1 DAY1 Engine Operation

Welcome To : 

Welcome To ENGINES CLASS Mr. Osborne SESSION 1 READ: Ch. 1 Pages 2 – 22 Home Work: ASE Questions 1-10 Page 23 -24 Due: Session 1

HOW ARE THEORY AND SHOP GRADES CALCULATED AND WEIGHTED? : 

HOW ARE THEORY AND SHOP GRADES CALCULATED AND WEIGHTED? THEORY and SHOP (Lab) Are reported as separate grades. You MUST pass both to pass course

HOW IS THEORY CALCULATED? : 

HOW IS THEORY CALCULATED? CLASS PARTICIPATION = 15% OF GRADE HOMEWORK = 25% OF GRADE QUIZZES = 50% OF GRADE FINAL EXAM = 10% OF GRADE

WHAT IS THE O.S.I GRADING SYSTEM USED FOR SHOP GRADE? : 

WHAT IS THE O.S.I GRADING SYSTEM USED FOR SHOP GRADE? O OUTSTANDING - STUDENT CAN PERFORM ALL ASPECTS OF TASK AND ANSWER ALL QUESTIONS = 90 TO 100% S SATISFACTORY - STUDENT WAS ABLE TO ANSWER MOST QUESTIONS = 75 -89% I IN NEED Of IMPROVEMENT- STUDENT COULD NOT SHOW BASIC KNOWLEDGE OF THE JOB = 0 TO 74%

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All Shop Work Sheets (Job Sheets) Will Receive A Numeric % Grade and the Average of ALL Grades Will Represent 80% of Final Shop Grade Final Engine Report Will Represent 20% of the Final Grade

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OBJECTIVES Discuss four (4) stroke engine operation Discuss two (2) stroke engine operation Discuss diesel engine operation Define compression ratio Explain and Understand compression testing, leak down testing, and vacuum testing.

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ENGINE OPERATION DIESEL 4 stroke 2 STROKE GAS 4 STROKE

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(4) FOUR STROKE ENGINE OPERATION

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(1) INTAKE STROKE Vacuum is Created On Intake Stroke Intake 19 in. Hg *

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(2) COMPRESSION STROKE Air/Fuel is Compressed 9 TO 1 *

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(3) POWER STROKR Combustion- Power Stroke *

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(4) EXHAUST STROKE Exhaust *

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Exhaust Intake

2 - Stroke Cycle Engine Operation : 

2 - Stroke Cycle Engine Operation Combustion event takes place above piston while transfer (Fuel) takes place below piston (piston travels downward and forces air/fuel to top of piston) Compression takes place above piston while intake takes place below piston (piston travels upward) Therefore, each crankshaft revolution (360*) produces a power pulse. Plug sparks every time piston reaches TDC

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/FUEL COMPRESSION INTAKE 1

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REED VALVE CLOSES Ignition 1

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COMBUSTION FUEL BURN POWER STROKE 2

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AIR/FUEL TRANSFER 2

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/FUEL COMPRESSION INTAKE 1

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DIESEL ENGINE OPERATION (CIE) Engine has no spark plugs Fuel is Timed into combustion chamber Fuel is ignited due to very high compression Modern diesel may use as much as 26,000 PSI of fuel pressure 5. Compression Ratio may be as high as 22 to 1

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CYLINDER ARRANGEMENTS 6 OR 8 cyl. 4, 6, or 8 cyl. 4 or 6 cyl.

DEVELOPING A DIAGNOSTIC STRATEGY : 

DEVELOPING A DIAGNOSTIC STRATEGY Know the system Know common problems Find out history of the complaint. Did it start gradually or all at once? When does problem occur(cold or warm, high or low speeds)? Find out service history Ask owner for as much specific info as possible

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(3) Basic Engine Tests 1. Compression Test (determines engines ability to produce adequate compression) 2. Vacuum Test (evaluates engine operation while running) 3. Leak Down Test (helps isolate poor compression to a specific component) We Will Do These Tests On Our Engines Day 2

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COMPRESSION RATIO A comparison of the volume (cc’s) of air/fuel in the cylinder, with piston at BDC (bottom dead center) versus the volume at TDC (top dead center) Expressed as a ratio 8:1 The higher the compression the easier it is to ignite the fuel and bigger the explosion The higher to compression the higher the horse power

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BDC 480cc

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480cc 60cc 480 = 8 to 1 60

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Compression Testing

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Measure Compression Use a compression tester Remove all plugs Install tester Hold throttle wide open Crank engine through four (4) compression strokes Record readings on all cylinders Compare readings to specs.

Dry Compression Test : 

Dry Compression Test Warm engine (optional) to operating temperature Remove all spark plugs Block open throttle plate Disable ignition Crank at least four “puffs”(4 compression strokes)

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Holding Throttle open with Special Tool Throttle Rod Special Tool For Holding Throttle Open Choke Lever

How do I evaluate resultsof dry compression test? : 

How do I evaluate resultsof dry compression test? Cranking – 125 to 160 psi Lowest should be at least 80% of highest reading, e.g., If highest is 150 psi, lowest should be at least 120 psi, since 20% of 150 =30 (150-30=120). Much higher readings may be due to carbon deposits in combustion chamber.

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Wet Compression Check Squirt about a tablespoon of oil into cylinder, oil will create a seal around worn rings. This should boost compression if rings are worn. With low dry readings but higher wet readings, worn or broken rings are indicated. If readings do not improve, rings are not the cause of low readings – look to valves or head gasket then. Adjacent cylinders with the same or similar low dry/wet readings are an indication of a broken head gasket. Hyper

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Leak Down Testing

How do I perform a leak down test? : 

How do I perform a leak down test? On a warm engine, remove oil fill cap, radiator cap, air cleaner and spark plugs. Block throttle wide open. Find TDC by a whistle or other means. Connect leak tester to shop air. Calibrate leak tester. Install test adapter to engine, connect to leak tester. Check leak down rate Listen at carburetor, tail pipe, oil filler and look for bubbles at radiator cap

What are acceptable/unacceptable leakage rates? : 

What are acceptable/unacceptable leakage rates? 2-10% Good 10-20% Fair 20-30% Poor Over 30% D.O.A.

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Perform A Leak Down Test Install leakage tester into each cylinder Calibrate tester TDC the cylinder Pressurize each cylinder Listen for escaping air Oil filler cap (Blow By Past Rings) Intake manifold (Leakage Past Intake Valves) Exhaust pipe (Leakage Past Exhaust Valves) Bubbles in coolant (Damaged Head Gasket)

What are the advantages/disadvantages of leak down testing? : 

What are the advantages/disadvantages of leak down testing? Is more specific than compression testing for leakage locating Is more difficult to perform than compression testing

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Spark plug hole adaptor ( no valve core) To adaptor To shop air Leakage % Gauge Calibration knob Hyper

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Vacuum Testing

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Perform A Vacuum Check 16 to22 inches of mercury running Start engine and allow for warm up (1 minute) Check cranking vacuum, disable Ign. (record Reading) Take Intake Manifold Vacuum Reading At Idle (record readings) 3. Perform a Snap Test (increase RPMs to 2000 and close throttle quickly) reading should be about a 2 to 6 psi greater than base vacuum (record readings)

Normal Cranking Readings are a steady 2.5 to 6 in/Hg reading : 

Normal Cranking Readings are a steady 2.5 to 6 in/Hg reading If readings are low, common causes are: 1)Too slow cranking speed. 2)Worn piston rings. 3)Leaking valves. 4) Excess air bypassing the throttle plate.

Running Vacuum : 

Running Vacuum Start warmed-up engine and observe gauge. An engine in good condition should read between 17 and 22 in/Hg ( steady reading) If a low steady reading is noted, common causes are late ignition or cam timing or air Leak Readings that fluctuate indicate air leak on one or more cylinders

”Snap Test” checks for compression loss using a vacuum gauge: : 

”Snap Test” checks for compression loss using a vacuum gauge: Quickly open throttle to reach 2000 rpm, release throttle, reading should increase more than 5 in/Hg before engine returns to idle speed. If less than 5 in/Hg, perform a compression test to verify low compression condition. Hyper

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Disassembly With engine operation verified and all readings recorded for future comparison, engine disassembly , clean up, and measuring can begin.

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REVIEW Name the four (4) strokes in a 4 cycle engine. 2. How many degrees of crankshaft rotation are required to produce one power stroke in a (2) cycle engine? In a (4) cycle? How many spark plugs per cylinder does a diesel use? How much difference in compression between cylinders is acceptable? Name (3) places air can escape on a leak down check On what stroke is vacuum created?

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Home Work Read: Chapter #4, pgs. 94 -143 Chapter #11, pgs. 350 - 363 Answer: ASE–Style Questions Ch4 1 – 10 pgs. 143 - 144 ASE–Style Questions Ch11 1 – 5 pgs. 381 – 382 Due Session 2