Small Engine Operation - PowerPoint Presentation

Slide1

Small Engine OperationSlide2

Objectives

Identify the main engine components of a 4 cycle engine

Identify the main engine components of a 2 cycle engineSlide3

Engine Block

Main Structure of an engine

Supports and maintains alignment of internal and external components

Can be produced as one or two piece unit

Consists of two pieces

Cylinder block

CrankcaseSlide4

Cylinder Block

Consists of the following components:

Cylinder bore

Cooling fins

Valve train componentsSlide5

Cylinder block Slide6

Cylinder bore

Hole in the engine block that houses and aligns the piston in the engine block

Bore- is the diameter of the cylinder bore

Stroke- is the linear distance that a piston travels from TDC to BDC in the cylinder boreSlide7

Displacement

Volume that a piston displaces when traveling from TDC to BDC

When bore and stroke are know displacement fro single-cylinder engine is found by

D=0.7854*

Bsquared

*SSlide8

Displacement

D=0.7854*B squared*S

D=displacement

0.7854= constant

B squared= bore squared in inches

S= stroke in inches Slide9

Practice

What is the displacement of a single cylinder engine that has a 2.5” bore and a 2”stroke?

D=0.7854* B squared* S Slide10

Answer

D= 0.7854* (2.5*2.5)*2

D=0.7854*6.25*2

D=9.82 cu in. Slide11

Multiple Cylinder Displacement

To calculate the displacement of multiple cylinder engine;

Find the displacement of a single cylinder and multiply by the total number of cylinders

The larger the displacement the more power produced Slide12

Cooling Fins

Used on an air cooled engine

Thin cast strip on block that dissipates heat away from engine cylinder

Increase the surface area of cylinder block to which ambient air has contact

Also cast into the flywheel

Act as fan blades providing air circulation Slide13

Crankcase

Houses and supports the crankshaft

In a four-stroke engine the crankcase also acts as oil reservoir for lubrication of engine componentsSlide14

Crankcase components

Sump

Removable part of engine crankcase that serves as an oil reservoir and provides access to internal parts

Horizontal shaft engines do not have a sump

The crankcase and engine block serve as an oil

resivoirSlide15

Crankcase Componenets

Crankcase cover

Provides access to internal parts

Supports the crankshaft

Crankcase breather functions as a check valve releasing pressure created by the cylinder moving towards BDC Slide16

Cylinder block construction

Cylinder blocks are commonly constructed from:

cast aluminum alloy

cast iron

or cast aluminum alloy with cast iron cylinder sleeves Slide17

Cast Aluminum Alloy

Pro’s

Cheap to produce

Lightweight

Dissipate heat more rapidly than cast iron

Con’s

More prone to heat distortion

Less resistant to wearSlide18

Cast Iron

Pro’s

Last longer more resistant to wear

Can handle higher temps

Con’s

Heavier

More expensive to produceSlide19

Cylinder Head

Component that is fastened to the end of the cylinder block farthest from the crankshaft

Head gasket is placed between cylinder head and cylinder block

Usually constructed of soft metals and graphite layered together

Used to completely seal the combustion chamberSlide20

Cylinder Head

In some two-stroke engines the cylinder head and block are made as one piece otherwise know as a jug.

This single cast unit provides the maximum strength

Eliminates possible leaks in combustion chamberSlide21

Cylinder Head Design

OHV- overhead valve

Valves and related components are housed in the cylinder head

L-head engine

Valves and related components located in cylinder block

DOV-direct overhead valvesSlide22

Crankshaft

Converts the up and down motion of the piston into a rotary motion

Orientation of the crankshaft in small engines is either

Horizontal or vertical shaftSlide23

Crankshaft Components

Crankpin journal

Throw- measurement of distance between crankshaft and crankpin journal

Throw is equal to one half the stroke

Bearing journal

Counterweights

Crank gear

and power take off (PTO)Slide24

Bearing journal

Crankpin journal

counterweight

Crank gear

Bearing journal

PTO

ThrowSlide25

Piston and Piston Rings

Component that is fitted into the cylinder bore

Pistons are usually built out of cast aluminum allow

Proper tolerance must be maintained to compensate for the expansion of metals under extreme heatSlide26

To little and an engine might seize

To much and proper compression will not be metSlide27

Piston componenets

Piston head

Piston pin

Skirt

Ring grooves

Ring lands

Piston ringsSlide28

Piston Head

The shape of a piston head is either

Flat

Contoured

Irregular

Domed

DishedSlide29

Piston rings

Usually composed of cast iron to hold their structural integrity

The most common types of rings found in small engines include

Compression ring

Wiper ring

Oil ring Slide30

Piston rings

Compression

Located closest to the top of the piston

Seals the combustion chamber

Wiper

Ring with a tapered face

Further seals combustion process/wipes cylinder wall clear of oil

Oil

Located closest to crankshaft

Wipe oil off cylinder walls return it to oil reservoir

2 stroke engines do not need an oil ringSlide31

Piston ring components Slide32

Connecting Rod

Transfers movement from piston to the crankshaft

Includes the following pieces

Piston pin (wrist pin) w/pin clips

Connecting rod

Rod cap w/rod cap screwsSlide33
Slide34

Flywheel

Helps maintain engine power and speed between power strokes

Cooling fins also provide air circulation during operationSlide35

Valving system

Includes valve components as well as the cam shaftSlide36

L-HeadSlide37

OHV