MTD AC3 Automobile Parts User Manual
Contents
1. V The exhaust valve seat may have come loose in the cylinder head This may cause a loss of com pression a flow blockage or it may randomly alternate between the two NOTE The cause of an exhaust valve seat coming loose is usually over heating VI Intake blockage a An intake blockage up stream of the carburetor will cause a rich fuel air mixture and constrict the amount of air that the engine can draw in limiting performance A blocked air filter is a common cause of this b An intake valve that does not open fully will cause a blockage A possible cause of this is loose valve lash VII Makes unusual smoke when running a Black smoke usually heavy usually indicates a rich air fuel mixture Not enough air air filter blockage or a partially closed choke Too much fuel needle valve stuck or metering emulsion issues with the carburetor b White smoke usually heavy e Oil in muffler usually the result of improper tipping the engine will fog for a minute or so then clear up on its own e Oil that is diluted with gasoline It may be caused by improper tipping It can also be caused by leaky carburetor needle valve if there is a down hill path from the carburetor to the intake port Check oil for gasoline smell repair carburetor c Blue smoke usually light VIII PCV system a May be blocked or unplugged b May be over come by massive over filling or oil dilution with gasoline c Will cause oil to exit2. du 2 3 4 Disconnect the fuel lines from the carburetor Pull the blue fuel line out of the tank Remove the fuel filter by following the steps described in the Chapter 2 Maintenance Pull the clear line out of the fuel tank To install the fuel lines 1 2 3 4 5 Cut a point on the new fuel lines Push the pointed end of the fuel lines into the holes in the tank Attach the fuel lines to the carburetor Install the fuel filter following the steps described in the Chapter 2 Maintenance Test run the engine before placing back into service 31 AC3 Series of Engines Carburetor The AC3 series of engines uses the Walbro WYL series carburetors or a carburetor of similar design from another manufacturer The main distinguishing features of this carburetor design are e It has a rotary throttle valve not a butterfly valve e A fuel metering needle in the carburetor venturi rises out of an orifice in direct proportion to the movement of the throttle valve pP d Throttle asset D 3 E The Rotary valve resembles a round drum with a hole p Fuel metering needle bored through it See Figure 5 8 This design allows fuel to be metered into the venturi in amounts that are directly related to the amount of air allowed to pass through the venturi The air flow is regu lated by the rotary throttle valve e When the hole through the drum is aligned with the throat of the carburetor the throttle is
3. opened Orifice I e When the drum is rotated so that the hole is not x aligned with the throat of the carburetor the F throttle is closed e A groove around the drum allows some air to Figure 5 8 pass by the drum when the throttle is closed providing the engine with enough air to idle The following picture sequence illustrates the opening of the rotary valve throttle 1 In the first frame the throttle is fully closed idling or stopped See Figure 5 9 Figure 5 9 32 Fuel System And Carburetor Throttle opening 2 Inthe second frame the throttle has been rotated slightly tip in admitting some air through the rotary valve See Figure 5 10 Figure 5 10 Throttle opening aaa SS 3 Atmid range throttle the throttle is rotated so that the bore is nearly aligned with the throat of the carbure tor See Figure 5 11 E c Seon FA L cam Figure 5 11 Throttle fully open Bb Bile y needle 4 At wide open throttle WOT the throttle is rotated so that the bore is in line with the throat of the carbure tor See Figure 5 12 5 As the throttle opens it also climbs up a ramp Figure 5 12 33 34 AC3 Series of Engines 6 In idle position the throttle is closed the hole through the drum is cross wise to the throat of car buretor and the drum is seated at the bottom of its travel See Figure 5 13 e Throttle closed e he top of the throttle ar
4. roughly a 1 15 16 diameter They can be removed by using clutch tool number 797 00070 Install the clutch rotor NOTE The big washer goes between the rotor and the starter housing See Figure 5 0 NOTE The lettering on the rotor must face away from the engine The thrust washer is placed on top of the rotor See Figure 6 0 Torque the rotor to 100 150 in Ibs 11 3 16 9 Nm Slide the clutch drum onto the crankshaft and tighten it to a torque of 38 40 in lbs 4 3 4 5 Nm Install the clutch housing and the upper drive shaft following the steps mentioned earlier in reverse order Test run the engine trimmer before returning it to service 4 LI Part number 791 180918 Figure 5 0 Lettering a Thrust washer Figure 6 0 Engine Assembly CHAPTER 8 ENGINE ASSEMBLY Economics and parts availability will determine how much engine disassembly is feasible There are three main levels of engine disassembly 1 Short block installation Short block installation consists of removing the engine transferring the external parts to the replacement short block and installing the engine External parts consist of e Starter e Ignition system e Fuel system e Muffler Top end repair Some internal parts may be available for service With minimal disassembly beyond what is involved in a short block replacement it is possible to replace the cylinder base gasket piston piston rin
5. 6 11 11 Check the clearance between the pulley and the retainer using a set of feeler gauges See Figure 6 12 12 Install the starter housing assembly be following the procedures described in the previous section of this chapter 13 Test run the engine before returning it to service Figure 6 12 47 AC3 Series of Engines Electric starter system For the 2009 model year MTD introduced an electric start option for some of its hand held engines The engines equipped with the electric start feature can be identified by the coupler in the sump cover There are two types of electric starters available The first is a 110V corded electrical motor assembly To start the engine 1 Plug the starter motor into a power source 2 Insert the shaft of the motor assembly into the cou pler in the sump of the engine 3 Push the switch to the ON position and the starter will spin the engine at 1 000 RPMs 4 Once the engine starts let go of the starter switch and remove the electric starter from the engine The second type of electric starter is an adapter that fits into an electric drill NOTE The electric drill must spin at 1 000 RPMs of faster The electric starter motor and the adaptor bit are not serviceable If they fail they must be replaced The coupler in the sump cover is the same for both systems The coupler is part of the sump cover and is ser viced replaced with the sump cover Both starter sys
6. Clean around the oil plug Hemove the oil plug See Figure 2 2 Tip the trimmer to the side and drain the oil in a safe approved container 4 Disposed of the used oil by following the federal state and local regulations 5 Fill the engine with 3 04 fluid ounces 90 ml of SAE 30 oil that meets or exceeds API SM standards NOTE The spark arrestor should be cleaned and the valves adjusted at every oil change Figure 2 2 AC3 Series of engines Spark plugs 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 severity of use If the edges of the center electrode are rounded off or any other appar ent wear damage occurs replace the spark plug before operating failure no start occurs Cleaning the spark plug z NOTE We do not recommend cleaning spark plugs e Use of a wire brush may leave metal deposits on the insulator that causes the spark plug to short out and fail to spark Use of abrasive blast for cleaning may cause Figure 2 3 damage to ceramic insulator or leave blast media in the recesses of the spark plug e When the media comes loose during engine operation severe and non warrantable engine damage may result Inspection of the spark plug can provide indications of the operating condition of the engine e Light tan colored deposits on insulator and electrodes is normal e Dry black deposits on the insulator and e
7. Figure 2 6 To clean replace the air filter 1 Remove the air filter cover by pressing in the tab on the bottom of the filter housing and lifting the cover off See Figure 2 5 Pull the filter out See Figure 2 6 If the filter is crumbling or brittle replace the filter Wash the air filter with warm soapy water Let the fil ter air dry DO NOT wring the filter out NOTE Wringing the filter can tear it Squeeze the filter but do not twist it Put a 1 4 teaspoon 1 25cc of oil to the filter and squeeze it through out the filter Insert the filter into air filter housing Install the air filter cover Test run the engine before returning it to service AC3 Series of engines Spark arrestor Engine cover The spark arrestor should be checked and or cleaned ar every 25 hours of use AT NP A NOTE The spark arrestor also serves to keep 3 pm mmda a Ya M blockages out of the exhaust system Typical block M j Be p zx IS pi a ages include insect nests built during the dormant b a season NOTE A spark arrestor is required by law when trimmer are used near unimproved land To check clean the spark arrestor 1 To clean the spark arrestor remove the engine cover using a T 20 driver See Figure 2 7 2 Remove the two screws holding the spark arrestor cover in place with a T 25 driver See Figure 2 8 QOUCIUM M passat vacare vc AN ELE Figure 2 8 Inspect the spark a
8. of what the problem is based on the information gathered by troubleshooting Introduction Diagnosing an engine is an art form that is built on several factors First and most importantly is a good under standing of how the engine works The second is a skill set that has been honed by experience Finally the use of visual observations and a structured systematic approach to troubleshooting a problem The first part of this chapter will outline the steps of troubleshooting an engine so a technician can form a proper diagnosis The second half of this chapter will describe specific procedures and tests to preform while troubleshoot ing The first two rules in troubleshooting are to cause no further harm to the engine and to pre AcaurioN vent injuries Always check the oil level and condition before starting an engine Check attachments for damage and make sure they are firmly mounted Steps to troubleshooting NOTE The steps and the order of the steps that follow are a suggested approach to troubleshooting the trim mer engine The technician does not necessarily have to follow them as described in this chapter Define the problem The first step in troubleshooting is to define the problem 1 Crankshaft will not turn e Hard to pull rope steady pressure e Rope jerks back e Rope will not pull at all 2 Crankshaft turns no start 3 Starts runs poorly e Starts then dies e Runs with low power out put e Makes unusual s
9. order NOTE Tighten the clutch to a torque of 100 150 in lbs 11 17 Nm Figure 4 7 NOTE Set the module air gap by following the steps described in the previous section of this manual 6 Test run the engine before returning it to service 25 AC3 Series of Engines 26 Fuel System And Carburetor CHAPTER 5 FUEL SYSTEM AND CARBURETOR The function of the fuel system is to store fuel mix the fuel with air and deliver it to the combustion chamber The fuel system consists of the following components e Fuel tank Fuel lines e Fuel filter e Carburetor NOTE When working on the fuel systems look at the whole system A problem will rarely be isolated to one component Figure 5 1 Vent Figure 5 2 To troubleshooting the fuel system Drain and inspect the fuel by following the steps described in the next section of this chapter Inspect the fuel filter If it is dirty replace it following the steps described in Chapter 2 Maintenance See Figure 5 1 Inspect the fuel lines 3a Are they cracked 3b Are they clogged 3c Are they brittle NOTE If the answer to any of the above is yes replace the fuel lines following the procedure described in the fuel line section of this chapter The fuel cap is vented Ensure that the vent is clean and working properly See Figure 5 2 Test and inspect the primer bulb 5a Isit leaking or is it brittle 5b If so replace the primer bulb 5c D
10. problems in the four critical factors an engine needs to run properly l Ignition sufficient spark to start combustion in the cylinder occurring at the proper time I Compression enough pressure in the cylinder to convert combustion into kinetic motion It also needs sufficient sealing to generate the vacuum needed to draw in and atomize the next intake charge Ill Fuel correct type and grade of fresh gasoline in sufficient quantity atomized tiny droplets and in correct fuel air proportions IV Flow if all of the above conditions are met but the flow of air is constricted on the inlet or exhaust side it will cause the engine to run poorly or not at all This also includes ensuring the valves are timed to open at the proper time e solate the ignition system and compression from the fuel system by preforming a prime test l Burns prime and dies This would indicate a fuel system issue I Does not burn prime Not a fuel system issue Check for an ignition compression or flow problem 13 AC3 Series of Engines e Compression or ignition problem l Check the engine stop and or ignition switch ll Test the ignition system using a proper tester Ill Replace the spark plug with a new one or a known good one IV Check compression V Check valve lash VI Check valve timing actuation VII Check exhaust 8 Starts runs poorly e Starts then dies Run the engine with a spark tester in line between the spark p
11. DAY Of the month Meu sorses ninenin arin high arae nne esent esee esee nene LASt digit of the year D Lesser nee Plant it was built in MTD Southwest m LEEREN ASSEDI ine number 0060 sereeeeerereereeerrrreseessresseeesssreeeeeeeeeeeeeeeeee Number of unit built Maintenance CHAPTER 2 MAINTENANCE MAINTENANCE The information in this manual applies to the AC3 series of engines Some basic principles may apply to engines produced by other manufacturers As the saying goes an ounce of prevention is worth a pound of cure The same can be said about preventive maintenance on outdoor power equipment By changing the spark plug air filter and oil at recommended intervals many failures can be avoided Sometimes just clearing off yard debris that has collected through use can make the difference between a properly running piece of equipment and the expensive inconvenience of unplanned repairs Cil Set r To check the oil P i mem 1 Clean around the oil plug 2 Place the trimmer on a level surface 3 Unscrew the oil plug See Figure 2 1 4 Theoil should be level with the bottom of the threads NOTE If needed add oil slowly until oil level is even with the bottom of the threads 5 Tighten oil plug finger tight Figure 2 1 Changing the oil The first oil change should be done at 10 hours and then it should be changed every 25 hours or at the start of the Season To change the oil 1
12. ER 4 IGNITION Troubleshooting the Ignition 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 To troubleshoot the ignition system 1 Examine the spark plug by following the steps described in the spark plug section of this chapter 2 After examining the spark plug reinstall it or a new one to ensure a good spark plug is being used Disconnect the spark plug wire Connect a spark tester to the spark plug wire Connect the other end of the spark tester to the engine block See Figure 4 1 Figure 4 1 Never remove the spark plug and hold it against the engine block to test for spark The fuel air mix coming out of the spark plug hole will catch on fire NOTE It only takes 1 000 volts to jump a 0 025 air gap in open atmosphere it takes 10 000 volts to jump the same gap at 120 psi therefore an open air spark test in not valid NOTE The spark should be a minimum of 10 Kv 10 000 volts at pull over speed 6 Make sure the engine stop switch is in the RUN position NOTE Most stop switches used on MTD handheld products are spring loaded to the RUN position when it is released This prevents no start situations caused by the customer failing to turn the switch on NOTE Once the engine stop switch is moved to the OFF position it sends a ground signal to the module The circuitry in the ignition module will latch the prim
13. MTD For A Growing World MTD Professional Shop Manual AC3 Series of 4 Cycle Engines NOTE These materials are for use by trained technicians who are experienced in the service and repair of outdoor power equipment of the kind described in this publication and are not intended for use by untrained or inexperienced individuals These materials are intended to provide supplemental information to assist the trained technician Untrained or inexperi enced individuals should seek the assistance of an experienced and trained professional Read understand and follow all instructions and use common sense when working on power equipment This includes the contents of the product s Oper ators Manual supplied with the equipment No liability can be accepted for any inaccuracies or omission in this publication although care has been taken to make it as complete and accurate as possible at the time of publication However due to the variety of outdoor power equipment and continuing product changes that occur over time updates will be made to these instructions from time to time Therefore it may be necessary to obtain the latest materials before servicing or repairing a product The company reserves the right to make changes at any time to this publication without prior notice and without incurring an obligation to make such changes to previously published versions Instructions photographs and illustrations used in this publication are f
14. ame time the engine dies XII Engine RPMs surge hunting a Lean Air fuel mixture condition When AFR Air Fuel Ratio is significantly below stoichiometric ratio 14 7 1 engine RPMs sink until they reach a point that can be supported by the available fuel This causes a momentary surge in power until the available fuel is consumed then the RPMs fall again repeating the cycle e Too much air look for an air leak in the intake tract e Not enough fuel look for fuel supply or carburetor problems 16 Troubleshooting Repairing the problem The third step in the diagnostic process is to repair the problem This step consists of 1 Form a diagnosis by using all of the information gathered from the troubleshooting that was performed 2 Physically perform the repair The fourth and hopefully final step in the troubleshooting process is the follow through This step consists of 1 Thoroughly test the repaired equipment confirming that the initial diagnosis was correct If it was wrong start the troubleshooting process over again NOTE Sometimes the engine will have multiple problems at the same time By performing one repair other issues may show up that are unrelated to the first repair 2 Delivery to customer We are not just repairing equipment we are repairing customers e noculate against recurring problem with education e g if the problem was caused by stale fuel make sure the customer is aware that fuel goes ba
15. ank purging the air from the carburetor The primer will not squirt fuel into the throat of the carburetor as dry bulb primers do 2 Remove the air filter cover 3 Remove the two screws in the air filter housing with a T 25 torx driver See Figure 5 15 Figure 5 15 4 Disconnect the fuel lines Disconnect the throttle cable from the carburetor 6 Inspect and clean the vent under the primer body for debris See Figure 5 16 7 f the fuel air mixture is lean Inspect the carburetor spacer for cracks Vent e Inspect the spacer gasket Figure 5 16 35 AC3 Series of Engines NOTE A cracked spacer or a leaking gasket between the spacer and the cylinder could result in a lean run or prevent the impulses from the engine from driving the fuel pump See Figure 5 17 8 Inspect the throttle valve assemble for debris and freedom of movement See Figure 5 18 grs Kae i barna a LM 2 LI his ZU a IM H7 r 9 Perform a needle valve pop off test by following the carburetor manufacturer s recommendations 10 Ifthere is a problem with the throttle valve assem bly check on availability and price of parts to deter mine if the carburetor should be repaired or replaced Figure 5 18 36 Disassembly of the carburetor Remove these screws Figure 5 19 Inspect for dirt or damage Figure 5 20 Figure 5 21 Fuel System And Carburetor Remove the four screws t
16. art of the fuel tank See Figure 5 7 5 Insert the two tabs into the two slots in the starter housing e Connect the fuel lines to the carburetor The blue line is the return line and the clear line is the supply line e Align the third tab on the fuel tank with the slot in the engine cover Position the engine cover and secure NOTE The three plastic thread screws go into the starter housing and the three machine threaded screws go into the engine block 6 Install the engine cover Figure 5 7 Test run the trimmer before returning it to service 30 Fuel System And Carburetor Fuel lines e The carburetor contains a pump that draws fuel through the filter and up the fuel line A hardened fuel line that has cracked or does not seal tightly to a fitting may draw air into the line without leaking fuel out e Air leaks will reduce the fuel pumps ability to supply the carburetor e Clear line fuel supply e Blue line return from primer to tank NOTE MTD started using low permeation fuel lines on some of the AC3 series of engines in 2009 In 2011 all MTD hand held engines will have the low permeation fuel line to comply with EPA guidelines The low permeation fuel lines can be identified by their black color IMPORTANT Low permeation fuel lines can NOT be serviced separately The lower halves of the fuel lines are serviced with the fuel tank and the upper halves comes with the carburetor To remove the fuel lines
17. ary winding to ground until the engine stops This prevents the need to hold the switch in the OFF position until the engine comes to a complete stop 7 Rapidly rotate the engine while watching the spark tester for sparks 8 If no sparks are seen in the spark tester test the module 21 AC3 Series of Engines Testing the module To test the module Disconnect the red 1 Remove the starter housing by following the proce dures described in Chapter 6 Starter 2 Check the air gap for the module Set it to 0 010 by following the steps described in the module section of this chapter Disconnect the red wire See Figure 4 2 4 Install the starter as described in the starter section of this chapter B Install the clutch as described in the clutch section of this chapter 6 Pull the starter rope with the spark tester still hooked up to the spark plug wire Figure 4 2 e If there is spark now test the engine stop switch and check the red wire for a short to ground e If there still in no spark hold a screwdriver against the magnets on the flywheel to feel if they are mag netic If the magnets are good replace the module If not replace the flywheel 22 Ignition Test the engine stop switch To test the engine stop switch Open the grip by removing the five screws with a T 20 torx driver 2 Disconnect the wires from the engine stop switch 3 Connect an ohm meter or continuity light
18. d over time e Make sure the customer understands the repair preventing superstitious come backs Diagnostic tests When troubleshooting an engine the diagnostic tests are done in a specific order The order is 1 Compression testing 2 Ignition testing Carburetor fuel system testing NOTE A prime test is a handy short cut It will test compression and ignition in a single step If the engine will start from a prime test the problem is in the fuel system If the engine will not start with the prime the compression and ignition tests will need to be performed 17 AC3 Series of Engines Prime test To perform a prime test 1 Prime the engine through the carburetor throat using a squirt bottle filled with clean fresh gasoline NOTE Inspect the air filter while priming the engine Look for a dirty or plugged filter that could prevent air flow or a missing filter that would indicate dirt ingestion 2 Make sure the ignition switch is in the run position 3 Attempt to start the engine 4 If the engine starts and runs long enough to burn the prime the problem is effectively isolated to the fuel system proceed to Chapter 5 The Fuel System and Carburetor 5 Check ignition system as described in Chapter 4 Ignition 6 Testing compression 18 Troubleshooting Compression testing To perform a compression test NOTE If the engine will run start the engine and let it warm up first for a better reading 1 Disco
19. duce as much heat as gasoline when burnt This results in less power for the engine The ideal fuel air mixture ratio stoichiometric ratio for an engine burning alcohol is much richer than the stoichi ometric ratio an engine running on gasoline An engine tuned to run on gasoline will not run well on alcohol The more alcohol there is in the fuel beyond the 10 that is anticipated the further the fuel air mixture will be from the correct ratio A 1096 ethanol E10 mix is acceptable for MTD engines Anything higher than that will result in perfor mance issues NOTE E20 and E85 fuels are not to be used in any MTD engines There are several alcohol test kit available commer cially See Figure 5 3 Figure 5 3 28 Figure 5 4 Fuel System And Carburetor Generally these kits involve mixing a measured 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 alcohol percentage 29 AC3 Series of Engines Fuel tank To remove replace the fuel tank 1 Remove the air filter cover 2 Disconnect the fuel lines from the carburetor See Figure 5 5 3 Hemove the engine cover by removing the six screws that hold it in place See Figure 5 6 4 The fuel tank will slide out to the rear To install the fuel tank NOTE Make sure the insulators are on the fuel Figure 5 6 tank NOTE The fuel lines are p
20. duct to the connecting rod bearing as a prelube 13 Slide the connecting rod onto the crankshaft pin Align the opening in the cylinder for cam bracket with the cam bracket See Figure 8 21 Slide th connecting rod on first 14 Apply a thread locking compound such as Loctite 266 to the cylinder head bolts Install the cylinder head bolts Torque them to 65 70 in lbs 7 8 Nm NOTE Tighten the cylinder head bolts in a X pattern See Figure 8 22 Push rods 15 Pivotthe rockers to the side and insert the push rods See Figure 8 23 16 Set the valve lash by following the procedure described in Chapter 2 Maintenance CE Figure 8 23 61 AC3 Series of Engines 17 18 19 20 21 22 23 24 25 62 Install the crankcase cover so that the two dimples are toward the cylinder NOTE On engines equipped with the electric start feature make sure the crank pin slides into one of the holes in the coupler attached to the crank case cover Install the flywheel and module by following the pro cedures described in Chapter 4 Ignition Install the muffler NOTE Apply a thread locking compound such as Loctite 266 to the muffler screws Tighten the screws to a torque of 50 55 in lbs 20 7 Nm Install the starter by following the procedures described in Chapter 6 Starter Install the carburetor spacer the carburetor and the fuel tank by following the procedures described i
21. eplace them if they are cracked Install a new filter by following the previous steps in reverse order Test run the engine before returning it to service AC3 Series of engines Valve lash To adjust the valves 10 NOTE Loose valve lash on these engines can mimic the symptoms of a lean fuel air mix ture Hemove the engine cover and spark plug following the steps described in the previous sections of this chapter Remove the valve cover using a T 25 driver See Figure 2 13 Rotate the crankshaft to bring the piston to top dead center of the compression stroke valves closed NOTE Use a probe in the spark plug hole to track the piston position NOTE The valve clearance for this engine is 0 003 006 08 15 mm for both valves Check the valve lash by inserting a feeler gauge between the rocker arm and the valve stem To adjust the valve loosen or tighten the fulcrum nut with a 8mm wrench until there is a slight drag on the feeler gauge See Figure 2 14 Inspect the valve cover gasket for damage If it is damaged or compressed replace it Heassemble the trimmer by following steps 1 and 2 in reverse order Test run the engine in a safe area before returning it to service Fulcr mnit Figure 2 13 as af Troubleshooting CHAPTER 3 TROUBLESHOOTING Definitions Troubleshooting The act of gathering information by preforming tests and direct observations Diagnosis A theory
22. filter housing See Figure 8 3 her PCV i Air filter housing screws Figure 8 3 54 Engine Assembly 8 Carefully disconnect the breather hose from the air filter housing N r i Ve jj mM E 4 L4 y i A TR Ww i h Figure 8 4 9 Disconnect the throttle cable See Figure 8 5 10 Remove the carburetor fuel tank and lines as one assembly Figure 8 5 A Press in the tabs mE 11 Remove the throttle cable by pressing in the tabs located in the slots while lifting the cable out See Figure 8 6 12 Remove the gasket between the carburetor and the spacer 4 Gasket Figure 8 6 55 AC3 Series of Engines 13 Remove the carburetor insulator block using a T 25 torx driver See Figure 8 7 14 Rotate the flywheel so that the magnets are away from the module 15 Remove the two screws that secures the ignition module to the block using a T 25 torx driver See Figure 8 8 16 Remove the module 17 Remove the flywheel by applying a sharp blow to the crankshaft while gently prying with a pry bar The flywheel will loosen then lift it off See Figure 8 9 Never strike the crankshaft A caution directly with a hammer To pre vent damage to the crankshaft use a brass punch or a piece of wood between the hammer and the crankshaft NOTE If replacing a short block exc
23. first screw See Figure 8 17 Insert the valves into the valve guides 10w30 motor oil to before putting the valve springs on 59 AC3 Series of Engines 10 11 60 Install the valve springs and keepers 6a Place the spring over the valve stem 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 and slide it into the notch on the valve stem See Figure 8 18 Install the piston rings on the piston so that the let tering on the rings are facing the top of the piston and the piston ring gaps are 180 away from each other in line with the piston pin 7a The top piston ring is convex 7b The middle ring is tapered 7c The third ring is a 3 piece oil ring Attach the piston to the connecting rod by inserting the piston pin NOTE The piston pin will only slide in from one side After sliding the piston pin in insert the plastic cap Pre lube the piston and cylinder wall with 10w30 motor oil Place the cylinder O ring on the crankcase Compress the piston rings and slide the cylinder over the piston just enough to cover the piston rings See Figure 8 20 Figure 8 18 Lettering must face up Piston skirt still showing Figure 8 20 Engine Assembly 12 Rotate the piston so that the lettering on the connect ing rod bearing faces the crank shaft journal when installed NOTE Apply a coating of Slick 506 or similar pro
24. garding locking or lubrication Whichever method is more appropriate will be used In many cases both will be used so that the manual is handy as a quick reference guide as well as a step by step procedure guide that does not require the user to hunt for information The level of assembly instructions provided will be determined by the complexity and of reassembly and by the potential for unsafe conditions to arise from mistakes made in assembly Some instructions may refer to other parts of the manual for subsidiary procedures This avoids repeating the same procedure two or three times in the manual Description The AC3 engine is used on a variety of handheld equip ment This engine has e 29cc s of displacement A cantilever crank design Pushrod activated OHV Genuine 4 cycle design not a hybrid 2 cycle 4 cycle like Stihl and Shindaiwa e Engine covers split front and back Currently there are engine models in this series of engine e AC3 e AC3 1 e AC3 2 The AC3 version has an 8 to 1 compression ratio The AC3 1 and the AC3 2 have a 9 to 1 compression ratio which increased power approximately 20 The AC3 1 and 3 2 engines are also available with electric start versions AC8 engine Figure 1 1 Identifying engines AC2 Full engine cover e 26 ccs of displacement e Engine cover surrounds the cylinder head and muffler Visible from the rear e Aplastic diagonal split crankcase sump e A di
25. gs valve and the cam gear Complete tear down A complete tear down may be done to re seal the crankcase or for failure analysis Repair of the hard parts such as the bearings crankshaft or connecting rod is likely to exceed the cost of a short block or a com plete engine Complete tear down information is included in this manual so that technicians can better under stand the parts they are likely to come in contact with such as the PVC system NOTE The repair replace choice in warrantable situations must be made using the 2 3 replacement cost rule Outside of warranty the decision is left to the dealer and the customer 53 AC3 Series of Engines Engine disassembly NOTE There are a few different paths that 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 component being removed 1 Drain the oil by following the steps described in Chapter 2 Maintenance 2 Remove the Clutch by following the procedures described in Chapter 7 Clutch and Drive Shaft 3 Remove the starter following the steps described in Chapter 6 Starter 4 Remove the three screws that hold the engine cover to the engine using a T 25 torx driver See Figure 8 1 5 Remove the three screws that secure the muffler to the cylinder head See Figure 8 2 6 Remove the air filter cover 7 Remove the two screws in the air
26. hange the crankcase and cylinder with the short block and follow the previous steps in reverse order 56 Insulator block Module screws Never hit the crank shaft with a hammer use a brass punch A D Figure 8 9 Crankcase cover Figure 8 10 Fulcrum nut Figure 8 11 Press down and slide back Grove on valve stem SINE Figure 23 0 18 Engine Assembly IMPORTANT Check parts price and availability before doing any internal engine repairs Remove the four screws that secure the crankcase cover to the block using a T 20 torx driver See Figure 8 10 NOTE On engines equipped with the electric start feature 19 20 21 22 23 24 25 26 there is a coupler in the sump cover that slides onto the crank pin See Figure 8 10 inset Remove the valve cover using a T 25 torx driver Loosen the rocker arm fulcrum nut with an 8mm wrench Pivot the rocker arms away from the valves and remove the push rods See Figure 8 11 Remove the 4 screws that fasten the cylinder to the crankcase using a T 25 torx driver Slide the cylinder off of the piston and connecting rod Press down on the valve keepers and slide the keeper off Remove the valve springs and keepers As each valve spring is removed the valve will fall freely out of the valve guide NOTE The valves and valve seats can be cleaned of car bon build up and inspected Neither the valves
27. hat hold the carburetor together See Figure 5 19 Separate the carburetor placing each part on the bench in the order they came apart Inspect the diaphragms If torn damaged or brittle install a diaphragm kit Inspect for dirt or varnish build up inside the carbure tor If there is a lot of dirt varnish in the carburetor replace it Check that the needle valve is set to the right height See the carburetor manufacturer for the proper pro cedure Inspect the metering valve and the metering valve seat for dirt and or pitting See Figure 5 20 If the seat is damaged replace the carburetor NOTE If there is a minor amount of dirt varnish in the car buretor it would be worth while to clean and rebuild the carburetor by following the procedures recommended by the carburetor manufacturer NOTE If there is a lot of dirt varnish in the carburetor replace the carburetor NOTE The alcohol in gasoline is hygroscopic meaning that it readily absorbs moisture The moisture that is trapped in the alcohol leads to corrosion of metal parts See Figure 5 21 37 AC3 Series of Engines 9 10 11 38 Remove the throttle valve assembly See Figure 5 22 The orifice can also be seen from the pump side of the throttle housing See Figure 5 23 The fuel pump in the carburetor is driven by vacuum pulses in the intake port The impulse port from the spacer lets the vacuum pulses into the pump cam ber See Fig
28. he engine was hard to start e Makes it impossible to confirm any running or hard starting symptoms by direct observation e Some inference can be made from checking other factors of the general condition of the equipment Troubleshooting Identify factors that could cause the problem This is the second step in the troubleshooting process 1 Crankshaft will not turn e Hard to pull rope steady pressure This usually indicates a mechanical bind of some sort the likely sus pects are ll A parasitic load from a jammed attachment or drive shaft Il An internal drag from a scored or seized piston e Rope jerks back This usually indicates that the piston is stopping before top dead center on the com pression stroke and is being driven back down by compression or combustion The likely suspects are l Compression that is unusually high a valve lash b a partial hydraulic lock Il Ignition timing is advanced a Improper air gap b Sheared or missing flywheel key c The wrong flywheel or module is installed on the engine e Rope will not pull at all This is usually either a quick fix or a catastrophic failure The likely suspects are A broken starter recoil easy fix ll Complete hydraulic lock easy fix Il External binding jammed attachment easy fix IV Internal binding crankshaft connecting rod or piston unrepairable o Crankshaft turns no start e Most gasoline engine diagnosis involves isolating
29. ing out of the clutch housing 9 If replacing the upper drive shaft housing remove the handle bar 10 Follow these steps in reverse order to install the upper drive shaft housing 11 Testrun the engine trimmer before returning it to service Figure 7 5 50 Clutch Removal replacement _ L pe T 5 7 r E j L PA 4 x AERE i Yu gas Qf Ac screws Figure 3 0 Clutch and Upper Drive Shaft NOTE The upper drive shaft may be left connected to the clutch housing Removing the three screws in the clutch housing will allow the clutch housing and the upper drive shaft to be removed as one 1 Remove the three screws holding the clutch housing on with a T 20 driver See Figure 7 6 2 Disconnect and remove the spark plug 3 Insert at least 18 5 M of starter rope in the spark plug hole to keep the crank shaft from rotating Keep some of the rope out so it can be removed later See Figure 7 7 driver 4 Hemove the clutch drum by removing the screw in the center of it with a T 20 driver See Figure 3 0 51 AC3 Series of Engines D 6 10 52 Remove the clutch rotor with 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 791 180918 or the newer clutch tool part number 797 00062 See Figure 7 8 NOTE New engines use a smaller clutch with
30. ith the module mounting screws 3 Remove the module by removing the two screws 4 To install the module turn the flywheel so that the magnets are away from the module 5 Install the two screws half way Do not tighten them down NOTE Make sure the black wire is on the proper mounting screw See Figure 4 6 6 Place a non magnetic 0 010 feeler gauge on the ii flywheel magnets and rotate the flywheel until the sr S Black wire magnets line up with the module Let the magnets T Vy n mounting screw draw the module against the flywheel with the feeler gauge trapped between them See Figure 4 6 NOTE The air gap range is 0 010 0 015 0 25 E 0 38mm Figure 4 6 7 Torque the module screws to 28 35 in Ibs 3 4 Nm 8 Reassemble the engine by following the above steps in reverse order Test run the engine in a safe area before returning it to service 24 Ignition Flywheel To remove the flywheel 1 Remove the spark plug by following the steps described in Chapter 2 Maintenance 2 Remove the starter by following the procedures described in Chapter 6 starter 3 Remove the flywheel by striking the crankshaft with a brass punch See Figure 4 7 NOTE It is not necessary to remove the module to remove the flywheel LN 4 Inspect the flywheel and key for any signs of dam m Lf MN age ng UR 5 Install the flywheel by following the previous steps in E reverse
31. lectrodes indicate an over rich fuel air mixture too much fuel or not enough air e Wet black deposits on the insulator and electrodes indicate the presence of oil in the combustion cham ber e Heat damaged melted electrodes cracked insulator metal transfer deposits may indicate detonation e A Spark plug that is wet with fuel indicates that fuel is present in the combustion chamber but it is not a jw w xs being ignited Spark plug removal and installation Spark plug re ad To replace a spark plug a N f Y 1 Disconnect the spark plug wire See Figure 2 4 mea Do not grab the spark plug wire YAcaurion with pliers Damage to the spark plug boot will result A damaged spark plug boot will weaken the spark of the spark plug 2 Remove the spark plug using a 5 8 spark plug socket Gap a new plug at 0 025 6 mm Install the spark plug and tighten to a torque of 100 Figure Da 110 in Ibs 11 12 Nm Follow steps 1 and 2 in reverse order Test run the trimmer in a safe area before returning it to service Air filter Maintenance A dirty air filter can reduce engine power increase fuel consumption increase CO emissions and make starting more difficult The air filter should be cleaned every 10 hours of use depending on area of use dusty areas require more frequent cleanings Air filter cover ba Press tab Figure 2 5
32. lug wire and the spark plug or use an oscilloscope and see if the spark goes away at the same time the engine dies Il Check choke operation a Black smoke b Wet plug Il Test for invisible damage to the air filter by starting the engine with the air filter removed IV Prime test immediately after engine dies If it restarts this may indicate a problem with fuel flow to the carburetor Check the gas cap fuel line fuel filter and the carburetor e Runs with low power output Look for unusual exhaust color smoke Il Unusually hot muffler may glow red a Retarded ignition b Exhaust valve opening early lash too tight Ill Mechanical bind a Aloose ignition module can drag on the flywheel or lock it up b Parasitic external load A bind in the equipment the engine is powering c Internal drag from a scored piston or similar damage IV Low compression a Check valve lash b Check compression Il Flow blockage a Exhaust blockage usually accompanied by an unusual exhaust sound NOTE Just as a throttle on the carburetor controls the engine RPMs by limiting the amount of air an engine can breathe in an exhaust blockage will limit engine performance by constricting the other end of the system 14 Troubleshooting ll The muffler itself my be blocked Ill The spark arrestor may be blocked IV The exhaust valve may not be opening fully possibly because of extremely loose valve lash set tings
33. m is 5 16 7 9mm above the top of the carburetor housing As the throttle drum rotates it also climbs up a ramp The rising throttle draws the fuel metering needle out of the orifice in the venturi of the carbure tor See Figure 5 14 e Throttle at WOT e he top of the throttle arm is 3 8 9 5mm above the top of the carburetor housing A y 4 7 Throttle closed is t 7 I2 5 16 98 k UE RU Jer Ee Figure 5 13 Figure 5 14 Fuel System And Carburetor Troubleshooting the carburetor Typically troubleshooting the carburetor is the last step in the diagnostic process The other factors are more readily identified spark vs no spark specific pressure readings on a compression gauge or a visible blockage in the muffler Carburetor function is more subtle While specific problems with a carburetor can be identified on tear down identification of the carburetor as the location of the problem is usually done by process of elimination Treat the carburetor as part of a system If damaged fuel lines or a blocked filter prevent the carburetor from get ting fuel it will never work right To troubleshoot the carburetor 1 Check the operation of the primer When the bulb is depressed and released fuel should move through the lines NOTE This is a wet bulb primer It draws fuel from the fuel tank through the pump and diaphragm chambers and pumps it back into the t
34. minently hazardous situation that if not avoided will result in death or DUELE serious injury This signal word is to be limited to the most extreme situations Disclaimer This manual is intended for use by trained professional technicians e Common sense in operation and safety is assumed e Inno event shall MTD be liable for poor text interpretation or poor execution of the procedures described in the text e If the person using this manual is uncomfortable with any procedures they encounter they should seek the help of a qualified technician or MTD Technical Support Fasteners e Most of the fasteners used on the engine are metric Some are sized in fractional inches For this reason wrench sizes are frequently identified in the text and measurements are given in U S and metric scales e Ifa fastener has a locking feature that has worn replace the fastener or apply a small amount of releas able thread locking compound such as Loctite 242 blue e Some fasteners like cotter pins are single use items that are not to be reused Other fasteners such as lock washers retaining rings and internal cotter pins hairpin clips may be reused if the do not show signs of wear or damage This manual leaves that decision to the judgement of the technician AC3 Series of engines Assembly Torque specifications may be noted in the text that covers assembly they may also be summarized in tables along with special instructions re
35. moke when running Black smoke usually heavy ll White smoke usually heavy Il Blue smoke usually light e Makes unusual sounds when running l Knock ll Click Il Chirp IV Unusual exhaust tone 11 AC3 Series of Engines 12 There are tools that the technician can use in order to define the problem such as Interview the customer e Get a good description of their complaint e If itis an intermittent problem verify what conditions aggravates the problem as best as possible e Get an accurate service history of the equipment e Find out how the customer uses and stores the equipment Direct observation e Do not take it that the customer is correct with their description of the problem Try to duplicate the prob lem e Check the general condition of the equipment visually l Cleanliness of the equipment will indicate the level of care the equipment has received I Make sure the engine and attachments are securely fastened Il The tune up factors NOTE Most hard starting and poor running conditions can be solved by preforming a tune up a Check the condition and amount of oil in the crankcase b Check the level and condition of the fuel c Check the air filter and look for signs of dirt ingestion d Check the ignition and read the spark plug e Look for obvious signs of physical damage bent blade exhaust system blockage or cooling sys tem blockage Broken starter rope e Usually means t
36. n Chapter 5 Fuel System and Carburetor Install the clutch clutch housing and drive shaft assembly by following the procedures described in Chapter 7 Clutch and Drive Shaft Install the spark plug Install the engine cover NOTE Use the machine threaded screws in the casting and the plastic threaded screws in the starter housing See Figure 8 25 Test run the engine before returning it to service Figure 16 0 tx w m am E E an a a r Ww r i F we 2a m v und di i w B xh _ c 3 d ur D E 4 t 2c Ps pate e Ir j PEL iT ae p mm VU wb UN E ce us P AacTirc ri m Ia SEE Arm s P ap n d mum MA ais p n eb A As ee acu i SS m i 2 ha a f 1s 4 M HAC Xr em a p EA s sh c ae Y Ww dw 7 e ia yea m e gd cg a AAS A as gt tr F E CN i E 3 s mi at s r un 3 k amp EE me b lt ey a r E L J W E i dm JM C eara 3 tee ear ae EST eit i r3 J ix d z Ln LIE H eee Sc il ha a i c YE sonet ce Machine thread fs MTD Products Inc Product Training and Education Department FORM NUMBER 769 02614A 07 202010
37. nnect the high tension lead from the spark plug and ground it well away from the spark plug hole 2 Remove the spark plug using a 5 8 spark plug Socket 3 Pull the starter rope several times to purge any fuel or oil from the combustion chamber NOTE Air compresses readily liquid does not Liquid in the combustion chamber will result in an artificially high compression reading Install a compression gauge in the spark plug hole Confirm that the gauge is zeroed then pull the starter rope repeatedly until the needle on the gauge Figure 3 1 stops rising See Figure 3 1 6 Read the gauge NOTE Most good quality compression gauge sets come with a 10mm adapter is needed to thread into the spark plug hole If an adapter is needed a Matco service part CT606 or a Mityvac 05505 Compres sion Tester Spark Plug Adapter can be used with most gauges NOTE When checking compression on small displacement engines use a compression gauge set with the shortest available or no hose Interpreting compression readings Most likely a stuck valve or too tight of a valve lash provided the starter rope pulls with normal effort 20 90 Valve seat damage or piston ring 1 4 3 Bar and or cylinder wear 90 125 Normal readings 6 2 8 6 Bar 2125 Excessive valve lash a partial gt 8 6 Bar hydraulic lock a bad cam or a bad automatic compression relief 19 AC3 Series of Engines 20 Ignition CHAPT
38. nor the seats can be effectively machined in the field If a valve is worn or damaged but the seat is good replace the valve If the valve seat is worn or dam aged replace the short block The cylinder is not available as a service part and it is not likely to become available at a price that makes cylinder replacement economically feasible 57 AC3 Series of Engines e 28 29 30 31 32 33 34 35 58 Slide the connecting rod off of the crank pin NOTE On engines equipped with the electric start feature the crank pin will be longer so that it can fit into the coupler in the crank case cover See Figure 8 12 Remove the plastic cap from the wrist pin bore of the piston See Figure 8 13 Withdraw the wrist pin and remove the piston NOTE If there has been metal transfer from the pis ton skirt to the cylinder wall replace the short block Immediately reinstall the wrist pin in the small end of the connecting rod to prevent damage to the bear ing The wrist pin can be held in place temporarily using a hair pin clip Carefully remove the piston rings If they are to be re used keep track of the original order and direc tion of installation Clean the piston Carefully clean any gasket and sealant residue from the mating surfaces on the crankcase and cylinder Remove the cam bracket assembly using a T 20 torx driver See Figure 8 14 IMPORTANT The crank shaft and cam gear are pres
39. oes it circulate fuel when pumped 5d If not replace the primer If compression ignition and fuel supply are OK but the engine does not run with fresh fuel repair or replace the carburetor as described in the Carburetor Repair section of this chapter Test run the engine before returning it to service 27 AC3 Series of Engines Inspecting the fuel NOTE Fuel is the maintenance item most often overlooked by consumers A lot of fuel system problems are caused by bad gasoline When inspecting the fuel e Look for water e Look for dirt e Look for discoloration e Sniff carefully to see if it smells like varnish or kerosene e Save the fuel to show to customer Look for oil in the fuel e Test the fuel for alcohol content NOTE Save a sample of the fuel collected to show the customer NOTE Customers pouring engine oil into the fuel tank seems to be a growing problem Test fuel for alcohol Fuels currently on the market contain a wide array of additives Some of these additives oxygenate the fuel Oxy genated fuel reduces emissions and is required in some parts of the United States Fuel make up varies seasonally and geographically Ethanol is the primary additive used to oxygenate fuel Ethanol in fuel creates a lot of problems for gasoline engines The biggest problem is that alcohol attracts and holds water This corrodes the metal components of the fuel system especially the carburetor Alcohol also does not pro
40. or reference use only and may not depict actual model and component parts Copyright 2010 MTD Products Inc All Rights Reserved Table of Contents Chapter 1 Ihiroductron ME 1 Professional shop manual intent llle 1 wd PP 1 PCSC MD Verse quamet bear sra qoe ta moque th qued arque eu qiia be Going hi od pardo d qus 2 pene mF 2 Identifying engines aca ae aga Ab S N Suigh a ri I rn 2 Model and serial numbets ii ope REGERE Ghaireas eae ale Shae Soe ES 4 Chapter 2 Maintenance oou o ei oe reu inqua 10 Ode Eo aerae cru a Gas Eo rco cvv E oU Sx Eo cosa uice sa P He PUE 5 Mantena e 2 neice So aad et dae aio dre d deeded ucc el sio det d dod nhu giu doin Leda 5 e M re os nore ents au a oo eee 5 SHerztareligiobun co MARTE T PLUIE 5 ser qelc T 6 AHE P rvc TTTUIT 7 Oba Kate i sax aos drea n Meee ee ho oup ue dr ui dt ee eee 8 gi Bildec PT 9 WAIVE NASI 5 neice Seater aaa ele cara Erbe ctae oath eA dca dE dE td 10 Chapter 3 Troubleshooting iuis eo diae tienes 11 I3ennilloriS Sz oves oa Ede REBELDE eS EA dE nS Ie E uS dues 11 IN OGUCHON MFCPE PPC cri m 11 Steps to troubleshooting llli 11 Identify factors that could cause the problem Ls 13 hebainng the DODIES 6 cara mei RH RP de i oit medie e ole
41. p stick that threads into the sump Figure 1 2 Introduction AC3 e 29ccs of displacement Engine covers split front and back Metal sump LIFT BM niens S EN Figure 1 3 ACA e 32ccs of displacement e Aluminum clutch housing e Extended oil fill tube that is near the carburetor e End mounted recoil starter AC5 e 25ccs of displacement Plastic clutch housing dentical to the AC4 except for the plastic clutch housing Figure 1 5 AC3 Series of engines Model and Serial Numbers The model item and serial number are on a little white sticker with bar code These are the numbers needed when ordering parts This sticker can be found on the side of the engine Serial number 9 MODEL TB590BC REV Pp mm T i TOT wil Assembled 4 ia Model number Figure 1 6 The model number is 41ADT59C711 The break down of what the number mean is as follows i mm RERO E AEE N AE A E E EEA Hand held product ms AA isses nennen nennen nennen nnns nensi DAES level Dn RU F e E IUe De mm T59 O UNIQUE Identifier c UR PACKAGING Code E 711 oOlstomer number The serial number is 1F296DZ0060 The serial number reads as follows p Die Engineering level n Month of production F June X 29 essssssssssssesessessesse senses nsesa senes nn nee entes eene
42. ready been de tensioned by breakage remove the starter handle and relieve tension from the rope 4 Cut off the starter pulley retaining ring 5 Carefully remove the pulley and starter assist accu mulator spring See Figure 6 4 Figure 6 4 44 Outer pulley Starter assist spring A kagcumulator spring ri 1 m mu am S Inner pulley Figure 6 5 Enclosed spring is e om M NU oS UE w a on the end of the spring seats in this notch Figure 6 6 NOTE NOTE NOTE Starters The recoil pulley assembly consists of three parts but it is serviced as one assembly The three parts are the inner pulley the starter assist accumula tor spring and the outer pulley See Figure 6 5 When the recoil rope is pulled it rotates the outer pulley winding up the starter assist spring When the spring accumulates enough force to over come the compression of the engine it releases its energy spinning the inner pulley and the flywheel rapidly This allows the operator to pull the recoil rope slowly yet still generate enough cranking speed to start the engine In the starter housing there is an enclosed recoil spring If the Starter rope failed to retract carefully remove the enclosed recoil spring for inspection Otherwise leave the enclosed spring in place See Figure 6 6 45 AC3 Series of Engines To assembly the starter pulley assembly 1 46 Inner pulley Starter assist sp
43. ring Install a new starter rope in the recoil pulley Aaccumulator spring assembly 1a Remove the old rope from the pulley er pulley 1b Cuta piece of 3 1 2 7 64 starter rope 43 109 cm long 1c Insert the new piece of rope through the hole A z in the starter pulley kat ms 1d Tie a half hitch knot at the end of the rope le Press the knot into the grove in the starter pul ley E Figure 6 7 Lightly lubricate the post that the recoil pulley assembly fits over with a good quality lithium base grease Figure 6 8 f Install the pulley assembly into the starter housing assembly See Figure 6 9 Install a new retaining ring Pass the free end of the starter rope through the eyelet in the starter housing Tie a slip knot in the recoil rope to keep it from get ting pulled back through the eyelet Wind the rope onto the pulley until there is enough tension to consistently draw the recoil handle up against the eyelet Figure 6 9 Starters 8 Secure the recoil handle to the rope using two half hitch knots See Figure 6 10 9 Release the slip knot 2 half hitch knots Figure 6 10 10 Install the pulley retainer using a deep socket to apply even pressure to the retainer while driving it into place See Figure 6 11 NOTE There must be 0 015 to 0 030 0 38 0 76 mm clearance between the pulley and the retainer A retainer that is too tight can bind the starter pulley Figure
44. rrestor See Figure 2 9 If it is blocked with carbon remove it It may be e Replaced e Cleaned by mechanical means e Solvent cleaned e Burned clean using a butane or propane torch D Reinstall the Spark arrestor screen By following the previous steps in reverse order NOTE Apply a thread locking compound such as Loctite 266 to the long bolt the one with a hex head it is the one closest to the other two hex head screws and torque it to 50 55 in lbs 5 7 6 2 Nm Hand tighten the short dida Figure 2 9 Fuel filer Figure 2 10 Figure 2 11 ber Figure 2 12 Kw wW Maintenance A dirty fuel filter can result in a lean run condition The fuel filter should be replaced every 25 hours of use NOTE The weighted fuel filter clunk keeps the filter sub merged in the fuel at any angle of operation The filter removes dirt and air bubbles from the fuel Running the trimmer without the filter may allow air into the fuel line creating a lean run condition at higher RPMs This will cause a catastrophic failure of the engine To replace the fuel filter 1 Bend a piece of wire to make a hook See Figure 2 10 Hemove the gas cap Stick the hook end of the wire into the fuel tank and fish out the fuel filter See Figure 2 11 Carefully remove the fuel line from the barb on the fuel filter Clean or discard the old fuel filter See Figure 2 12 Inspect the fuel lines R
45. sed into the crankcase Do not try to remove the crankshaft If the crank shaft needs to be replaced replace the whole crankcase assem bly Remove the crankcase O ring and clean the sealing surface Wrist pin plasticcap Connecting rod Figure 8 13 Cam bracket screws Crankcase Cam bracket assembly Figure 8 14 Engine Reassembly Crank shaft arm La E P E a Figure 8 15 Apply lithium grease b 2 3 Figure 8 17 1 5 NOTE Pre lube each valve stem with a couple drops of Engine Assembly Rotate the crankshaft to top dead center crank pin at the top See Figure 8 15 NOTE There are no timing marks on the crankcase Install the cam onto the cam bracket e The side of the cam with the hash marks on it faces away from the cam bracket Lubricate the cam bearing surface with a small amount of lithium grease Install the cam followers e Apply a dab of lithium grease to the cam follower pivot as a pre lube Install the cam bracket assembly aligning the timing mark with the crankcase NOTE The timing marks on the cam gear should be paral lel with the top surface of the crankcase See Figure 8 16 Apply a thread locking compound such as Loctite 266 to the cam bracket crews Tighten the screws to a torque of 30 35 in lbs 3 4 Nm When torquing the screws torque the first screw to 15 in lbs Torque the second screw all the way Finish torquing the
46. t deo eS 17 DIAGNOSICICSIS s n a ett do teo ds redo wa Pb bebe oda udo ts doa ee deed 17 HIT IOS cersesc eiae mal deg are Sed nudare ra ee wate c Ger wg 18 Compression teslllig a3 bes dh acs UU ES E a Bha a car AE Shoird WINES ERES 19 Chapter 4 Ignition iieeeeeeeeeeseeeeeseeees va pools as eme nue sn e tesa cuc osan et ea ieu c ind ve nnnm 21 Troubleshooting the Ignition System llle 21 Tesung the module s 953 SEED ae e Oe a ede pui m aba dde de es 22 Test the engine stop switch llli 23 Mee qe vas ck tt eos Seine ea eas NESES E eats ease es E 24 FIVWINCCL Tr PP 25 Chapter 5 Fuel system and carburetor esee esee 27 InspeclHg the TUB 93 pd acd ana ardeat dede C tcd NR us qe a deo RI dca eene 28 EST TCI TOF SIC OO s ir re it dU ar Bi ts eedem wp NER E QU wea qeu 28 PUSAN parissa Song Se oh ties Se TU 2 hh ee TI LL E A hr n Seat 30 PUCIIINGS 2 uai ue atiende Re bo dws ee don co de ut Be Ne sod n dto ee d 31 STU DM RENERILISUTTIS TIPO TII ew Rae a ee oe 32 Troubleshooting the carburetor seen ee ee ee ee ee ee ie ee ee ee 35 Disassembly of the carburetor nannaa cc eee ees 37 Re assembly of the carburetor 0 0 00 ccc eee 39 GarburetorinsulelOf 3 32 reei A OEE e at ew RO lew ees Soe we e nt e TA 41 II Chapter 6 Starters aucueasicutultc noche iE ih a ED uUo uve ETE E edv De Do PE TEVE ha tote 43 Recoil Starter Remo
47. tems have two things in common e A 5 sided pentagon drive coupler e A one way clutch so the engine does not drive the electric motor drill when it starts 48 Electric starter motor 49MESCBP953 Coupler Figure 6 13 Figure 6 14 Clutch and Upper Drive Shaft CHAPTER 7 CLUTCH AND UPPER DRIVE SHAFT Upper drive shaft assembly The drive shaft assembly consists of the drive shaft housing and a flexible inner drive shaft The housing and the drive shaft are serviced as one assembly Press button while pulling lower attachment To remove the upper drive shaft assembly out s 1 Loosen the knob on the ez link coupling 2 Press in the metal button while pulling the lower attachment out See Figure 7 1 Figure 7 1 3 Inspect the coupling inside the upper drive shaft housing NOTE If the coupling is worn or rounded out the upper drive shaft housing must be replaced See Figure 7 2 If rounded or worn replace the upper drive shaft housing Figure 7 2 49 AC3 Series of Engines 4 Remove the six screws in the grip with a T 20 Torx driver See Figure 7 3 screws for the grip 5 Let the grip hang off to the side NOTE There are a half dozen parts inside the grip assembly Be careful that they don t fall out of the grip 6 Remove the anti rotation screw with a T 20 driver Loosen the clamping bolt with a T 20 driver See Figure 7 5 8 Slide the upper drive shaft hous
48. the engine via any low resistance paths IX Piston rings a Confirm with leak down test b Smoke will be more pronounced under load c Repair may not make economic sense X Valve guides and intake valve stem seal a Smoke will be more pronounced on over run b Makes unusual noise when running 15 AC3 Series of Engines e Knock Check for loose mounting of engine 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 e Spark knock Advanced ignition timing Low octane fuel Over heating engine check for blocked cooling air flow Carbon build up in cylinder glowing carbon chunks pre igniting air fuel mix Xl Unusual exhaust tone a Splashy blatty wheezing or whistling e Splashy or blatty idle usually indicates a slightly rich condition e Whistling or wheezing may indicate an exhaust blockage usually slightly muffled e Backfire On over run unburned fuel igniting past exhaust valve Mixture not burning completely in combustion chamber It may be too rich or it may be a spark plug or an ignition problem e Skip Usually ignition related Run the engine with a spark tester in line between the spark plug wire and the spark plug or use an oscilloscope and see if the spark goes away at the s
49. to the switch 4 With the switch in the engine run position I the meter should indicate no continuity See Figure 4 3 NOTE Most stop switches are spring loaded to the run position when it is released This prevents no start situations caused by the customer failing to turn the switch on 5 Hold the switch in the stop position 0 The meter should indicate continuity See Figure 4 4 e Ifthe results are not as described the switch is bad and should be replaced If the switch is working properly there is a short in the wires If there is reason to suspect that the ignition timing is off Remove the starter by following the steps described in Chapter 6 Starter Make sure the module air gap is correct by follow ing the steps described in the module section of this chapter Inspect the flywheel If the flywheel is damaged replace the flywheel Remove the flywheel by following the steps in the flywheel section of this chapter Figure 4 4 e Inspect the flywheel key if damaged replace the key Inspect the key way on the crank shaft for damage if damaged short block the engine 6 Assemble and test run the engine before returning it to service 23 AC3 Series of Engines Module Remove the ignition module 1 Remove the starter by following the procedures described in Chapter 6 starter 2 Disconnect the two wires from the module See Figure 4 5 NOTE The black wire will come off w
50. ure 5 24 Make sure this port is clean and free of debris Orifice from the Venturi aa Figure 5 23 Impulse port Vent through meter d orifice to atmosphere Figure 5 24 Fuel System And Carburetor Re assembly of the carburetor 1 Place the carburetor in a clean area on the work bench 2 Inspect the throttle valve assembly for dirt and or var nish Install the throttle valve assembly 4 Ifthe needle valve seat is damaged replace the car buretor See Figure 5 25 5 There are ports in the metering valve body Inspect them for dirt and or varnish See Figure 5 26 NOTE The carburetor used in this manual is a Walbro Depending on the application the engine may have a different carburetor All carburetors have a manufacturer name cast on them It is advisable to contact the carburetor manufacturer for the proper rebuild procedure 6 Inspect the primer pump body for dirt and or varnish See Figure 5 27 Figure 5 27 39 AC3 Series of Engines T Clean the metering orifice with carburetor cleaner Do not insert anything into the A caution orifice to clean it That will dam age the orifice resulting in the carburetor being unrepairable See Figure 5 28 8 Set the needle valve lever as per the carburetor manufacturer s recommendations using a W tool See Figure 5 29 9 Follow steps in reverse order to rebuild the carbure tor 10 Perform a needle valve pop off test by follo
51. us ing 2 Remove the screws that hold the engine cover to the starter housing See Figure 6 1 3 Remove the four screws in the front of the starter housing See Figure 6 2 4 Slide the starter housing off of the engine Install the starter assembly by following the previous steps in reverse order 6 Test run the engine before returning it to service 43 AC3 Series of Engines The starter rope pulley and springs The AC3 series of engines are equipped with the Assist Spring Technology AST starters The AST system allows the customer to pull the recoil rope at any pace they please yet still generate enough force to start the engine The system is simple and adds a grand total of two parts to the trimmer a recoil pulley assembly which includes an accumulator spring As the rope is pulled the accumulator spring winds up When the force on the accumulator spring over comes the engine compression it releases it s accumulated energy spinning the crankshaft rapidly To service the rope pulley and springs Eye protection should be worn A caurion when working on these starters There are 2 clock springs inside that can come out of the starters at a great velocity 1 Remove the starter housing assembly by following the procedures described in the previous section of this chapter 2 Remove the three screws securing the pressure plate to the housing using a T 20 torx driver 3 If the recoil rope has not al
52. val see ee ee ee ee ee ee ee eren 43 The starter rope pulley and springs llle 44 EICCING starter SVSIOITI a o ae eia RD Do es e t po CR S e E 48 Chapter 7 Clutch and Upper Drive Shaft 49 Upper drive shaft assembly llllllllel nh 49 Clutch Removal replacement l l llle 51 Chapter 8 Engine assembly 5 9 6e aede iuo Eus ie ec idu in ios av CUR ia sq a decus a vedeu eiu nnmnnn nn 53 Engine GISASSEMDIY ai seirce cn rct C Eee dese od xn Sedibus 54 Engine Reassembly 2 000 cece eee rn 59 Introduction CHAPTER 1 INTRODUCTION Professional Shop Manual intent This Manual is intended to provide service dealers with an introduction to the mechanical aspects of the AC3 series of 4 cycle engines Disclaimer The information contained in this manual is correct at the time of writing Both the product and the infor mation about the product are subject to change without notice About the text format NOTE is used to point out information that is relevant to the procedure but does not fit as a step in the proce dure e Bullet points indicate sub steps or points Caution is used to point out potential danger to the technician operator bystanders or sur rounding property Warning indicates a potentially hazardous situation that if not avoided could result in death or serious injury A Danger indicates an im
53. wing the carburetor manufacturer s recommendations 11 Install the carburetor on the engine 12 Testrun the engine before returning it to service 40 Orifice from t e pump side Figure 5 28 E a 9 m ge eedle valve lever Z TU dyes pr im E H Figure 5 29 Carburetor insulator 7 f Press in the tabs L ro Gasket Figure 5 31 Fuel System And Carburetor NOTE A cracked spacer or a leaking gasket between the spacer and the cylinder could result in a lean run or prevent the impulses from the engine from driving the fuel pump To remove replace the carburetor insulator 1 ta Remove the carburetor by following the procedures described in the carburetor section of this chapter Remove the throttle cable by pressing in the tabs located in the slots while lifting the cable out See Figure 5 30 Remove the gasket between the carburetor and the spacer Remove the carburetor insulator block using a T 25 torx driver See Figure 5 31 Install the insulator by following the previous steps in reverse order Test run the engine before returning it to service 41 AC3 Series of Engines 42 Recoil Starter Removal Figure 6 2 Starters CHAPTER 6 STARTERS To remove the starter assembly 1 Remove the clutch following the steps described in the section on clutch removal NOTE The drive shaft will come off with the clutch ho
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