ENGINES How 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 stroke Engines Four stroke operation Two revolutions of the crankshaft 1.Intake 2.Compression 3.Power 4.Exhaust

(4) FOUR STROKE ENGINE OPERATION Head Gasket Valve Seat

(1) INTAKE STROKE Vacuum is Created 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 *

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

Timing Mechanisms pg237

TDC

Page 347 Timing Belt Cam Drive

Chain Tensioner Chain Drive Overhead Cams

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 out of valve train

Out of round

3 degrees of lifter wear, never install a lifter on the wrong cam lobe

Steel insert in an aluminum engine block Sleeves may be wet or dry Very few engines may be resleaved

Overheating causes most engine failures

Oil Consumption Oil-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 Consumption Valve 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 Worn Valve 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

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 Pressure Furthest 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 oil provides hydraulic support for the crankshaft Low oil pressure will cause metal to metal contact CRANKSHAFT JOURNAL MAIN BEARING CAP MAIN BEARING OIL

Oil Consumption and Common Causes Valve Guide and Seal Wear Piston ring wear PCV system Valve Guide Valve Stem Seal

ROD KNOCK Excessive Bearing Clearance Plastigage Used To Measure Bearing Clearances

Rock gauge back & forth until minimum readings obtained

Cam Shaft Lob Wear Caused 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 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

PCV system

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 Clearance Defective Lifter – Sticking Valve

Super Charger

Turned Mechanicly