Small Engines Instructional Outline 2003 - quia.com

INSTRUCTIONAL OUTLINE

6833

Summer 2003

AGRICULTURAL EDUCATION

AGRICULTURAL MECHANICS – SMALL ENGINES

Summer 2003 2 6833 Agricultural Mechanics II - Small Engines

COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT A: LEADERSHIP DEVELOPMENT COMPETENCY: SE001.00 Demonstrate the major components of leadership involved in successful employment. OBJECTIVE: SE001.01 Identify leadership qualities desired by the small engine industry. Leadership Qualities Cooper (90-92) 1. Integrity – honesty 2. Courage – willing to go forward under difficult conditions 3. Management – using people, resources and processes to reach a goal 4. Unselfishness – placing the desires and welfare of others above yourself 5. Loyalty – reliable support for an individual, group or cause 6. Enthusiasm – energy to do a job and the inspiration to encourage others 7. Plan – think through, determine procedures 8. Knowledge – awareness, understanding 9. Tact – saying or doing the right thing without offending


COURSE: AGRICULTURAL MECHANICE II - SMALL ENGINES

UNIT A: LEADERSHIP DEVELOPMENT COMPETENCY: SE01.00 Demonstrate the major components of leadership involved in successful employment. OBJECTIVE: SE01.02 Develop leadership qualities through participation in the small engines instructional program. Components of Instructional Program Cooper (90-92) 1. Supervised Agricultural Experience (SAE) – provides opportunities to explore interests and to gain work experiences. 2. Classroom instruction – studying and learning subject matter in the classroom 3. Laboratory instruction – learning by demonstrations and practice in shops, greenhouses, nurseries, and other settings. 4. FFA – the club or organization that develops leadership and citizenship skills. Communication skills are developed through speaking; career development events such as public speaking, creed, parliamentary procedure, extemporaneous speaking, agricultural sales and poultry, dairy and livestock oral reasons. COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES


UNIT A: LEADERSHIP DEVELOPMENT

COMPETENCY: SE02.00 Apply Robert’s Rules of Order to conduct business meetings needed by agricultural organizations.

OBJECTIVE: SE02.01 Analyze the role that Robert’s Rules of Order plays in the orderly conduct of business.

Parliamentary Law (FFAH) pp. 57-64

1. Robert's Rules of Order is the book of authority. 2. Assures that all sides of an issue are treated fairly and that everyone has an opportunity to discuss and vote. 3. Main objectives a. focus on one item at a time b. extend courtesy to everyone c. observe the rule of the majority d. ensure the rights of the minority 4. Methods of voting a. voice – aye (pronounced “I”) for yes, or “no” b. rising – standing or show of hands c. secret ballot – written vote d. roll call – secretary asks each member to state vote 5. Single majority – one vote more than 50% or 1/2 of votes cast 6. Two-thirds majority – 2/3 of members voting must vote for motion, usually used when motion will limit rights of members 7. Quorum – number of members required to conduct business 8. Gavel – symbol of authority 9. Meaning of taps of gavel: a. One tap means be seated, the meeting is adjourned or the result of a vote has been announced. b. Two taps means that the meeting is called to order. c. Three taps means that the members should stand on the third tap. d. A series of taps means “be quiet and orderly.”


10. Table of Motions – should know for each motion: a. privileged b. incidental c. subsidiary d. unclassified e. ranking – top is highest ranking and takes precedence over those below f. debatable or can be discussed – yes or no g. amendable – yes or no h. vote required – majority, 2/3 majority or none i. second required – yes or no j. can it be reconsidered – yes, no, or special requirement


COURSE: AQGRICULTURAL MECHANICE II - SMALL ENGINES UNIT A: LEADERSHIP DEVELOPMENT COMPETENCY: SE02.00 Apply Robert's Rules of Order to conduct business meetings needed by agricultural organizations. OBJECTIVE: SE02.02 Conduct the transaction of business using

Robert's Rules of Order.

Conducting Business Meetings – Use the information learned from Objective SE02.01 (FFAH) pp. 57-64


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES

UNIT A: LEADERSHIP DEVELOPMENT COMPETENCY: SE03.00 Adapt public speaking techniques to the audience and to the purpose of the communication taking place. OBJECTIVE: SE03.01 Discuss the major types of speeches and the variables to be considered when presenting speeches.

A. Types of Speeches Rickets (pp. 135-55), FFAH, Use Prepared Public Speaking CDE Rules 1. To inform – gives knowledge or information to audiences 2. To persuade – convinces people to believe or do something 3. To integrate – pep talks, welcome speeches, introductions

4. Prepared – speech is written and learned

5. Extemporaneous – speech with little or no preparation

B. Variables to Consider

1. Purpose of the speech – Why are you giving the speech?

2. Audience – What group is hearing the speech?

3. Occasion – What is the event?

4. Content – What is in the speech?

5. Composition – How is the speech written and organized?

6. Oral delivery variables: a. voice – pitch, quality, articulation, pronunciation, force b. stage presence – appearance, poise, attitude, confidence, ease before audience, personality, posture c. power of expression – fluency, sincerity, emphasis, directness, communicative ability, conveyance of thought and meaning. d. response to questions – accurate, ability to think quickly e. general effect – interesting, understandable, convincing, pleasing, holds attention


COURSE: AGRICULTURAL MECHANICE II - SMALL ENGINES

UNIT A: LEADERSHIP DEVELOPMENT

COMPETENCY: SE03.00 Adapt public speaking techniques to the audience and to the purpose of the communication taking place.

OBJECTIVE: SE03.02 Deliver a speech to a small engines industry organization.

Delivering a Speech Rickets (pp. 135-53), FFAH, Use Prepared Public Speaking CDE Rules

1. Outline – introduction, body, and conclusion 2. Apply the information learned from Objective 002.01 including types of speeches and variables to consider especially the audience and the occasion.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT A: LEADERSHIP DEVELOPMENT COMPETENCY: SE03.00 Adapt public speaking techniques to the audience and to the purpose of the communication taking place. OBJECTIVE: SE03.03 Identify various components of the techniques involved in agricultural sales.

“Supplemental – This material is to be developed at the discretion of the teacher.”


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT A: LEADERSHIP DEVELOPMENT COMPENTENCY: SE03.00 Adapt public speaking techniques to the audience and to the purpose of the communication taking place. OBJECTIVE: SE03.04 Demonstrate sales techniques with a 7-minute sales presentation on small engine products or services.



COURSE: AGRICULTURAL MECHANICS II - SMALLENGINES UNIT B: SUPERVISED AGRICULTURAL EXPERIENCE PROGRAM COMPETENCY: SE04.00 Design an individual written school-to-work employment plan based upon career objectives. OBJECTIVE: SE04.01 Describe the procedures to follow in planning and implementing a school-to-work employment plan. A. Factors to Consider When Selecting a Career (Rickets, pp. 409-413) 1. Standard of living – Pay, location 2. Personal contact – working more with people or with things 3. Educational requirements 4. Practice experiences or skills required 5. Location of employment 6. Your interests, likes and dislikes 7. Working conditions 8. Working hours and time for leisure activities 9. Retirement benefits 10. Your health and happiness


B. Steps in Choosing a Career 1. “Consider your interests, abilities, and other characteristics” should be the first step. 2. Narrow the field of jobs. 3. Study the requirements of the job – get good information. 4. Plan for alternative occupations – the first choice may not work out. 5. Prepare a plan for career preparation – early career planning can help you take the right courses in high school 6. Be willing to pay the price for success – education, dedication 7. Get work experience – SAE, coop., part-time job

C. For a school-to-work written plan to be effective, it must be implemented.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT B: SUPERVISED AGRICULTURAL EXPERIENCE PROGRAM COMPETENCY: SE04.00 Design an individual written school-to-work employment plan based upon career objectives.

OBJECTIVE: SE04.02 Create an individual written school-to-work employment plan based upon career objectives.

Use the information from Objective SE04.01 to create a career development plan (CDP) based upon career objectives. Consider high school academic courses, agriculture education courses, supporting electives, work experiences and education after high school. Rickets pp. 409-413


COURSE: AGRICULTURAL MECHANICE II - SMALL ENGINES UNIT B: SUPERVISED AGRICULTURAL EXPERIENCE PROGRAM COMPETENCY: SE05.00 Develop a financial record system for use in the small engines industry. OBJECTIVE: SE05.01 Describe the elements in a financial statement. Terms (NCSU SAE Record Book) A. Asset – something tangible of value that a person owns. 1. current – items quickly converted to cash or that will be sold within 12 months; Examples: cash, checking, saving, stocks and non-depreciable inventory of motors, parts, etc. 2. non-current – items that have a useful life of more than one year; Examples, land, machinery, etc. B. Liability – debts 1. current – debts that are due to be paid this year; Examples: fertilizer bills, tractor and building payments, and part of mortgage due this year. 2. non-current – debts not due this year ; Examples: mortgages not including this year’s payment. C. Net worth = total assets minus total liabilities current assets + non-current assets = total assets current liabilities + non current liabilities = total liabilities D. Inventory – an itemized list of things owned by a business with the beginning value and depreciated value. 1. non-depreciable – items that will be used up or sold within a year; Example: fertilizer, etc. 2. depreciable – items that have a useful life of more than one year and lose value because of age, wear or becoming out-of-date because of technology advancements. Land is NOT depreciable property.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT B: SUPERVISED AGRICULTURAL EXPERIENCE PROGRAM COMPETENCY: SE05.00 Develop a financial record system for use in the small engines industry. OBJECTIVE: SE05.02 Compose a financial statement. Use the information from Objective SE05.01 to make correct entries in a financial record system. (NCSU SAE Record Book)


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT C: WORKPLACE SAFETY COMPETENCY: SE06.00 Interpret shop management safety factors. OBJECTIVE: SE06.01 Discuss potential shop hazards. Shop Safety (Small Gas Engines, Ch.1, pp. 13 & 14) A. Students must recognize potential hazards to insure safety. 1. Notify instructor of unsafe work practices or conditions. 2. Safety can prevent injury or save a life. 3. Keep area clean, especially floors. Non-slippery floors prevent accidents. 4. Store tools properly. 5. Practice overall good housekeeping. B. Handle hazardous materials properly. 1. Keep rags, etc. in an appropriate container. 2. Keep flammable liquids in proper cans and in a safety cabinet. 3. Handle batteries with care to prevent acid damage or explosions from hydrogen gas. 4. Never use gas as a cleaning solvent. 5. Wear gloves and goggles when handling solvents. 6. Use a spill control pallet for containers of hazardous materials.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT C: WORKPLACE SAFETY COMPETENCY: SE06.00 Interpret shop management safety factors. OBJECTIVE: SE06.02 Explain how to react to shop emergencies. Handling emergencies (Small Gas Engines, Ch. 1, pp 17 & 18) A. Prepare for emergencies. 1. Emergency equipment should be highly visible. 2. Emergency telephone numbers should be by each telephone in shop area. 3. Have first aid kits stocked and in a prominent location. B. Fire Extinguishers 1. Use proper extinguisher for fire type (improper extinguishers can cause worse problems). a. Class A – wood, cloth and paper b. Class B – flammable liquids c. Class C – electrical d. Multiuse – Example – ABC 2. Inspect extinguishers monthly. 3. Keep extinguishers unobstructed and visible.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT C: WORKPLACE SAFETY COMPETENCY: SE07.00 Practice proper personal procedures. OBJECTIVE: SE07.01 Explain the importance of shop safety. A. Wear proper clothing (Small Gas Engines, Ch. 1, pp. 15-17) 1. Avoid loose fitting clothes. 2. Avoid neckties and jewelry. 3. Long hair should be worn up or under a hat. 4. Safety eyewear should be based on the activity. For example, wear: a. Goggles when working with chemicals, etc. b. Glasses when working with drills, grinders, or basically everything else. 5. Use hearing protection when noise is a problem. B. Use ventilation 1. When operating engines in enclosed areas. 2. When using gasoline, solvents, etc. that create toxic fumes. C. Use compressed air properly 1. Always use safety goggles. 2. Never use compressed air to clean a person. D. Lift properly 1. Ask for help if necessary. 2. Lift with legs, not the back and keep the back straight.


E. Use proper electrical procedures 1. Always check wires on a piece of equipment before using. 2. Always make sure electrical equipment is grounded. F. Operating engines 1. Do not operate an engine at speeds greater than recommended to avoid engine damage and accidents. 2. Never tamper with governor settings to increase maximum engine speed.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT C: WORKPLACE SAFETY COMPETENCY: SE07.00 Practice proper personal procedures. OBJECTIVE: SE07.02 Use tools and equipment safely. Use Tools Properly (Small Gas Engines, Ch. 1, pp. 15-16) A. Hand Tools 1. Maintain tools – Clean, sharp tools are safer and easier to use. 2. Use tool only for its intended purpose. 3. Pull wrenches toward you. 4. Always check a tool’s condition prior to use. B. Power Tools 1. Make sure all guards are in place prior to use. 2. Wear eye protection. 3. Know a power tool’s proper operation before using it. 4. Power tools should always have a dead man switch.



UNIT D: SMALL ENGINE TOOLS AND MATERIALS

COMPETENCY: SE08.00 Demonstrate the use of small engine tools.

OBJECTIVE: SE08.01 Describe small engine hand tools and measuring instruments.

Common Hand Tools (Small Gas Engines, Ch. 2, pp. 21-28)

A. Wrenches 1. Open end 2. Box end 3. Combination 4. Tubing 5. Adjustable 6. Allen 7. Torque a. inches, lbs. b. foot, lbs. B. Pliers 1. Vice grip 2. Needle nose 3. Diagonal side cutting 4. Combination slip-joint 5. Retaining ring C. Screwdrivers 1. Standard or slotted 2. Phillips 3. Offset D. Hammers (small engine related) 1. Ball Peen 2. Soft faced E. Punches 1. Center 2. Prick 3. Pin 4. Drift F. Cold Chisels G. Gear Pullers H. Vise I. Cleaning Tank



UNIT D: SMALL ENGINE TOOLS AND MATERIALS

COMPETENCY: SE08.00 Demonstrate the use of small engine tools.

OBJECTIVE: SE08.02 Demonstrate the use of small engine hand tools and measuring instruments. Measuring Instruments (Small Gas Engines, Ch. 2, pp. 31-39)

A. Micrometers – precision instrument that accurately measures small engine parts.

1. Types a. Outside – thickness and outside diameters b. Inside – internal dimensions c. Blade – narrow slots d. Vernier – more exacting and precise 2. Measuring techniques – hold properly and use carefully 3. Calibrating 4. Reading standard types a. Three decimal places, or thousandths of an inch b. diagrams and picture on pp. 31 & 32 5. Digital types 6. Micrometer depth gauges 7. Vernier calipers – used for internal and external measurements (Diagrams on pp. 34 & 35)

B. Telescoping Gauges

1. Do not take direct readings. 2. Called transfer readings. Can use to show a distance (i.e. cylinder ID) or to set a specific measurement and then determine if something falls within the tolerances.

C. Small Hole Gauge – measures ID of small holes (i.e. valve guides)


D. Thickness Gauges – to measure distances between items (spark plug gap, valve clearances, etc.)

1. Flat or feeler gauge type 2. Round type

E. Dial Indicator – measures movement of parts (pictures – pg. 40) F. Screw Pitch Gauge – finds number of threads per inch on a screw.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT D: SMALL ENGINE TOOLS AND MATERIALS COMPETENCY: SE09.00 Describe the use of common small engine fasteners, adhesives, and gaskets. OBJECTIVE: SE09.01 Identify common small engine fasteners, adhesives, and gaskets. A. Fasteners (Small Gas Engines, Ch. 3, pp. 43-59) 1. Screws – various head types (pg. 44) related to use 2. Bolts – available in various types 3. Nuts – various sizes and shapes (pg. 47) 4. Bolt and Nut Terms a. Bolt size – largest diameter of threads b. Bolt head size – dimension across the head’s flat sides c. Bolt length – distance from base of head to threaded end. d. Thread pitch – number of threads per inch e. Bolt grade – Minimum tensile (pulling), strength of bolt - 3m or metric B. Washers – various types for different uses (pg. 56) C. Gaskets – used between engine parts to prevent leakage and seal. Must replace a used gasket with identical type.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT D: SMALL ENGINE TOOLS AND MATERIALS COMPETENCY: SE09.00 Describe the use of common small engine fasteners, adhesives, and gaskets. OBJECTIVE: SE09.02 Describe the uses of small engine fasteners, adhesives, sealants, and gaskets. A. Fasteners (Small Gas Engines, Ch. 7, pp. 45-47 & pp. 56-60) 1. Screws a. Set – secures things like pulleys to gears to shafts b. Self tapping – will cut its own threads in a predrilled hole 2. Cotter Pins – used with castle (or castleated) not to keep nut on bolt 3. Lock Nuts – Designed to reduce the possibility of nut coming off. (pg. 48) B. Pins – various types for different uses (pg. 56) C. Retaining Rings – various types for different tarrying uses (pg. 57) D. Keys – used to secure a shaft to the part that rotates with it (pg. 58) E. Adhesives – come in various forms and types – most common is thread adhesive to prevent loosening of threads during use. F. Sealants – used to seal area between two surfaces – different purposes; specific types G. Antiseize Compounds – prevents metal components that are exposed to heat from becoming “cold welded” together H. Gaskets – used between engine parts to seal and prevent leakage. Must replace a used gasket with identical type.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT D: SMALL ENGINE TOOLS AND MATERIALS COMPETENCY: SE09.00 Describe the use of common small engine fasteners, adhesives, and gaskets. OBJECTIVE: SE09.03 Describe the important concepts of thread types and threading as it relates to small engines. Threads and Threading (Small Gas Engines, Ch. 3, pp. 49-55) A. Thread Types – refers to the number of threads per inch 1. Unified National Coarse (UNC) - not used in vibration situations and has less threads per inch. 2. Unified National Fine (UNF) – used where vibration is a problem. Have more threads per inch. 3. Metric (m) B. Tightening and loosening threaded fastener 1. Right hand thread – tightens clockwise and loosens counter clockwise; very common 2. Left hand thread – opposite of right hand thread C. Chasing Threads 1. Use a threading tap to repair threads damaged in a nut or threaded hole. 2. Use a threading die to repair threads damaged on a bolt or screw. D. Tapping new threads – involves drilling an appropriate sized hole for intended purpose, and using a tap to put in new threads (pp. 52-55) E. Threading with a die – involves putting external threads on a piece of stock.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT E: SMALL ENGINE CONSTRUCTION, PRINCIPLES, AND THEORIES COMPETENCY: SE10.00 Explain basic small engine operation principles. OBJECTIVE: SE10.01 Discuss the purposes of the major components of a small engine. Small Gasoline Engines (Small Gas Engines, Ch. 4, pp. 63, 67, 70, 71, 73 & 75) A. General Concepts 1. Gasoline engine is designed to transform chemical energy of burning fuel to mechanical energy. 2. Gasoline engines are internal combustion. Fuel is combined with air and burned inside the engine. 3. Piston closely fits in cylinder, yet it is free to move. 4. Connecting rod is connected to the piston at one end and the crank case on the other end. 5. Gas is atomized and mixed with air. The mixture is forced through an intake port into the cylinder where it is compressed by the piston on the upstroke and ignited by an electrical spark. 6. The rapidly burning gasses expand and force the piston down. 7. The connecting rod then turns the crank shaft. 8. The burned mixture is then forced out through an exhaust port. 9. New gas:air mixture enters the cylinder and the process repeats itself.


B. Parts 1. Cylinder block (pg. 67) – keeps all parts in alignment; largest part of the engine. 2. Crankshaft (pg. 68) – major rotating part of the engine. 3. Crankcase (pg. 68) – is rigid and strong to withstand forces of crankshaft rotating. Contains oil for lubricating engine. 4. Piston (pg. 70) – connected to connecting rod by piston pin. Has piston rings to help contain explosion. 5. Connecting rod – is attached to crankshaft by bearing cap. 6. Intake and exhaust ports and valves a. Port – opening covered and exposed by pistons on two-cycle engine. b. Valve – a piece of metal that opens and closes; also called poppet valves. 1. Held in alignment by a valve slide. 2. Held closed by a valve spring. 3. Spring connected to valve by a washer and a keeper. 4. Has a head, with a face that fits into the seat. 7. Camshaft (pg. 73) - has lobes that open the valves when rotated. 8. Valve lifter or tappet (pg. 73) Camshaft pushes against it to open the valves. Can be made to be adjustable. 9. Flywheel (pg. 75) – fastened to one end of crankshaft. Keeps engine turning during non-power strokes. Has fins to cool air cooled engines. Has magnets to provide spark with a magneto ignition system.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT E: SMALL ENGINE CONSTRUCTION, PRINCIPLES AND THEORIES COMPETENCY: SE10.00 Explain basic small engine operation principles. OBJECTIVE: SE10.02 Explain the principles of fuel combustion in relation to small engine operation. (Small Gas Engines, Ch. 4, pp. 61, 65, 69, 70, & 71-75) A. Gasoline 1. Needed properties for engine operation a. Ignite readily and burn cleanly, and resist detonation (violent explosion) b. Vaporize easily without causing vapor lock c. Be clean d. Has octane number that corresponds to its ability to resist detonation. (1) Regular grades have lower numbers. (commonly used in small engine) (2) Higher grades have higher numbers. 2. Gas must be atomized. Atomized means to be broken up into small droplets and mixed with air. B. Explosion must be contained and controlled. This is done inside the cylinder (refer to SE10.01)


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT E: SMALL ENGINE CONSTRUCTION, PRINCIPLES, AND THEORIES COMPETENCY: SE11.00 Explain the theories of small engine operation. OBJECTIVE: SE11.01 Define terms related to small engine theory, performance, and operation. Terms (Small Gas Engines, Ch. 5, pp 77-79 & Ch. 6, pp. 92-97) 1. Stroke – movement of piston from one end of cylinder to the other end. 2. TDC/Top Dead Center – when the piston is as far up as it can go in the cylinder. 3. BDC/Bottom Dead Center – when the piston is as far down as it can go in the cylinder. 4. Compression Ratio – is the proportionate difference in volume of cylinder and combustion chamber at BDC and TDC. 5. Scavenging – removal of exhaust gases from the cylinder. 6. Bore – diameter or width of cylinder. 7. Engine Displacement – the total volume of space increase in the cylinder when piston moves from TDC to BDC. 8. Force – is the pushing or pulling of one body on another. 9. Work – is accomplished when a force is applied through some distance. 10. Power – is the rate at which work is performed. 11. Energy – is the capacity to perform work.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT E: SMALL ENGINE CONSTRUCTION, PRINCIPLES AND THEORIES COMPETENCY: SE11.00 Explain the theories of small engine operation. OBJECTIVE: SE11.02 Explain what takes place during each stroke of four- stroke and two-stroke engines. A. Four-Stroke Cycle (Small Gas Engines, Ch. 5, pp. 77-80) 1. Intake Stroke – When piston travels down the cylinder, volume is increased which creates a partial vacuum. Intake valve is opened which allows air-fuel mixture into the cylinder. 2. Compression Stroke – When piston travels up in the cylinder., both valves are closed. The air-fuel mix is squeezed together which creates more potential power in the mix. 3. Power Stroke – The spark plug ignites the air-fuel mix, which forces the piston down. Both valves are closed to contain the combustion, or force. 4. Exhaust Stroke – The exhaust valve opens, and then the piston travels upward to force the exhaust out of the cylinder. 5. Requires two revolutions of crankshaft. B. Two-Stroke Cycle (Small Gas Engines, Ch. 5, pp. 80-89) 1. General Points a. Lighter in weight than 4-stroke cycle. b. Less moving parts than 4-stroke cycle. c. Performs same functions as 4-stroke cycle, only in one revolution of the crank.


2. Principles of Operation (pp. 82-83) a. Intake – As the piston moves upward in the cylinder, the crankcase pressure drops. This also exposes the intake port. This causes the air-fuel mix to enter the crankcase. In addition to the gas-air mix, two-stroke cycle fuel contains oil which lubricates the engine. b. Fuel Transfer – As the piston moves downward, the air-fuel (and oil) mix gets compressed and forced into the intake (or transfer) port, which lubricates, cools, and charges the cylinder. c. Ignition/Power – As the piston moves upward, the fuel-mix is compressed. Somewhere near TDC, the mixture is ignited. d. Exhaust – As the piston is forced downward, the exhaust leaves the cylinder through the exposed exhaust port. Also, this begins the process of intake. See number one. 3. Summary (pg. 89)


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT E: SMALL ENGINE CONSTRUCTION, PRINCIPLES AND THEORIES COMPETENCY: SE11.00 Explain the theories of small engine operation. OBJECTIVE: SE11.03 Discuss how horsepower is determined. A. Terms/Concepts (Small Gas Engines, Ch. 6, pp. 98-102) 1. Output of engines is compared to output of horses because horses were used for power for many years. 2. Horses could lift 100 lb. a distance of 330′ in one minute. 3. If one lb. is lifted in one minute, a ft.-lb. of work is done. 4. Using the formula (work = distance x force), it was determined that a horse performed 37,000 ft./lb. of work. In other words, One horsepower translates to 550 ft.-lb./sec., or ability to lift 550 lbs. a distance of one foot in one second. B. Kinds of Horsepower 1. Brake horsepower (bhp) – Is the actual horsepower delivered at the crankshaft. 2. Indicated horsepower (ihp) - measures power developed by the burning fuel mix inside the cylinder. 3. Frictional Horsepower (fhp) – represents that part of the potential or indicated horsepower lost due to engine parts rubbing together. 4. Corrected Horsepower – is a guess at horsepower of a given engine under specific operating conditions that are not the same as those present. 5. Rated Horsepower (rhp) – generally considered to be 80% of maximum bhp. This is done because engines at full horsepower overheat and wear prematurely. C. Measuring Horsepower 1. Prony Brake – is a friction device that grips the flywheel and transfers force to a measuring scale. 2. Dynamometer – takes the power from the engine and transfers it to a measuring device that uses other hydraulic or electrical loading to provide the resistance.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT F: SMALL ENGINE FUEL, EMISSION CONTROL, AND CARBURETION COMPETENCY: SE12.00 Discuss common engine fuel systems and their uses. OBJECTIVE: SE12.01 Summarize types and applications of fuels and mixtures. Engine Fuels (Small Gas Engines, Ch. 7, pp. 109-111) A. Gasoline 1. Should be around 90 octane for normal small engine use. Premium fuel may be used in hot climates to prevent detonation. 2. Should be: a. Clean b. Free from moisture c. Reasonably fresh and not stale B. Liquefied petroleum Gas (LPG) 1. Must have properly designed fuel system. 2. Burns cleanly with less noxious fumes so it is suitable for indoor use in factories and warehouses. C. Kerosene and diesel fuels 1. Some gasoline engines are converted to use kerosene or diesel fuels by changing to low compression head and special carburetor. 2. Some small engines do run on diesel fuel. D. Two-cycle fuel mixtures 1. Two-cycle fuel is a gas and oil mix to lube the engine as well as provide fuel for combustion. 2. Too much oil : incomplete combustion, buildup of carbon that fouls spark plugs and adds weight to pistons.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT F: SMALL ENGINE FUEL, EMISSION CONTROL, AND CARBURETION COMPETENCY: SE12.00 Discuss common engine fuel systems and their uses. OBJECTIVE: SE12.02 Describe the types, operation, and maintenance of common fuel delivery systems. (Small Gas Engines Ch. 7, pp. 112-120) A. Fuel filters (pp. 112-113) 1. Placement/types a. Mounted at end of pick up line 1. Can be hard to access. 2. Can have ball check valve to prevent gas from draining back into tank while engine is running. b. Mounted at the bottom of the tank with a shut-off valve 1. Requires tank to be empty to check/clean. 2. Requires care during installation. c. Glass sediment bowl 1. Can be visually checked without removing any parts. 2. Can be serviced easily. 3. Often found on many older small engines. B. Fuel pumps – Because of the way the fuel tank is mounted,, it is needed on engines to provide a gravity supply. 1. Impulse diaphragm fuel pump a. Works y having the pulsing vacuum in the intake manifold or crankcase pump the fuel. b. Four-cycle engines use intake manifold vacuum. Two-cycle engines use crankcase vacuum. 2. Pressurized fuel system – used when fuel tank is located considerable distance below the fuel tank. a. Uses pressure from crankcase transferred to fuel tank to force gasoline to engine. b. Commonly used in outboard (boat) engines. c. Most complex system.


C. Small engine emissions (pp. 116-120) 1. Small engines have long been a source of emissions. 2. Mowing a lawn with a typical older mower for one-half hour can produce as much smog as driving the average car 172 miles. 3. Refueling losses from lawn-and-garden equipment can account for 72% of evaporative emissions from non-road engines. In other words, Americans spill over 17 million gallons of gasoline every summer when refueling lawn-and- garden equipment. 4. In 1970 the United States passed the Federal Clean Air Act. 5. Environmental Protection Agency (EPA) is the federal agency involved in reducing air pollution. 6. EPA developed “Phase I Standards for Small Spark-Ignition Engines” a. Set emission regulations for engines at or below 25 HP. b. Took effect in 1997. c. Those standards were chosen because they have shown to be achievable and cost effective using currently available technology.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT F: SMALL ENGINE FUEL, EMISSION CONTROL, AND CARBURETION COMPETENCY: SE12.00 Discuss common engine fuel systems and their uses. OBJECTIVE: SE12.03 Discuss emission control related agencies and regulations.



COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT F: SMALL ENGINE FUEL, EMISSION CONTROL, AND CARBURETION COMPETENCY: SE13.00 Demonstrate knowledge of carburetors and their operation. OBJECTIVE: SE13.01 Explain the principles and operation of carburetors. (Small Gas Engines, Ch. 8, pp. 123-126 & pp. 129-133) A. Carburetor principles 1. Carburetors main purpose is to make a mixture of fuel and air. 2. There are many ways of mixing it so engine can run properly over a range of speeds. 3. Engines cannot run on liquid gasoline, the carburetor must vaporize fuel and mix it with air in proper proportion for varying conditions. 4. Basically, air enters carburetor and is mixed with fuel, then fed through carburetor passages and sprayed into the air stream. 5. Air fuel mixture requirements vary depending on operating conditions (pg. 124) (less air/richer mixture needed) during starting and acceleration. Engine is leanest (larger amount of air in the mix) when engine is running at normal speed. 6. Venturi principle (pg. 125) A venturi is a restriction or narrowing in a passageway which causes air to move faster, or increase velocity. The area in the middle of the restriction is where the air moves the fastest, and where a lower pressure (vacuum) develops. 7. Fuel discharge nozzles are usually located at the center of the venturi which aids in fuel being drawn into the air stream and atomized more easily. 8. Some carburetors have more than one fuel discharge point. Some are equipped with an economizer circuit which is designed to retard fuel flow when the engine is idling.


9. When engines go beyond idling speed, many carburetors have primary and secondary discharge holes that are both working. 10. At high speeds, the main discharge is working at full capacity to allow all the needed fuel to enter. 11. Some carburetors have a primer. When depressed, it forces additional fuel through the main discharge nozzle to aid in starting. 12. Diaphragm carburetors use engine vacuum to pulsate a flexible diaphragm to bring fuel into the engine. 13. Many carburetors have chokes, the function of which is to create stronger vacuum in the venturi which in turn sucks out more gas. This combined with a reduced air flow makes the mixture richer (greater gas amount in the mix) which aids in starting.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT F: SMALL ENGINE FUEL, EMISSION CONTROL, AND CARBURETION COMPETENCY: SE13.00 Demonstrate knowledge of carburetors and their operation. OBJECTIVE: SE13.02 Summarize common carburetor systems and their parts. (Small Gas Engines, Ch. 8, pp. 126-128 & pp. 134-141) A. Types of carburetors (pg. 126) 1. Natural draft – used when there is little space on top of engine. Air flows horizontally into the manifold. 2. Up draft – placed low on the engine and uses a gravity-fed fuel supply. Air flows up; air velocity must be high; small passages used. 3. Downdraft – Air flow is down through the carburetor. Operate with lower air velocities and large passages. Because gravity works with it, this type can provide large volumes of fuel when needed. 4. Float-type – type that has a small sealed vessel that rises and falls with the fuel level in the carburetor. The purpose of this type is to maintain a constant supply of fuel in the carburetor’s float bowl. a. Has a choke to make fuel mix richer (larger amount of gas) for starting. b. Also has throttle valve, which regulates the amount of air entering the cylinders. 5. Diaphragm type (pg. 132) – A diaphragm is pulsated by the difference between atmospheric pressure and vacuum created in the engine; which in turn, pumps fuel into the carburetor. B. Types of throttle Controls (pg. 134) - Throttle controls are needed to regulate and adjust engine speed. 1. Manual – either a mechanical linkage or flexible cable. One end is attached to the throttle shaft lever and other end are connected to a lever, slide or dial that is operated manually to open and close the throttle valve.


2. Governor throttle controls – used in situations where engine load can change instantly. a. Purposes 1. Maintain a speed selected by generator. 2. Prevents over speeding. 3. Limits both high and low speeds. b. Types 1. Air vane (or pneumatic) (pp. 136-137) – operated by stream of air created by flywheel coding fins which are directly related to engine speed. Must be carefully maintained and adjusted using a tachometer. Blade tip speed on lawn mowers is important as well, should not exceed 19,000 feet per minute. This is related to blade length and engine RPM. 3. Centrifugal or Mechanical (pp. 138-139) – regulates engine speed using weights driven by the engine. C. Adjusting 1. Should be done using engine specifications and a tachometer to determine engine RPMs. 2. Common problem of governors is called “hunting.” This is when governor speed fluctuates. Can usually be adjusted following engine specifications. Putting spring in hole marked ″3″ is usually a good recommended starting place. 3. Air Cleaners a. Purpose 1. Small engines take in much air, often it is dirty. If air is not cleaned, dirt and grit enters cylinder and will cause rapid wear and scoring of mechanical parts in the engine. 2. If filter pores become plugged, engine runs as though it had the choke on. Results in a rich mixture, engine runs poorly, uses more fuel, generates less power and internal parts accumulate carbon. As it becomes more dirty, engine may be difficult to start and run with black smoke coming from exhaust. b. Manufacturers recommend either cleaning or replacing filters at various times specific to an engine. An average time for a lawn mower is 25 hours of use, or once a season, whichever comes first.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT G: SMALL ENGINE IGNITION SYSTEMS COMPETENCY: SE14.00 Explain the concepts of small engine ignition systems. OBJECTIVE: SE14.01 Describe the operation of a basic ignition system. (Small Gas Engines, Ch. 9, pp. 147-148) Basic ignition concepts 1. Purpose of ignition system is to provide sufficient voltage to discharge a spark between spark plug electrodes at the correct time. 2. Ignition system must be capable of producing as many as 30,000 volts in order to push or force current (electrons) across the gap. 3. It is the heat produced by the spark that ignites the fuel mix in the cylinder to create power. 4. The spark must be produced at a very high rate. A single cylinder four-cycle engine running at 3,600 RPM needs 1,800 sparks per minute. A two-cycle engine running at same speed needs 3, 600 sparks per minute. 5. Most small engines have a magneto ignition system to produce sparks and some have a battery ignition system.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT G: SMALL ENGINE IGNITION SYSTEMS COMPETENCY: SE14.00 Explain the concepts of small engine ignition systems. OBJECTIVE: SE14.02 Explain the fundamental electrical principles and measurement. (Small Gas Engines, Ch. 9, pp. 148-150) A. Basic electrical principles 1. All matter is made of atoms. 2. All atoms are made of protons, neutrons and electrons. 3. Electrons travel in orbits around the center of the atom and have a negative (-) charge. 4. Electrons can move from atom to atom. 5. The ease with which these electrons move from atom to atom in a substance determines if the substance will conduct or carry electricity. 6. In conductors of electricity, copper, aluminum and silver, the electrons move from atom to atom freely. 7. In non-conductors, or insulators, it is difficult or impossible for these electrons to move from atom to atom. 8. Electrons will move only if there is a complete circuit and a difference in electrical potential. 9. A difference in electrical potential means that the electrons that are negatively charged will flow to a positively charged material. This is because unlike charges attract. 10. Electrical potential can be produced by three methods: a. Mechanically – a generator, magneto, etc. b. Chemically – a battery. c. Statically – lightening, clothes, etc.


B. Electrical units of measurement (pp. 149-150) 1. Amperes – also called amps or A. Is the measurement of the number of electrons flowing past any given point in a specific length of time. Larger wires are needed to carry more amps. Can be compared to the gallons per minute of water flowing through a hose. 2. Volts or V. - This is the difference in electrical potential between two points. It is also the force or pressure that causes electrons to flow. Can be compared to the pressure behind water in a hose causing it to flow. 3. Ohms - (pg. 150) This is the resistance that a material has to electron flow. Some materials offer much resistance and some materials offer little resistance. If a wire is too small for the current it is carrying, the ohms or resistance will be great. Can be compared to using a small hose to attempt to carry a lot of water. One major source of resistance in an ignition system is the air gap in the spark plug that the electrical current must jump. C. Ohm’s Law is a mathematic way to state the relationship of volts, amps and ohms. The formula for Ohms Law is: I = E, when I = amperes, E = volts and R R = ohms. Using the chart on page 150, it can be determined that if you set the Ohms Law up visually as _E_, the unknown value by covering up the unknown I/R value and doing the resulting computations. To find I (amperes), cover the I and see that you would divide volts by ohms.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT G: SMALL ENGINE IGNITION SYSTEMS COMPETENCY: SE14.00 Explain the concepts of small engine ignition systems. OBJECTIVE: SE14.03 Discuss spark plugs and their uses. A. General spark plug concepts (Small Gas Engines, Ch. 9, pp. 152-157) 1. There are a variety of different types of plugs. 2. Plugs are designed to function in a specific engine. 3. Plugs must be able to conduct the electricity to the gap and create the spark and heat needed to ignite the air-fuel mix inside the engine cylinder. 4. Plugs must be able to withstand high temperature. The shock of combustion insulates the electrode against current loss and seals against compression leakage.


B. Spark plug parts and terminology (pp. 153-157)

1. Terminal nut – where the wire from the ignition system, also called high tension lead, attaches to the plug.

2. Insulator – the part of the plug that insulates the plug to prevent voltage leak and flashover.

3. Flashover – is the tendency for the current to flow over the outside of the plug and not through the center electrode.

4. Center electrode – carries the current from the terminal nut through the plug to the plug electrode gap.

5. Reach – the length of the threaded part of a spark plug. Is related to the thickness of the engine’s head. Too long could damage piston, too short causes poor combustion.

6. Heat Range/Heat Transfer – How readily the plug transfers heat from the firing end into the head. Cold running plugs transfer heat readily. Used in engines that have high combustion temperatures to avoid overheating. Hot running plugs do not transfer heat readily and are used in cooler running engines to prevent fouling, or carbon build up, on the plug. C. Spark plug symbols ( pg. 154) 1. All spark plugs have letters and numbers to indicate information about the plug. Example from book: BP5 E5-15 and explanation of specific symbols. a. B = thread diameter (1.4 mm) b. P = construction (projected insulation type) c. 5 = heat rating, or range (5 = higher heat but not hottest) d. E = reach (19 mm or ¾”) e. S = firing and construction (standard center electrode) f. 15 = wide gap (1.5 mm or .060”)


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT G: SMALL ENGINE IGNITION SYSTEMS COMPETENCY: SE15.00 Analyze the operation of small engine magneto ignition systems. OBJECTIVE: SE15.01 Explain the principles and operation of magneto systems. (Small Gas Engines, Ch. 9, pp. 150-152 & pp. 157-166) A. Principles of magnetism (as it relates to magnetos) 1. Magnetism a. Molecules make up matter. (materials) b. Molecules are made of atoms. c. Molecules have magnetic poles. (similar to bar magnets) d. Usually, the molecules are arranged randomly. (pg. 150, figure 9-7) e. When a material is magnetized, molecules line up. (pg. 151, figure 9) f. Magnets produce a magnetic field. (pg. 151, figure 9) 2. Magnets and electricity a. Magnets can be used to produce electricity. b. Discovered by Michael Faraday. c. Faraday found that if a wire is moved past a magnet, the magnetic field of the magnet is cut, and current will flow through the wire. When the wire is stopped, current flow stops also. d. A magnetic field is developed when current flows through a COIL of wire pg. 152, figure 9-12). e. Magneto ignition systems use the theory in (d) by passing electric current through a coil and developing a magnet. f. The ignition coil in ignition systems is the engine part that produces electricity using these principles. g. An ignition coil is made of two separate windings (coils) of wire insulated from each other that are wound around a laminated (made of many thinner pieces) iron core. The primary winding is thicker, heavier wire with few turns. The secondary winding is made of many turns of thinner wire (pg 152, figure 9-13). h. When a current is passed through the primary winding, a magnetic field is created around the iron cores. i. When the current is stopped in the primary winding, the magnetic field collapses rapidly and cuts through the secondary windings. j. The rapid cutting of the magnetic field by the wire creates high voltage in the secondary circuit. k. This high voltage passes through a wire called the high tension lead, or play wire, to the spark plug.


l. In order to stop the flow of the current through the primary circuit, various types of switches are used. m. One type of switch is called breaker points. When points are closed, current flows creating a magnetic field. When points open, current stops flowing causing the field in the primary coils to collapse through the secondary circuit (pg. 157, figure 9-25). n. Another type of switch is one that is electronically controlled. B. Types of magnetos (pp. 158-166) 1. The MBI Magneto System (pg. 158, figure 9-26) a. MBI stands for mechanical breaker point ignition, meaning that the switch that turns off the primary circuit consists of points that are mechanically opened and closed. b. In addition to the parts of an ignition system already discussed, other parts include: (1) condenser – (pg. 159, figure 9-27) primary purpose is to prevent arcing across the breaker point gap when the points open. This prevents damage to the points and allows for proper energy distribution. (2) magnets – already discussed, but in MBI system, they are imbedded permanently in the flywheel. (3) air gap – this is the distance between the flywheel and the magneto core ends. Tolerances are critical to proper magneto operation. c. MBI magneto cycle (pp. 159-160) (1) refer to complete explanation in the book. (2) Generally, the magnets in the flywheel cause current to flow in the primary circuit which causes a magnetic field. The points open at the proper time, the magneto field in the primary circuit collapses through the secondary circuit and cause high voltage in the secondary circuit. (3) Dwell (cam angle) (pg. 163, figure 9-36) is the time the points stay closed during one revolution of the engine. (Equal to the number of degrees measured around the cam from the point of closing to the point of opening.)


2. Electronic Ignition – also called solid state. Refers to any ignition system that uses electronic semi-conductor (diodes, transistors, silicon controlled rectifiers, etc. in place of one or more mechanical ignition components. It has numerous advantages (refer to pg. 3) 3. CDI system (pp. 163-168) a. CDE stands for capacitive discharge ignition system. b. new system c. improved engine reliability d. is breaker less e. Much of MBI system components are replaced by CDE ignition module. f. A rectifier is an important part of CDI system. This is an electrical component that changes alternating current (ac) to direct current (DC). g. Complete cycle is covered in data in book. 4. TCI system (pp. 165-166) a. TCI stands for transistor controlled ignition system. b. covered in detail in book. c. General concept is that transistors (T) control electrical flow to create the high voltage in the secondary coil. d. Has a diode to protect the TCI from damage. e. Has an ESG circuit to retard the ignition timing.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT G: SMALL ENGINE IGNITION SYSTEMS COMPETENCY: SE15.00 Analyze the operation of small engine magneto ignition systems. OBJECTIVE: SE15.02 Compare the three magneto ignition systems. (Small Gas Engines, Ch. 9, pp. 166-167) A. Magneto ignition systems compared 1. Refer to figure 9-44, pg. 167 for comparison chart.. 2. Generally, a. MBI or mechanical breaker ignition has mechanical breaker contacts that trigger the system. b. CDI or capacitor/capacitive ignition system is a solid state using a capacitor to store energy and semi-conductors for timing and triggering the system. c. TCI or transistor controlled ignition system. Uses transistors, diodes, etc. semiconductors) for switching purposes.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT G: SMALL ENGINE IGNITION SYSTEMS COMPETENCY: SE16.00 Analyze the operation of battery ignition systems. OBJECTIVE: SE16.01 Explain the principles and functions of battery ignition systems. (Small Gas Engines, Ch. 9, pp. 167-170) Note to Teacher: Magneto ignition systems should be covered prior to this. A. Battery Ignition System 1. General concepts of producing high voltage electricity are the same as a magneto system. 2. Major difference is that the source of current for primary circuit is a lead-acid battery. 3. Current flows through primary circuit when ignition switch is turned on to the points. 4. When points are opened, primary field collapses through secondary field and high voltage is produced. 5. Coil purpose and general construction is the same as a magneto ignition system, except there are three terminals on the coil (pg 169, figure 9-49). They are: a. Positive primary marked with (+) which is connected to the positive battery terminal. b. Negative primary – marked with a (-) which is connected to the points. c. High tension – where high tension lead attaches.


B. Lead acid battery 1. This is the only source of current for the battery ignition system. 2. Must have a system associated with it to recharge battery, such as generator or alternator. 3. Construction (figure 9-50) a. hard rubber coils b. six compartments called cells c. Cells contain plates made of lead with sulfuric acid and water (called the electrolyte) surrounding the plates. d. Each cell of a battery in good condition contributes about 1.95V-208V. Therefore, a battery has at least 12 V to be considered fully charged. 4. Electricity production – A chemical reaction causes each negative plate to lose electrons and each positive plate to gain electrons. This will happen only when they are surrounded by electrolyte. All plates of a like charge are connected to allow for the accumulative charge.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT G: SMALL ENGINE IGNITION SYSTEMS COMPETENCY: SE16.00 Analyze the operation of a battery ignition system. OBJECTIVE: SE16.02 Compare magneto ignition systems and battery ignition systems. Comparison 1. Many small engines used magneto systems because they are generally simpler and lighter in weight. 2. Magneto systems are usually self contained, needing no outside source of electricity. 3. Battery ignition systems are more complex due to the need for a storage battery and a method to recharge it. 4. Batteries can, and often are, used to power other things as power implements and tractors. 5. Battery ignition system requires more maintenance.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT H: SMALL ENGINE LUBRICATION SYSTEMS COMPETENCY: SE17.00 Describe general concepts of oils and lubrication in small engines. OBJECTIVE: SE17.01 Recognize the purposes, properties, and importance of oil to small engines. A. Principles of lubrication 1. Lubrication is the process of reducing friction between sliding surfaces by introducing a slippery substance between them. 2. Friction is the resistance to motion created when one dry surface rubs against another. 3. Lubricants come in three forms. a. dry (powdered) b. semi-dry (grease) c. liquid (oil) 4. Oil is the most important lubricant in small engines because it is often the only lubrication an engine needs. 5. Oil lubricates by separating surfaces with a thin film, that when in motion has molecules that roll over one another like tiny ball bearings (pg. 175, figure 10-1). 6. To help prevent wear due to friction, engines are made of certain materials. Bearing shells found in connecting rods and caps are made of steel with a Babbitt surface ( pg. 176, figures 10-3, 4, 5). Babbitt is an alloy of tin, copper and antimony.


B. Properties of oil – Oil must have the following properties, or do the following “jobs.” 1. Permit easy starting. 2. Lubricate. 3. Protect against rust and corrosion - needed because for each gallon of gas burned, a gallon of water is formed. Some of this water goes into the engine. 4. Keep engine parts clean. – Oils have detergent/dispersant additions. 5. Cool engine parts. 6. Seal combustion pressure. 7. Prevent foaming. 8. Aid fuel economy.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT H: SMALL ENGINE LUBRICATION SYSTEMS COMPETENCY: SE17.00 Describe general concepts of oils and lubrication in small engines. OBJECTIVE: SE17.02 Define oil viscosity information and terms. (Small Gas Engines, Ch. 10, pp. 179-181) A. Oil Selection – Oil is available in many forms that have certain properties suitable for a specific engine. The specifications are given in two ratings. 1. Society of Automotive Engineers (SAE) Viscosity. a. Also called viscosity grade. b. Is a measure of the oil’s resistance to flow. c. An oil viscosity must be suited for an engine because it must be thick enough to keep the oil from flowing too easily from between engine parts when under pressure. d. Oil has to be thin enough to allow for cold cranking, good circulation, and adequate degenerative protection. e. Oils are assigned a grade to show the range in which it falls. f. Low numbers (5W, 10W, etc.) are thin, free flowing oils. g. High numbers (40, 50, etc.) are thicker, slower flowing oils. h. The “W” means it is used for low temperatures. i. There are commonly used oils that are called multigrade or multiviscosity oils. Examples are SAE: 5W-20, 5W-30, etc. This means the oil meets the viscosity requirements of more than one oil.


2. API Engine Services Classification – also called the type of oil. a. Oils are classified according to what they may be used for. b. The designation is two letters, with sometimes a number following the letters. c. First letter indicates general approved use with a ″S″ meaning passenger cars, vans, and light trucks and ″C″ meaning heavy duty diesels. d. Second letter indicates the level of service within the first letters category. e. There are currently 18 categories, of which 5 are considered suitable for vehicles in use today. (see pp. 181-182) 3. API Engine oil service classification symbol (pg. 181, figure 10-11) a. Is a symbol that is found on the label of an oil container, and sometimes on oil filter caps or owner’s manuals. b. Provides consumers with information about the oil. c. Symbol composed of three parts: (1) Top – has oil’s service classification. (2) Center – has oil’s viscosity. (3) Bottom – has information on the oil’s fuel saving properties.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT H: SMALL ENGINE LUBRICATION SYSTEMS COMPETENCY: SE18.00 Demonstrate the general concepts of small engine lubrication. OBJECTIVE: SE18.01 Explain the importance of proper gas:oil mixture in 2-cycle engines. Two-cycle engine lubrication (Small Gas Engines, Ch. 10, pp. 181-182) 1. Two-cycle engines are lubricated by the oil which is mixed with the gasoline. 2. It is a mist of the gas:oil mix that lubricates the internal engine parts. 3. There are many ratios for mixing the gas:oil mix. The ratio or a specific ratio can be found either on the engine or in the manual. 4. Normally the ratio is stated in a proportion of parts of gas to parts of oil (Example 16:1 means 16 parts gas to 1 part oil). 5. There are charts used to convert the ratio in parts, to how many ounces of oil are added to how many gallons of gasoline (pg. 181, figure 10-12). 6. There are specially formulated oils for mixing a two-cycle fuel mix. For this reason, it is not recommended that automotive oils be used.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT H: SMALL ENGINE LUBRICATION SYSTEMS COMPETENCY: SE18.00 Demonstrate the general concepts of small engine lubrication. OBJECTIVE: SE18.02 Describe the common lubrication systems for a 4-cycle small engine. Four-cycle engine lubrication systems (Small Gas Engines, Ch. 10, pp. 182-186) 1. Splash lubrication systems a. Found in smaller four-cycle engines. b. Has a dipper attached to the connecting rod cap that splashes oil around the inside of the engine as the crankshaft rotates (pg. 182, figure 10-15) c. The oil ring on a piston prevents excess oil from entering the combustion chamber. 2. Constant level splash system a. Improves on the simple splash system by having a simple pump, a splash trough and a strainer. b. Maintains a more constant oil level in the engine. c. Two pump types (1) Ejection pump (2) Barrel pump 3. Positive displacement oil pump a. Has a pump system to circulate engine oil to the desired locations. b. Is a more direct and definite way to circulate the oil. c. The pump has a pressure relief valve that prevents excess pressure from building.


4. Full pressure lubrication system a. The entire system is pressurized to allow for more positive direct lubrication. b. Normally found on car engines. 5. Oil filter systems a. Generally only found on larger small engines. b. Filters trap impurities and prevent them from circulating through the engine. c. By pass system – pumps part of the oil through the filter, remaining oil is pumped to bearings. d. Shunt filter system – Part of oil is filtered and directed to the engine bearings. Some oil is shunted past the filter. e. Full flow filter system – All of the oil is sent through the filter to the bearings. If filter becomes clogged, pressure increases and opens a relief valve that allows oil to flow past filter. f. Must use appropriate oil filter for each of the systems. Example: A partial low cartridge used in a full flow system would drastically reduce oil pressure.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT H: SMALL ENGINE LUBRICATION SYSTEMS COMPETENCY: SE18.00 Demonstrate the general concepts of small engine lubrication. OBJECTIVE: SE18.03 Mix an appropriate gas:oil mixture for a given 2-cycle engine. A. General concepts 1. Must use oil approved for use in a 2-cycle engine. a. Automotive oils are not recommended. b. Multiviscosity and detergent oils may have additives not good for 2-cycle engines. c. Two-cycle engines are lubricated by the fuel. Therefore, the mix enters the combustion chamber. d. Using the wrong oil in the mix can foul spark plugs and leave a residue in the exhaust ports. B. Mixing the fuel mix (Small Gas Engines, Ch. 10, pp. 181-182) 1. First step is to correctly determine the ratio needed by consulting engine labels or manual. 2. Consult a table, such as the one found in the book on page 181, or on a 2-cycle oil container. This will tell how much oil, in ounces, is to be added to a specified amount of gasoline to get the desired ratio. 3. Always weigh the oil. There are pre-measured oil containers available as well as oil containers with measuring devices built in. 4. Always mix fuel in a separate storage container that’s approved for gasoline, never directly in the fuel tank. 5. Add enough gas to make about one-half of the mix in the container, then thoroughly shake. 6. Finish the mixture preparation by adding the rest of the gas and oil and then shaking thoroughly.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT I: SMALL ENGINE COOLING SYSTEMS COMPETENCY: SE19.00 Demonstrate an understanding of small engine cooling concepts. OBJECTIVE: SE19.01 Explain the importance of properly cooling a small engine. Principles/concepts of engine cooling (Small Gas Engines, Ch. 11, pp. 191-192) 1. The life and efficiency of an engine depends on how well it is cooled. 2. The average temperature of burned gasses in the combustion chamber is 3600 degrees. 3. The exhaust carries away about 1/3 of the heat. 4. The cooling system removes about 1/3 of the heat. 5. The rest of the heat is used to produce power. 6. See pg. 192, figure 11-2 for a diagram of engine temperatures.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT I: SMALL ENGINE COOLING SYSTEMS COMPETENCY: SE19.00 Demonstrate an understanding of small engine cooling concepts. OBJECTIVE: SE19.02 Compare the various methods of cooling small engines.. A. Air cooling (Small Gas Engines, Ch. 11, pp. 192-193) 1. Air is forced over the cooling fins, directed by the shrouds and baffles and by the flywheel of most air cooled small engines. 2. Heat travels from the cylinder through the cylinder walls by conduction. Conduction is heat transfer through a solid material. 3. The heat is removed from the fins by convection. Convection is the transfer of heat through the movement of a gas. Air is the gas in small engines. 4. The cooling fins increase the surface area around the outside of the cylinder. The more surface area in contact with air; the more rapidly cooling will take place. 5. Cooling fins are not needed on water cooled engine because water is four times more effective than air for engine cooling. 6. It’s very important to keep fins cleaned to allow the cooling air to pass over. B. Exhaust cooling (Small Gas Engines, Ch. 11, pp. 192-193) 1. About 1/3 of engine’s heat is removed by the exhaust system. 2. The exhaust system must be kept free of obstructions or heat will build up in the engine.


C. Water cooling 1. Water is an excellent medium for cooling engines because it is: a. inexpensive b. readily available c. absorbs and carries heat well 2. Many water cooled small engines are water cooled because they are used in or around a water source. Good examples are boat motors. 3. No cooling fins are needed. 4. Generally, water cooled engines have passages called water jackets that surround the cylinder. 5. Water circulates through the water jackets to remove the engine’s heat. 6. Water cooled engines that have stored water generally use antifreeze which prevents freezing in the winter and overheating/boiling in the summer.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT I: SMALL ENGINE COOLING SYSTEMS COMPETENCY: SE20.00 Explain the operation of cooling system components. OBJECTIVE: SE20.01 Describe the types of water pumps found in small engines. Types of water pumps –All pumps must have an (Small Gas Engines, Ch. 11, inlet to allow water in and an outlet to allow water pp. 193-195) out. 1. Sliding vane pump – (pg. 194, figure 11-7) Has a cam, or eccentric that rotates to allow water in and then force it out. 2. Rotor-type pump – Operates like the sliding vane pump. The vane and rotor are one piece and the eccentric gyrates the rotor. 3. Plunger pump – (pg. 194, figure 11-8) A plunger arrangement pumps the water. 4. Vari-volume pump – Uses a synthetic rubber impeller that varies its size, results in the pump pumping at different rates. 5. Outboard water circulation system – (pg. 195, figure 11-10) Some outboards use a pressure-vacuum water flow system. The water flow from the propeller tips and motion of the boat creates the water flow. Another variation is to use the centrifugal force created by the propeller to discharge the water. Centrifugal force is the tendency of spinning matter to move away from the center of its gravity.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT I: SMALL ENGINE COOLING SYSTEMS COMPETENCY: SE20.00 Explain the operation of cooling system components. OBJECTIVE: SE20.02 Explain the operation of a thermostat. Thermostats (Small Gas Engines, Ch. 11, pp. 196-197) A. Purpose – The purpose of a thermostat in a water-cooled system is to act as a valve to stop the circulation of water until it reaches operating temperature. B. Types 1. Bellows type – an older style. Valve is attached to a bellows made of thin copper. Heat causes expansion of the copper which opens the valve. 2. Pellet type – more popular/common. Upon heating, the wax in a wax-filled upper cylinder pushes against a disk that moves a piston to open a valve to allow and water to flow. C. Checking a thermostat (pg. 197, figure 11-13) Put the thermostat in a beaker of cooled water with a thermometer. Heat the water until the thermostat opens. Observe the temperature.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT I: SMALL ENGINE COOLING SYSTEMS COMPETENCY: SE20.00 Explain the operation of cooling system components. OBJECTIVE: SE20.03 Describe a radiator and its operation Radiators (Small Gas Engines, Ch. 11, pp. 197) 1. Radiators are water reservoirs that hold coolant for engines. 2. They are made of thin copper or aluminum tubes, surrounded by cooling fins that increase the surface area which increases the tube’s cooling area. 3. The tubes are connected to water tanks either on the sides or at top and bottom. 4. The tube and fin assembly is called the cone. 5. The heated water from the engine is pumped into either the top or one side of the radiator. 6. The hot water travels through the tubes downward or side-to-side to the bottom tank. 7. As the water passes through the tubes air passes between the fins and cools the water. 8. The air flow is created by a fan usually driven by the motor. 9. Radiators work with thermostats which open when water temperature reaches the desired temperature. The opened thermostat allows the water to pass through the radiator. 10. If an engine does not reach the temperature to open the thermostat, the water by- passes the radiator and is recirculated through the engine until it reaches the temperature to open the thermostat. 11. The properly working thermostat and radiator maintain the correct temperature during various times of the year and operating conditions.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT I: SMALL ENGINE PREVENTIVE MAINTENANCE AND TROUBLESHOOTING COMPETENCY: SE21.00 Perform general preventive maintenance on a small engine. OBJECTIVE: SE21.01 Service air-cooled engines. A. Keeping engines clean (Small Gas Engines, Ch. 12, pp. 201-105 & Ch. 8, pp. 140-144) 1. It is important to keep engines clean to prevent over heating as well as reduce dirt getting into the engine. 2. Cooling fins should be clean to avoid heat retention, overheating and possible part distortion and seizing up. 3. Methods of cleaning: a. blowing off debris with compressed air (1) must be careful (2) wear safety goggles (3) never direct air towards skin or clothes b. scraping with wood and wiping with rag c. aerosol cleaners B. Checking oil level and condition 1. Should check oil level every time fuel is added. 2. Oil condition should also be checked. Engine manufacturers usually have recommendations. (pg. 202, figure 12-2).


3. Two methods of checking oil a. dipstick – Withdraw dipstick, wipe it off, reinsert it properly. Take it back out and check oil level. Most dipsticks have at least 2 marks, a full and a low (add) mark. Oil level should be between those two marks. Too much oil can damage an engine if over full. If the oil level indicates the engine is over filler, extra oil should be drained out. Add recommended oil if the oil level is low. b. Filler plug – (pg. 202, figure 12-3) Clean off area around filler plug and remove. Check oil level. Generally, oil level should be at top of filler hole or at a mark just below the hole. Check operation manual for specifics. 4. If an engine appears to use oil excessively, the engine should be checked to determine the problem. C. Changing oil 1. Determining when to change oil a. Usually based on hours of running time. b. New engine’s oil should be changed after a few hours of operation. c. Should check manual to find manufacturer’s recommendations. 2. Process of changing a. Run engine until warmed up. Warm oil will drain more completely and more contaminants will drain because they have to be stirred up in the oil. b. Stop engine and remove plug wire. c. Clean area around drain plug. d. Remove drain plug using the proper wrench. e. Allow oil to drain into a pan for at least 5 minutes. If necessary, tilt engine towards drain hole to help draining. f. If the engine has a filter, change it also following recommendations. g. Replace drain plug. h. Clean funnels, area around oil filler site, etc. i. Add proper oil to recommended level. j. Replace filler cap and spark plug wire.


D. Air cleaner service – (Ch. 12, pp. 204 and Ch. 8 pp. 141-144) 1. Frequency – should be done at the beginning of the season of use and at intervals recommended by the manufacturer. Under severely dusty conditions, the air cleaner should be changed more often. 2. Importance – plugged air filter can cause hard starting, loss of power, and spark plug fouling. 3. Oil wetted air cleaner – should be removed, rinsed in soapy water or other appropriate solvent, wrung out, allowed to dry, reoiled and reinstalled. 4. Dry type air cleaner – can attempt to clean by tapping on a flat surface. If the air cleaner does not clean by tapping it, it needs replacing. Compressed air should not be used because it can enlarge the filter’s pores and it will allow dirt to pass through to the engine. 5. Dual element air cleaner – the paper pre-cleaner should be treated the same as #3 (oil wetted type) and the main cartridge the same as #4 (dry type). E. Crankcase breather service – located over the valve stem chamber if an engine has one. Should be removed and cleaned periodically following manufacturer’s recommendation. F. Muffler service – dirty mufflers do not allow exhaust gases out properly and air fuel in properly which leads to overheating and power loss. Some mufflers are designed to be taken apart and cleaned while others are not and must be replaced. Those that can be cleaned should never be cleaned with gas. Consult engine manual for proper procedures to follow.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT J: SMALL ENGINE PREVENTIVE MAINTENANCE AND TROUBLESHOOTING COMPETENCY: SE21.00 Perform general preventive maintenance on a small engine. OBJECTIVE: SE21.01 Service a water-cooled small engine cooling system. Maintaining a water-cooling system (Small Gas Engines, Ch. 12, pg. 205) 1. A rust inhibitor should be used to prevent water and metal from forming harmful reactions that can damage cooling system components. 2. If scale, etc. is allowed to form, it may plug radiator and prevent even, thorough cooling. 3. Cooling fins should be kept clean to allow for proper heat transfer. Use water or air over the fins in the opposite direction that the cooling air flows through the radiator. 4. Radiator and engine blocks can be cleaned out by reverse flushing. This involves removing radiator hoses and forcing clean water in the opposite direction from normal flow. Flush should continue until water is clear. 5. Water should have antifreeze/coolant added in a 50% mix of this with 50% water.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT J: SMALL ENGINE PREVENTIVE MAINTENANCE AND TROUBLESHOOTING COMPETENCY: SE22.00 Troubleshoot a small engine. OBJECTIVE: SE22.01 Explain the terms and rationale behind small engine troubleshooting. Engine troubleshooting concepts (Small Gas Engines, Ch. 12, pp, 106 & 213-214) 1. Intelligent troubleshooting done using logic and reasoning can easily find problems most of the time. 2. Should always use systematic troubleshooting. This means checking/testing one component after another in the proper order. 3. Basic principles of troubleshooting. a. Check easiest things first. b. Verify the fundamental operating requirements. 4. Checking easiest things first means to start with simplest things. For example, does engine have gas? 5. Verify the fundamental operating requirements. (pg 206) This means, an engine needs five basic things to operate correctly. It must be determined that these five are present and working. Refer to the book for a complete explanation. a. Proper carburetion. b. Correct ignition system generation. c. Adequate lubrication. d. Sufficient cooling. e. Proper compression. 6. Use these requirements, and isolate the problem through the process of elimination. 7. Before troubleshooting begins, either ask the owner of the engine, or analyze the engine’s operation to determine which requirements are functioning and which are not.


8. Understand tolerances and clearances – Many small engine parts must be the correct distance apart to function correctly. For example, the spark plug gap is often at .030″ and the point gap at .020.″ a. Clearance is the actual distance that two things should be apart. b. Tolerance is when the values or specifications have a range that is acceptable. 9. Understand torque specifications – Fasteners in an engine must be tightened to the correct level. This is checked by using a torque wrench using the specifications found in the manual. 10. When tightening many fasteners that hold one item There is a sequence, or order that it should be done in. (Example: head bolts –see pg. 216, figure 12-18)


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT J: SMALL ENGINE PREVENTIVE MAINTENANCE AND TROUBLESHOOTING COMPETENCY: SE22.00 Troubleshoot a small engine. OBJECTIVE: SE22.02 Demonstrate small engine troubleshooting techniques according to service manuals. Troubleshooting Techniques and Procedures (Small Gas Engines, Ch. 12, There are basic technique procedures pg, 207-213) that must be done to troubleshoot an engine. A. Check RPM – Very often an engine’s RPM (revolutions per minute) must be checked. These are four methods commonly used: 1. Vibration tachometer (pg. 207, figure 12-9) A wire vibrates due to engine vibration. 2. Optical tachometer (pg. 208, figure 12-10) An instrument that measures visually. 3. Stroboscope (pg. 208, figure 12-11) Measures RPMs from a mark on the crankshaft and gives off light. 4. Mechanical tachometer – Measures RPMs directly from the crankshaft. B. Test Compression 1. A compression test can determine if there are any problems in the upper mechanical engine parts. 2. A compression test is especially good to do if engine lacks power and runs poorly. 3. Procedure (pg. 208) a. Warm up engine. b. Disconnect all drives to engine. c. Open choke and throttle valves wide. d. Remove air cleaner. e. Remove plug and insert compression gauge. (pg. 209, figure 12-12_ f. Crank engine as fast as possible. g. Repeat for best accuracy. h. If engine has a compression release, turn the engine in reverse rotation. 4. Compression test can show problems such as:


a. Leaking head gasket. b. Warped head. c. Worn rings. d. Valve problems – not seating, etc. C. Test differential pressure (pp. 209-210) 1. This checks the compression of an engine by measuring leakage from the cylinder to other engine parts. 2. The procedures are outlined in the book along with indicators. 3. Testing differential pressures can indicate: a. Defective valves. b. Defective rings. D. Use a troubleshooting chart (pp. 211-213) 1. Troubleshooting charts are provided in the textbook, as well as in manuals for specific engines. 2. Troubleshooting charts outline the proper steps to take to accomplish troubleshooting steps effectively. 3. Troubleshooting charts often have exploded views which are drawings of the engine and its components which show how parts should go together. 4. The use of the basic chart in the book should be learned thoroughly.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT K: SERVICING SMALL ENGINE SYSTEMS COMPETENCY: SE23.00 Service a small engine fuel system. OBJECTIVE: SE23.01 Troubleshoot a small engine fuel system. Troubleshooting Fuel System – If symptoms Small Gas Engines, of a malfunctioning engine point to the (Ch. 13, pg, 217-219) fuel systems, it could be caused by several things. A. Fuel supply – No fuel getting to carburetor 1. Gravity fed system a. Check for fuel in tank. b. Check for blockage in filter or in fuel line. 2. Fuel pump a. Check for fuel in tank. b. Check fittings in the fuel line for tightness. Air entering the line can cause problems. c. Check filter to see if clean. d. Check the pump to see that it is properly working. B. Carburetor adjustments – If carburetor is getting fuel, but engine surges or lacks power, the problem can be in carburetor. Some carburetors are preset and sealed and are not adjustable. 1. High speed and idle mixture adjustments a. Manuals will give rough settings and adjustment locations to give a starting point. b. Engine should be warmed up first before making adjustments. c. Generally, open throttle wide and turn high speed adjustment forward and backward until maximum speed is reached. d. After reaching maximum speed, turn needle valve counter clockwise slightly so engine is running rich. e. To adjust idle mixture, put the throttle in slow position. Turn idle mixture slowly first in one direction, then the other. Continue until idle is smooth.


2. Testing two-cycle reeds a. Remove air cleaner from carburetor. b. Run engine while holding a strip of paper about one inch from carburetor throat. c. If paper becomes spotted with fuel, reeds are not working correctly. d. Leaking reeds will cause fuel starvation, poor lubrication and overheating. e. Replace reeds if defective.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT K: SERVICING SMALL ENGINE SYSTEMS COMPETENCY: SE23.00 Service a small engine fuel system. OBJECTIVE: SE23.02 Repair the components of a small engine fuel system. A. Basic service information (Small Gas Engines, Ch. 13, pp, 220-235) 1. Generally, the best procedures to use are outlined in the engine’s repair manual. Follow the instruction carefully and properly. 2. Safety Note: Do not allow flames, sparks, pilot lights or arcing equipment near the fuel system while working on it or the igniting of the fuel can result in severe injury or death. B. Steps in carburetor servicing (Small Gas Engines, Ch. 13, pp, 220-235) 1. Remove carburetor. 2. Disassemble carburetor. 3. Inspect carburetor parts. 4. Repair carburetor parts. Never force parts while working on them. Also never enlarge passages. Use care when cleaning carburetor parts. 5. Reassemble carburetor. 6. Small engine repair – People should read and familiarize themselves with the general troubleshooting charts on pp. 225-229 and pp. 232-235.

7. Examples of carburetor problems include: a. dirty, stuck, or damaged needle and seat (pg. 226, pg. 230 Fig. 13-26) b. Cracked, brittle or improperly positioned diaphragm (pg. 233)


C. Governor adjustments (Small Gas Engines, pg. 235 – 236)

1. There are two basic governor types on small engines: air vane and centrifugal.

2. Centrifugal governors work by centrifugal force and spring force opposing

each other.

3. Many governors can be adjusted by changing spring location to change tension on the spring.

4. Some governors are controlled by a thumbscrew that changes spring tension

(pg. 235, Fig. 13-34).

5. Tension should be adjusted according to engine specifications.

6. A common problem is hunting or engine speed increasing and decreasing when not under a load.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT K: SERVICING SMALL ENGINE SYSTEMS COMPETENCY: SE24.00 Service a small engine ignition system. OBJECTIVE: SE24.01 Test a small engine ignition system. Testing Ignition Systems – Remember to refer (Small Gas Engines, to the engines service/repair manual for specific Ch. 13, pp. 242-247) procedures. Also the textbook outlines the basic procedures. A. Testing for spark – (pg. 243 – figures 14-13, 12, 13) 1. Remove spark plug lead and hold it by the insulated part (away from the metal connector!) 2. Put the metal connector about 3/16” away from the plug tip. 3. Pull the starter cord. 4. Look for an orange-blue spark to jump from lead to plug. 5. A good spark indicates the ignition system is working properly. 6. Can also be done using a spark tester. 7. If no spark is visible, hold wire 3/16: away from base of plug. 8. Pull starter cord. 9. If spark is visible, then the plug is defective. 10. If no spark is visible, problem is in ignition system.


B. Testing the magneto – Remember, check with the manual! 1. Some small engines have the magneto visible. 2. If magneto is visible, check the gap between the fly wheel magnets and the core of the magneto. 3. Follow the manufacturer’s procedures and specifications to check the magneto. C. Check the flywheel key – (pg. 245, figure 14-18) 1. Check the condition of the flywheel key. 2. If the key is not fitting properly in both the flywheel and crank shaft keyways, replace the key. 3. Also check if the flywheel key is partially or fully sheared. A sheared key should be replaced. D. Checking the flywheel 1. The flywheel should be checked for damage or poor magnet strength. 2. With some engines the magnet strength can be checked with flywheel still on the engine. 3. If the flywheel can be removed, follow the recommended procedures and remove it. 4. Then check the magnet strength by putting a ½" socket on the magnets and shaking the flywheel. The socket should remain on the flywheel.


E. Check magneto’s primary windings (pg. 246, figure 14-21) 1. Using a multimeter, check the magneto’s primary windings. 2. Do this by setting multimeter on its lowest resistance setting (or use a continuity tester). 3. Put one lead on the coil-ground connection and the other lead on the coil primary lead. 4. There should be essentially no resistance. In other words, there should be continuity in the magneto. 5. If there is not continuity, or high resistance, the magneto is defective. F. Check magneto’s secondary windings. 1. Set multimeter to R x 100 or R x 1000. 2. Connect one lead to ground connection and the other to the high tension (spark plug) lead. 3. Check the resistance according to manufacturer’s specifications. 4. If coil is defective, replace it.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT K: SERVICING SMALL ENGINE SYSTEMS COMPETENCY: SE24.00 Service a small engine ignition system. OBJECTIVE: SE24.02 Maintain a small engine ignition system. Small Gas Engines, Ch. 14, pp. 239 and 242, 247-252) A. Spark plugs 1. A spark plug can fail and not allow the ignition voltage to go across the plug gap to ignite the air:fuel mix. 2. The condition of a plug can be used to analyze the combustion of an engine. (pg. 240, figures 14 – 1, 2, 3, 4 and pg. 481) a. Beige to gray-tan colored deposits show the plug is operating at normal condition. b. An oil fouled plug has wet oil. 3. Removing spark plugs a. Gently remove the spark plug lead by rotating and pulling. b. Use correct size deep plug socket with a rubber sleeve insert. c. Allow plug to cool first. d. Blow dirt away from around base of plug. e. Remove plug and check its appearance using the references mentioned in A.2. 4. Cleaning spark plugs a. Clean all surfaces. b. Check firing and, if oily, etc., remove with solvent and dry with compressed air. c. Clean in a plug cleaner machine. d. File plug electrodes to square them after first opening the gap with a gapping tool. e. Clean threads. 5. Gapping plugs a. Use a gapping tool if possible to open gap (if not already done). b. Use a feeler gauge to regap. The wire type or round gauge is the best because it can give a truer reading. (pg. 242, figures 14 – 8, 9, 10) Be sure to follow manufacturer’s recommendations.


6. Reinstall the plug a. Before reinstalling, clean threads carefully and check type of seat (pg. 241, figure 14-7). Clean seat if needed. b. Snugly hand tighten into head. c. Torque to specifications. B. Points adjustment (MBI magneto) (pp. 248, figure 14 - 25, 26) 1. Consult manual for proper gap and procedures for accessing points. 2. Turn crank shaft until high point of cam is directly under the wear block or cam follower on point assembly. 3. Check the gap – if correct, reassemble components you removed to access points. 4. If gap is incorrect, loosen point screws slightly. 5. Slowly move the stationary point until its proper gap is achieved. 6. Tighten screws carefully. 7. Recheck gap. C. Adjusting piston height 1. This is done to insure that the piston is at the proper location when the spark occurs. 2. Generally, a timing tool is used ( pg. 249, figure 14 – 29). 3. Procedures differ among engine types. The manual should be consulted and the recommended procedures followed.


D. Timing ignition spark 1. It is necessary to check the breaking of the points or when the points open to determine when voltage is sent to the spark plug for proper ignition. 2. This is done with a multimeter or continuity tester. 3. This procedure varies by engine manufacturer; consult manual for correct procedure. E. Cleaning the points 1. When inspecting points, they should also be cleaned if needed. 2. This is done by sliding a lint-free paper back and forth between the points. F. Reinstalling the flywheel 1. After all necessary work is done, then flywheel should be reinstalled using the procedures and tools recommended by the manufacturer.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT K: SERVICING SMALL ENGINE SYSTEMS COMPETENCY: SE25.00 Service a small engine block assembly. OBJECTIVE: SE25.01 Explain small engine block assembly terms. (Small Gas Engines, Ch. 16, pp. 281-288; Ch. 17, pp. 297 & 298 & pp. 304-311) A. Piston construction (pg. 282, figure 16-1) 1. Pistons are made from aluminum or steel. 2. The parts of a piston are outlined on pg. 282, figure 16-1. 3. The head is usually thick to provide strength and resistance to overheating. and is slightly smaller than the skirt. Heads also come in an assortment of shapes (pg. 283, figure 16-6) 4. The grooves or lands are where the piston rings go. 5. The skirt is the lower part, and is designed to be light and prevents the piston from twisting. B. Piston rings 1. The purpose of rings is to seal compression in the cylinder and keep cylinder walls lubricated properly. 2. The rings are designed according to their use. 3. Compression rings are usually the top two rings on a piston. a. Hold compression in combustion chamber. b. Have a variety of shapes (pg.285, figure 16-11). 4. Oil control rings remove excess oil from the cylinders by lightly scraping off the surplus oil. Oil control rings are often made in three pieces.


C. Bearings (Ch. 17, pp. 297-298) 1. Where connecting rod attach to the crankshaft, there are some type of bearing to reduce friction. 2. The type used depends on the engine type and manufacturer. 3. There are: a. Friction bearings. b Needle bearings. c. Roller bearings. D. Crankcase seals (Ch. 17, pg. 304, figure 17-21) 1. Designed to prevent leakage of oil from the areas where crankshaft and crankcase come together. 2. Made of an outer steel shell with neoprene center. E. Valves (Ch. 17, pp. 206-307 & 310-311) 1. Valve margin is the area on a valve between the top of the valve head and the valve face (pg. 306, figure 17-29) 2. Valve springs must have proper tension to close the valves. Checking them will be covered later in the unit. 3. The valve seat is the part of the block that the valve face rest on (Ch. 17, pg. 311, figure 17-4)


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT K: SERVICING SMALL ENGINE SYSTEMS COMPETENCY: SE25.00 Service a small engine block assembly. OBJECTIVE: SE25.02 Inspect a block assemble and related components. (Small Gas Engines, Ch. 15, pp. 274-275; Ch. 16, pp. 290- 292, Ch. 17 pp 303, 306-307 & 319-32???) A. Cylinder inspection 1. There are two basic different cylinder types on small engines. a. Separate from block. b. Integral to block. 2. Procedures differ for each type. Manual should be checked for specific engine. 3. Cylinders should be checked for a heavy ridge on the inside top of the cylinder. Pistons will not pass this without damaging them. 4. If ridge is present, it must be removed using a ridge reaming tool. (pg. 274, figure 15-9) 5. Cylinders should be checked for wear. a. Generally greatest on two opposite sides of the cylinder at 90 degrees from crankshaft center line. b. Also check for cylinder taper. Usually a telescoping gauge is used (pg. 275, figure 15-10), (1) Measurement taken at top of cylinder. (2) Measurement taken at bottom of cylinder. (3) Measurements compared to engine specifications.


B. Piston inspection (pp. 290-293, figures 16 – 23-29) 1. Pistons become damaged in many ways. 2. Damaged pistons should be inspected and replaced if needed.

3. The source of damage should also be identified and corrected. 3. Some types of damage include: a. Scoring and light scuffing due to overheating. b. Rings stuck and broken due to high temperatures. c. Oil rings worn due to abrasives in engine. d. Burned top land due to detonation. e. Hole in top due to pre-ignition. C. Measuring bearing clearance (pg. 303) 1. Bearing clearances are measured using plastigage. 2. Plastigage is available in different colors relating to different clearances. 3. Plastigage is placed in the space across the bearing surface and then tightened to specifications. 4. The resulting width of the plastigage is compared to the standards on the container. D. Inspecting valves (pp. 306-307) 1. Valves must be inspected for various defects after they are cleaned. Generally most defects require using a new valve. Examples include: a. Eroded, cracked or pitted valve faces, heads or stems. b. Warped head (figure 17-29). c. Worn or ground stems (figure 17-29). d. Bent stems. e. margin less than 1/64.” f. Partial seating.


2. Valve springs must be tested for tension length and squareness (figures 17 – 30 & 31). a. Use a combination square and surface plate to check length and squareness. b. Use a tester to check for tension. c. Compare to specifications and either use or discard. E. Inspecting valve guides (pp. 307-308) 1. Valve guides must be cleaned first using the cylindrical wire brush. 2. After cleaning, inspect with a small hole gauge and micrometer (pg. 308, figure 17-33). 3. Compare to specifications. 4. Repair if needed. Covered in the next section. F. Adjusting valve clearance (pp. 319-320) 1. Remove breather cover. 2. Turn camshaft until lobe is away from tappet. 3. Hold valve against its seat. 4. Measure clearance with a thickness gauge and compare to engine specifications. 5. Valves that are too short need replacing. 6. Valves that are too long can be ground off carefully at about .001” - .002” at a time. 7. After replacement or repair, reinstall valve and recheck clearance.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT K: SERVICING SMALL ENGINE SYSTEMS COMPETENCY: SE25.00 Service a small engine block assembly. OBJECTIVE: SE25.03 Service a block assembly and related components. (Small Gas Engines, Ch. 15, pp. 276-279; Ch. 16, pp. 288-290; Ch. 17, pp. 308, 310-313, 317-319) A. Cylinder service (pp 276-279) 1. If cylinder inspection determines that the bore is not damaged and within specifications, only a light deglazing is needed. 2. If reboring is needed, there are a few options (pg 277, figures 15-15, 16, 17). a. Chrome plated aluminum cylinders must be discarded and replaced. b. Cylinders with cylinder sleeve can be repaired by removing the sleeve and installing a new sleeve. c. Cylinders with cast-in sleeve or solid cast iron cylinders can be rebored. 3. Reboring must be done with a machine called a boring machine. Only .010" should be removed in each step. Reboring should not be tried without this machine or damage is likely. 4. Honing a cylinder (pg. 279, figures 15-20, 21, 22) a. Process done with an abrasive (sandpaper-like) tool called a hone. b. Major reasons to do this is to remove boring marks and surface fractures and produce the desired cylinder wall finish. c. Process is covered in detail on pg. 278.


5. Measuring ring end gap (pp. 288-290) a. Rings must have proper end gap which is an indication of wear. b. To check the gap: (1) Remove rings from piston using a ring expander (pg. 289, figure 16-20). (2) Place rings in cylinder, one at a time. (3) Place piston in cylinder upside down and push ring to its proper location in the cylinder. (4) Measure end gap with feeler (thickness) gauge and compare to specifications (5) If gap is too great, ring must be replaced. (6) If gap is too small, it can be dressed with a file (pg. 288, figure 160-?) c. Reinstall rings in piston. d. Push piston in cylinder using a ring compressor (pg. 289, figure 16-21). 6. Valve guide reaming (pg. 308) a. If a valve guide is too large, it can be reamed and a correctly oversized valve can be used. b. Reaming must be done using a valve guide reamer. 7. Valve guide replacement (pg. 308) a. If a valve guide is replaceable (determined by referring to the manual), it can be done (pp. 309 and 310, figures 17-36, 37, 38). 8. Valve seats repair a. If the valve seat does not meet the specifications of the valve seat angle and valve seat width, it must be remedied. b. Can be done by: (1) Using a valve seat – cutting tool. (2) Replacing the seat. c. Valve seat cutting tool procedures are outlined on pg. 313. d. Value seat replacement covered on pp. 312-317. Involves removing old seat using the proper tools, and installing new seat also using proper tools. e. Procedures can vary for different engines. The specific manual should always be referred to.


9. Lapping valves (pp. 312-314) a. This is a process that can be done with a good used valve that will help it seat better. b. Some manufacturers do not recommend this being done because of heat expansion; therefore, the manual must be referred to. c. If it is done, lapping compound is used, along with a lapping stick. d. Process covered on pp. 312-314. 10. Refacing valves (pp. 317-318) a. If it is determined that a valve needs refacing, there is a machine designed for the purpose. b. If the machine is not available, it is not generally recommended that refacing be attempted any other way and valve be replaced.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT K: SERVICING SMALL ENGINE SYSTEMS COMPETENCY: SE26.00 Service a small engine electrical system. OBJECTIVE: SE26.01 Check DC starter/generator circuits.


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COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT K: SERVICING SMALL ENGINE SYSTEMS COMPETENCY: SE26.00 Service a small engine electrical system. OBJECTIVE: SE26.02 Maintain alternator charging system and related parts.

“Supplemental – This material is to be developed at the discretion of the teacher.” ****************************************************************************** COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT K: SERVICING SMALL ENGINE SYSTEMS COMPETENCY: SE26.00 Service a small engine electrical system. OBJECTIVE: SE26.03 Troubleshoot an alternator charging system.



COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE27.00 Demonstrate safe work habits and procedures when working with power equipment. OBJECTIVE: SE27.01 Describe basic safe work procedures specific to power equipment. (Small Gas Engines, Ch. 18, pp. 331-332) A. General safety points when working on lawn equipment 1. Always remove the high tension wires (leads) from spark plugs while working. 2. Never allow bystanders around machinery while it is being worked on. 3. Do not wear rings, watches or loose fitting clothing while working on equipment. It could get caught. 4. Wear sturdy work shoes. 5. Wear safety glasses or goggles essentially all the time. 6. Reinstall all safety guards, shrouds and shields. 7. Always handle gasoline with care. a. Use approved container. b. Never remove cap, or refill, when engine is hot. c. Avoid fires by insuring any metal cans, funnels do not touch battery. Also, by not smoking. d. Always clean up spilled fuel. e. Replace all caps securely. 8. Never use any electric powered tool or light with a damaged cord or one that isn’t grounded. 9. Never run engines in an enclosed non-ventilated area to avoid carbon monoxide (CO) poisoning.


10. Remove all tools when done. 11. Use care around batteries. They give off hydrogen gas that is flammable and explosive, as well as producing electricity. 12. Use care around hydraulics. The pressure when escaping can be dangerous. 13. Use approved safety procedures when using an oxyfuel torch. 14. Use safety stands under a raised piece of equipment. 15. Use appropriate gear pullers when needed. 16. Use caution when using compressed air. 17. Use caution when using flammable solvents to clean, etc.


COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE27.00 Demonstrate safe work habits and procedures when working with power equipment. OBJECTIVE: SE27.02 Demonstrate basic safe work procedures specific to power equipment.

“Supplemental – This material is to be developed at the discretion of the teacher.” COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE28.00 Perform basic operation and maintenance on a lawn mower. OBJECTIVE: SE28.01 Identify parts of commonly used lawn mowers.

“Supplemental – This material is to be developed at the discretion of the teacher.” COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE28.00 Perform basic operation and maintenance on a lawn mower. OBJECTIVE: SE28.02 Suggest a mower and accessories for a given situation.



COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE28.00 Perform basic operation and maintenance on a lawn mower. OBJECTIVE: SE28.03 Demonstrate proper use of common lawn mower starting systems.

“Supplemental – This material is to be developed at the discretion of the teacher.” COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE28.00 Perform basic operation and maintenance on a lawn mower. OBJECTIVE: SE28.04 Sharpen a lawn mower blade.


***************************************************************************** COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE28.00 Perform basic operation and maintenance on a lawn mower. OBJECTIVE: SE28.05 Discuss storage procedures for a lawn mower.



COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE28.00 Perform basic operation and maintenance on a lawn mower. OBJECTIVE: SE28.06 Demonstrate safe handling of a lawn mower.

“Supplemental – This material is to be developed at the discretion of the teacher.” ****************************************************************************** COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE29.00 Perform basic operation and maintenance on a chain saw. OBJECTIVE: SE29.01 Discuss purchasing considerations for a chain saw.

“Supplemental – This material is to be developed at the discretion of the teacher.” COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE29.00 Perform basic operation and maintenance on a chain saw. OBJECTIVE: SE29.02 Demonstrate safe handling of a chain saw.



COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE29.00 Perform basic operation and maintenance on a chain saw. OBJECTIVE: SE29.03 Demonstrate chain saw troubleshooting.

“Supplemental – This material is to be developed at the discretion of the teacher.” COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE29.00 Perform basic operation and maintenance on a chain saw. OBJECTIVE: SE29.04 Demonstrate chain saw maintenance.



COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE30.00 Perform basic operations and maintenance on a string trimmer. OBJECTIVE: SE30.01 Discuss purchasing considerations for a string trimmer.

“Supplemental – This material is to be developed at the discretion of the teacher.” ****************************************************************************** COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE30.00 Perform basic operations and maintenance on a string trimmer. OBJECTIVE: SE30.02 Demonstrate safe handling of a string trimmer.

“Supplemental – This material is to be developed at the discretion of the teacher.” COURSE: AGRICULTURAL MECHANICS II - SMALL ENGINES UNIT L: SERVICING SMALL ENGINE POWERED EQUIPMENT COMPETENCY: SE30.00 Perform basic operations and maintenance on a string trimmer. OBJECTIVE: SE30.03 Demonstrate string trimmer maintenance.


Summer 2003 127 Agricultural Mechanics II – Small Engines

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Small Engines Instructional Outline 2003 - quia.com