MTD AC3 manual

Pr of essional Shop Manual A C3 Series of 4-Cyc le Engines NOTE: These materials are for use by trained technicians who ar e experie nced in the service and repair of outdo or power equipment of the kind de scribed in this publication, an d are not in tended for u se by untr ained or inexp erienced individu als. These materials ar e intended to pro[...]

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I Chapter 1: Introduction ............. ................................ ................................. ..............1 Professional shop manual intent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Fasteners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1[...]

II Chapter 6: Starters ....... ............................................................................... ........... 43 Recoil Starter Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 The starter rope, pulley and spring s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Elect[...]

Introduction 1 Professional Shop Manua l intent This Manual is intended to provide service deale rs with an introduction to the mechanical aspects of the AC3 series of 4-cycle engi nes. Disclaimer : The information contain ed in this manual is correct at the time of writing. Both the product and the infor- mation about the prod uct are subject to c[...]

AC3 Series of engines 2 Assembly T orque specifications may be noted in the text that co vers assembly , they may also be summarized in table s along with special instructions regarding locking or lubrication. Whichever method is mo re appropriate will be used. In many cases, both will be used so that the manual is handy as a quick-reference guide [...]

Introduction 3 AC3 • 29cc’s of displacement. • Engine covers split front and back. •M e t a l s u m p AC4 • 32 cc’ s of displacement. • Aluminum clutch housing. • Extended oil fill tube that is near th e carburetor . • End mounted recoil starter . AC5 • 25 cc’ s of displacement. • Identical to the AC4 except for the plastic [...]

AC3 Series of engines 4 Model and Serial Numbers The model (item) an d serial number are on a little white sticker with bar code. These are the numbers needed when ordering part s. This sticker can be found on the side of the engine . The model number is 41ADT59C7 1 1. The break do wn of what the number mean is as follows: 41 ..... ................[...]

Maintenance 5 MAINTENANCE The information in this m anual applies to the AC3 se ries of engines. Some basic pr inciples may apply to engines produced by other manu facturers. As the saying goes “an ounce o f prevention is wor th a pound of cure”. The same can be said ab out preventive maintenance on out door power equipment. By chan ging the sp[...]

AC3 Series of engines 6 Sp ar k pl ug s The spark plug used in the 32cc trimmer is a Cham- pion RDZ19H gapped to 0.025” ( .655 mm). See Figure 2.3. Wear rate will vary with severi ty of use. If the edges of the center electrod e are rounded-of f, or any other appar- ent wear / damage oc curs, replace the spark plug before operating failur e (n o [...]

Maintenance 7 Air filter A dirty air filter can reduce engine power , increase fuel consumption, increase CO emissions and make starting more dif ficult. The air filter should be cleaned eve ry 10 ho urs of use (depending on area of use, dusty areas require more frequent c leanings). T o clean/replace the air filter: 1. Remove the air filter cover [...]

AC3 Series of engines 8 Sp ark arrestor The spark arrestor should be checked and/or cleaned every 25 hours of use. NOTE: The spark arrestor also serves to keep blockages out of the exhaust system. T ypical block- ages include insect nests b uilt during the dormant season. NOTE: A spark arrestor is required by law when trimmer ar e used near “unim[...]

Maintenance 9 Fuel file r A dirty fuel filter can re sult in a lean run condition. The fuel filter should b e replaced every 25 hours of use. NOTE: The weighted fuel filter ( clunk) keeps the filter sub- merged in the fuel at an y angle of oper ation. The filter removes dirt and air bubbles from the fuel. Running the trimme r without the filter may[...]

AC3 Series of engines 10 V alve lash T o adjust the valves: NOTE: Loose valve lash on these engines can mimic the symptoms of a lean fuel/air mix- ture. 1. Remove the engine cover and sp ark plug, following the steps described in the previou s sections of this chapter . 2. Remove the valve cover using a T -25 driver . See Figure 2.13. 3. Rotate the[...]

Troubleshooting 11 Definition s T roubleshooting - The act of gathering information by preforming test s and direct observations. Diagnosis - A theory of what the problem is, base d on the information ga th e re d by trou ble sh o ot ing . Introduction Diagnosing an engine is an art form that is built on several factors. First and most impo rtantly[...]

AC3 Series of Engines 12 There are tools that the te chnician can use in order to define the problem, such as: 1. Interview the customer . • Get a go od description of t heir complaint. • If it is an intermittent problem, verify what conditions aggrav ates the problem as best as possible. • Get an accurate service history of the equipment. ?[...]

Troubleshooting 13 Identify factors th at could cause the proble m This is the se cond step in the tr oubleshooting process. 1. Crankshaft will not turn. • Hard to pull rope, steady p ressure - This usually indicates a mechanical bind of some sort. the likely sus- pects ar e: II. A parasitic load from a jammed attachme nt or drive shaft. III. An [...]

AC3 Series of Engines 14 • Compression or ignition problem I. Chec k the engine stop an d/or ignition switch. II. T est the ignition system using a proper tester . III. Replace the spark plug with a new one or a known good one. IV . Check co mpression. V . Check valve lash. VI. Check valve timing/actuation. VII. Check exhaust. 8. S tart s, runs p[...]

Troubleshooting 15 II. The muffler itse lf my be blo cked. III. The spark arrest or may be blocked. IV . The exhaust valve may not be opening fully , poss ibly because of extremely loose valve lash set- tings. V . The exhaust valve seat may ha ve come loose in the cylinder head. This may cause a loss of com- pression, a flow blockage or it ma y ran[...]

AC3 Series of Engines 16 •K n o c k * Check for loose mounting of en gine or driven implement * Rotate crankshaft back-and-forth to check for loose connecting rod. • Click * Half-engine speed clatter: loose valve lash. * Half-engine speed clatter , slightly heavier: wrist-pin. * Rhythmic heavy-light engine speed click: piston slap • S park-kn[...]

Troubleshooting 17 Rep airing the pr oblem The third step in the diagno stic pro cess is to repair the problem. This step consists of: 1. Form a diagnosis by using a ll of the information gathered from th e troubleshooting th at was performed. 2. Physically perf or m th e re pair . The fourth, and hopefully fina l, step in the troubleshooting proce[...]

AC3 Series of Engines 18 Prime test T o perform a prime test: 1. Prime the engine thro ugh the carburetor throat us ing a squirt bottle , filled with cle an fresh gasoline. NOTE: Insp ect the air filter while priming t he engine. Look fo r a dirty or plugged filter that could preven t air flow or a missing filter that would indicate dirt ingestion.[...]

Troubleshooting 19 Compression testing T o perform a compression test: NOTE: If the engine will run, start the engine and let it warm up first fo r a better reading. 1. Disconnect the high-tension lead from the spark plug and ground it well away from th e spark plug hole. 2. Remove the sp ark plug using a 5/8” spark plug socket. 3. Pull the start[...]

AC3 Series of Engines 20[...]

Ignition 21 T roubleshooting the Ig nition System The purpose of the ignition system is to provide a spark in the combustion chamber at the proper time to ignite the fuel/air mixture. T o troubleshoot the ignition system: 1. Examine the spark plug by following the step s described in the sp ark plug section of this chapter . 2. After examining th e[...]

AC3 Series of Engines 22 T esting the module T o test the module: 1. Remove the starte r housing by following the proce- dures described in Chapte r 6: St arter . 2. Check the air gap for the m odule. Set it to 0.010” by following the step s described in the mod ule section of this chapter . 3. Disconnect the red wire. See Figure 4.2. 4. Install [...]

Ignition 23 T est t he engine sto p switch T o test the engine stop switch: 1. Open the grip b y removing the five screws with a T -20 torx driver . 2. Disconnect the wires from the eng ine stop switch. 3. Connect an ohm meter or continuity light to the switch. 4. With the switch in the engine run position (l), the meter should indica te no continu[...]

AC3 Series of Engines 24 Module Remove the ig nition module: 1. Remove t he starter by following the procedures described in Chapte r 6: starter . 2. Disconnect the two wires from the module. See Figure 4.5. NOTE: The black wire will come off with the module mounting screws. 3. Remove t he module by rem oving the two scr ews. 4. T o inst all the mo[...]

Ignition 25 Flywheel T o remove the flywheel: 1. Remove the spark plug by following the step s described in Chap ter 2: Maintenance. 2. Remove the st arter by following the procedures described in Chap ter 6: starter . 3. Remove th e flywheel by striking the crankshaft with a brass punch. See F igure 4.7. NOTE: It is not necessary t o remove the mo[...]

AC3 Series of Engines 26[...]

Fuel System And Carburetor 27 The function of the fuel system is to store fu el, mix the fu el with air and deliver it to the combustion chamber . The fuel system consist s of the following component s: • Fuel tank • Fuel lines • Fuel filter • Carburetor NOTE: When working on the fuel s ystems, look at the whole system. A problem will rarel[...]

AC3 Series of Engines 28 Inspecting the fuel: NOTE: Fuel is the maintenance item most of ten overlooked by consumers. A lot of fuel system problems are caused by bad gasoline. When inspecting the fuel: • Look for water . • Look for dirt. • Look for discoloration. • Sniff carefully to see if it smells like varnish or kerosene. • Save the f[...]

Fuel System And Carburetor 29 Generally thes e kit s involve mixing a m easured amount of water and gas together and seeing were the boundary layer is. See Figure 5.4. The test kit should come with a chart to compare the boundary layer height to alcoh ol percentage. Figure 5.4[...]

AC3 Series of Engines 30 Fuel t ank T o remove/replace the fuel t ank: 1. Remove the air filter cover . 2. Disconnect the fuel lines from the carburetor . See Figure 5.5. 3. Remove the engine cover by re moving the six screws that hold it in place. See Figure 5.6. 4. The fuel tank will s lide out to the rear . T o install the fuel tank: NOTE: Make [...]

Fuel System And Carburetor 31 Fuel lines • The carburetor cont ains a pump that draws fu el throu gh the fil ter and up the fuel line. A har dened fuel line that has cracked or does not seal tightly to a fitti ng may draw air into the line without le aking fuel out. • Air leaks will reduce the fuel pump s ability to supply the carburetor . • [...]

AC3 Series of Engines 32 Carburetor The AC3 series of engine s uses the W albro WYL series carburetors, or a carburetor of similar design from another manufacturer . The main distinguishing fea tures of this carburetor design ar e: • It has a rotary throttle valve, not a bu tterfly valve. • A fuel metering needle in the carburetor ve nturi rise[...]

Fuel System And Carburetor 33 2. In the second frame, the throttle has be en rotated slightly (tip-in), admitti ng some air through the ro tary valve. See Figure 5.10. 3. At mid-range throttle, the thro ttle is rot ated so that the bore is nearly aligned with the throat of th e carb ure- tor . See Figure 5.1 1. 4. At wide-open throttle (WOT), the t[...]

AC3 Series of Engines 34 6. In idle position, the throttle is closed, the hole through the drum is cross-wise to the thro at of car- buretor and the drum is seated at the bottom of its travel. See Figure 5.13. • Throttle closed. • The top of the throttle arm is 5/16” (7 .9mm) above the top of the ca rb ur et or hou s in g . 7. As the thr ottl[...]

Fuel System And Carburetor 35 T roubleshooting the car buretor T ypically , troublesho oting the carburetor is the last step in the diagnostic process. The other factors are more readily identified; spark vs. no sp ark, specific pressure r eadings on a co m pression gauge, or a visible blocka ge in the muf fler . Carburetor function is more subt le[...]

AC3 Series of Engines 36 NOTE: A crack ed spacer or a leaking ga sket between the spacer and th e cylin de r co uld result in a lean run or prevent the impulses from the engine from driving the fuel pump. See Figure 5.17. 8. Inspect the thro tt le valv e assemble for debris and freedom of movement. See Figure 5.18. 9. Perform a needle valve pop of [...]

Fuel System And Carburetor 37 Disassembly of th e carburetor 1. Remove the four scre ws that hold the carburetor together . See Figure 5.19. 2. Separate the carburetor , placing each part on the bench in the order they came apart. 3. Inspect the diaphragms. If torn, dama ge d or brittle install a diaphragm kit. 4. Inspect for dirt or varnish build [...]

AC3 Series of Engines 38 8. Remove the throttle valv e assembly . See Figure 5.22. 9. The orif ice can also be se en from the pum p side of the throttle housing. See Figure 5.23. 10. The fuel pump in th e carburetor is driven by vacuum pulses in the inta ke port. The impul se port from the spacer let s the vacuum pu lses into the pump cam- ber . Se[...]

Fuel System And Carburetor 39 Re-assembly of the carburet or 1. Place the carburetor in a clean area on the work bench. 2. Inspect the thrott le valve assembly for dirt and/or var- nish. 3. Install the throttle valve assembly 4. If the needle valve seat is damaged , replace the car- buretor . See Figure 5.25. 5. There are port s in the metering val[...]

AC3 Series of Engines 40 7. Clean the meterin g orifice with carburet or cleaner . 8. Set the needle valve lever as pe r the car buretor manufacturer’s recommendations using a W -tool. See Figure 5.29. 9. Follow steps in reverse or der to rebuild the carbure- tor . 10. Perform a needle valve po p off test by following the carburetor manufacturer?[...]

Fuel System And Carburetor 41 Carburetor insulator NOTE: A cracked spacer or a leakin g ga sk et be tw ee n th e spacer an d the cylinder could result in a lean run or prevent the impulses from the engine from driving the fuel pump. T o remove/replace the carburetor insu lator: 1. Remo ve the carburetor by following the pr ocedures described in the[...]

AC3 Series of Engines 42[...]

Starters 43 Recoil St arter Removal T o remove the starter assembly: 1. Remove the clutch following the step s described in the section on clutch removal. NOTE: The drive shaft will come off with the clutch hous- ing. 2. Remove the screws that hold the engine co ver to the starter ho using. See Figure 6.1. 3. Remove the four screws in the front of [...]

AC3 Series of Engines 44 The st arter rope, pulley and springs The AC3 series of engine s are equip ped with the Assist S pring T echnol ogy (AST) s t ar ters .The AST system allows the customer to pull the recoil rope at any pace they please, yet still gene rate enough force to start the engine. The system is simple, and adds a g rand tot al of tw[...]

Starters 45 NOTE: The recoil pulley assembly consist s of three part s, but it is serviced as one assembly . The three pa rt s are: the inner pu lley , the sta rter assist (accumula- tor) spring, and the outer pulley . See Figure 6.5. NOTE: When the recoil rope is pulled, it rot ates the outer pulley , winding-up the st arter assist spring. When th[...]

AC3 Series of Engines 46 T o assembly the star ter pulley assembly: 1. Install a new starter ro pe in the recoil pulley assembly . 1a. Remove the old rope from the pulley . 1b. Cut a piece of #3 1/2 (7/6 4” ) starter rope 43” (109 cm) long. 1c. Insert the new piece of rope through the hole in the starter pulley . 1d. T ie a half hitch knot at t[...]

Starters 47 8. Secure the recoil handle to the rope using two half hitch knots. See Figure 6.10. 9. Release the slip knot. 10. Install the pu lley re tainer using a dee p socket to apply even pressure to the retainer while driving it into place. See Figure 6.1 1. NOTE: There m ust be 0.015” t o 0.030” (0.38 - 0.76 mm) clearance between the pull[...]

AC3 Series of Engines 48 Electric st arter system For the 2009 model year , MTD introduced an electric start option for some of its hand held engines. The engines equipped wi th the electric start feature can be identified by the coupler in the sump cover . There are two types of electr ic starters available. The first, is a 1 10V corded electrical[...]

Clutch and Upper Drive Shaft 49 Upper drive shaf t assembly The drive shaft assembly consists of the drive shaf t housing and a flexible inner drive shaft. Th e housing and the drive shaf t ar e serviced as one assembly . T o remove the upper drive shaft asse mbly: 1. Loosen the knob on the ez-link coupling. 2. Press in the metal butt on while pull[...]

AC3 Series of Engines 50 4. Remove the six screws in th e grip with a T -20 T orx ® driver . See Figure 7.3. 5. Let the grip hang off to the side. NOTE: Ther e ar e a ha lf do ze n parts inside the grip assembly . Be careful th at they don’t fall out of the grip. 6. Remove the anti-rot ation screw with a T -20 driver . 7. Loosen the clamping bol[...]

Clutch and Upper Drive Shaft 51 Clutch Remova l/replacement NOTE: The upper drive sh af t may be left conn ected to the clutch housin g. Re mo vin g the th re e scr ew s in the clutch housing will allow the clutch housing and the upper drive shaf t to be removed as one. 1. Remo ve the three screw s holding the clutch h ousing on with a T -20 driver[...]

AC3 Series of Engines 52 5. Remove t he clutch rotor wi th a clutch removal tool. NOTE: Older engines will have a larger clutch that has roughly a 2 7/ 16” diameter . They can be removed with part number 7 91-180918 or the newer clutch tool part number 79 7- 00062. See Figu re 7.8. NOTE: New engines use a smaller clutch, with roughly a 1 15/16”[...]

Engine Assembly 53 Economics and parts availability will de termine how much engine disassembly is feasible . There are three main levels of engine disassembly . 1. Short block installation. Short block inst all ation consists of removing the engine, transferring the extern al p arts to the replacement short block, and installing the en gine. Exter[...]

AC3 Series of Engines 54 Engine disassembly NOTE: Ther e are a few different paths th at can be followed when disassembling an engine. This chapter will cover the removal of com- ponents in one order , but it is written so that the technician can go to the com p on e nt being remove d . 1. Drain the oil by following the steps described in Chapter 2[...]

Engine Assembly 55 8. Carefully disconnect the breather hose from the air filter housing. 9. Disconnect the throttle cable. See Fig ur e 8.5. 10. Remove th e carburetor , fuel t ank and lines as one assembly . 1 1. Remov e the throttle cable b y pressing in the tabs located in the slot s while lifting the cable out. See Figure 8.6. 12. Remove the g[...]

AC3 Series of Engines 56 13. Remove the carb ur etor insulator block using a T - 25 torx driver . See Figure 8.7. 14. Rota te the flywheel so that the magnet s are away from the m odule. 15. Remove the two screws that se cures the ignition module to the block using a T -25 torx driver . See Figure 8.8. 16. Remove the module . 17. Remove the flywhee[...]

Engine Assembly 57 IMPORT ANT : Check pa rts price and availability before doing any internal engine repairs. 18. Remove the fo ur screws that secure the crankcase cover to the block using a T -20 torx driver . See Figure 8.10 . NOTE: On engines equipped with th e electric start featur e, there is a coupler in the sump cover that slides onto the cr[...]

AC3 Series of Engines 58 27. Slide the connectin g rod of f of the crank pin. NOTE: On eng ine s eq uip p ed with th e elec tr ic start feature, the crank pin will be longer so that it can fit into the couple r in the crank case cover . See Figure 8.12. 28. Remove the plastic cap from the wrist pin bo re of the piston. See Fig ur e 8. 13 . 29. With[...]

Engine Assembly 59 Engine Reassembly 1. Rotate the cra nkshaf t to top de ad center ( crank pin at the top). See Figure 8.15. NOTE: There are no timing ma rks o n th e cr ankcase. 2. Install the cam onto th e cam bracket. • The side of the cam with the hash mar ks on it faces awa y from the ca m bracket. • Lubricate the cam bear ing surface wit[...]

AC3 Series of Engines 60 6. Install the valve spring s and keepers: 6a. Place the sp rin g ove r the va lve ste m . 6b. Set the valve keeper on top of the spring. 6c. While holding the valve in place, press down on the keeper with two fingers an d slide it in to the notch on the valve stem. See Figure 8.18. 7. Install the piston ring s on the pisto[...]

Engine Assembly 61 12. Rota te the piston so th at the lettering on the co nnect- ing rod bearing faces the crank shaft journa l when installed. NOTE: Apply a coating of Slick 50 ® or similar produ ct to the connecting ro d bearing as a prelube. 13. Slide the connecting ro d onto the crankshaft pin. Align the opening in the cylin der for cam brack[...]

AC3 Series of Engines 62 17. Install the cran kca se cover so that the two dimples are toward the cylinder . NOTE: On eng ine s eq uip p ed with th e elec tr ic start feature, m ake sure the crank p in slides into one of the holes in the co up ler attached to the crank case cove r . 18. Install the flywhee l and module by following the pro- cedures[...]

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MTD Products Inc - Product Trai ning and Education Department FORM NUMBER - 769-02614A 07/202010[...]