For Parts Call 606-678-9623 or 606-561-4983 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.
For Parts Call 606-678-9623 or 606-561-4983 www.mymowerparts.
For Parts Call 606-678-9623 or 606-561-4983 Table of Contents Chapter 1: Introduction ............................................................................................1 Professional shop manual intent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Fasteners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
For Parts Call 606-678-9623 or 606-561-4983 Chapter 6: Starters .................................................................................................43 Recoil Starter Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 The starter rope, pulley and springs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Electric starter system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
For Parts Call 606-678-9623 or 606-561-4983 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 information about the product are subject to change without notice.
For Parts Call 606-678-9623 or 606-561-4983 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 regarding 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.
For Parts Call 606-678-9623 or 606-561-4983 Introduction AC3 • 29cc’s of displacement. Engine cover splits front to back • Engine covers split front and back. • Metal sump Figure 1.3 AC4 • 32 cc’s of displacement. • Aluminum clutch housing. Aluminum clutch housing • Extended oil fill tube that is near the carburetor. • End mounted recoil starter. oil fill tube Figure 1.4 AC5 • 25 cc’s of displacement. Plastic clutch housing • Identical to the AC4 except for the plastic clutch housing. Figure 1.
For Parts Call 606-678-9623 or 606-561-4983 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 Model number Figure 1.6 The model number is 41ADT59C711. The break down of what the number mean is as follows: 41 ............................................................................................
For Parts Call 606-678-9623 or 606-561-4983 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.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of engines Spark plugs The spark plug used in the 32cc trimmer is a Champion 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 apparent wear / damage occurs, replace the spark plug before operating failure (no start) occurs. Cleaning the spark plug: NOTE: We do not recommend cleaning spark plugs.
For Parts Call 606-678-9623 or 606-561-4983 Maintenance Air filter 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). To clean/replace the air filter: Air filter cover 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. 2.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of engines Spark arrestor Engine cover 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. Typical blockages include insect nests built during the dormant season. Screws NOTE: A spark arrestor is required by law when trimmer are used near “unimproved” land. To check/clean the spark arrestor: 1.
For Parts Call 606-678-9623 or 606-561-4983 Maintenance Fuel filer 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 submerged 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.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of engines Valve lash To adjust the valves: NOTE: Loose valve lash on these engines can mimic the symptoms of a lean fuel/air mixture. 1. Remove the engine cover and spark plug, following the steps described in the previous sections of this chapter. 2. Remove the valve cover using a T-25 driver. See Figure 2.13. 3. Rotate the crankshaft to bring the piston to top dead center of the compression stroke (valves closed).
For Parts Call 606-678-9623 or 606-561-4983 Troubleshooting CHAPTER 3: TROUBLESHOOTING Definitions Troubleshooting - The act of gathering information by preforming tests and direct observations. Diagnosis - A theory 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 understanding of how the engine works.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines There are tools that the technician can use in order to define the problem, such as: 1. 2. Interview the customer. • Get a good description of their complaint. • If it is an intermittent problem, verify what conditions aggravates the problem as best as possible. • Get an accurate service history of the equipment. • Find out how the customer uses and stores the equipment.
For Parts Call 606-678-9623 or 606-561-4983 Troubleshooting Identify factors that could cause the problem This is the second step in the troubleshooting process. 1. Crankshaft will not turn. • • Hard to pull rope, steady pressure - This usually indicates a mechanical bind of some sort. the likely suspects are: II. A parasitic load from a jammed attachment or drive shaft. III. An internal drag from a scored or seized piston.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines • Compression or ignition problem I. Check the engine stop and/or ignition switch. II. Test the ignition system using a proper tester. III. 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 • Starts, then dies I.
For Parts Call 606-678-9623 or 606-561-4983 Troubleshooting II. The muffler itself my be blocked. III. The spark arrestor may be blocked. IV. The exhaust valve may not be opening fully, possibly because of extremely loose valve lash settings. V. The exhaust valve seat may have come loose in the cylinder head. This may cause a loss of compression, 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.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines • 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.
For Parts Call 606-678-9623 or 606-561-4983 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.
For Parts Call 606-678-9623 or 606-561-4983 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.
For Parts Call 606-678-9623 or 606-561-4983 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. Gauge is zeroed 1. Disconnect 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.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 20 www.mymowerparts.
For Parts Call 606-678-9623 or 606-561-4983 Ignition CHAPTER 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. Spark tester 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. 3.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines Testing the module To test the module: 1. Remove the starter housing by following the procedures 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. 3. Disconnect the red wire. See Figure 4.2. 4. Install the starter as described in the starter section of this chapter. 5.
For Parts Call 606-678-9623 or 606-561-4983 Ignition Test the engine stop switch To test the engine stop switch: Switch in the engine run position 1. 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 to the switch. 4. With the switch in the engine run position (l), the meter should indicate no continuity. See Figure 4.3.
For Parts Call 606-678-9623 or 606-561-4983 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. Module NOTE: The black wire will come off with the module mounting screws. 3. Remove the module by removing the two screws. Flywheel Figure 4.5 4. To install the module, turn the flywheel so that the magnets are away from the module. 5.
For Parts Call 606-678-9623 or 606-561-4983 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. Gently pry while striking 4. Inspect the flywheel and key for any signs of damage. 5.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 26 www.mymowerparts.
For Parts Call 606-678-9623 or 606-561-4983 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: • Fuel tank • Fuel lines • Fuel filter • Carburetor NOTE: When working on the fuel systems, look at the whole system. A problem will rarely be isolated to one component. To troubleshooting the fuel system: 1.
For Parts Call 606-678-9623 or 606-561-4983 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: • Look for water. • Look for dirt. • Look for discoloration. • Sniff carefully to see if it smells like varnish or kerosene. • Save the fuel to show to customer. • Look for oil in the fuel. • Test the fuel for alcohol content.
For Parts Call 606-678-9623 or 606-561-4983 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. Figure 5.4 29 www.mymowerparts.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines Fuel tank Disconnect the fuel lines To remove/replace the fuel tank: 1. Remove the air filter cover. 2. Disconnect the fuel lines from the carburetor. See Figure 5.5. Figure 5.5 3. Remove 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. Six screws Engine cover removed To install the fuel tank: Figure 5.
For Parts Call 606-678-9623 or 606-561-4983 Fuel System And Carburetor Fuel lines • 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. • Air leaks will reduce the fuel pumps ability to supply the carburetor.
For Parts Call 606-678-9623 or 606-561-4983 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: • It has a rotary throttle valve, not a butterfly valve. • A fuel metering needle in the carburetor venturi rises out of an orifice in direct proportion to the movement of the throttle valve.
For Parts Call 606-678-9623 or 606-561-4983 Fuel System And Carburetor Throttle opening 2. In the second frame, the throttle has been rotated slightly (tip-in), admitting some air through the rotary valve. See Figure 5.10. 3. At mid-range throttle, the throttle is rotated so that the bore is nearly aligned with the throat of the carburetor. See Figure 5.11. 4. At wide-open throttle (WOT), the throttle is rotated so that the bore is in-line with the throat of the carburetor. See Figure 5.12. 5.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines Throttle closed 6. In idle position, the throttle is closed, the hole through the drum is cross-wise to the throat of carburetor 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 carburetor housing. 5/16” Figure 5.13 Throttle open 7. As the throttle drum rotates, it also climbs-up a ramp.
For Parts Call 606-678-9623 or 606-561-4983 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.
For Parts Call 606-678-9623 or 606-561-4983 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. Spacer Figure 5.17 8. Inspect the throttle valve assemble for debris and freedom of movement. See Figure 5.18. 9. Perform a needle valve pop off test by following the carburetor manufacturer’s recommendations. 10.
For Parts Call 606-678-9623 or 606-561-4983 Fuel System And Carburetor Disassembly of the carburetor 1. Remove the four screws 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, damaged or brittle install a diaphragm kit. 4. Inspect for dirt or varnish build up inside the carburetor. If there is a lot of dirt/varnish in the carburetor, replace it. 5.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 8. Remove the throttle valve assembly. See Figure 5.22. Orifice from the Venturi side Figure 5.22 9. The orifice can also be seen from the pump side of the throttle housing. See Figure 5.23. Orifice Pump spring Figure 5.23 10. 11. 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 camber. See Figure 5.24.
For Parts Call 606-678-9623 or 606-561-4983 Fuel System And Carburetor Re-assembly of the carburetor Needle valve seat 1. Place the carburetor in a clean area on the work bench. 2. Inspect the throttle valve assembly for dirt and/or varnish. 3. Install the throttle valve assembly 4. If the needle valve seat is damaged, replace the carburetor. See Figure 5.25. 5. There are ports in the metering valve body. Inspect them for dirt and/or varnish. See Figure 5.26. Figure 5.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 7. Clean the metering orifice with carburetor cleaner. Do not insert anything into the orifice to clean it. That will damage the orifice resulting in the carburetor being unrepairable. See Figure 5.28. ! CAUTION Orifice from the pump side 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 carburetor. 10.
For Parts Call 606-678-9623 or 606-561-4983 Fuel System And Carburetor Carburetor insulator Press in the tabs 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: Gasket 1. Remove the carburetor by following the procedures described in the carburetor section of this chapter. 2.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 42 www.mymowerparts.
For Parts Call 606-678-9623 or 606-561-4983 Starters CHAPTER 6: STARTERS Recoil Starter Removal To remove the starter assembly: Remove these screws 1. Remove the clutch following the steps described in the section on clutch removal. NOTE: The drive shaft will come off with the clutch housing. 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.
For Parts Call 606-678-9623 or 606-561-4983 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.
For Parts Call 606-678-9623 or 606-561-4983 Starters NOTE: 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 (accumulator) spring, and the outer pulley. See Figure 6.5. NOTE: When the recoil rope is pulled, it rotates the outer pulley, winding-up the starter assist spring.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines To assembly the starter pulley assembly: 1. Install a new starter rope in the recoil pulley assembly. 1a. Remove the old rope from the pulley. 1b. Cut a piece of #3 1/2 (7/64”) starter rope 43” (109 cm) long. 1c. Insert the new piece of rope through the hole in the starter pulley. 1d. Tie a half hitch knot at the end of the rope. 1e. Press the knot into the grove in the starter pulley. Figure 6.7 2.
For Parts Call 606-678-9623 or 606-561-4983 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. Deep well socket NOTE: There must be 0.015” to 0.030” (0.38 - 0.76 mm) clearance between the pulley and the retainer.
For Parts Call 606-678-9623 or 606-561-4983 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. Electric starter motor 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.
For Parts Call 606-678-9623 or 606-561-4983 Clutch and Upper Drive Shaft CHAPTER 7: CLUTCH AND UPPER DRIVE SHAFT Upper drive shaft assembly Press button while pulling lower attachment out 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. To remove the upper drive shaft assembly: 1. Loosen the knob on the ez-link coupling. 2. Press in the metal button while pulling the lower attachment out.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 4. Remove the six screws in the grip with a T-20 Torx® driver. See Figure 7.3. 5. Let the grip hang off to the side. Screws for the grip Figure 7.3 NOTE: There are a half dozen parts inside the grip assembly. Be careful that they don’t fall out of the grip. Trigger release Cable Trigger Trigger spring Figure 7.4 6. Remove the anti-rotation screw with a T-20 driver. 7. Loosen the clamping bolt with a T-20 driver. See Figure 7.
For Parts Call 606-678-9623 or 606-561-4983 Clutch and Upper Drive Shaft Clutch Removal/replacement 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. Clutch housing screws 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”(.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 5. Remove the clutch rotor with a clutch removal tool. Part number 791-180918 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 79700062. See Figure 7.8. NOTE: New engines use a smaller clutch, with roughly a 1 15/16” diameter. They can be removed by using clutch tool number 79700070. Figure 7.8 6.
For Parts Call 606-678-9623 or 606-561-4983 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: 2.
For Parts Call 606-678-9623 or 606-561-4983 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 components 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.
For Parts Call 606-678-9623 or 606-561-4983 Engine Assembly 8. Carefully disconnect the breather hose from the air filter housing. 9. Disconnect the throttle cable. See Figure 8.5. Carefully remove the breather/PCV hose Figure 8.4 10. Remove the carburetor, fuel tank and lines as one assembly. Throttle cable Figure 8.5 Press in the tabs 11. Remove the throttle cable by pressing in the tabs located in the slots while lifting the cable out. See Figure 8.6. 12.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 13. Remove the carburetor insulator block using a T-25 torx driver. See Figure 8.7. Insulator block 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. Module screws Figure 8.8 17.
For Parts Call 606-678-9623 or 606-561-4983 Engine Assembly IMPORTANT: Check parts price and availability before doing any internal engine repairs. 18. 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, there is a coupler in the sump cover that slides onto the crank pin. See Figure 8.10. inset. Crankcase cover Figure 8.10 Fulcrum nut 19. Remove the valve cover using a T-25 torx driver.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 27. 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. Crank pin Figure 8.12 28. Remove the plastic cap from the wrist pin bore of the piston. See Figure 8.13. 29. Withdraw the wrist pin and remove the piston.
For Parts Call 606-678-9623 or 606-561-4983 Engine Assembly Engine Reassembly 1. 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. Crank pin Crank shaft arm Figure 8.15 Apply lithium grease 2. Timing mark Install the cam onto the cam bracket. • 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.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 6. 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. Keeper Figure 8.18 7. 8.
For Parts Call 606-678-9623 or 606-561-4983 Engine Assembly 12. Rotate the piston so that the lettering on the connecting rod bearing faces the crank shaft journal when installed. NOTE: Apply a coating of Slick 50® or similar product 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 the connecting rod on first Figure 8.21 14.
For Parts Call 606-678-9623 or 606-561-4983 AC3 Series of Engines 17. Install the crankcase cover so that the two dimples are toward the cylinder. Dimples toward the top Figure 16.0 Crank pin slides into hole Coupler 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. 18. Install the flywheel and module by following the procedures described in Chapter 4: Ignition. 19. Install the muffler.
For Parts Call 606-678-9623 or 606-561-4983 www.mymowerparts.
For Parts Call 606-678-9623 or 606-561-4983 MTD Products Inc - Product Training and Education Department FORM NUMBER - 769-02614A 07/202010 www.mymowerparts.