particle of an element that can exist, alone or incombination.

c. Components of an atom. (TM 2-1)

(1) Electrons

(a) Negatively (-) charged electrical charges

(b) They are very light and travel around the center of the atom.

(2) Protons

(a) Positively (+) charged electrical charges

(b) They are large, heavy particles when compared with theelectrons.

(3) Neutrons

(a) Electrically neutral and are located in the nucleus of the atom.

(b) Made up of an electron and proton bound tightly together.

2. Electron flow (TM 2-2)

a. In order to have electric current, electrons must move from atom to atom.

b. The ease with which an electron can move from one atom to another atomdetermines whether a material is an electrical conductor or nonconductor.

(1) Conductor

(a) Materials having electrons that can easily leave orbit of oneatom and move to orbit of another atom. When many electronsdo this, electricity is produced.

(b) Copper, aluminum, and silver are examples of conductors.


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(2) Nonconductor (insulators)

(a) Materials having no electrons that can leave their orbit. Noflow of electrons is possible.

(b) Glass, mica, rubber, plastic, and paper are examples ofnonconductors.

c. The flow of electrons will take place only when there is a complete circuitand a difference in electrical potential.

d. A difference in potential exists when the source of electricity lackselectrons, or is positively (+) charged.

e. Since electrons are negatively (-) charged and unlike charges attract, theelectrons move toward the positive source.

3. Electrical units of measurement

a. Amperes - Rate of electron flow

(1) An ampere is a measurement of the number of electrons flowing pastany given point in a specific length of time.

(2) Since electricity is transmitted through wires, the greater the numberof electrons flowing, the larger the wire size must be.

b. Volts - Force that causes electrons to flow

(1) The difference in electrical potential between two points in a circuitis measured in volts.

(2) Voltage is the force, or potential, that causes the electrons to flow.

c. Ohms - Resistance to electron flow

(1) Some materials produce a strong resistance to electron flow, othersproduce little resistance.

(2) If a wire is too small for the amount of current produced at thesource, the wire will create excessive resistance and get hot.

(NOTE: The air gap between spark plug electrodes is highly resistant toelectron flow, creating the need for high voltage to cause the electrons to jumpthe gap. The high resistance also creates heat which, in this case, ignites the fuelin the cylinder.)


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4. Sources of electricity.

a. Chemical (Battery)

b. Magnetic (Generator)

c. Statically (Lightning)

5. Parts of a circuit.

a. Voltage source (Battery)

b. Resistor (Light bulb)

c. Conductor (Copper wire)

C. Ohm's Law

1. Letters and their terms

a. E - Electromotive force in volts

b. I - Intensity (current) in amps

c. R - Resistance in ohms

2. Formulas

a. E = I X R or Volts = Amps X Ohms

b. I = E/R or Amps = Volts/Ohms

c. R = E/I or Ohms = Volts/Amps

(Note: E.I.R. formula reminder is the phrase "Even I Remember")

3. Application of the Formula

a. If circuit voltage is 12 and resistance is 8 ohms, the current would be:

b. If amperage is 15 and voltage is 6, resistance would be:

c. If amperage is 3, and resistance is 10 ohms, the voltagewould be:

III. Ignition systems


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A. Purpose

1. To provide enough electrical voltage to discharge a spark between theelectrodes of the spark plug.

2. To provide the spark at exactly the right time to ignite the highly compressed air-fuel mixture in the combustion chamber of the engine.

a. The ignition system must be capable of producing as much as 20,000 voltsto force the electrical current (electrons) across the spark plug gap.

b. The intense heat created by the electrons jumping the gap ignites the air-fuel mixture surrounding the electrodes.

(NOTE: Considering the high voltage required, the precise degree oftiming and the high rate of discharges, the ignition system has aremarkable job to do.)

B. Types of ignition systems

1. Magneto Power (A spark-ignition system which receives its source of powerfrom a magnet rotating near an armature).

a. With breaker-points

-"Mechanical Breaker Ignition" (MBI) system is a flywheel magnetoinductive system. It employs mechanical breaker contacts for the timingand triggering of the system.

b. Solid-State (Breakerless)

(1) "Transistor Controlled Ignition" (TCI) system is an inductive system.Semiconductors (transistors, diodes, etc.) are used for switchingpurposes instead of mechanical breaker contacts.

(2) "Capacitor Discharge Ignition" (CDI) system has no moving partsand stores its primary energy in a capacitor and uses semiconductorsfor the timing and triggering of the system.

(3) Advantages of a solid state ignition system

(a) Elimination of ignition system maintenance.

(b) No breaker points to burn, pit or replace.

(c) Increased spark plug life.

(d) Easy starting, even with fouled plugs.


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(e) A flooded engine will start easily.

(f) Higher spark output and faster voltage rise.

(g) Spark advance is electronic and automatic. It never needsadjusting.

(h) Electronic unit is hermetically sealed and unaffected by dust,dirt, oil, or moisture.

(i) System delivers uniform performance throughout componentlife and under adverse operating conditions.

(j) Improves idling and provides smoother power under load.

2. Battery powered (A spark-ignition system receives its source of power from a

battery).

a. With breaker-points

b. Solid-State (Breakerless)

C. Magnetism

1. Molecules are the smallest particles of matter which are recognizable.

2. In most materials, the magnetic poles of adjoining molecules are arranged in arandom pattern, so there is no magnetic force. (TM 2-3)

3. A magnetized substance has all molecules in alignment, north to south.

4. Individual molecules combine magnetic forces to produce a strong overallmagnetic force. (TM 2-4)

5. The fact that there is a close relationship between electricity and magnetismserves as the basis for making a workable magneto.

6. If a conductor, such as copper wire, is moved so that it cuts magnetic lines offorce, an electron flow is induced in the conductor. Flow of electrons(electricity) can be measured with a sensitive meter.


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7. A conductor that is not moving and not cutting magnetic lines of force will notinduce electrical current. Electricity will flow when the magnetic lines of forceare being cut by the wire.

8. A coil of wire with current flowing through it will produce a magnetic fieldaround itself and around each turn of wire in the coil.

D. Ignition coil (TM 2-5)

1. Used in a magneto system and operates like a transformer.

2. The coil contains two separate winding of wire insulated from each other andwound around a common laminated iron core. (TM 2-6)

a. Primary winding - Winding of heavy gage wire with few turns.

b. Secondary winding - Winding of light gage wire with many turns.

3. When electric current is passed through the primary winding, a magnetic field iscreated around the iron core.

4. When the current is stopped, the magnetic field collapses rapidly, cuttingthrough the secondary windings. This rapid cutting of the field by the wire in thecoil induces high voltage in the secondary circuit.

5. The high secondary voltage, in turn causes a spark to jump the spark plug gapand ignite the air-fuel mixture.

E. Spark plugs (TM 2-7)

1. Carries high voltage current produced by the ignition system.

2. Made to withstand the high temperatures and shock of combustion.

3. Center electrode is insulated to prevent current loss.

a. Has good heat conducting quality.

b. Resistant to heat shock.

c. Ribs on the insulator extend from the terminal nut to the shell of the plugto prevent flashover. (TM 2-8)

4. If the electrical potential is great enough to cause the current to jump the pluggap, the grounded electrode will complete the circuit to ground.

5. Sealed to prevent compression leakage.


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6. Advantages to using the correct spark plug for a given engine application:

a. Increased efficiency

b. Increased economy

c. Extended service life

7. Spark plug "reach" varies with type of spark plug. (TM 2-9)

a. Some are short

b. Some are long.

c. Never use a spark plug that has a longer reach than specified.

(NOTE: Serious engine damage can result if the piston hits the plug.)

8. Common high tension lead connectors.

a. Exposed clip type

b. Neoprene boot type

F. Spark plug heat transfer

1. Heat transfer in spark plugs is an important consideration.

2. Spark plugs are manufactured in various heat ranges from "HOT" to "COLD".

a. Cold running spark plugs are those which transfer heat readily from thefiring end. They are used to avoid overheating in engines having highcombustion temperatures.

b. Hot running spark plugs are those which do not readily transfer heat fromthe firing end.

c. Heat is controlled by insulator nose.

G. Types of electrodes

1. Retracted Gap

2. Surface Gap

3. Clipped Gap

4. Automotive gap


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VI. Mechanical Breaker point ignition system

A. Components of ignition system (TM 2-10)

1. Magneto - Self-contained units that produce electrical current for ignitionwithout any outside primary source of electricity.

a. Basic parts of the magneto are:

(1) Permanent magnets.

(2) High tension coil with laminated iron core and primary secondarywindings.

(3) Breaker points and breaker cam.

(4) Condenser.

(5) High tension spark plug wire.

(6) Spark plug

2. Magneto cycle

a. As the flywheel turns, the magnets pass the legs of the laminated core ofthe coil. When the north pole of the magnet is over the center leg of the

coil, current passes across the bottom of the lamination and up the side legto the south pole. (TM 2-11)

b. As the flywheel continues to turn the north pole of the magnet comes overthe side leg and the south pole is over the center leg of the lamination.Now the lines of force move from the north pole down through the side legand up through the center leg and the coil to the south pole. At this point,the lines of force have reversed direction. (TM 2-12)

c. Field reversal takes place in the center leg of the lamination and coil. Thereversal induces low voltage current in the primary circuit through thebreaker points. Current flowing in the primary winding of the coil createsa primary magnetic field of its own, which reinforces and helps maintainthe direction of the lines of force in the center leg of the lamination. Itdoes this until the magnets' pole move into a position where they can forcethe existing lines of force to change direction in the center leg of thelamination just before this happens the breaker points are opened by thecam. (TM 2-13)

d. Opening of the points breaks the primary circuit and the primary magnetic


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field collapses through the turns of the secondary winding. The condensermakes the breaking of the primary current as instantaneous as possible byabsorbing the surge of primary current to prevent arcing between thebreaker points. (TM 2-14)

e. As the magnetic field collapses through the secondary winding of coil,high voltage current is induced in the secondary winding. At exactly thesame time, the charge stored in the condenser surges back into the primarywinding and reverses the direction of current in the primary windings.This change in direction sets up a reversal in direction of the magnetic field

cutting through the secondary and helps increase the voltage in thesecondary circuit. The potential of the high voltage causes secondarycurrent to arc across the spark plug gap. (TM 2-15)

3. The stop switch (TM 2-16)

a. The spark plug can only fire when the ignition points open.

(1) The switch is designed to ground the movable breaker point so thatthe points never open.

(2) When the points are grounded the engine quits running.

b. A single-cylinder engine can be stopped by means of a metal fastened toone of the cylinder head bolts.

(1) When the engine is running, the strip is suspended about 1/2 inchfrom the spark plug wire terminal.

(2) By depressing the strip against the plug wire, the current flows downthe strip to the cylinder head to prevent a spark at the plug.

(NOTE: There is no danger of shock to the operator).(CAUTION: Do not touch the spark plug directly).

4. Ignition advance systems

a. Some small engines have mechanical systems that retard occurrence ofspark for starting.

b. For intermediate and high speed operation, the advance mechanism causes

spark to occur earlier in the cycle.

c. Two different spark timings are provided, one for starting and one forrunning. (TM 2-17)

(1) Starting - The spark advance flyweight holds the cam in a position so that the ignition sparkoccurs at 6 degrees of crankshaft rotation before the piston reaches


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top dead center.

(2) Running - When the engine reaches a speed of nearly 1000 rpm,centrifugal force moves the flyweight out, forcing the cam to rotate.This position of the cam causes the points to open and a spark tooccur at 26 degrees before top dead center.

5. Dwell and cam angle

a. Dwell (cam angle) is the time the breaker points stay closed during onerevolution of the cam.

b. Dwell is the number of degrees measured around the cam from the point ofclosing to the point of opening.

c. The cam is driven directly from the crankshaft. When the breaker pointsopen, the spark plug fires.

(NOTE: Changing the point setting can also change spark timing. The enginemanufacturer specifies which gap setting is best (usually between .020 to .030inches) and the number of degrees before top dead center (TDC) that the sparkshould occur. (TM 2-19 & 2-20)

VI. Solid state ignitions

A. Capacitive discharge ignition (CDI)

1. Solid state ignition system

(NOTE: It is standard equipment in many applications and has improved thereliability of modern small gasoline engines).

2. The mechanical points and accessories are replaced with electronic components.

3. The only moving parts are the permanent magnets in the flywheel.

4. Operation of CDI system (TM 2-21)

a. Flywheel magnets rotate across the CDI module laminations, inducing alow voltage alternating current (ac) in the charge coil.

b. The ac passes through a rectifier and changes to direct current (dc), whichtravels to the capacitor (condenser) where it is stored.

c. The flywheel magnets rotate approximately 351 degrees before passing theCDI module laminations and inducing a small electrical charge in thetrigger coil.


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(NOTE: At starting speeds, this charge is just great enough to turn on thesilicon controlled rectifier (SCR), a solid state switch in a retarded firingposition (9 degrees before TDC) for easy starting.

d. When the engine reaches approximately 800 rpm, advanced firing begins.The flywheel magnets travel approximately 331 degrees, at which timeenough voltage is induced in the trigger to energize the silicon controlledrectifier in the advanced firing position (29 degrees before TDC).

e. When the silicon controlled rectifier is triggered, the 300 volts of dc storedin the capacitor travels to the spark coil, where the voltage is stepped upinstantly to a maximum of 30,000 volts. This high voltage current isdischarged across the spark plug gap. (TM 2-22)

B. Operation of transistor controlled ignition (TCI) system (TM 2-23 & 2-24)

1. Many components that make up the transistor controlled ignition system.

2 There are a variety of transistor controlled circuits. Each has its own uniquecharacteristics and modifications.

3. As the engine flywheel rotates, the magnets on the flywheel pass by the ignitioncoil. The magnetic field around the magnets induces current in the primarywinding of the ignition coil.

4. The base circuit of the ignition system has current flow from the coil primarywindings, common grounds, resistor (R1), base of the transistor (T1), and backto the primary windings.

5. Current flow for the collector circuit is from the primary windings of the coil,common grounds, collector of transistor (T1), emitter of transistor (T1), andback to the primary windings.

6. When the flywheel rotates further, the induced current in the coil primaryincreases. When the current is high enough, the control circuit turns on andbegins to conduct current. This causes transistor (T2) to turn on and conduct. Astrong magnetic field forms around the primary winding of the ignition coil.

7. The trigger circuit for this ignition system consists of the primary windings,common grounds, control circuit, base of transistor (T1) stops conductingcurrent.

8. When transistor (T2) begins to conduct current, the base current flow is cut.This causes the collector circuit to shut off and transistor (T1) stops conductingcurrent.

9. When transistor (T1) stops conducting, current stops flowing through theprimary of the ignition coil. This causes the primary magnetic field to collapse


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across the secondary windings of the ignition coil. High voltage is then inducedinto the secondary to "fire" the spark plug.

10. The secondary circuit includes the coil secondary winding, high tension lead,spark plug, and common grounds returning to the coil secondary.

11. With the ignition switch stops the primary circuit is grounded to prevent the plugfrom firing.

12. Diode (D1) is installed in the circuit to protect the TCI module from damage.

13. The ESG circuit is used to retard the ignition timing. At high engine rpm, theESG circuit conducts. This bypasses the trigger circuit and delays when currentreaches the base of transistor (T2).

VII. Battery Ignition Systems (TM 2-25)

A. A low voltage primary circuit and a high voltage secondary circuit system.

1. Primary circuit

a. Battery - A device that stores chemical energy in reserve for later use.May be wet or dry type.

b. Ignition Switch - Opens and closes the primary circuit from the battery orcoil to the contact points.

c. Resistor - A device used to reduce voltage.

d. Primary Winding - The heavy gage wire with fewer turns than thesecondary winding, which carries low voltage.

e. Contact Points - Connect and break the primary circuit to allow the coil toproduce high voltage at the spark plug.

f. Condenser (Capacitor) - A device for temporarily collecting and storing asurge of electrical current for later discharge.

g. Low Voltage Wire - Carries low-voltage from the battery or armature tothe primary side of the ignition coil.

2. Secondary circuit

a. Secondary Winding - The fine wire coil in the ignition coil, which carrieshigh voltage.

b. Distributor - A device that directs electrical current to the spark plugs.


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c. Rotor - The rotating part of a generator, motor, alternator, or distributor.

d. Spark Plug - Device which ignites the fuel-air mixture in an engine'scylinder.

e. High Voltage Wire - Carries high voltage from the secondary side of thecoil to the spark plug.

B. Parts included in the system

1. Coil (TM 2-6)

2. Condenser (TM 2-26)

3. Breaker Points (TM 2-18)

4. Spark Plug (TM 2-9)

C. The major difference between the battery ignition system and other ignition systems isthat the battery ignition system uses a lead-acid battery to supply the primary circuitwith current.

D. Operation of the battery ignition system (BIS)

1. If the ignition switch is turned on, current will flow from the positive terminal ofthe battery to the ignition coil.

2. As current travels through the primary windings of the coil a magnetic field is

built. (TM 2-27)

3. The breaker points are closed and ignition at the plug is required.

4. Current is completing a circuit by returning to the battery through the commonground.

5. When ignition is required at the plug, the breaker points are opened by the camand current flow stops abruptly. (TM 2-28)

6. The magnetic field surrounding the coil collapses as the current stops.

7. The rapid change of magnetic flux causes voltage to be induced in every turn ofthe primary and secondary windings.

8. Voltage of approximately 250 volts in the primary winding is quickly absorbedby the condenser.

9. The condenser prevents the current from arcing at the breaker point gap.


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10. The surge of power in the primary windings of the coil are absorbed by thecondenser, which acts as a reservoir. (TM 2-29)

11. The current is held for an instant in the condenser; then released to the primarycircuit.

E. High voltage produced in the secondary current

1. The secondary winding of the coil builds up voltage to as high as 25,000 volts.

2. The secondary windings have approximately 100 times as many turns as theprimary windings.

3. When the voltage increases to the number of volts required to jump the sparkplug gap, the voltage drops.

4. The amount of voltage required to jump the spark plug gap varies between 6000

and 20,000 volts.

(NOTE: The amount of voltage required to jump the spark plug gap isdependent upon: compression, engine speed, shape and condition of theelectrodes, spark plug gap, etc.).

F. Auto-transformer type ignition coil (TM 2-30)

1. Some small engines use this type of ignition coil.

2. Serves as a step-up transformer.

3. Increases low voltage primary current to high voltage.

4. The primary and secondary windings are connected, and the common ground ofthe battery and primary circuit is used to complete the secondary circuit.

5. The center core of the coil, is made of laminated iron.

6. The top of the coil is provided with two primary terminals marked positive (+)and negative (-).

G. The lead-acid battery (TM 2-31)

1. For a battery ignition system the battery is the sole source of energy.

2. To replenish energy in the battery a generator is used.

(NOTE: The generator does not supply energy directly to the ignition system).

3. The cell plates are made of lead.


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4. The liquid content (electrolyte) is made of sulfuric acid and water solution.

H. Battery construction

1. A 12V battery has a hard rubber case and six compartments called cells.

2. The number of negative and positive plates per cell determines the ampere-hourrating.

(NOTE: The ampere-hour rating is the battery's ability to provide current for aspecific length of time).

3. The positive plates have a lead oxide covering.

4. The negative plates have a porous or spongy surface.

I. Battery voltage (TM 2-32)

1. Voltage is caused by a chemical reaction which causes each negative plate tolose electrons and each positive plate to gain electrons when surrounded byelectrolyte.

2. The plates of the battery are connected in series causing cumulative charges tobe present at the positive and negative terminals.

3. Each cell in a battery contain approximately 2V. Six fully charged cells produceat least 12V.

J. Discharging battery.

1. Sulfuric acid is chemically withdrawn from the electrolyte as a batterydischarges.

2. When a battery is recharged, direct current is passed through the battery inreverse direction from normal operation.


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ATOM


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ELECTRON FLOW



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UNMAGNETIZED IRON


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MAGNETOZED IRON


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IGNITION COIL INSIDE VIEW


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IGNITION COIL



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SPARK PLUG PARTS



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FLASHOVER


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SPARK PLUG REACH



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IGNITION SYSTEM COMPONENTS


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IGNITION SYSTEM MAGNETO CYCLE (1)


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SPARK TIMING


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NORMAL GAP AND DWELL


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WIDE GAP -- DWELL DECREASES


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NARROW GAP -- DWELL INCREASES



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CDI SYSTEM (1)

Flywheel operation. 1A - Magnets induce low voltage alternating

current into charge coil at 2.

3 - Rectifier changes alternating to direct current.

4 - Direct current from rectifier is stored in capacitor (condenser).


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CDI SYSTEM (2)


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TCI SYSTEM (1)


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TCI SYSTEM (2)



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BATTERY IGNITION SYSTEM


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CONDENSOR


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BATTERY IGNITION SYSTEM OPERATION (1)



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AUTO-TYPE IGNITION COIL



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BATTERY


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BATTERY VOLTAGE



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ELECTRONIC IGNITION SYSTEM


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SMALL ENGINES/LUBRICATION SYSTEM


A. Additives - Chemicals added to oil to increase performance.

B. API - American Petroleum Institution

C. Blow-by - Leakage of air-fuel mixture and some burned gases past the piston ringsduring the combustion and power strokes.

D. Dipper - A device fastened to the connecting rod used to splash oil.

E. Friction - Resistance to movement between two bodies placed in contact with oneanother.

F. Multi - Grade Oils - Oils compounded to serve as light oils at cold temperatures andheavy oils at hot temperatures.

G. Oil - A liquid lubricant derived from crude oil used to provide lubrication betweenmoving parts.

H. Oil Filter - The filter through which the crankcase oil passes to remove any impurities.

I. Oil Pan - The detachable lower part of the engine, made of sheet metal, whichencloses the crankcase and acts as an oil reservoir.

J. Oil Pump - The device that delivers oil from the oil pan to the various moving engineparts.

K. SAE - Society of Automotive Engineers.

L. Slinger - A device rotated by the camshaft for splashing oil.

M. Sludge - Heavy, thick residue that accumulates on the bottom of the oil pan;containing water, dirt, and oil.

N. Viscosity - The resistance to flow that a liquid has (a thick oil is greater than a thin

oil).

II. Purposes of the lubrication system

A. Reduce friction

B. Cool engine parts


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C. Absorbs shock and reduces engine noise

D. Forms a seal between the piston rings and the cylinder wall.

E. Acts as a cleansing agent.

III. Types of lubricating systems

A. Splash system

1. Dipper type (TM 3-1)

2. Slinger type (TM 3-2)

B. Pump system (TM 3-3)

1. Barrel and plunger type

2. Gear and rotor type

IV. Types of oil

A. Crude or mineral types - These types are derived from petroleum oil.

B. Synthetic types - These types are man-made products.

V. SAE viscosity ratings

A. Lighter oils for winter use are specified at 0 degrees F.

1. 5W

2. 10W

3. 20W

B. Heavier oils for summer use are specified at 210 degrees F.

1. 20

2. 30

3. 40


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4. 50

C. Multi-grades used for summer and winter (TM 3-4).

1. 10W-30

2. 10W-40

3. 5W-30

4. 5W-40

5. Others

VI. API engine service motor oil types (TM 3-5).

A. "S" - Spark plug ignition (cars and pickups)

1. SA - Very light gasoline and diesel use (no compounding).

2. SB - Light gasoline use (oxidation, bearing corrosion and antiscuff additives).

3. SC - For 1964-67 cars and pickups (oxidation, antiscuff and corrosion, detergent- dispersant additives).

4. SD - For 1968 - up cars and pickups (same additives but a higher level than SCoils).

5. SE - For 1971 - up cars and pickups (same additives as SC and SD oils but at ahigher level).

6. SF - For 1980 - up cars and pickups (same additives as SC, SD and SE oils but ata higher level).

7. SG - For all late model cars and pickups (same additives as SC, SD, SE and SFbut at a higher level).

B. "C" - Compression ignition (Tractors, trucks, power units, etc.)

1. CA - light diesel and truck use. Using high quality diesel fuel. No blowers.

2. CB - Moderate diesel and mild truck use. High sulfur diesel fuel. No blowers.

3. CC - Moderate diesel and gasoline engine use. Lightly super-charged.

4. CD - Severe diesel service. Low to high quality diesel fuel. Super-chargedengines.


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VII. Oil contaminants

A. Foreign particles

B. Dirt

C. Water

D. Antifreeze

E. Fuel

F. Oxidation

G. Acids

IX. Additives found in oil

A. Detergents - Put in oil to help hold contaminants in suspension to prevent clumpingand formation of sludge.

B. Antioxidants - Put in oil to help reduce the formation of corrosive acids that areparticularly damaging to bearing surfaces.

C. Rust inhibitors - Put in oil to protect against rust.

D. Foam inhibitors - Put in oil to help prevent the build-up of foam that is caused when

oil is agitated.

X. Selection and use of oils for best engine performance.

A. Use brands which meet engine manufacturer's specifications.

B. Drain and change oil at recommended intervals.

C. Select oils which have been performance tested.

D. Never mix oils of various specifications.

E. Bring engine up to normal operating temperature each time it is used.

F. Replace or clean filters before they become plugged.

G. Use clean oil containers and keep covered, sealed, and protected to preventcontamination.

XI. Facts about oil.


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A. Oil becomes unfit for further use as it absorbs contaminants and as additives aredepleted.

B. Multi-viscosity oils are not always preferred.

C. Black oil does not mean time for an oil change.

D. Buy quality oil filters as recommended by machine operator's manual.

E. Oil oxidation results in thicker oil.

F. Using a light oil until consumption increases, and then switching to a heavier oil, isnot a good practice.

G. Following operator's manual recommendations is critical to insure good performance.


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DIPPER LUBRICATION SYSTEM



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SLINGER LUBRICATION SYSTEM



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PUMP SYSTEM



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COMPARISON OF CRANKCASE OILS



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API CLASSIFICATION SYSTEM



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SMALL ENGINES/COOLING SYSTEM


A. Baffle - Cover over the finned area of the engine to hold the air around the fins.

B. Conduction - Heat transfer through a solid material.

C. Convection - Heat transfer through movement of a gas.

D. Cooling System - The system that removes heat by the circulation of liquid coolant or

of air to prevent engine from overheating.

E. Fin - Metal projections cast on the head and cylinder to provide increased surface foradditional cooling area.

F. Shroud - Cover over the flywheel, which directs air to the engine fins.

II. Purposes of the cooling systems

A. Remove excess heat from the engine.

B. Keep the engine at its most efficient operating temperature at all engine speeds andunder all operating conditions.

C. Prevent overcooling.

III. Effects of engine overheating

A. Burning of valves

B. Engine ping or knock

C. Vapor lock

D. Increased wear due to poor lubrication

E. Sticking valves and lifters


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F. Localized hot spots.

G. Possible cracking of engine head or block

H. Scuffing and scoring of cylinder walls.

IV. Causes of overheating

A. Restricted air flow

B. Poor engine condition

C. External leakage

D. Internal leakage

V. Features of air cooled systems

A. No "plumbing" problems (radiator, water pump, etc.)

B. Fewer operational problems caused by cooling system.

C. No antifreeze problems.

D. Good serviceability.

E. Lighter in weight.

F. Less horsepower.

G. Good service life.

H. Less susceptible to minor damage.

VII. Components of air cooled system (TM 4-1)

A. Flywheel

B. Filter screen

C. Blower shroud

D. Cylinder head baffle

E. Cylinder baffle


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PARTS OF A COOLING SYSTEM



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PARTS OF A COOLING SYSTEM - QUIZ

Transparency Master 4-1a


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SMALL ENGINES/FUEL SYSTEMS


A. Airfoil - Tube, in a stream of air, inside the venturi which creates an air patternwith low pressure on one side.

B. Atomization - Breaking of a liquid into tiny particles or globules to aid vaporformation.

C. Fuel - The substance that is burned to produce heat and create motion in anengine.

D. Fuel pump - The electrical or mechanical device in the fuel system, whichtransfers fuel from the fuel tank to the carburetor.

E. Fuel tank - The storage reservoir for fuel on the engine.

F. Gasoline - Made up of hydrocarbon chains, which when ignited produce rapidlyexpanding heat energy.

F. Metering - The correct proportion of fuel and air needed for good combustion.

G. Vaporization - Transferring a substance into a gaseous state.

H. Venturi - Restriction in the carburetor which makes the air speed up, causing ahigh vacuum.

II. Purpose of the fuel system - To deliver the combustible mixture of vaporized fuel and airto the engine cylinder(s).

III. Fuel quality

A. Clean - Free from water, rust and dirt.

B. Octane rating - measure of tendency to resist detonation (resist self-ignition).

C. Starting

1. For easy starting good fuel vaporization is needed.

2. Gasolines are blended for summer and winter use.

3. Never keep gasoline for more than 30 days.

D. Burning


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1. Want even burning no explosions.

2. Explosions are the pinging noise heard when octane level is too low.

IV. Problems with low fuel quality

A. Detonation, pinging, engine knock - explosion of gases ahead of flame after fuelhas been ignited opposite spark plug.

B. Preignition - ignition of fuel before spark.

C. Cause of knock:

1. Low octane fuel.

2. Combustion chamber deposits.

3. Cooling system failure - hot engine.

4. Carburetor failure - air/fuel mixture too lean.

5. Spark setting problem - too advanced.

6. Damaged or wrong plug (heat range or size).

7. Temperature of air-fuel mixture too high.

V. Protecting fuel quality

A. Means

1. Control evaporation

2. Reduce gum deposits

3. No contamination by dirt and water

B. Storage

1. Above ground storage - evaporation of volatiles (hard starting).

2. Underground storage - no evaporation due to low temperatures.

a. Fuel evaporation is not a serious problem.

b. Little tendency for water of condensation in the tank.


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c. Gum depositing tendency slowed.

d. Fire hazard reduced.

e. Tank is hidden (not an eyesore).

f. Cost is less.

g. Ground water and limited flooding have little effect.

h. It is easily moved.

i. Easily cleaned.

j. Lower replacement cost (less frequently).

C. Winter Evaporation - summer evaporation due to difference in blend (more

volatiles).

D. Gum deposits - Do not store gas supply over 1 month.

E. Moisture forms Condensation - Keep tank top off (if possible) and drain wateronce a year.

F. Tank placement

1. Underground - 1 foot from building.

2. Above ground - 40 feet from building.

VI. Types of fuel systems (TM 5-1)

A. Gravity feed - The tank is located above the carburetor and feeds down to thecarburetor float bowl by gravity.

B. Suction-feed - The fuel tank is located below the carburetor, and fuel is feedupwards directly from the fuel tank to the carburetor discharge holes.

C. Pressure-feed - A type of pump is used is maintain a constant flow of fuel to thecarburetor regardless of where the fuel tank is located.

VII. Components of the fuel system

A. Air cleaner - Filters collect grit and dust from the air entering the carburetor.

B. Carburetor - Mixes fuel and air in the proper proportion for a combustiblemixture.


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C. Fuel Filter - Prevents dirt or foreign matter from entering the carburetor.

D. Fuel Line - Carries fuel from the fuel tank to the carburetor.

E. Fuel Pump - The electrical or mechanical device in the fuel system whichtransfers fuel from the fuel tank to the carburetor

F. Fuel Tank - The storage reservoir for fuel on the engine.

G. Governor - A device used to control another device.

H. Pump diaphragm - Sheet of metal or other material that is sufficiently flexible topermit vibration.

VIII. Types of fuel filters

A. Glass sediment bowl and screen (TM 5-2).

B. Screen in fuel tank (TM 5-3).

C. Filter attached to the end of flexible fuel hose in tank (TM 5-4).

D. In-line filter (TM 5-5).

IX. Types of air cleaners (TM 5-6)

A. Oil bath

B. Paper element

C. Polyurethane

X. Carburetors

A. Function - Provide correctly proportioned air-fuel ratio to the cylinder.

B. Types

1. Float Feed - This type has the fuel tank located some distance from thecarburetor. The fuel flows either by gravity, or due to the force of a fuelpump, through fuel lines to the lower part of the carburetor. (TM 5-7)

2. Diaphragm - The carburetor has a rubber - like diaphragm exposed tocylinder intake stroke vacuum. As pressure decreases (vacuum), thediaphragm moves against the inlet needle allowing it to move from its seat.A spring returns the needle to its seat when the vacuum stops. Thisopening and closing permits fuel to flow through the inlet valve tomaintain the correct fuel level in the fuel chamber. (TM 5-8)


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3. Pulsa-Jet (Vacu-Jet) - This style is characterized by having two tubes orpipes out the bottom of the carburetor body. One pipe is long and picks upthe fuel from the tank by the pulsation of the pump diaphragm. It pumpsfuel in the smaller tank. The short pipe sticks into the smaller tank and thispipe is the tube that leads directly to the venturi area of the carburetor.(TM 5-9)

C. Idle air-fuel mixture (14-15 to 1)

D. Lean mixture causes

1. Overheating

2. Detonation

3. Short valve live

4. Rough irregular operation

5. Lower horsepower output than the engine is rated at.

E. Rich mixture causes1. Pollution (hydrocarbon & CO)

2. Wastes fuel

3. Fouls spark plug

4. Leaves carbon deposits on combustion chamber parts.

5. Raw fuel wash past rings.

a. Wear rings and cylinder.

b. Dilute oil-causing wear in bearings.

XI. Governors

A. Types

1. Air vane (TM 5-10)

2. Mechanical (TM 5-11)

B. Purpose - To maintain a given engine speed within the limits even though theload may vary.


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1. With "no load" the components responsibility is to cause the engine to runas slow as possible.

2. With a "load" the components main responsibility is to cause the engine torun as fast as possible.

3. The spring is responsible for speeding the engine up.

4. The wind vane is responsible for slowing the engine down.

C. Adjusting the governor

1. Place remote control in idle position.

2. Hold throttle shaft in closed position with finger.

3. Adjust the idle speed screw to 1550 RPM.

4. Release throttle.

5. Set remote control to 1750 RPM.

6. Turn screw in until it contacts remote control lever.

XII. Fuel pumps (TM 5-12)

A. Used on engines that have the fuel tank mounted and the gravity supply system

will not work.

B. Fuel pump provides constant fuel flow under pressure to the carburetor underchanging conditions.

C. Insures that the engine provides quick acceleration and full power.

D. Operates by means of a diaphragm and atmospheric pressure on surface of fueltank (TM 5-13).

1. Camshaft revolves the rocker arm to pull the rod and diaphragmdownward.

2. Creates a depression in the pump chamber.

3. Fuel enters the glass bowl from pump intake.

4. Passes through filter screen and inlet valve.

5. Enters pump chamber.


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6. On the return stroke pressure of the spring pushes the diaphragm upward.

7. Forces fuel from chamber through outlet valve and outlet to carburetor.

8. When carburetor bowl is full, float will seat needle valve preventing flowfrom the pump chamber.

9. This holds the diaphragm down against the spring.

E. Fuel pump hand primer (TM 5-14)

1. Used when the bowl is empty.

2. Due to the primer it is impossible to over prime the carburetor.


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FUEL SUPPLY SYSTEMS



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FUEL FILTER

(Screen in Fuel Tank)


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FUEL FILTER

(Filter Attached to Flexible Fuel Hose in Fuel Tank)



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FUEL FILTER

(In Line)


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AIR CLEANER TYPES



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FLOAT CARBURETOR



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FLOAT SYSTEM

Transparency Master 5-7b


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THROTTLE SYSTEM

Transparency Master 5-7c


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CARBURETOR FUEL SYSTEMS

Venturi Fuel System

Float Fuel System


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Transparency Master 5-7d


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ATMOSPHERIC AIR PRESSURE

Transparency Master 5-7e


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ATMOSPHERIC AIR PRESSURE

Transparency Master 5-7f


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DIAPHRAGM CARBURETOR



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DIAPHRAM CARBURETOR



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DIAPHRAM CARBURETOR



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PULSA-JET CARBURETORS



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PULSA-JET CARBURETORS



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AIR VANE GOVERNOR SYSTEM



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MECHANICAL GOVERNOR SYSTEM



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FUEL PUMP SYSTEM



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FUEL PUMP OPERATION



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PRIMER (BULB TYPE)



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SMALL ENGINES/COMPRESSION SYSTEM

I. Terms and definitions

A. Bearing - The part that transmits the load to the support and takes the friction causedby moving parts to contact.

B. Big End - The crankpin end of the connecting rod.

C. Bore - The diameter of an engine cylinder.

D. Cam - The rotating lobe which changes rotary motion to reciprocating motion.

E. Camshaft - The shaft in the engine that has a series of cams for operating the valvemechanisms. It is driven by the crankshaft through gears or sprockets and chains

F. Compression Rings - The upper ring(s) on a piston to hold the compression in thecylinder and prevent blow by.

G. Connecting Rod - The rod that connects the crank on the crankshaft with the piston.

H. Crankcase - The lower part of the engine in which the crankshaft rotates.

I. Cylinder - The tubular-shaped structure in a block or casting in which the piston

moves up and down.

J. Exhaust Valve - The valve that opens to allow the burned gases to escape from thecylinder during the exhaust stroke.

K. Intake Valve - The valve that opens to permit air-fuel mixture to enter the cylinderduring the intake stroke.

L. Oil Control Rings - The lower ring on a piston designed to prevent excessive amountsof oil from working up into the combustion chamber.

M. Piston - The part that receives the thrust of combustion.

N. Push Rod - In some engine types it is the rod between the valve lifter and the rockerarm.

O. Small End - The end of the connecting rod through which a piston pin passes toconnect the piston to the connecting rod.

P. Valve - A device that can be opened or closed to allow or stop the flow of a liquid,


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gas, or vapor from one place to another.

Q. Valve Seat - The surface in the cylinder head upon which the valve rests.

II. Valve system

A. Valves operate under severe conditions.

1. Time of operation 1/50 to 1/75 of a second to open and close.

2. Heat - Exhaust valve operates at 1200 - 1300 degrees F. in an area heated as highas 2500 - 2700 degrees F.

3. Pressure - 500 psi + on ignition in combustion chamber.

B. Effect of air-fuel ratio on heat in combustion chamber.

1. Lean mixture causes the engine to run hot, thus valves burn more readily.

2. Rich mixture causes carbon deposits, which may hold valves open.

C. Valve parts (TM 6-1)

1. Head

2. Margin

3. Face

4. Seat

5. Valve guide

6. Stem

D. Interference angle

1. Face to seat difference in angle that is ground to provide rapid seating of valves.

2. 1 to 1 1/2 degree difference (i.e. valve ground at 45 degrees seat ground at 46degrees).

3. Must seat at top to prevent carbon deposits from holding the valve open.

E. Valve Failures

1. Warpped


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2. Burned

3. Dished

4. Necked

5. Thin margin

III. Camshaft lobe (TM 6-2)

A. Start TDC intake stroke (both valves open).

B. Intake closes 30 degrees past BDC.

C. Ignition 20 degrees before TDC (compression stroke)

D. Exhaust opens 35 degrees before BDC (compression stroke).

E. Intake opens 10 degrees before TDC (exhaust stroke).

F. Exhaust closes 10 degrees past TDC (intake stroke).

G. Duration range - Length of time a valve is open.

1. Intake 220 degrees (out of 720 degrees) 10 degrees + 180 degrees + 30 degrees =220 degrees.

2. Exhaust 225 degrees (out of 720 degrees) 35 degrees + 180 degrees + 10 degrees

= 225 degrees.

H. Overlap

1. Length of time valves are both open.

2. Intake stroke 20 degrees around TDC before intake.

I. Lift

1. Cam Lift - Height of lift or amount of lift applied to the valve.

2. Valve Lift - Height valve is lifted from seat. (Rocker arms on I-head engines areusually made at either a 1.2 or 1.5 to 1 ratio; therefore, the valve lift is more thanthe cam lift.

IV. Pistons

A. Operating conditions


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1. Strong enough to withstand tremendous heat and pressure.

2. Light enough to avoid excessive inertia forces when changing direction of traveltwice per revolution.

3. Must withstand heat from burning gas.

4. Must slide freely within the cylinder; cannot be fitted too tightly.

5. If fitted loosely, they will knock and rattle.

B. Piston construction (TM 6-3)

1. Crown - Flat, concave or convex to promote turbulence or help controlcombustion.

2. Heat dam - Narrow groove above top ring to reduce the amount of heat getting

to the top ring.

3. Piston ring grooves - Carry rings and separated by lands.

4. Skirt - Under part of the piston, provides the bearing area, which is in contactwith the cylinder; it takes the thrust forces caused by crank pin location.

a. Major thrust side - Side opposite the crank throw on the power stroke.

b. Minor thrust side - Side opposite the crank throw on the compressionstroke.

5. Piston bracing

a. Ribs - Cast into the inside of piston to strengthen area between crown andboss.

b. Steel inserts - Control expansion and add strength.

6. Piston design - Allows close fit of aluminum piston in cast iron blocks.

a. Strut - Use steel insert (skeleton-like and aluminum cast around it).

b. Steel belt - Steel ring cast into piston.

c. Aluminum pistons are cam ground.

(1) Close fit on thrust surfaces, perpendicular to pin bosses and boss areafits loose when cold. As heat increases, piston expands and morethrust surface is available for use.


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(2) Pin boss area doesn't change position appreciably.

(3) Pistons tapered narrower at top than bottom especially above topring. (Reason: top runs hotter than bottom and expands more).

(4) Piston relief - Indentation in mid skirt around boss to help preventfreeze up in overheating.

C. Advantages of aluminum over cast iron or steel.

1. Lighter weight means less inertia forces for reciprocating parts -- allowinghigher speed operation.

2. Lowered inertia forces also allows decreased bearing loads.

3. Lighter weight also means less side thrust on cylinder thus reducing wear.

4. Greater heat conductivity allows cooler running and higher compression ratios.

D. Disadvantages of aluminum pistons

1. Expand more than cast iron; therefore, they must be fitted somewhat looser(piston design and alloying have overcome this problem to a great extent).

2. Aluminum strength is reduced when heated causing broken or deformed lands;engine normal operating range is ok but overheating an engine can be serious.

E. Alloying materials for aluminum piston include: copper, magnesium, nickel, andsilicon.

F. Measurements important in cylinder piston area.

1. Measure taper from approximate first ring TDC to oil ring BDC. (Guide: 2 to 3thousandths per inch of diameter is maximum allowed without reboring).

2. Measure piston clearance with a feeler gauge beside piston 1-inch down onthrust sides to piston skirt. (Guide: 1 to 2 thousandths per inch of diametermaximum).

V. Rings (cast iron - oil control rings may be multi-sectioned steel rings).

A. Function

1. Seal compression

2. Control lubrication


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3. Reduce friction

B. Classification (TM 6-4)

1. Compression

2. Scrapper (functions as both compression and oil control but is primarilycompression).

3. Oil control

C. Measurements

1. Ring end gap (gap at the end of the ring when inside the cylinder).

2. Ring groove clearance (side clearance between the ring and the piston land).

D. Design

1. Top ring - Rectangular in cross section and bevel cut on inside upper corner(allows ring to tilt and seal).

2. Second ring - Primarily a compression ring but also works in oil control; bevelcut may be on inner or outer corner and may be tapered on inside or outside.

3. Third ring - May be multi-section, has slots for oil return through slot in pistonto oil sump and may be either cast iron or hardened steel, may have a chrome ormoly-plated face to reduce friction and increase life.

VI. Connecting rod - aluminum or steel (TM 6-5)

A. Pin Bearing - Insert aluminum if the rod is steel or precision drilled hole if the rod isaluminum.

B. Spray Hole - Spray oil on piston bottom side for cooling.

C. Connecting Rod Bearing - Precession aluminum insert if rod is steel and aluminumrods are precision machined to crankshaft journal size.

D. Oil Splash System - Dipper or slinger

E. Installation - Match marks of rod and cap and make sure inserts are installed withmarks in correct position.

VII. Crankshaft and main bearings

A. Crankshaft design (forged steel or cast steel).


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1. Parts (TM 6-6)

a. Magneto journal

b. Crank pin journal

c. PTO journal

d. Throw

e. Counterweights

2. Bearings - Aluminum precision inserts

B. Balance of crankshaft

1. Static Balance - Weight equal in all directions from center when the crankshaft

is at rest.

2. Dynamic Balance - Balance while crank is turning.

3. Counterweights balance the weight of the piston and rod assembly. In additionto balancing the crankshaft properly, the entire rotating assembly is balanceddynamically including:

a. Timing gears

b. Crankshaft

c. Flywheel

d. Blades on lawnmowers

4. Piston - Rod assemblies are balanced one with another so that the rotating masswill have as little vibration as possible.

5. Torsional Vibration - Twist (torque) applied by piston on the power stroke putsthat slight twist in the crankshaft as the flywheel inertia

forces lag behind. (Solution: weight at both ends).

6. Critical Speeds - No matter how well balanced, an engine will have vibration atcertain speeds.

VIII. Sleeves - Cylinder inserts (Some aluminum blocks have steel sleeves for long wear).


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A. Sleeve fitted in the block cylinder are a thin, high strength sleeve.

B. No leakage problems.

C. Sleeve Rattle - score and wear (Steel expands at a different rate than aluminum).

D. Sleeves add weight to an engine.


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VALVE PARTS



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VALVE PARTS



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VALVE PARTS - QUIZ



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CAMSHAFT LOBE

Transparency 6-2a


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CRANKSHAFT TIMING



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CRANKSHAFT TIMING



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CRANKSHAFT TIMING

Transparency Master 6-2d


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PISTON CONSTRUCTION AND VARIATIONS

Transparency 6-3a


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PISTON CONSTRUCTION



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PISTON RING CLASSIFICATION

Transparency 6-4a


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PISTON RING REMOVAL



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PISTION PARTS - QUIZ



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CONNECTING ROD

Transparency 6-5a


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VALVE OPERATION



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VALVE PROBLEMS



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CRANKSHAFTS



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CRANKSHAFT - QUIZ



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VALVE LAPPING



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VALVE REMOVAL



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COMPRESSION RATIO



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TIMING GEAR - SETTING



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TIMING GEAR - SETTING



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CYLINDER HEAD DESIGNS



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EXHAUST SYSTEM/SMALL ENGINES

I. Terms

A. Exhaust manifold - A housing with a series of connecting pipes between the exhaustports and the exhaust pipe through which hot burned gases from the engine cylinderflow.

B. Exhaust pipe - Pipe connecting exhaust manifold to muffler.

C. Exhaust port - Hole in the cylinder wall that allows exhaust gases to escape.

D. Exhaust valve - The valve which opens to allow the burned gases to exhaust from theengine cylinder during the exhaust stroke.

E. Muffler - A devise through which the exhaust gases must pass and which muffles the

sound.

F. Tail pipe - Pipe from muffler that carries exhaust fumes away from engine.


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SMALL ENGINES/TROUBLE SHOOTING

I. Troubleshooting - The systematic diagnosis of engine malfunctions.

II. Areas to check for troubleshooting procedure.A. Compression

B. Ignition

C. Carburetion

III. Troubleshooting for ignition

A. Check ignition

1. Remove the spark plug

2. Spin the flywheel rapidly holding one end of the ignition cable 1/8" away fromthe head.

3. If spark jumps this gap, you may assume the ignition system is functioningsatisfactorily.

*Try a new spark plug

4. If spark does not occur, look for;

a. Incorrect armature gap.

b. Worn bearings and/or shaft on flywheel side.

c. Sheared flywheel key.

d. Incorrect breaker point gap (when so equipped).

e. Dirty or burned breaker points (when so equipped).

f. Breaker plunger stuck or worn (when so equipped).

g. Shorted ground wire (when so equipped).

h. Shorted stop switch (when so equipped).

i. Condenser failure

j. Armature failure


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k. Inoperative or malfunctioning interlock system.

IV. Troubleshooting for Carburetion

A. Check Carburetion

1. Check to make sure the fuel tank has an ample supply of fresh,clean gasoline.

2. On gravity feed types check to see that the shut-off valve is openand fuel flows freely through the fuel line.

3. Inspect and adjust the needle valves.

4. Check to see that the choke closes completely.

5. If engine will not start, remove and inspect the spark plug.

6. If plug is wet, look for:

a. Over choking

b. Excessively rich fuel mixture.

c. Water in fuel.

d. Inlet valve stuck open.

7. If plug is dry, look for:

a. Leaking carburetor-mounting gaskets.

b. Gummy or dirty screen or check valve.

c. Inlet valve stuck shut.

d. Inoperative pump.

e. Plugged or dirty fuel filters.

f. Fuel tank shut-off valve closed.

*A simple check to determine if the fuel is getting to the combustion chamber throughthe carburetor is to remove the spark plug and pour a small quantity of gasolinethrough the spark plug hole. Replace the plug. If the engine fires a few times and thenquits, look for the same condition as for a dry plug.


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V. Troubleshooting for compression

A. Check compression

1. Spin the flywheel against compression, counterclockwise.

2. If the flywheel rebounds sharply there is satisfactory compression to operate theengine.

3. If compression is poor, look for:

a. Loose spark plug.

b. Loose cylinder head bolts.

c. Blown head gasket.

d. Burnt valves and/or seats.

e. Insufficient tappet clearance.

f W d li d h d

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Engines Teaching Manual