Section 3 - Engine Diagnosis

Transcript

- SECTION 3 ENGINEDIAGNOSIS DIAGNOSIS IS IMPORTANT Remember the last time you didn't feel just right, and went to see your doctor? Did he say "hello," then rush you right into the operating room and remove your appendix? If he did, he would probably soon lose most of h i s patients, in one way o r another. What he probably did first was to set youdown and ask you some questions. Thenheprobably blood pressure, made a few tests, such as temperature, etc., before arriving at any sort of diagnosis. With the results, he could make more specific tests and arrive at an accuratediagnosisbeforetreating you. Because of your doctor's training and careful diagnosis, you haveconfidence in him. You, as a service repairman, can instill confidence in your customers by a careful diagnosis of their mower troubles. which must be learned and Diagnosis is a talent, a talent continually practiced. A N Y E X P E R TA TD I A G N O S I S FOLLOWS A SET PROCEDURE Your doctor takes your temperature, checks your pulse, heart, etc. before attempting a diagnosis. A service repairman must also follow a set procedure in trouble diagnosis to make fast and accurate repairs. SERVICE BULLETIN REFERENCES ..... ..... ..... ..... ..... ..... . .... ..... 3-1 O B T A I N GENERAL PRELIMINARY INFORMATION 1.. Fill out a brief report with the-customers help. Put this information on the repair ticket which will be attached to the mower. Unless the failure is obvious, this may help the mechanic later on, especially if work is delayed for several days. look overthe mower with you. Note obvioH damage, removal or alteration of safety equipment such as trailing shield, toeguard,interlockcable etc. on therepair ticketin the presence of thecustomer.This may protect you if any questions arise later as to the responsibility for damage. 2. Have thecustomer 3. Find out how the mower is used: Was it used in a small or large yard, at home only o r often lent out? Was it used on level, clean lawns, rough ground, vacant lots, heavy weeds, etc? 4. Findout what kind of gasolineandoil is used.Pull the engine through with starter rope, and if it binds o r is dry internally (indicating lack of oil) show the customer. 5. If damage is apparent, find out how damage occurred, WITH THIS INFORMATION, YOUR MECHANIC CAN PROCEED W I T H SPECIFICTESTS 3-2 ..... , .... , .,.. , .... ..... ...., ..... ..... REVISED 1977 SERVICE BULLETIN REFERENCES Trainyourmechanicsin set diagnosisprocedures.Normally,diagnosis takes very little time in the beginning, and will probably save a great deal of time in eliminating unnecessary repair work. 1. BEFORE YOU TRY TO STARTENGINE a. Be sure there is clean fuel in tank. b. Be sure gas cap vent and fuel shut-off valve are open. c. Be sure ON-OFF Switch is in ON position. d. Check ON-OFF switch lead - must be connected to switch. 2. CHECKCOMPRESSION a. With ON-OFF switchinOFFposition,pull engine through several times with starter. Feel for compression as you pullenginethrough. If engine spins very easily, it has little (if any) compression. With little compression, there will be little o r no power. b. If engine resists pull of starter rope, it has compression. If you spin an engine with good compression fast enough, you can hear the carburetor sucking air--and kick- back noise. c. While checking for compression, also listen for any scraping or squeaking internal noises. These noises indicate piston and cylinder scoring. If you hear such noises, do not t r y to start the engine, but turn to Section 8, Engine Repair Procedure, 3. I G N I T I O N CHECK a. Take out the spark plug and examine it. Be sure that theelectrodesareclean and the gap is .O25" for D-400 SERIES, ,035'' for D-600 SERIES, and .035" for "F" SERIES. Check theporcelain, If it is cracked,the plug won't fire. If the end of the plug i s wet, at least youknow fuel is gettingthrough. As a further check toseethat fuel is gettingthrough,placeyourthumboverthe spark plug hole, and pullthe starter cord several times. Your thumb should be wet with fuel, b. Check spark plugusing specialtoolpart no. 426814. If spark plugtool is not available, remove plug from the cylinder, hold it approximately 1/4"-3/16" away from engine,pullthe startercordseveraltimes and check the spark betweentheplugandground.The spark should be hot blue and snapping. A weak spark is orange, and makes little, if any, noise. If there is no spark, or a very weak spark, ALWAYS t r y another plug. It only takes a few minutes,andthese few minutes could save you hours. BESURE YOU USE THE RIGHT PLUG DON'T GUESS. C. - d. If the new plug won't fire, remove the plug from the lead wire and place a bolt in the rubber hood, 'making contact with the spring terminal. Hold the bolt head 1/4"-3/16" away from a metal part of theengine o r housing, and pull starter cord several times. should jump the gap. e. If you don't get a spark at this point then you have ignition problems. for detailed service information. SERVICE BULLETIN REFERENCES ..... A good spark Refer to Section 6 ..... ..... ..... ..... ..... ..... ..... REVISED 1977 33 4. C A R B U R E T I O ND I A G N O S I S If you have a spark at the plug (even though a weak spark), check to see that the fuel mixture is getting into the combusion chamber. a. Remove spark plug from cylinder. SAFETY WARNING ALLOW 10 SECONDS TIME BEFORE REMOVING SPARK ALLOWS CHARGE IN CD PACK TO LEAK OFF. PLUG LEAD. THIS b. Place finger over spark plug hole in cylinder and pull starter rope several times. c. If fuel mixture is entering cylinder your finger will be wet. If fuel is not entering cylinder refer to Section 4 for complete carburetor repair. IMPORTANT - Always check fuel tank make sure it is clean and contains no water. Instruct customer in use of correct fuel mixture - Refer to Operator’s Manual. Air filter element must be clean. Check for dirt or obstructions D-400 Series - Turn carburetor adjusting make sure needle is open. knob counterclockwise two turns from seat to D-600 Series - Check atmospheric pressure adjustment turns from closed setting. - “F” Series Check atmosphericpressureadjustment turn from closed setting. D-600 Series - Check atmosphericpressure closed setting. “F” Series setting. - “F” Series - Fuel flow needle valveadjustment in carburetor throat. - Correct normal setting is 1-1/2 - Correctnormalsetting is 1/2 adjustment - normal pre-setting is 1-1/2 turns from Check atmospheric pressure adjustment - normal pre-setting is 1/2 turns fromclosed - normal pre-settingis 2 turns from closed setting. Check fuel line to see if fuel is flowing into carburetor. EXHAUST PORT CLEANING If yourchecks have indicatedthattheenginehas good spark,fuel flow andcompression,yetengine won't run, o r "4-cycles,"(ignition every other revolution) check the following: EXHAUST PORT CLEANING Loss of enginepowercanbeattributed,in many cases, torestrictedexhaustports. This restriction, results from a build-up of carbon deposits. Therefore, the muffler plate should be removed every 50 hours of operation o r at the end of the mowing season and the exhaust ports checked for carbon accumulation. This routine maintenance check is not only of vitalimportanceto eliminate loss of engine power, but to eliminate particles of carbon from breakingaway, enteringthepowerhead and causingpiston scoring. NOTE Using LAWN-BOY 2 cycleoilin the requiredamount will minimizecarbon build-up. Most oilis not made for burning and therefore, results in heavy accumulation of carbon. SAFETY WARNING: TO PREVENT DISCONSTARTING O F ENGINE, NECT AND REMOVESPARKPLUG PRIORTO REMOVING MUFFLER. Tocleanexhaustports,tip mower on its side and secureinthis position. Remove nuts securing muffler cover to muffler plate and remove muffler cover. On some models the blade, blade stiffener, and adapter plate must be removed prior to removing muffler plate. Pull starter rope slowly until piston covers theexhaustports. Using a 3/8 inchdiameter dowel, insert dowel into ports to break away carbon. Place mower in upright position and pull starter rope several times to blow out carbon.Cleanmufflercoverand coverplate and re-securecoverplateto mufflerplate. If it wasnecessary to remove blade, torque blade nut to 50 ft. lbs. Torque blade bolt to 30-32 ft. lbs. Replace spark plug and reconnect high-tension lead. NOTE Replace blade nut o r bolt if removed o r installed MORE THAN FOUR times. SAFETY WARNING: WHEN REASSEMBLING METAL MUFFLER COVER, ASSEMBLE FASTENERS (SCREWS)WITHFINGERS TOENPREVIOUSLY GAGE FORMED THREADS. DO NOT FORCEREINSTALLATION AS THE SCREW WILL FORM A NEW SETOF WEAKER THREADS WHICH MAY EVENTUALLY STRIP AND THE SCREW MAY BECOME A THROWN OBJECT. TORQUE TO 140-170 INCH LBS. SERVICE BULLETIN REFERENCES . . . . . . . . . . REVISED 1978 . . . . . . . . . . . . . . . . . . . . . . . . 3-5 ENGINE DIAGNOSIS - Upper and lower crankshaft seals Worn seals maydevelop leaks, which permit air to enter o r leave crankcase, impairingthecompression and vacuumcycle. Upper (armatureplate)sealon.later "D" modelengines is a spring loaded type. Thisprovidesmorepositivesealing to prevent oil leaking past and fouling breaker point. - Gaskets Defective gaskets can allow a i r leakageinadditiontooilleakage.The results are the sameas leaky seals. - Screws and bolts Inspect for tightness. Loose screws or bolts can alsopermit air to enter or leave, impairing the compression and vacuum cycle. - Majorcastings Check forporosityin the carburetor, crankcase, cylinder, and magneto plate.Porosityresultsfrom a defect in the casting process, and is indicated by tiny a i r holes i n thecasting. This condition also results in air leaks. In some cases, the use of a penetrating ink will reveal hidden holes. 3-6 ..... ... .. ..... ... .. ..... . ... . . . . .. . ... . SERVICE BULLETIN REFERENCES SERVICE r BULLETIN REFERENCES t ..... . . ,., ..... . ... ..... .... ..... .... 3-7 3-8 I L a r . . . .. . . . .. . . . . . . . . . . .. .. . . . ... . . .. . . . . . . SERVICE BULLETIN REFERENCES t L SERVICE BULLETIN REFERENCES ... W .. ... .... . ..... ..... . . ... .... . ..... 3-9 L .. ..... . ..... .. ... , ..., , .... SERVICE BULLETIN REFERENCES "F" SE SECTION 3 ENG DIAGNOSIS ENGINE DIAGNOSIS Loss of engine power may be attributed, in many cases,toimpropersealing of the crankcasehalvesand/orincorrecttorque appliedto the crankcasecover to crankcase mounting screws. A poor seal results in air and oil leakage, impairing the compression and vacuum cycle. Referto Section 8 for correct installation of crankcase halves. INTAKE PLUGS Check (4) intakeplugs forpossible leaks. Use special tool part no. 609964 to correctly install intake plugs. Check f o r worn o r damaged upper and lower main seals. Worn seals may develop leaks, which permit air to enter or leave crankthe compression and case, impairing vacuum cycle. SERVICE BULLETIN REFERENCES ..... ..... . .... ..... .. ... .... . .. ... ..... 3-11 "F" SERIES (Cont.) - SELF PROPELLED MODELS Check gear housing gasket -- defective gaskets canallow air or oil leakage.' This causes same results as leaky seals. Check power take-off shaft seal for damage or wear. A worn or damaged sealresults in oil leakage and lower crankcase pressures. 3-12 .... . .... . ... .. ..... ..... , ... ..... ..... SERVICE BULLETIN REFERENCES “F” SERIES (Cont.) EXHAUST PORT CLEANING Excessivecarbondepositspresentinthe exhaust ports and muffler baffle cause additionalwearto engine parts and create a noticeable power loss. Approximately every 50 hours and at theclose of the mowing season check for excessive carbon accumulationinexhaust ports and muffler baffle. This routinemaintenancecheck is not only of vital importance to eliminate loss of enginepower,but toeliminateparticles of carbonfromenteringthecylinder,causing piston scoring. NOTE Using Lawn-Boy Special lubricant in will therequiredfuel/oilmixture minimizecarbon build-up. Most oil is not made for burning and therefore,resultsin heavy accumulation of carbon. MUFFLER BAFFLE AND EXHAUST PORTS SAFETY WARNING TO PREVENT STARTING O F ENGINE, DISCONNECT SPARK PLUG WIRE AND REMOVE SPARK PLUG PRIOR TO REMOVING MUFFLER. To cleanmufflerbaffleandexhaustports, its side. Remove theblade nut, blade,bladestiffener(washer on 21” models) and bladeadapter hub. The hub is taperedto fit thetaper of thecrankshaft. Tap the hub with a fiber hammer to loosen it from the crankshaft. Remove three bolts securing crankshaft support and muffler to mufflerplate. Remove crankshaftsupport and muffler baffle. tip moweron SERVICE BULLETIN REFERENCES ..... .. ... ... .. .. . .. ..... ..... ... .. ..... 3-13 "F" SERIES (Cont.) Using a 3/4 inch diameter wooden dowel remove carbon deposits from opening in muffler baffle and muffler tube. SAFETY WARNING WHEN REASSEMBLING MUFFLER COVER, ASSEMBLE FASTENERS (SCREWS)WITHFINGERS TO ENGAGE P R E V I O U S L Y FORMED THREADS. DO NOTFORCEREINSTALLATION AS THE SCREW WILL FORM'ANEWSETOFWEAKER THREADS WHICH MAY EVENTUALLY STRIP AND THE SCREW MAY BECOME A THROWN OBJECT. TORQUE T O 140-170 INCH LBS. Reinstall adapter hub, blade stiffener (washer on 21" models),blade and blade nut. Torque blade nut to 50 ft. lbs. Replace spark plug and reconnect high-tension lead. Pull starter handle slowly until piston covers the exhaust ports. Using a 7/16 inch diameter wooden dowel, insert dowel into portsto loosencarbondeposits. DO NOT DAMAGE PISTONBYUSINGMETAL INSTRUMENT. Place mowerin operating position and pull starter handle several times to blow out carbon deposits. Reinstall mufflerandcrankshaftsupporttomower. Use special tool partno. 609968 to correctly aligncrankshaftsupport. 3-14 . .... ... .. ..... .... . .... REVISED 1978 ... ..... SERVICE BULLETIN REFERENCES SERVICE BULLETIN REFERENCES ''F" SERIES (Cont. t I . .... . . . . . ... . ..... .. I ..... ..... ..... 3-15 3-16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .SERVICE BULLETIN REFERENCES