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ENGINESHow They Work
&Why They Fail
Classifications• Operational design (four-stroke, two-stroke, rotary, etc.) • Number of cylinders (four, five, six, eight, 12, etc.) • Arrangement of cylinders (V-type, inline, etc.) • Displacement (3.8 liter, 3800 cubic centimeters, 350 cubic
inches, etc.) • Number of valves and valve train type (overhead cam,
pushrod, 24-valve, etc.) • Fuel type (gasoline, diesel, propane, etc.) • Cooling system (air or liquid)
Causes of engine failure
• Lack of Maintenance• Lubrication (or the lack thereof)• Overheating (excessive heat) • Incorrect Assembly • Design flaws (pattern failures)• Detonation (spark knock)• 10 million miles
Is a engine just an air pump?
• Atmospheric pressure• Intake manifold pressure
High pressure always goes to Low
Low intake pressure created by the void of space left by the piston travelling down (syringe) draws air into the engine.
Engine pressure• 14.7psi Atmospheric pressure• Technicians work with Gauged pressure
PSIG–Not running and WOT 0psig–Remember anything less that zero we
measure in inhg–Mid range about -10inhg–Idle -20inhg
Let’s talk about 4 strokeEngines
• Four stroke operation• Two revolutions of the
crankshaft
1. Intake 2. Compression3. Power4. Exhaust
(4) FOUR STROKEENGINE OPERATION
Head Gasket Valve
Seat
(1)INTAKE STROKE
Vacuum isCreated in Intake
Intake
19 in. Hg
*
(2) COMPRESSION STROKE
Air/Fuel is Compressed
9 TO 1
*
is compressed
(3)POWER STROKR
Combustion-Power Stroke
*
(4)EXHAUST STROKE
Exhaust
*
Exhaust Intake
Four (4) Overhead Cams
One cycle equals
• Four piston strokes
• Two revolutions of the crankshaft
• One revolution of the camshaft
Common camshaft drives
• Gear• Chain• Belt
Turns ½ the speed of the crank shaft
TDC
Page 347
Timing BeltCam Drive
Chain Tensioner
Chain DriveOverheadCams
TDC
Some engines have multiple camshafts
• Double overhead cam drives may use a chain drive.
• Some designs uses a chain tensioner that is operated by spring tension or oil pressure
• Double overhead cams can use a belt drive
During manufacturing sand cores are used, the sand must be removed through the holes in the block
What is excessive oil consumption?
• New or low mileage engines may have higher than normal consumption
• Low tension rings - increase fuel economy• Per GM - normal oil consumption is 1 quart
every 2000 miles
What Happens When A Timing Belt Breaks On An Interference
Motor
?
Plunger has oil pressure applied to keep slack outof valve train
Out of round
3 degrees of lifter wear, never installa lifter on the wrong cam lobe
Steel insert in an aluminum engineblock
Sleeves may be wetor dry
Very few engines maybe resleaved
Overheating causes most engine failures
Oil ConsumptionOil-fouled spark plugs can tell you if the engine
has been using oil.• Oil enters the combustion chamber past worn
valve guides and seals, and also past worn or broken piston rings and worn cylinders.
Oil ConsumptionValve Guide (Stem) Seals
• Valve guide seals that are worn, cracked, missing, broken or improperly installed
• The engine will suck oil down the guides and into the cylinders.
• The engine may still have good compression, but will use a lot of oil.
Valve Guide
Valve Guide Seals
Result of WornValve Guides or Damaged Seals
Lubrication system
• Lubricates• Absorbs shock• Cools• Cleans
Moving Parts Do Not Touch
In a modern engine all the moving parts are separated by a film of oil and rarely is there metal to metal contact. Because of this, engines that are properly lubricated may last over 200,000 miles if well maintained.
Oil Film
Bearing Clearance.002 - .003
Lube system components
• Pan• Pick Up• Pump• Oil galleries• Bearing clearances
The importance of proper oil level
• Prevents oil starvation to engine components
• Provide proper cooling which prevents premature oil additive break down
Lack of Lubrication
• Oil starvation is usually the result of a failed oil pump, a plugged oil pickup screen inside the oil pan, or a low oil level.
• Bearings that have been damaged as a result of insufficient lubrication will be shiny and worn where the crankshaft journal wiped away the bearing material. This will lower oil pressure.
Plugged or Restricted Oil Pick Ups
Effects of oil starvation on an engine bearing
Proper oil
• Follow Manufacture’s recommendations for SAE and API ratings
• SAE = Viscosity – Thickness
• API = Service rating - Application
API “S” RATINGS
• SM (Spark Ignition)• CURRENT HIGHEST RATING
API DIESEL OIL (C) CLASSIFICATIONS
• CI-4 PLUS (Compression Ignition) • CURRENT HIGHEST RATING
Page 249
Pick Up
Pump
Filter
Page 178
Failed Journals Due To Low Oil PressureFurthest From Pump
When does damage from oil starvation begin?
Instantly
When does it show up?Sometimes several hundred or several
thousand miles later
Page 251
The First Place Wear Takes Place Is On Bearings
Pressurized oilprovides hydraulicsupport for the crankshaft
Low oil pressure will cause metal to metal contact
CRANKSHAFTJOURNAL
MAIN BEARING CAP
MAIN BEARING OIL
Oil Consumptionand Common Causes
• Valve Guide and Seal Wear
• Piston ring wear
• PCV system Valve Guide
Valve Stem Seal
ROD KNOCK Excessive Bearing Clearance
PlastigageUsed To Measure Bearing Clearances
Rock gauge back & forth until minimum readings obtained
Cam Shaft Lob WearCaused By Lack Of Lubrication
Bearing clearance controls operating oil pressure
• Most pressure indicators operate off of an electrical signal from a sender
• If the sender is defective, it may cause an incorrect pressure reading on the instrument cluster
• Always verify low oil pressure with a mechanical gauge before condemning the engine
Page 146
Use Manual Gauge To Verify Low Oil Pressure
Oil Pressure testing
Adaptor Mounted Where Oil Filter Mounts
1. Install oil pressure adapter and gauge
2. Start engine; increase RPM to 1400
3. Make sure vehicle is at operating temperature to get accurate reading
4. Check oil pressure reading and compare to specifications
How often should the oil be changed?
• Refer to the manufactures recommendations• Keep in mind that the recommendation is the
MAXIMUM mileage interval• Pushing the interval will cause oil additive break down• Commonly causes “sludge”
Poor Oil Maintenance, Moisture, Incorrect Engine Cooling and By-products of combustion
Cause Sludge
PCVsystem
Inoperative PCV
Oil Pump Pickup Restricted No or Low Oil Pressure
How is an engine quickly checked to see why there is
a lack of power, back fire, low vacuum, blown head
gasket, worn piston rings, or a burnt valve??
Damaged Head Gasket(Water Leak or Loss of Compression)
What about hydrostatic lock?
Filling the combustion chamber until the piston cannot move up.
What could cause this?
Lifter Noise
Low Oil Pressure – Excessive ClearanceDefective Lifter – Sticking Valve
Super Charger
Turned Mechanicly