ENGINES How They Work & Why They Fail Classifications Operational design (four-stroke,...

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