Helpful Helper's Hints

Level 2, Warm It Up!

What's Your Type?Help youth gain an understandingof how engines are grouped. Oftensmall engines are grouped by size,in terms of horsepower. Enginescan also be grouped by thenumber strokes (four or two) for acomplete cycle and the orientation(vertical or horizontal) of thecrankshaft. One stroke is themovement of the piston from oneend of the cylinder to other end(bottom to top or top to bottom).During one stroke, the crankshaftrotates one-half revolution.

On a four-stroke cycle engine, thepiston moves through four pistonstrokes for a complete cycle and tworevolutions of the crankshaft. The

four strokes are intake, compression,power, and exhaust. The four-strokeengine has greater power at lowspeeds and creates less pollution.A two-stroke cycle engine has thecompression and power strokes.The exhaust of the burned gases andintake of the new air:fuel mixture

occurs near the end of power andthe beginning of compression. Atwo-stroke engine has fewer movingparts and is lighter. In most cases,engine-lubricating oil is mixedwith the gasoline.The orientation of the crankshaft is

based on the engine's application.The walk behind lawnmower is themost common vertical crankshaftengine application where the mowerblade is attached to the crankshaft.There are many examples ofhorizontal crankshaft engines suchas riding lawnmower, ATV, snowthrower, roto-tiller, and snowmobile.Have the youth look at engines inthe neighborhood or at a repair shopand determine the type of each.If you are unsure, ask the question"Is gasoline mixed with oil?" If theanswer is yes, the engine is usuallya two-stroke engine.

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Name That Part!Your engine service manual willprove very helpful in completingthe matching exercise and labelingthe engine parts.

Parts Key for Figure,(top to bottom)

Left side: j, m, c, e, a, f, i

Right side: b, k, d & n, h, g, I

Following is a key for you to use:

camshaft-a;crankcase-e;crankshaft -i;

connecting rod-g;cylinder block-k; .cylinder head-j;exhaust valve-b;flywheel-I;intake valve-m;piston-h;piston pin-o;piston ring compression-d;piston ring oil control-n;timing gear-f;valve spring-c.

Keep in mind, the name ofa part often describes its shapeor function. This may provevery helpful. Consider a visitto an engine repair shop to seedisassembled engines and identifyparts.

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Which Tool'll Do It?The tools from level I, CrankIt Up!, were general tools whichcan be used in many other placesaround the house or shop. Specialtytools are designed for special uses,in this case small engines. Thesetools tend to be more costly.Thereforepurchasingthem shouldbe considered only if youth planto work on more engines. Someof these tools may be used onlyon one brand of engine. A visitto a small engine repair shop anda small engine repair manual willprove useful in identifying thesetools.The tool name often indicatesits purpose.

Sizing Up!You may want to help youth find adiscarded engine to disassemble tomake the necessary measurements.The power output of an engine isdirectly related to the pistondisplacement (size) or the volumedisplaced by the piston as it movesthrough one stroke. The shapeof this volume is a cylinder. Theformula to calculate this volumeis provided. Youth may havedifficulty obtaining an enginefor measurements. Although notthe most accurate, a tape measureor ruler may be used for themeasurements. For more accuratemeasurements, a caliper shouldbe used.Anotherlow-cost alternativeis to obtain the bore and strokeinformation for an engine andcalculate the displacement.Check the answer by obtainingthe displacement specification.If you are doing this, compareseveral engines and their power(horsepower).

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Under PressureDuring the compression stroke,the air and fuel are compressed inthe cylinder. In general, increasingthe compression of this mixtureincreases the engine efficiency.By compressing the mixture, it willmore readilyignite.The compressionratio is the ratio of the volume atthe start of compression to thevolume at the end of compression.When youth check compression bypulling the starter rope or spinningthe flywheel, be sure the sparkplug wire is disconnected. In orderto spin the flywheel by hand on anengine with an electric start, someshields may have to be removed.Be sure shields are replaced beforestarting the engine.

Mixing It Up!Youth may need help making thecarburetor adjustments. Be sureto have youth identify all thecarburetor adjustments beforestarting the engine. It may behelpful to draw a diagram on paperidentifying these adjustments. Inmost cases, the adjustments canbe made with a screwdriver. Besure to follow the proper startingprocedure. If the engine is runningfine before the adjustments, besure youth count the numbers ofadjustment revolutions from thestarting point. This will allowyouth to return the adjustmentto its initial setting.

Tearing It DownTearing an engine down willprovide a good opportunityto learnthe engine parts. Be sure the propertools are availablebefore this projectis started.The tools used in earlieractivitieswill meet most of yourneeds. A good source for an engineis a discarded engine aroundhomeor at a local small engine repairshop. Be sure to clean the enginebefore disassembly,and additionalcleaning may be necessary asparts are removed.As each part isremoved, it shouldbe labeled andbriefly discussedwith regard to itsfunction. It will be useful to connect

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the name of the part to its functionor shape; e.g., cylinder head-locatedat the top of the cylinder. Duringdisassembly, some detective workmight be done to determine whythe engine failed and was discarded.Examples of things to consider arediscoloration, bent parts, missingparts, and broken parts.

Seasoning Your Engine!When equipment with smallengines is not used for thirty daysor more, many manufacturersrecommend some service to insuregood performance. Much of thissmall engine equipment is usedseasonally and therefore willrequire attention at least twicea year. Many of these steps areconsidered general cleaning.Examplesof some of these stepsand their benefits are

1. Removing fuel from the engine,which prevents gasoline fromforming gums that createdifficulty starting.

2. Removing leaves, grass, andother debris, which reducesthe possibility of corrosion.

3. Changing the oil, whichprevents the dirt from separatingfrom the oil and formingdeposits on the bottom of thecrankcase which are hard toremove.

Many other things are seasonalsuch as clothing and recreationalsports. Youth may need a littlehelp, especially with the disposalof drained oil and cleaningsupplies. A lawnmower is a goodmachine to prepare for storage.

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Helpful Helper's Hints

Feel the Power!Having youth experimentwith changing gears andsprocketson bicycleswill helpthem understandthe transferofenergy that happens in a smallengine. The transmission ofpower from one machinepartto another is very importantin changing speed and torque.This is accomplished withchains and sprockets, gears,and belts and pulleys. Thechain and sprocket systemfound on bicycles serves todemonstrate the principles ofpower, torque and speed. Forthis activity a multi-speedbikeworks best instead of a singlespeed bicycle. The youth mayrequire some assistance inturning the bicycle upsidedown and collecting the data.It may be beneficial to adjustthe angle of the handlebars toinsure greater bicycle stabilitywhen it is upside down. Asthe youth turns the crank, heor she should pay attentionto degree of force needed.Higher shifter speeds willrequire a greater force to turnthe crank arm. Exampleswherea change of speed is requiredare riding lawnmowers and thecamshaft and crankshaft.

Project Information, Helper's Guide

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Helpful Helper's Hints

Riding SafetyNumerous deaths and seriousinjuries have OCCUITedwith ridingequipment powered by smallengines. Finding the center ofgravity will indicate the risk of arollover. A low center of gravityprovides a smaller risk. Youshould gain an understandingof what direction is safest for

mowing hills; up and down forriding mowers and across the hillsfor walk-behind mowers. It maybe useful to study lawns that havehills and discuss the best mowingpattern. You may want to observeyouth mowing a lawn to see if thecorrect mowing directions arefollowed.

Make the Cut!

You may want to help youth fmdthe lettuce and other items forthis activity. A magnifying glasswill be helpful with seeing thedifferences at the cut edges of thelettuce. The primary objective isto show that more plant cells areinjured with a dull knife or blade,which increasesthe risk of disease.

Information OverloadAnytime you go shoppingwhether it's groceries or clothingyou have choices with respect toquality. This is also true of smallengine equipment and their parts.Youth may need help determiningquality differences although quite

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often price is an indicator. Alsoyouth may need assistance incompletingthe table in the activity.

Business Time?Youth in grades six through eightare often looking for ways to earnmoney. Mowing the neighbors'lawns or roto-tilling gardens aregood ways to earn money. Youthmay need help completing thequestions in this activity. Whenanswering these questions,consideration should be givento time needed for school andtime spent on other activities.Determination of costs will beuseful in determining what tocharge.

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Coming Apart - Coming TogetherIf youth plan to do the following six activities, they may want to obtaina discarded engine from a small engine repair shop or an engine discarded intheir neighborhood. The youth may need help in obtaining the engine. Thesesix activities are designed to be done in pairs, i.e., Fuel and Air Systems-Corning Apart, Fuel and Air System - Corning Together, Electrical System -Coming Apart, Electrical System - Coming Together, Engine Base -Coming Apart, Engine Base - Coming Together.

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availablein the localhardwarestorebut probably'

will be available at the manufacturers' authorized. '¥

Motor Music repair shops andExperienced small engine repair people can analyze stores. Youth may

Answer Key foran engine's problem by the noise it creates. Youth will need help locatingbe recording the sound produced by a small engine them. Unlessyouth Advanced Toolsunder several conditions. Youth may need help to plan to do extensive Tool Letter No.determine differences in the sounds for the different small enginerepair, Dial indicator E 4conditions. Be sure to have youth identify each the purchase of

Digital multimeter F 7condition on the tape by speaking into a recorder. these tools wouldnot be advised. Piston ringAdvanced ToolsThese tools may be compressor D 6

As more specialized work is done on a small engine, availablein schools Piston ringthe more advanced or specialized the tools become.

that that have small expander C 1Some of these tools also become more costly and,

engine repair Spark tester G 5in some cases, the tools are specificto a small enginemanufacturer. Descriptions of these tools may be programs. Tang bender A 2

found in the service manual specific to the engine. Vibrating wireThese tools may not be tachometer B 3