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Professional Shop Manual - MTD: Support Center

1. bA 4 3 of ar en ti Ch in 0 1 EEA EET Figure 11 9 81 Engine Overspeed The MTD engine is designed for a maximum speed of 3600 rom When the governor is unable to control the engine rom the engine can accelerate past the safe maximum speed When an engine runs beyond its designed speed a few things happen 1 As the piston moves up and down in the cylinder it builds momentum The higher the rom s the more momentum produced by the pistons As the momentum builds the connecting rods will start to stretch When the connecting rods stretch they get weaker Generally speaking this is at the narrowest part of the connecting rods On most engine that would be about an inch below the wrist pin but on the MTD engine it is at the wrist pin The force on the connecting rod is greatest when the piston transitions from the upward stroke to the downward stroke Because of this most overspeed connecting rod failures will occur with the piston at top dead center When a connecting rod fails the piston stops moving but the crankshaft is still moving This will allow the broken connecting rod to get knocked around in the cylinder causing more damage to it Usually the connecting rod will be in several pieces after it breaks making it hard to find where the first failure was 2 All engines have vibrations and are designed to handle those vibrations but in over
2. powers Remove the governor arm by following the previ ously described steps Remove the flywheel by following the steps described in Chapter 7 Ignition Systems Remove the sump and crankshaft from the engine by following the steps described in Chap ter 10 Cam Crankshaft and Piston Remove the hairpin clip from the governor shaft See Figure 4 27 hairpin clip Figure 4 27 Slide the governor arm out of the engine block from the inside of the engine See Figure 4 28 Figure 4 28 Check the movement of the fly weights and cap on the governor gear Install the shaft by following the above steps in reverse order Install the engine on the equipment it powers Test run the engine and adjust the top no load engine rpms by following the steps described in the carburetor section of this chapter Governor cup and the governor gear To remove or replace the governor gear and cup 1 Remove the engine from the unit 2 Remove the governor arm by following the previ ously described steps 3 Remove the flywheel by following the steps described in Chapter 7 Ignition Systems 4 Remove the sump and crankshaft by following the steps described in Chapter 10 Cam Crank shaft and Piston 5 Drive out the governor gear shaft using a 5 32 pin punch See Figure 4 29 30vernor 0 ay i Figure 4 29 NOTE If the engine is equipped with an altena tor remov
3. Hook the spark plug wire from the clip in the car buretor insulator Install the Heatbox snow engines and intake elbow by following the steps described in Chap ter 3 Air Intake Systems Connect the spark plug wire to the spark plug Test run the engine before returning to service 55 Flywheel The flywheel holds the magnets that induce a field in the module which in turn produces a spark But it also controls the timing of the ignition system by controlling when the magnets are introduced to the module A sheared flywheel key will throw off the ignition timing They are uncommon on the MID engine If one is found check for a bent crankshaft To Remove and or inspect the flywheel and key 1 Remove the recoil assembly by following the steps describe in Chapter 6 Starter and Charg ing System Remove the blower housing Loosen the flywheel nut until it is a couple of threads past the end of the crankshaft using a 19mm wrench Remove the flywheel by applying a sharp blow to the crankshaft using a brass drift punch and a hammer while gently prying with a prybar The flywheel will loosen then lift it off NOTE Never strike the crankshaft directly with a hammer To prevent damage to the crankshaft use a brass drift punch or a piece of wood between the hammer and the crankshaft See Figure 7 15 l 1 rg Brags Drit a gt punch Figure 7 15 CAUTION If the flywheel shows any signs
4. ae 3 x Engine md del number Figure 3 17 3 24 Unhook the spark plug wire from the clip molded into the insulator plate See Figure 3 18 S i Spark 4 wire 2 i 2 br Clip pP A Figure 3 18 AIR INTAKE SYSTEMS NOTE An insulator block separates the carbu retor from the cylinder head There is a gasket on each side of the insulator See Figure 3 19 6 2 EN Gaskets x Insulator plate ha MP j i i 6 F Es Figure 3 19 NOTE The gaskets are different and there is an orientation to the insulator The gasket with the shaped opening goes between the insulator and the cylinder head matching the shape of the gasket to the shape of the intake port The bowl vent channel in the insulator faces the carburetor with the exit toward the bottom There is a small hole in the insulator to carbure tor gasket The hole should be aligned to allow passage of air through the bowl vent channel to the throttle side bowl vent in the carburetor body Install the insulator by following the above steps in reverse order NOTE Tighten the carburetor mounting nuts to a torque of 80 106 in lbs 9 12 Nm Test run the engine before returning to service 25 THE FUEL SYSTEM AND GOVERNOR CHAPTER 4 THE FUEL SYSTEM AND GOVERNOR The function of the fuel system is to store mix the fuel with air and deliver it to t
5. Spark arrestor SS Figure 8 1 The spark arrestor needs to be cleaned or replaced 1 Remove the four screws that retain the muffler shield using a 8mm wrench and lift it off of the engine See Figure 8 2 genre i A Remove these 4 gt 80605 Figure 8 2 2 Remove the spark arrestor retaining screw using a 2 phillips screwdriver See Figure 8 1 3 Pry the spark arrestor out of the muffler See Figure 8 3 i FTS 4 Figure 8 3 EXHAUST 4 The spark arrestor can be Replaced Cleaned by mechanical means Solvent cleaned Burned clean using a butane or propane torch 5 Install the spark arrestor by following steps 1 3 in reverse order To remove replace the muffler 1 Remove the two muffler nuts using a 13mm wrench See Figure 8 4 sate a lin Ne Gi ee D Figure 8 4 2 Lift the muffler off of the engine 3 Clean all of the gasket material off of the cylinder head and the muffler if reusing the muffler See Figure 8 5 Remove all gasket material Figure 8 5 NOTE The MTD engine uses a graphite exhaust gasket It is not reusable and must be replaced every time the muffler nuts are loos ened NOTE The graphite exhaust gasket transfers heat from the cylinder head to the muffler The heat transfer helps to keep the engine operating temperature under control Do not substitute an exhaust gasket made from ano
6. the tool is drawn to the magnet the rotor is good 49 IGNITION SYSTEM CHAPTER 7 IGNITION SYSTEM 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 The steps in troubleshooting the ignition system are 1 Examine the spark plug s by following the steps described in the spark plug section of this chap ter NOTE It is convenient to check the compres sion when the spark plug is removed for exami nation Connect a spark tester between the spark plug wire and a good ground point on the engine See Figure 7 1 A a 1 oe Figure 7 1 50 CAUTION Never remove the spark plug and hold it against the cylinder head 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 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 Place the stop switch in the run position Insert key for snow engines and move throttle to the full throttle position Pull the starter rope If sparks can be seen in the spark tester the ignition system is working NOTE If there are sparks present in the spark tester install a known good spark plug an
7. 0 F 20 0 20 10 60 20 30 40 40 80 100 Snow engines 0 20 40 30 20 10 0 Figure 5 1 F 40 20 CC 39 Oil dip stick To check the oil level NOTE Be sure to check the engine on a level surface with the engine stopped 1 Remove the oil filler cap and wipe the dipstick clean 2 Insert the dipstick into the engine block but do not screw it in See Figure 5 2 Dip stick 2 Figure 5 2 3 Pull the dip stick out again and read the oil level See Figure 5 3 upper limit ER lower limit eet E gt 5 E fob 5 6 oe oft 5 5 8 ee 4 3 gt 8 8 5 5 5 5 ree he 5 0 5 5 5 5 8 4 te b t 5 ibua ba ddyd boa ae 2 8 8 6 bon ee gt gt ee ee Figure 5 3 4 the level is low slowly add oil to the upper limit on the dipstick LUBRICATION Dip stick tube removal 4 Pull the dip stick tube out of the engine block To remove replace the dip stick tube 1 Remove the dip stick 2 Remove the two screws securing the dip stick cover in place using a 2 phillips screw driver See Figure 5 4 T An 1 Remove these KP screws Fig
8. 1 Clean the cylinder NOTE Use an old piece of microfiche or a seal protector to protect the oil seal lip while inserting the crank shaft See Figure 10 17 1a Remove all gasket material from all mating surfaces 1b Clean the cylinder and crank case cover 2 Oil seals 2a Install a new oil seal in the cylinder block 2b Install a new seal in the crank case cover See Figure 10 16 NOTE Use a Troy Bilt tiller seal service tool TWX 4006 to install the sump oil seal Figure 10 17 4 Install the piston by NOTE If the piston and connecting rod were separated Reconnect them so that the arrow on the piston head points to the oil hole in the con necting rod See Figure 10 18 Figure 10 16 3 Insert the crank shaft into the cylinder block bearing NOTE Pre lube the crank shaft with clean 10W 30 motor oil Figure 10 18 4a Compress the piston rings using a piston ring compressor 4b Pre lube the cylinder wall with clean 10W 30 motor oil 73 CRANKSHAFT PISTON AND CONNECTING ROD 4c Slide the connecting rod and piston into the cylinder NOTE The arrow on the piston must point towards the push rod cavity See Figure 10 19 r o Ti a arrow Figure 10 19 4d Tap the piston through the ring compressor into the cylinder using a wooden hammer handle See Figure 10 20 NOTE Make sure the crankpin is at BDC bot tom dead center to prevent damage from the connect
9. Install the rocker arms Adjust the valve lash by following the steps described in Chapter 1 Introduction Install the carburetor and air cleaner using new gaskets by following the steps described in Chapter 3 Air Intake Install the muffler by following described in Chapter 8 Exhaust the steps Test run the equipment in a safe area before returning it to service Check all safety features CYLINDER HEAD Valves Valves and valve parts like springs and keepers are not available as service parts The valves and valve seats can be serviced by grinding and lapping or the head can be replaced Depending on local machine and labor costs it is probably more economical to replace the cylinder head versus servicing the valves To service the valves NOTE Servicing valves during the warranty period will void the warranty Warranty valve repairs are to be accomplished by replacing the cylinder head 1 Remove the cylinder head by following the steps described earlier in this chapter 2 Remove the rocker arms by 2a Remove the jam nuts 2b Remove the fulcrum nut 2c Slide the rocker arms off of the rocker studs 3 Remove the valve retainers by applying light fin ger pressure and moving the retainer so that the valve stem passes through the large part of the keyhole opening in the retainer See Figure 9 10 Figure 9 10 NOTE The exhaust valve has a secondary keeper on it Press down on the valve ke
10. metal transfer deposits may indicate detonation A spark plug that is wet with fuel indicates that fuel is present in the combustion chamber but it is not being ignited Chapter 1 INTRODUCTION Air filters Generally air filters come in two different types a pleated paper element or a foam plastic sometimes a combination of the two will be used like the one on the MTD engine See Figure 1 2 Paice iter a ilter aoe l Paper Pleated Element Foam Pre Filter Figure 1 2 1 The main function of the air filter is to trap air borne particles before they enter the engine Dirt ingestion can cause serious internal engine damage NOTE Snow engines do not have air filters because the snow will plug up the filter Gener ally the air is clean enough that there is minimal risk of dirt ingestion when the ground is covered with snow 2 Air filters used on the MTD engine are designed to prevent particles larger than 5 microns from passing through into the engine The filter should be checked on a regular basis possibly several times in a season Typically an air filter should be changed before every season a foam air pre cleaner is dirty but not in bad of condition it can be cleaned and reused The paper pleated filters can be shaken or lightly tapped to free the debris from the filter NOTE Never use compressed air on a paper air filter Compressed air will remove the tiny fibers that catch
11. 2 is recommended to use compressed air to Figure 1 11 blow all of the debris off of the engine NOTE A pressure washer may be used to clean 11 Use a 10mm wrench to loosen the jam nut and outdoor power equipment but only after the unit nut See Figure 1 11 NOTE Debris can build up under the deck and Tighten the rocker arm fulcrum nut to close up cause the engine to operate under an unin the clearance between the end of the valve stem tended load and the contact point on the rocker arm Loosen the rocker arm fulcrum nut to open up the clearance between the end of the valve stem and the contact point on the rocker arm 12 Hold the fulcrum nut with a 14mm wrench tighten the jam nut to a torque of 79 7 106 2 in lb 9 12 Nm using a 10mm wrench INTRODUCTION General torque specifications size M4 M5 M6 M8 size M10 M12 M14 Grade 4 8 in lbs 11 22 38 93 ft lbs 16 27 43 Nm 1 2 2 5 4 3 10 5 Nm 21 7 36 6 58 5 8 in los 15 28 50 0 ft lbs 20 35 55 Nm 1 7 3 2 5 7 13 6 Nm 27 1 47 5 76 8 8 in lbs 26 51 88 216 ft lbs 35 61 97 Nm 2 9 58 99 24 4 Nm 47 5 82 7 132 10 9 in los 36 72 124 300 ft lbs 49 86 136 Nm 4 1 8 1 14 33 9 Nm 66 4 116 6 184 12 9 in los 44 86 146 360 ft lbs 60 103 162 Nm 5 9 7 16 5 7 Nm 81 4 139 7 220 Noncritical Feten ih in lbs 18 35 60 150 ft lbs 25 45 70 Aluminum Nm 2 4 6 8 17 Nm 33 9 61 95 Maintenance Chart Maintenance item Each use Each 25 hrs use Each 50 hrs use Check ai
12. Cut a piece of 4 recoil rope 7 2 1 meters long 4 Heat fuse the ends of the starter rope and tie a double half hitch in one end 5 The rope may be easily installed from the out side in Pull the rope tight to seat the knot firmly in the recess in the back of the pulley See Figure 6 4 Figure 6 4 NOTE It may be necessary to wind the pulley clockwise to line up the hole in the pulley to the hole in the starter housing If so use a punch or screwdriver to block the pulley preventing it from rewinding See Figure 6 4 6 Wind the spring tightly Then relieve it minimum 1 full turn counting when the pulley knot aligns with the rope bushing in the housing This usu ally results in about 1 5 1 75 complete turns of relief and block it with a punch or screwdriver to keep it from rewinding 7 Install the handle and handle insert on the loose end of the rope again using a double half hitch See Figure 6 5 Figure 6 5 8 Remove the blocking tool and at a controlled rate let the rope rewind into the starter 9 Give the starter a couple of test pulls to verify the right amount of tension on the starter rope NOTE If starter rope tension needs to be adjusted hook the rope into the notch in the pul ley and wind the pulley a couple of turns to add tension See Figure 6 6 Rope return tension maybe increased by an ig the Re and ly A counter i lO Rute x a Figure 6 6 10 Install the st
13. 10 6 WR 1 3 i 1 Remove the crankshaft Figure 10 6 The internal components of the MTD engine are not available as service parts The intent of this chapter is to provide the technician the procedures to examine an engine and to provide the specification to determine if an engine is worn out All of the specifications are listed in a chart at the end of the chapter Crank shaft inspection 1 Inspect the crank shaft journals for galling scor ing pitting or any other form of damage 2 Measure the journals at the bearing contact points using a vernier caliper or a micrometer See Figure 10 7 NOTE Micrometers are the preferred and most accurate way to measure the journals Figure 10 7 3 Inspect the crankpin for galling scoring pitting or any other form of damage NOTE This is mostly a visual check Measure ment is to determine if it is within the specifica tions after it is found to be OK visually 69 CRANKSHAFT PISTON AND CONNECTING ROD 4 Measure the crankpin using a vernier caliper or a micrometer See Figure 10 8 Figure 10 8 5 Check the crank shaft for straightness by mea suring the run out The crank shaft run out can be check by 5a Place the crank shaft on a pair of matched V blocks or in the engine block with the sump installed 5b Place a dial indicator at a smooth point at either end of the crank shaft 5c Sl
14. a A A O aa aa metering plug for the pilot and transition ports Remove the screw to reach the plug See Figure 4 20 Welch plug Fuel feed leg on central column for pilot and transition aL shot plug in feed bore Fuel drawn from the central column via the long fuel feed leg is metered by the brass orifice in the tip of the metering plug Fuel port to central column l Air drawn from the emulsion air port is metered Figure 4 20 by the size of the brass orifice at the entrance to the port The fuel and air that feed the pilot and transition ports are mixed at the metering plug The metering plug creates a small venturi The pressure drop of the air passing through the metering plug draws the fuel into the passage to the pilot and transition ports in an emulsified mixture 34 THE FUEL SYSTEM AND GOVERNOR 10 11 12 13 NOTE The pilot screw regulates how much of this pre mixed fuel air emulsion is allowed to enter the throat of the carburetor to atomize down stream of the throttle plate On current production units it is set at the factory and the screw head is removed See Figure 4 23 Transition ports Pilot port Pilot screw before head is removed Figure 4 23 NOTE The transition ports are fixed They are drilled into the throat of the carburetor down stream of the venturi They lie behind the brass welch plug near the pilot screw Soak the Carburetor body in
15. a suitable solvent until clean Rinse it thoroughly Dry the carburetor body using compressed air Reassembly the carburetor and install it by fol lowing steps 1 8 in reverse order 4 Adjustment screw Start engine and check the idle RPM using a tachometer NOTE Idle speed If applicable is 1 800 RPM 160 RPM set using throttle stop screw Check the top no load speed of the engine NOTE The top no load speed will vary depend ing on the application The specification for it will be listed in the manual for each application The top no load speed is easily adjusted by tightening loosing the speed adjustment screw Tighten the screw to decrease speed and loosen itto increase speed See Figure 4 24 a lt i 3 Figure 4 24 Governor The engine speed is controlled by a balance between the force applied by a spring pulling the throttle open and a flyweight mechanism within the engine applying force to the governor arm pushing the throttle closed See Figure 4 25 peers S Governor action TIT 8 Vig i i T i 7 Figure 4 25 NOTE While the mechanism is simple and robust it is important to pay attention when working on parts near the governor Binding caused by interference with mis routed lines or cables may make the governor unresponsive NOTE When a governed engine hunts it is generally an indication of a lean fuel air mixture rathe
16. abrasives Figure 11 7 FAILURE ANALYSIS Insufficient lubrication The bearing surfaces in an engine are not smooth As a result of the machining processes to make the engine parts there are little peaks and valleys that are only visible on a microscopic scale These peaks are called asperities As the engine breaks in the asperities break off leaving plateaus that become the bearing sur face The valleys become reservoirs for the lubricant When an engine is properly lubricated all of the mov ing parts glide on a thin film of oil If that film breaks down or carries enough grit to bridge the film damage will occur 1 When the parts are at rest they push the lubri cant or oil away resting on the bearing surfaces As the parts rotate they climb over the oil pull ing the oil between the bearing and the part riding on a film of oil The asperities are the first thing to make contact between two moving engine parts with an insuffi cient oil film between them This creates friction and causes a transfer of metal between the parts The heat and friction further breaks down the oil film accelerating the process 2 Insufficient lubrication failures include Low oil level Wrong oil for the application e Contaminated oil Degraded oil heat age acids 3 Metal transfer is the primary indicator that the film of oil between two engine parts has been violated the damage is localized a general failure of
17. all the way to the right stop the multimeter should read at or near 0 09 indicating continuity See Figure 7 3 Throttle lever j ma T j r if E ri k ES Ground N 4 A Switch lead continuity z m Figure 7 3 When the throttle is all the way to the left full throttle the multimeter should not show conti nuity See Figure 7 4 no continuity Figure 7 4 Remote ignition stop switch To test the remote stop switch 1 2 Remove the muffler cover Disconnect the two wires from the remote switch See Figure 7 5 nect wires L 26016 switch Figure 7 5 Connect a digital multimeter to the two tabs on the back of the remote switch Set the multimeter to the ohms Q scale With the key fully inserted the multimeter should not show continuity See Figure 7 6 No 60 1 a T Figure 7 6 52 IGNITION SYSTEM With the key removed the meter should show continuity See Figure 7 7 Continuity Figure 7 7 If the test results do not match the results described in step 4 replace the remote switch NOTE If the engine does not stop when the key is removed and the remote switch is working properly proceed to step 6 Connect one lead of the multimeter to the blue wire that goes to the remote switch Connect the other lead of the multimeter to a good
18. as much heat as gasoline when burnt This results in less power for the engine A 10 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 4 1 Figure 4 1 THE FUEL SYSTEM AND GOVERNOR Generally these kits involve mixing a measured amount of water and gas together and seeing were the bound ary layer is See Figure 4 2 1 2 3 4 5 6 7 9 10 Figure 4 2 The test kit should come with a chart to compare the boundary layer height to alcohol percentage Fuel tank vent The fuel tank vent performs the important task of allow ing air into the fuel tank As fuel is being used by the engine the fuel level in the tank drops The dropping fuel level then creates a vacuum in the tank If the fuel tank could not draw air through the vent the vacuum would prevent the fuel from getting to the carburetor The vent is located in the fuel cap See Figure 4 3 Figure 4 3 To test the cap vent 1 Clean off the vent 2 Blow air into the vent hole The air should blow throw the vent with little back pressure 3 Suck air through the vent hole Air should freely enter through the vent Replace the cap if the vent builds pressure or restricts air movement A cap that maintains pressure will cause the e
19. assembly Some instructions may refer to other parts of the man ual for subsidiary procedures This avoids repeating the same procedure two or three times in the manual Chapter 1 INTRODUCTION MTD Horizontal Engine Model Designators 161 SHA Starter Alternators 1 Recoil start Change 2 Electric start i 3 E start alt 20W 20W Compliance 4 E start alt 3A DC 5A United States 50 State Europe California Zero 49 State U S 49 and Europe U S 50 and Europe Bore Dia mm End Product Chipper Shredder Snow No tank Logsplitter Tiller slow reverse Snow Tiller V erticutter MTD Engine Serial Numbers 1P65FH 0510271A0023 Producing Line and Shift 1A Line 1 1st Shift 1B Line 1 2nd Shift 2A Line 2 1st Shift 2B Line 2 2nd Shift MAINTENANCE The information in this manual applies to the MTD engine Some basic principles may apply to engines producted 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 chang ing 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 Spark plugs 1 The spark plug used in the MTD engine is a Torch model F6RTC gap
20. condition May indicate an exhaust blockage usually slightly muffled Backfire On over run unburned fuel ignit ing past exhaust valve Mixture not burning completely in combustion chamber It may be too rich or it may be spark plug or ignition prob lem Occasional under load engine momentarily runs lean usually will cycle with float bowl level or gover nor pull in sometimes sounds like a slight stumble Ethanol content exceeding 10 will make the 14 BASIC TROUBLESHOOTING engine run artificially lean 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 oscil loscope and see if the spark goes away at the same time the engine dies E Engine over speed a Continual over speed Binding or damaged external gov ernor linkage or carburetor throttle Mis adjusted governor arm Internal governor failure Momentary over speed Intermittent bind very unusual Interference This is fairly common when debris can fall on the gover nor linkage during normal opera tions F Engine RPMs surge hunting a Over governed condition Return spring replaced with wrong part or hooked into wrong hole NOTE This is an extremely rare condition usu ally created by tampering b Lean Air fuel mixture condition When AFR Air Fuel Ratio is sig nificantly below stoichiometric ratio 14 7 1 engine RPMs sink until th
21. constricting the other end of the system The muffler itself my be blocked The exhaust valve may not be opening fully possibly because of extremely loose valve lash set tings The exhaust valve seat may have come loose in the cylinder head This may cause a loss of compres sion a flow blockage or it may ran domly alternate between the two NOTE The cause of an exhaust valve coming loose is usually over hearing B Intake blockage 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 NOTE A blocked air filter is a common cause of this The intake valve not fully opening A possible cause of this is loose valve lash C Makes unusual smoke when running a Black smoke usually heavy usu ally indicates a rich air fuel mixture Not enough air air filter blockage or a partially closed choke Too much fuel carburetor float or 13 float valve stuck or metering emulsion issues with the carbure tor White smoke usually heavy Oil in muffler usually the result of improper tipping the engine will fog for a minute or so then clear up its own Massive oil dilution with gasoline may be caused by improper tip ping It can also be caused by leaky carburetor float valve if there is a down hill path from the carb to the intake port Check oil for gasoline smell
22. found Engines can fail in a variety of ways but most failures can be classified in the following categories Abrasive ingestion Insufficient lubrication Over heating Over speed Mechanical breakage wear NOTE There may be a combination of failures Finding the cause of an engine failure requires the complete disassembly of an engine and careful exami nation of the parts With a good understanding of how the engine works close examination of the parts and experience an understanding of why the engine failed can be reached Abrasive Ingestion Abrasive Ingestion is when hard particles are intro duced into the engine Particles can be introduced into the engine by leaks in the air intake system through a dirty oil fill plug or by particles of metal that wore off of a part especially during the break in cycle Particles may also be introduced through worn or improperly installed seals or gaskets 1 Abrasive particles that enter the engine through the intake system can be sand or dirt See Figure 11 1 Figure 11 1 2 An abrasive particle can enter the engine by bypassing an improperly installed air filter or through leaks in the intake system Usually there will be tracking marks were the particles enter the system Use these marks to find the source of the abrasives NOTE Dirt can also work its way through a poorly maintained air filter See Figure 11 2 FAILURE ANALYSIS 3 Particles th
23. ground See Figure 7 8 Continuity Figure 7 8 IGNITION SYSTEM 8 Set the multimeter to the ohms Q scale the multimeter shows continuity replace the module the multimeter does not show continuity check the wire for a break and check the ground connection See Figure 7 9 Ground co Figure 7 9 53 The module The coil in this ignition system is an inductive discharge magneto contained in a single module The inductive discharge magneto has a two leg design The magneto is energized by the passing of a pair of magnets mounted in the flywheel Ignition timing is set by the location of the fly wheel in relation to the crankshaft Proper timing is maintained by a steel key Normal performance of the coil is to produce at least 10 000 volts at starter rope pull through speed The presence or absence of strong spark with the stop switch known to be good is generally enough to iden tify the ignition coil as good or bad Resistance read ings may help confirm the source of the failure but are generally meaningless because they only measure a small part of the module NOTE Presence of a weak spark maybe the result of an improper air gap The air gap space should be 008 016 2 4mm Simple spark testers are readily available and inexpen sive Thexton Part 404 Is available from a variety of retailers and similar units are available form other manufacturers S
24. it heat up above nor mal operating temperatures Preignition is similar to detonation but on a smaller scale Preignition is cause by a localized hot spot or a hot deposit in the cylinder As the fuel air mixture is drawn into the cylinder it is ignited This creates pres sure that tries to push the piston down against the direction of rotation of the crankshaft The sounds and damage created by this is the same as detonation
25. metal gasket If the rubber is not ripped or deformed it can be reused See Figure 3 14 Figure 3 14 Re install by following the above steps in reverse order NOTE Tighten the carburetor nuts to a torque of 80 106 in Ibs 9 12 Nm 23 AIR INTAKE SYSTEMS Carburetor Insulator CAUTION When working around the fuel sys tem do not bring any sources of heat spark or open flame near the work area 1 Remove the intake elbow by following the previ ously described steps NOTE Drain the fuel tank before starting work to prevent spillage NOTE Dispose of drained fuel in a safe and responsible manner 2 Remove the carburetor 2a Disconnect the fuel line from the fuel tank See Figure 3 15 gp a Remove the fuel line from the fuel a j Figure 3 15 NOTE The barb on the carburetor inlet is very sharp If The fuel line is pulled off of it the line will be damaged and must be replaced AIR INTAKE SYSTEMS 2b Disconnect the throttle linkage and return spring See Figure 3 16 ys 1 bee 1 f ry N Af 4 Return spring 4 A h gt hrottle linkage Figure 3 16 NOTE The carburetors are not inter changeable from one engine model to another To help pre vent carburetor mix ups the engine model num ber is stamped on the carburetor by the fuel nipple See Figure 3 17 M 4 lt 5
26. of physical damage such as cracks broken vanes or damaged key way replace it A damaged fly wheel poses a threat of burst failure Burst fail ures are extremely hazardous to surrounding people and property 5 Inspect the key keyway and tapered mating sur faces of the flywheel and crankshaft See Figure 7 16 Key flat ul Figure 7 16 NOTE the key is damaged it must be replaced If there is damage to the crankshaft the engine must be short blocked because the crankshaft is not available as a service part NOTE On installation confirm that the key is properly seated the flat of the key parallel with the threaded section of the crankshaft in the keyway and that the tapers are fully seated Key or keyway failure may result from improper seating IMPORTANT The tapers in flywheel and the on the crankshaft must be clean and dry The fly wheel is held in place by the friction between the flywheel and the crankshaft not the key The key is only to guide the flywheel to the proper posi tion until it is torqued down 6 Install the flywheel nut to a torque of 47 52 ft lbs 64 70 Nm 7 Adjust the air gap by following the steps described in the previous section of this chapter 8 Reassemble the engine Test run the engine before returning to service 56 IGNITION SYSTEM About the spark plug The spark plug is a Torch model FERTC gapped to 024 032 60 80 mm e Champion RN14YC or NG
27. repair carbure tor Blue smoke usually light PCV system May be blocked or unplugged May be over come by massive over filling or oil dilution with gaso line Will cause oil to exit the engine via any low resistance paths Piston rings Confirm with leak down test Smoke will be more pronounced under load Repair may not make economic sense Valve guides and intake valve stem seal Smoke will be more pronounced on over run D Makes unusual noise when running a Knock Check for loose mounting of engine or driven implement Rotate crankshaft back and forth to check for loose connecting rod Click Clicks and pops on engine shut down Compression release com ing into play as the engine RPMs cross the activation threshold This will have no ill effects on engine performance Half engine speed clatter loose valve lash Half engine speed clatter slightly heavier wrist pin Rhythmic heavy light speed click piston slap engine Spark knock Advanced ignition timing Low octane fuel Over heating engine check for blocked cooling air flow Carbon build up in cylinder glow ing carbon chunks pre igniting air fuel mix Chirp Compression blowing by the fire ring of adamaged head gasket will sometimes produce 8 chirping noise Confirm with a compression test and leak down test Unusual exhaust tone Splashy or blatty splashy idle usually indicates a slight rich
28. the dirt in the air Without these fibers the filter is useless Foam pre filters can be washed in warm soapy water NOTE When drying a foam filter either squeeze it in side of a paper towel or let it air dry DO NOT wring it because the filter will tear Before installing any foam filter after it has been washed it needs to be free of moisture NOTE Always check with factory specification prior to servicing replacing any engine compo nents NOTE Do not oil the foam pre filter The paper filer will absorb the oil and it will become plugged Oil type and capacity Ts To check the oil twist and remove the dip stick from the engine Clean the oil off of the tip of the dipstick Re insert the dipstick without threading it in to get the oil level reading See Figure 1 3 Figure 1 3 SAE 10W 30 oil with a SF CD API rating or bet ter is recommended for spring and fall weather operations SAE 5W 30 is recommended for winter weather operations The oil capacity is 17 0 20 3 fl oz 0 5 0 6 liters The oil level is determined by the lowest point on the dipstick that is completely covered with oil the oil is noticeably thin or smells of gasoline a carburetor repair may be needed before the engine can be safely run Check the oil level frequently and change the oil more frequently in severe operating conditions such as high ambient temperature dusty condi tions or high load use in exc
29. the recoil wheel assembly to the engine using a 8mm wrench 1 Inspect the inside of the starter cup See Figure See Figure 6 1 6 2 m lnspect slots nu Remove these screws Starter cup Ny Figure 6 1 Figure 6 2 2 Install the starter by following the above step in NOTE If the starter was failing to engage the fly reverse order Tighten the screws to a torque of wheel and the edges of the teeth inside the cup 53 71 in lbs 6 8 Nm are burred or damaged replace the starter cup NOTE If the starter cup is replaced the com plete starter should be replaced as well to pre vent a repeat failure 2 Remove the starter cup by removing the fly wheel nut 43 STARTER AND CHARGING SYSTEMS 3 Install a starter cup by placing it on the flywheel with the dimple on the bottom of the starter cup in the dimple in the flywheel See Figure 6 3 Flywheel dimple o 2 j Figure 6 3 4 Install the flywheel nut and tighten it to a torque of 47 52 ft lbs 64 70 Nm 44 Starter Rope The most common failure mode for most recoil assem blies is a broken rope NOTE If the spring was not damaged when the recoil sprung back It is possible to simply remove the remnants of the old rope and install a new rope 1 Remove the starter by following the steps described earlier in this chapter 2 Remove the old starter rope by prying out the starter cord knot and pulling the rope out with it 3
30. the spring is undamaged but has been removed from the pulley the spring may be re wound Hook the end of the spring into the slot in the outer lip of the recess of the pulley and wind the spring into the recess in a counter clockwise direction 46 NOTE Evaluate the damage including parts prices and local labor rates In some parts of the country it makes economic sense to replace the complete assembly in other areas labor rates favor repair To re assemble apply a small amount of lithium based chassis grease to the surface of the recoil housing that contacts the spring NOTE Use low temperature grease on the snow engines Carefully position the pulley and spring in the recoil housing Rotate the pulley gently counter clockwise until the spring seats allowing the pul ley to fall into position Install the torsion springs and pawls so that the long arm of the spring reaches outside of the pawl and draws it toward the center of the assembly See Figure 6 8 NOTE The rolled end of the pawl fits in the recess in the starter pulley The hooked end engages the starter cup The roll faces inward and the hook faces outward NOTE The extrusions on the pressure plate should fall inside of the pawls as the starter is assembled NOTE Drag on the pressure plate from the fric tion between the compression spring and the head of the shoulder screw causes these extru sions to force the pawls outward engaging the starte
31. ForA For A Growing World World MTD Professional Shop Manual 61 65 70 Series Horizontal Shaft 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 thi
32. K BPR4ES are physi cally similar but do not match the F6RTC in heat range This difference in heat ranges will effect performance and emissions It is recommended that the Torch F6RTC plug be used for service e Wear rate will vary somewhat with severity of use If the edges of the center electrode are rounded off or any other apparent wear dam age occurs replace the spark plug before oper ating failure no start occurs Cleaning the spark plug Cleaning the spark plug is not recommended If the plug needs to be cleaned replace it e Use of a wire brush may leave metal deposits on the insulator that cause the spark plug to short out and fail to spark e Use of abrasive blast for cleaning may damage the ceramic insulator or leave blast media in the recesses of the spark plug When the media comes loose during engine operation severe and non warrantable engine damage may result Inspection of the spark plug Inspection of the spark plug can provide indications of the operating condition of the engine Light tan colored deposits on insulator and elec trodes is normal Dry black deposits on the insulator and elec trodes indicate an over rich fuel air mixture too much fuel or not enough air Wet black deposits the insulator and elec trodes indicate the presence of oil in the com bustion chamber Heat damaged melted electrodes cracked insulator metal transfer deposits may indicate deto
33. arter and tighten the starter nuts to a torque of 53 71 in lbs 6 8 Nm 45 STARTER AND CHARGING SYSTEMS Starter pulley and recoil spring The recoil spring is nested within the starter pulley and both parts are sold as a single part number CAUTION Eye protection should be worn if the starter pulley is to be removed damage is suspected the recoil may be disassem bled by 1 Remove the starter by following the steps described earlier in this chapter 2 Relieve the spring tension by 2a Pull some slack in the rope in side of the starter 2b Hook the rope into the notch in the starter pulley 2c Wind the pulley clockwise until all tension is removed 3 Remove the shoulder screw and pressure plate using a 10 mm wrench See Figure 6 7 Figure 6 7 NOTE Beneath the pressure plate is a com pression spring and two starter pawls that are held in the disengaged position by two torsion springs STARTER AND CHARGING SYSTEMS 4 Inspect the pawls and torsion springs for wear and damage See Figure 6 8 PE Torsion springs Figure 6 8 5 Carefully lift the spring and pulley out of the recoil housing See Figure 6 9 CAUTION The recoil spring is under tension and can release as the pulley is removed CAUTION Eye protection should be worn while removing the starter pulley ee ee T 00900 E 1 1 Figure 6 9 NOTE If
34. at enter the intake system travel at great speed and act like sand blasting media inside the engine This causes wear to the parts affected NOTE Choke and throttle shafts are very vul nerable to this wear If an air filter becomes clogged the vacuum produced by the engine will try to draw air in by any means possible This usually happens around the throttle and choke shafts Because the throttle shaft moves more than the choke it will wear faster 4 The particles can pass through the intake sys tem to the valves and valve seats 5 When particles enter the combustion chamber the up and down motion of the piston grinds the particles into the side of the cylinder walls and damages the cylinder wall piston and piston rings 6 This can be identified by the scoring along the vertical axis of the piston and cylinder wall or the cross hatch on the cylinder wall being worn off NOTE To help in the lubrication of the cylinder walls and help with the seating of the piston rings a diamond cross hatch is honed into the cylinder wall Debris entering the cylinder will polish the cross hatch off of the cylinder wall See Figure 11 3 Cross hatch polished off A A 5 Pe i ag ri 44 Fi P i 2 A r Fy 4 P iz a r gt Figure 11 3 NOTE Abrasives that enter the engine through the intake system will cause the upper portion of the combustion chamber to wear more than the lower portion Measurements o
35. by following the above steps in reverse order NOTE Tighten the rocker studs to a torque of 16 18 ft lbs 22 25 Nm Adjust the valve lash by following the steps described in Chapter 1 Introduction 11 Test run the mower in a safe area before return ing it to service Check all safety features CRANKSHAFT PISTON AND CONNECTING ROD CHAPTER 10 CRANKSHAFT PISTON AND CONNECTING ROD There are a 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 jump around the exact method depends on the type of repair that needs to be made The first step to disassemble the engine is to remove the engine from the equipment it powers by following the steps described in the service manual for that par ticular application a Drain and save the oil from the engine by follow ing the steps described in Chapter 1 Introduc tion 2 Remove the fuel tank by following the steps described in Chapter 4 Fuel system and Gover nor 3 Remove the air intake and carburetor by follow ing the steps described in Chapter 3 Air Intake Systems 4 Remove the starter by following the steps described in Chapter 6 Starter and Charging Systems 5 Remove the flywheel and ignition module by fol lowing the steps described in Chapter 7 Ignition system 6 Remove the muffler by following the steps described in Chapt
36. can shake an engine to pieces The technician must find the source of the vibration in order to properly diagno sis an engine Manufacturing defects are wrongly blamed for alot of failed parts A manufacturing defect is when a part is made wrong It could be a porous casting parts assembled wrong the wrong parts used or so on A manufacturing defect will generally show up within the first couple of hours of use 83 Detonation preignition Detonation is the undesirable condition of the fuel spontaneously combusting the combustion chamber prior to the spark plug firing In this state the flame front from the detonation will start to travel through the com bustion chamber and a second flame front from the spark plug will crash into it The pressure differential caused by this will send shock waves through the engine The shock wave cause a knocking or pinging noise This is why detonation is sometimes called knocking spark knocking or pinging The shock wave will also try to push the piston down against the direction of rotation of the crankshaft The shock wave from detonation can cause piston fail ures melting or breakage piston skirt damage con necting rod breakage and in extreme cases crankshaft failures A build up of carbon deposits in the combustion cham ber will increase the compression ratio This is a major factor for the development of detonation It insulates the combustion chamber allowing
37. connecting rod can not splash the oil into the engine If the oil level is too high the oil will not change into a mist to reach the upper side of the engine LUBRICATION Positive crankcase ventilation valve The PCV valve is located inside the valve cover The function and test procedures for the PCV valve is cov ered in Chapter 2 Basic Troubleshooting To remove the valve cover and PCV valve 1 Disconnect and ground the spark plug wire 2 Squeeze the spring clamp that secures the breather hose to the valve cover nipple and slide it back Then remove the breather hose from the valve cover nipple See Figure 5 9 Pliers Figure 5 9 3 Remove the four screws that hold the valve cover to the cylinder head using a 10mm wrench See Figure 5 10 Figure 5 10 NOTE The PCV valve is not serviceable If it is faulty the valve cover must be replaced Reassemble the PCV and valve cover by follow ing the above steps in reverse order NOTE Tighten the cover bolts to a of torqued to 62 79 7 5 7 9 Nm Inspect the PCV tubing for cracks brittleness or signs of leaking Replace the PCV tube if any are found Test run the engine before returning to service STARTER AND CHARGING SYSTEMS CHAPTER 6 STARTER AND CHARGING SYSTEMS Recoil Starter Removal Starter Cup To remove recoil assembly from the engine The starter cup is a steel cup that is bolted to the fly 1 Remove the three nuts that secure
38. content before diagnosing anything else on the engine NOTE It is important to perform a compression or leak down test before condemning a carbure tor An engine can have a borderline compres sion reading and not create enough of a vacuum to draw in a sufficient fuel air charge NOTE If the engine has border line compres sion a quick test to see if that is the problem is to remove the spark plug Squirt a little bit of oil into the combustion chamber to seal the rings Reinstall the spark plug If the engine starts and runs ok then that was the problem If it does not start move on to the carburetor Inspecting the carburetor 1 Remove the float bowl and check for dirt and or varnish Inspect the needle valve and needle valve seat for dirt and or damage Inspect the gaskets and O rings for damage Inspect the vents and orifices verify that they are free of debris NOTE If a little cleaning and new gaskets will fix the carburetor do it If the carburetor requires extensive cleaning it is better to replace the car buretor IMPORTANT Never try to mechanically clean orifices That will damage them and ruin the car buretor NOTE The jet markings if present may be used for identification purposes but the techni cian should not attempt to infer orifice sizes from the identification numbers NOTE Installing the wrong main jet or a carbu retor with the wrong main jet will produce perfor mance and emiss
39. d prime test the engine If the engine does not start the problem is not in the ignition system Check the engine s compression If no sparks are seen in the spark tester further testing is required Test the stop switch by following the steps described in the stop switch section of this chap ter the stop switch is working properly replace the module Inspect the flywheel IGNITION SYSTEM Stop switch All MTD horizontal engines that are in use in North America have a stop switch built into the throttle lever assembly MTD engines used on snow blowers have an additional stop ignition switch in the engine shroud Test the stop switch throttle by NOTE On snow engines test the remote igni tion stop switch first 1 Remove the fuel tank by following the steps described in Chapter 4 The Fuel System And Governor 2 Remove the engine shroud Snow engines by following the steps described in Chapter 3 Air Intake Systems Remove the blower housing 4 Disconnect the lead that runs from the module to the stop switch See Figure 7 2 Disconnect switch i 5 j r f Figure 7 2 5 Connect one lead of a digital multimeter to the lead going to the stop switch Connect the other lead of the digital multimeter to a good ground 6 Set the multimeter to the ohms Q scale Operate the throttle lever while watching the multimeter 51 When the throttle is
40. e 3 2 5 Disconnect the wire from the ignition switch and the primer line from the primer button 6 Remove the two screws that fasten the upper heatbox housing to the lower housing and lift out the upper housing See Figure 3 3 Remove these Fiqure 3 3 NOTE Write down or take a picture of how the prime line and ignition wires are routed through the upper heat box housing AIR INTAKE SYSTEMS 7 Remove the screw that fastens the engine shroud by the fuel tank using a 2 phillips screw driver See Figure 3 4 4 Remove this screw Figure 3 4 8 Remove the two carburetor nuts using a 10 mm wrench See Figure 3 5 Figure 3 5 20 9 Work the engine shroud off of the carburetor studs NOTE Be careful to pop the primer line out of the notch that secures it while working the engine shroud off See Figure 3 6 Pop primer line out of notch while working the shroud off l Figure 3 6 10 Disconnect the fuel line from the fuel tank NOTE The barb on the carburetor fuel inlet nip ple is very sharp and will damage the inside of the fuel line if the fuel line is removed Therefore if the line is removed from the carburetor it must be replaced 11 Disconnect the throttle linkage and return spring from the carburetor See Figure 3 7 linkage fuel line Le discon 4 4 r eZ Figure 3 7 Slide the carburetor off of the carburetor studs NOTE The choke linkage w
41. e Figure 1 10 jam nut to confirm that it did not shift Re adjust if necessary 004 feeler_ 2 gauge i 14 Rotate the engine through several compression 3 cycles Observe the movement of the valve gear Return the piston to TDC compression stroke and re check the valve lash to confirm consistent movement of the valve gear including the slight bump to the exhaust valve from the automatic compression release Clean up any oil around the valve cover open 15 ing clean the valve cover replace the valve cover gasket if necessary 16 Install the valve cover tightening the valve cover screws to a torque of 62 80 in lbs 7 9 Nm IMPORTANT Over tightening the valve cover will cause it to leak 4 ee 1 Si avr aon 4 2 Figure 1 10 10 Exhaust valve lash muffler side should be 005 007 15 02mm See Figure 1 11 17 Install the spark plug Spark arrestor 006 feeler gauge y pn The spark arrestor should be checked and or cleaned every 25 hours Clean spark arrestors by following the steps described in Chapter 8 Exhaust NOTE The spark arrestor also helps to keep potential blockages out of the exhaust system Typical blockages include insect nests built dur ing the dormant season Cleaning the engine 1 maintain a proper operating temperature and to keep the equipment looking good all debris should be removed from the engine
42. e is no fuel in the primer bulb The primer works by pushing air into the float chamber of the carburetor when the primer bulb is depressed This will force fuel to be sprayed out of the main nozzle into the throat of the carburetor To test the primer 1 Remove the engine shroud by following the steps described in Chapter 3 Air Intake Sys tems 2 Reconnect the primer hose to the carburetor See Figure 4 12 se Carburetor throat Figure 4 12 3 Press the primer bulb while looking down the carburetor throat If there is fuel squirting into the carburetor throat the primer is working properly If not replace the primer and hose NOTE The primer and primer hose come as an assembly so there is no need to determine which part is bad THE FUEL SYSTEM AND GOVERNOR To replace the primer Carburetors 4 the primer is bad disconnect hose from the diagnosis indicates a fuel problem inspect the carbu carburetor Remove the hose camp at the rear of the primer bulb See Figure 4 13 Figure 4 13 The primer is held to the shroud by a pair of split barbed posts Squeeze the posts to release the barbs See Figure 4 13 NOTE The primer bulb and hose will slide out as an assembly Install the new primer by following the above steps in reverse order 31 retor This is important even if problems are identified elsewhere in the fuel system IMPORTANT the fuel must be tested for alcohol
43. e the stator for easier access to the shaft See Figure 4 30 Remove the Stator ear shaft Figure 4 30 THE FUEL SYSTEM AND GOVERNOR 6 Slide the shaft out of the gear and cup See Figure 4 31 Governor gear Gear shaft Governor cup Figure 4 31 NOTE A second thrust washer goes between the governor gear and the cylinder block Make sure it is in place when installing the governor gear See Figure 4 32 Figure 4 32 7 Install the governor gear and cup by following the above steps in reverse order NOTE Check the governor arm for freedom of movement before test running the engine 8 Test run the engine and adjust the top no load engine rpms by following the steps described in Disassembly and rebuilding the carburetor sec tion of this chapter LUBRICATION CHAPTER 5 LUBRICATION Oil type and quantity Use a quality motor oil certified to meet or exceed American Petroleum Institute A P I requirements for service classification SG SF Motor oils classified SG SF will show this designation on the container SAE 10W 30 is recommended for general all tempera ture use If single viscosity oil is used select the appro priate viscosity for the average temperature in your area from the chart below See Figure 5 1 NOTE Using synthetic oil during the break in period can prevent the rings from breaking in Summer engines 20w40 20w50 15w40 15w50 10w30 C 30 20 10
44. ecting rod max ID crank side J 1 173 30 071mm 1 173 1 173 30 071mm 071mm Connecting rod to crank pin max running clear 0 002 057mm 0 002 063mm 0 002 a ance Connecting rod to crank pin max side clearance Connecting rod to crank pin max side clearance to crank pin max side clearance 0 037 0 952mm 037 0 0 037 0 952mm 0 014 350mm 0 011 275mm 0 011 275mm Crank shaft bearing max ID cylinder block Crank shaft bearing max ID crank case cover 0 551 14 131mm 0 551 14 131mm 0 551 14 131mm 0 556 14 248mm 0 556 14 248mm 0 556 14 248mm 1 078 27 628mm 1 078 27 628mm 1 078 27 628mm Compression ring max end gap 0 029 750mm 0 029 750mm Scrapper second ring max end gap 0 029 750mm 0 029 750mm 0 029 750mm 76 CRANKSHAFT PISTON AND CONNECTING ROD Engine torque values chart Table 2 NOTE apply a small amount of releasable thread locking compound such as Loctite 242 blue 77 FAILURE ANALYSIS CHAPTER 11 FAILURE ANALYSIS A properly maintained engine will provide years of ser vice Occasionally an engine will fail An important part of working on engines is finding out why they failed Was it something the customer did Was it a manufac turing defect Did the engine just wear out All of these questions need to be answered when a failed engine is
45. ects 71 Cynder MSPeCCHON era hasea na ricaiehcaet a hoe heehee 71 0 12 73 eharte 76 Preine torque Values Ghart 0 JI Chapter Falure Analysis scoscececsvscunedccacecacacecapenceceecacesscazebeeecsusstonassuccssecuncccadescacesecenebeness 78 0 oa E E S 78 UDCA Osere E E E a a 80 Sine OVS ped aona E Neier aneakess 81 ONE E o E E E E E A DE A E ee i E E eoe AS 82 Mechanical break ase WW Cal aceea E cae iaies 83 83 8 INTRODUCTION CHAPTER 1 INTRODUCTION Professional Shop Manual intent This manual is intended to provide service dealers with an introduction proven diagnostic and repair proce dures for the MTD horizontal shaft 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 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 procedure CAUTION is used to point out potential danger to the technician operator bystanders or sur rounding property Bullet points indicate sub steps or points Disclaimer This manual is intended for use by trained professional technicians e Common sense in operation and safety is assumed In no event shall MTD or Cub Cadet be liable for for poor text interpretation or poor execution of the procedures described in the tex
46. ee Figure 7 10 numbers 15186 hee are suggested minimum setings or no slan diagnosis Application Adasi Lawn bowers Tilers Snowmobiles atc SE Vehicles with conventional point Type ignition 7 il Ford 551 Dwaspark IL H 8 Ford Thick Fim W 4 avi 10517000005 on GM Distibuteeless 44 ote back of package relat ag And Ue fee TYPICAL SPARK TESTER CONNECTION L f ey FL et Ta i E ea 1 MADE IN jii ill Att Bakar TAN I Ill Comp Office Indianapolis IN 46241 INSTRUCTIONS FOR VEHICLES WITH NON INTEGRAL COILS Figure 7 10 NOTE If the complaint is that the engine quits running when it gets warm the ignition module should be tested with the engine at normal oper ating temperature IGNITION SYSTEM At operating speed the ignition should produce Module removal voltage approaching 12 000 See Figure 7 11 1 Unplug the spark plug 1 reticle 4 000 Volk 2 Remove the Heatbox Snow engines and intake waveform is eae elbow by following the steps described in Chap 3 reticles tall Siam ter 3 Air Intake Systems 3 Unhook the spark plug wire from the clip in the carburetor insulator See Figure 7 13 Unhook spark Figure 7 11 plug wire At pull over speed 600 RPM voltage should be at least 10 000V See Figure 7 12 Pull over speed waveform is half way y between 2nd and 3rd reticle 10 000 V Figure 7 13 4 Remove the recoil a
47. enance interval and cleaning instructions for the air filter AIR INTAKE SYSTEMS To service the air filter See 1 Press in on the tab in the air filter cover Figure 3 10 Press here A Ra 5 A tS x Ai liaas 4 P E gt 1 b ya ev ja gt 0 J A 4 1 PiE 0 gt A 2 r Orc Pe ae VIA A ue NS me gt Figure 3 10 2 Swing open the cover and lift it off of the air filter base Lift the air filter out of the base 4 Replace the air filter or clean it following the steps described in Chapter 1 Introduction NOTE When installing the air filter make sure the tabs on the filter fit in between the pins in the air filter base See Figure 3 11 Figure 3 11 5 Re assemble by following the above steps in reverse order 22 Air filter base and intake elbow To remove the air filter base 1 Remove the air filter following the steps described in the previous section 2 Remove the two screws that hold the air filter base to the intake elbow See Figure 3 12 Mounting screws Intake elbow Figure 3 12 Lift the base off of the elbow Remove the two carburetor nuts using a 10 mm wrench See Figure 3 13 Carburetor nuts Figure 3 13 5 Slide the elbow off of the carburetor studs Vulcanized metal Inspect the air intake gasket NOTE The air intake gasket is a Vulcanized
48. engine shroud must be removed to reach the fuel line Refer to Chapter 3 Air intake systems for direc tions on how to remove it WARNING To avoid personal injury or property damage use extreme care in handling gasoline Gasoline is extremely flammable and the vapors are explosive Serious personal injury can occur when gasoline is spilled on yourself and or your clothes which can ignite Wash your skin and change clothes immediately 1 Drain the fuel 2 Gently pry up on the tap that holds the fuel line in place 3 Remove the fuel line 4 Remove the fuel tank nipple using a 12 mm wrench See Figure 1 6 6 Fuel filter 12 mm wrench Figure 1 6 5 Install a new filter by following the above steps in reverse order NOTE Apply a small amount of releasable thread locking compound such as Loctite 242 blue and tighten the filter by hand and the an additional 3 4 to 1 full turn to compress the gas ket Valve lash Valve lash is the clearance between the top of the valve stem and the rocker arm The valve lash should be checked after the first 25 hours of use and every 100 hours after that Valve lash can be checked and adjusted using the following steps 1 the engine has been run allow it to cool thor oughly Position the equipment for easy access to the cylinder head 2 Disconnect the high tension lead from the spark plug and ground it well away from the spark plug hole 3 Remove the spark
49. eper and the secondary keeper will pop off Then slide the keeper off of the valve stem See Fig ure 9 11 Secondary valv keeper a keeper Figure 9 11 Lift the springs off of the valve stems Slide the valves out of the cylinder head NOTE Only the intake valve has a valve guide seal See Figure 9 12 Figure 9 12 6 043 050 Inspect the valve seat See Figure 9 13 Seat angle is 45 Margin eee Figure 9 13 Valve seats are 45 degrees with a 15 degree topping cut and a 75 degree narrowing cut Seat width should be 043 050 1 1 1 3mm with a margin of 024 6mm on the exhaust valve and 027 7mm on the intake valve NOTE The valve seat can be ground to clean it up as long as the finished seat is within the toler ances listed above Inspect the valve stem See Figure 9 14 Figure 9 14 65 11 12 13 CYLINDER HEAD Inspect the valve springs NOTE Valve spring free length should be at least 1 22 28 5mm Original length is 1 44 36 6mm Install the valves in the cylinder head by follow ing steps 2 5 in reverse order Test the valves for leaks by 10a Place the cylinder head on a couple of wood blocks with the valves facing up 100 Pour a small amount of gasoline or parts into the combustion to cover the cleaning solvent chamber just enough valves 10c Let the cylinder head sit for ten minutes 10d Check for ga
50. eptionally thick grass Synthetic oil is a suitable alternative but it does not extend service intervals NOTE MTD recommends the use of petroleum oil during the break in period to ensure the piston rings correctly break in Synthetic vs Petroleum based oil To simply look at synthetic oil and to compare it with Petroleum based oil there is very little difference However when you look at the two through a microscope it is easy to see the difference Synthetic is made up of smaller molecules This allows the oil to get into areas that petroleum based oil cannot INTRODUCTION No oil additives or viscosity modifiers are recom mended The performance of a good oil meeting the API specifications will not be improved by oil additives NOTE Some oil additives may cause severe and non warrantable engine damage constitut ing a lubrication failure Changing the oil NOTE If the engine has been running allow the engine to cool before doing any maintenance work NOTE The oil should be changed after the first 5 hours of operation and every 25 hours there after Drain the oil by removing the drain plug located at either the base of the engine or from an exten sion drain threaded into the base of the engine using a 10mm wrench See Figure 1 4 Oil drain Figure 1 4 NOTE Tighten the drain plug to a torque of 124 159 14 18 Nm on installation Chapter 1 INTRODUCTION Fuel Gasolines currentl
51. er 8 Exhaust 7 Remove the cylinder head by following the steps described in Chapter 9 Cylinder Head Remove the dipstick tube Remove the crank case cover bolts using a 12mm wrench 67 10 Carefully slide the crank case cover off of the crank shaft 11 Align the timing marks to allow easier removal of the cam shaft and to help protect the compres sion relief from damage See Figure 10 1 Timing marks fe HEN A P Figure 10 1 12 Remove the camshaft See Figure 10 2 m an K Y i th A E F a i iy P 4 a8 ae i Ji i amp L 4 th _ i 1 n E x i q 7 i o Remove the cat Figure 10 2 CRANKSHAFT PISTON AND CONNECTING ROD 13 Remove the valve tappets See Figure 10 3 Figure 10 3 NOTE Keep track of which tappet was originally riding on which lobe Be sure there are reassem bled that way 14 Remove the connecting rod cap using a 10mm wrench See Figure 10 4 a Remove the connecting rod bolts Figure 10 4 NOTE Rotating the crank shaft after the con necting rod bolts are removed will help to sepa rate the connecting rod from the cap 68 16 Push the piston out of the cylinder Remove the piston rings from the piston using a pair of piston ring pliers See Figure 10 5 Piston ring pliers Figure 10 5 Remove the crank shaft See Figure
52. erating time replacing the head double nut and remove the exhaust and carburetor studs 62 13 Remove the cylinder head bolts using a 12mm wrench See Figure 9 6 bolts Figure 9 6 14 Lift the cylinder head off of the engine 15 Carefully clean all sealing surfaces of all gasket residue Do not scratch the sealing surfaces See Figure 9 7 NOTE Make a visual inspection of the valves and cylinder bore to confirm the initial diagnosis Oil supply passage Clean gasket P ea surface 5 7 2 Ney Alignment dowelss b oa n Figure 9 7 To install a cylinder head 16 Place a new head gasket on the cylinder allow ing the alignment dowels to hold it in place See Figure 9 8 NOTE MTD uses graphite head gaskets that have a bead of silicon on them They are not reusable an Graphite head cus tats sss gasket 8 65 ae i ert 2 i ul 3 Figure 9 8 17 Position the cylinder head on the engine block 18 Install the 4 head bolts and tighten them to a step torque of 16 18 ft lb 22 25 Nm in an alternating diagonal pattern See Figure 9 9 NOTE The bolt closest to the exhaust valve must be the last bolt tightened failure to do so will result in the head bolt loosening up Figure 9 9 63 19 20 21 22 23 24 CYLINDER HEAD Insert the push rods
53. es the drag may increase and decrease as the crankshaft rotates This produces a pulsing feeling that is different than a jerk back Il A parasitic load from a drive belt that is not releasing or an implement that is jammed Ill An internal drag from a scored or seized piston Rope jerks back This usually indicates that the piston is stopping before top dead center on the compression stroke and is being driven back down by compression or combustion The likely suspects are 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 Ill Insufficient inertia to over come normal compression a Loose implement b A light flywheel used on a heavy flywheel application 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 Il Complete hydraulic lock easy fix IIl External easy fix binding jammed implement IV Bent crankshaft unrepairable V Internal binding crankshaft connect ing rod or piston unrepairable 2 Crankshaft turns no start 2a Most gasoline engine diagnosis involves iso lating problems in the four critical factors an engine needs to run properly Ignition sufficient spark to start com bustion in the c
54. ey 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 Too much air look for and air leak in the intake tract Not enough fuel look for fuel sup ply or carburetor problems BASIC TROUBLESHOOTING Repairing the problem The third step in the troubleshooting process is to repair the problem This step consists of IR 2 Form a diagnosis by using all of the information gathered from the troubleshooting that was per formed Physically preform the repair The fourth and hopefully final step in the troubleshoot ing process is the follow through This step consists of 1 Thoroughly test the repaired equipment con firming 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 unre lated to the first repair Delivery to customer We are not just repairing equipment we are repairing customers A Inoculate against recurring problem with education e g if the problem was caused by stale fuel make sure the customer 5 aware that fuel goes bad over time B Make sure the customer understands the repair preventing superstitious come backs 15 Prime test To perform a prime test 1 Pr
55. f the cylinder bore at the top and bottom will show this Other sources of abrasives that get into the engine includes carbon that builds up on the top side of the piston metal shavings from the wear of engine parts or dirt entering through the oil fill port leaking gaskets and seals also have the potential of allowing debris to enter the engine A symptom of abrasive ingestion is smoky exhaust As the cylinder walls wear pressure from the combustion chamber blows by the piston and pressurizes the engine sump This overpowers the PCV valve and allows oil to build up in the combustion chamber See Figure 11 4 Figure 11 4 Abrasive materials that enter the engine get absorbed by the oil and thickens it See Figure 11 5 Figure 11 5 Because the oil absorbs the abrasive particles the engine components that are immersed in oil will show definite signs of abrasive ingestion especially around the connecting rod and main bearing journals See Figure 11 6 Figure 11 6 NOTE Abrasives that are trapped in the oil will cause the lower portion of the combustion cham ber to wearing more than the upper portion NOTE Wear of only one bearing surface on a new engine could be a sign of a manufacturing defect NOTE Abrasive particles can also be imbedded into materials that are softer than the abrasive This will cause the affected part to act like a piece of sand paper or a grinding wheel See Figure 11 7 Imbedded
56. he air filter through a molded rubber hose The rubber hose directs crankcase fumes to a chamber within the air filter housing See Figure 2 3 crankcase air chamber Figure 2 3 NOTE On snow blower engines the breather hose connects to a chamber inside the lower half of the heat box assembly See Figure 2 4 Bottom of heat IN y crankcase air chamber Figure 2 4 18 BASIC TROUBLESHOOTING When functioning properly the PCV valve Posi tive Crankcase Ventilation works with the inher ent pumping action of the piston in the bore to expel pressure from the crankcase NOTE Normally small engines run with slightly negative case pressure This case pressure can be measured using a slack tube water manome ter or an electronic version of the same tool Less than between 3 and 4 7 6 10 2cm of water is a typical reading at idle An engine that fails to purge extra case pressure in a controlled manner will build case pressure The pressure will find its own way out of the engine in undesirable ways Oil will be forced by the rings and valve guides being burnt in the combustion chamber The cause of this oil burning can be mistaken for a worn out engine if proper diagnosis compres sion leak down and case pressure is not per formed Experimentation by MTD s Training and Educa tion Department has revealed the following char acteristics of MTD engines A leaky PCV system will not build up sub
57. he combustion chamber The fuel system consists of the following components e Fuel tank Fuel lines Fuel filter e Carburetor NOTE When working on the fuel systems look at the whole system A problem will rarely be iso lated to one component Inspecting the fuel NOTE Fuel is the maintenance item most often overlooked by consumers A lot of fuel systems problems are caused by bad gas or too much alcohol in it When inspecting the fuel Look for water Look for dirt Look for discoloration Sniff carefully to see if smells like varnish or kerosene Save the fuel to show to customer Look for oil in the fuel Test the fuel for alcohol content if there is a rea son to suspect it 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 26 Test fuel for alcohol Fuels currently on the market contain a wide array of additives Some of these additives oxygenate the fuel Oxygenated 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 produce
58. igure 10 11 pa m j 4 Feeler gauge Figure 10 11 Connecting rod inspection 1 Inspect the connecting rod for cracks or any signs of damage 2 Install the rod cap and tighten to a torque of 6 124 5 12 14Nm 3 Measure the inside diameter of the connecting rod and compare the measurements to those listed in the chart at the end of this chapter See Figure 10 12 NOTE Take two measurements 90 degrees apart This will check the out of roundness of the connecting rod Measure at Bag Figure 10 12 NOTE Connecting rods are not available as ser vice parts If the connecting rod is bad the engine must be short blocked 4 Take the crank shaft journal measurement and subtract it from the connecting rod measurement to get the connecting rod to journal running clearance Compare that number to the one listed in the chart at the end of this chapter NOTE Plasti gauge can be used to measure the connecting rod to journal running clearance but it is very technique sensitive and it is not as reli able as the method described above CRANKSHAFT PISTON AND CONNECTING ROD Cylinder inspection 1 Clean and inspect the cylinder inside and out NOTE If there is any sign of damage especially cracked cooling fins short block the engine NOTE Take two measurements of the cylinder bore 90 degrees apart at the top bottom and middle of the cylinder See Figure 10 13 Measure i a b
59. ill come off with the carburetor Unhook the spark plug wire from the clip in the carburetor insulator Slide the insulator off of the carburetor studs See Figure 3 8 w a 7 4 Ee Es KS pe 7 i t Figure 3 8 Remove the carburetor insulator gasket and clean the cylinder head sealing surface Reassemble by following the above steps in reverse order NOTE Tighten the carburetor nuts to a torque of 79 7 106 5 9 12 Nm NOTE Do not over tighten the carburetor nuts Doing so can cause the vent channel in the car buretor insulator to collapse which will plug the carburetor bowl vent this can result in the engine stalling or not running 21 AIR INTAKE SYSTEMS Chore engines Air filters Generally air filters come in two different types a pleated paper element or foam A combination of the two are used on the MTD engine See Figure 3 9 Both filters together E i oe Foam pre filter Paper pleated element Figure 3 9 Air filters used on the MTD engine are designed to prevent particles larger than 3 5 micron from passing through into the engine The filter should be checked a regular basis possibly several times in a season NOTE Never use compressed air on a paper air filter Compressed air will remove the tiny fibers that are used to catch the dirt in the air Without these fibers the filter is useless NOTE Refer to Chapter 1 Introduction for the maint
60. ime the engine through the carburetor throat using a squirt bottle filled with clean fresh gaso line 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 Make sure the ignition switch safety key is in the run position Attempt to start the engine the engine starts and runs long enough to burn the prime the problem is effectively isolated to the fuel system proceed to Chapter 4 The Fuel System and Governor Check ignition system as described in Chapter 7 Ignition System If the ignition system is working check the com pression or perform a leak down test Leak down test A leak down test is the preferred method to test the engine s ability to compress the charge It will also show where pressure is leaking from To perform a leak down test NOTE A leak down test pressurizes the com bustion chamber with an external air source and will allow the technician to listen for air leaking at the valves piston rings and the head gasket NOTE These are general instructions Read and follow the instructions that came with the tester before attempting to preform this test possible run the engine for 3 5 minutes to warm up the engine Remove the spark plug and air filter Find top dead center of the compression stroke CAUTION If the engine is not centered a
61. ine crankshaft rotates with normal force If the engine does not rotate with normal force identify and repair the engine problem NOTE This includes adjusting the valve lash If the crankshaft rotates with normal force but the starter is unable to turn it replace the starter If the starter does not work replace the starter Install the starter by following the above steps in reverse order NOTE Make sure the alignment dowels are in the engine block before in stalling the starter See Figure 6 12 A i Figure 6 12 NOTE Tighten the starter screws to a torque of 53 71 in lbs 6 8 Nm STARTER AND CHARGING SYSTEMS Charging system Description Some engines are equipped with a charging system The charging system consists of Alternator stator copper field windings around an iron core The stator is attached to the engine block beneath the flywheel Four magnets on the inside of the flywheel refer to figure 6 13 that rotate around a stator that is mounted to the cylinder block As the crankshaft and flywheel rotate the moving magnets induce a charge in the stator Magnets Figure 6 13 A rectifier A set of diodes that turn the AC cur rent into DC current 48 Testing The charging system will produce AC and DC voltages The rectifier for the DC voltage is inside of the stator and is not serviceable To test the charging system 1 Disconnect the charger harness 2 Con
62. ine dies Check choke operation a Black smoke b Wet plug Test for invisible damage to the air fil ter by starting the engine with the air filter removed Prime test immediately after engine dies If it restarts this may indicate a problem with fuel flow to the carbure tor Check the gas cap fuel line fuel filter and the float in the carburetor 30 Runs with low power output Look for unusual exhaust color smoke Unusually hot muffler may glow red a Retarded ignition b Exhaust valve opening early lash too tight Mechanical bind a A slightly bent crankshaft in some cases the drag my increase and decrease as the crankshaft rotates This produces a pulsing feeling that is different than a jerk back b Parasitic external load A bind in the equipment the engine is pow ering c Internal drag from a scored piston or similar damage Low governor setting or stuck gover nor a Check RPMs using a tachometer b RPMs should not droop under moderate to heavy loads BASIC TROUBLESHOOTING V Low compression a b Check valve lash Check compression Check leak down to identify the source of the compression loss VI Flow blockage A Exhaust blockage usually accompanied by an unusual exhaust sound Just as a throttle on the carburetor controls the engine RPMs by limit ing the amount of air an engine can breath in an exhaust block age will limit engine performance by
63. ing rod Tap piston with hammer handle Figure 10 20 4e Pre lube the connecting rod with clean 10W 30 motor oil 4f Install the connecting rod cap Apply a small amount of releasable thread locking com pound such as Loctite 242 blue to the connecting rod bolts and tighten the cap 74 bolts to a torque of 106 124 in lbs 12 14Nm See Figure 10 21 1 Do Connecting Tod cap sak Figure 10 21 Install the valve tappets Install the cam shaft by 6a Pre lube the cam shaft with clean 10W 30 motor oil 6b Rotate the crank shaft until the timing mark points to the tappets 6c Insert the cam shaft while aligning the timing marks See Figure 10 22 removed install the governor arm by following the steps described in Chapter 4 Fuel systems and Governor Place a new gasket on the crankcase cover let the alignment dowels hold it in place 9 Using a seal protector slide the crankcase cover on to the crank shaft See Figure 10 23 i gt n l 4 9 Seal protector oi a can 7 Figure 10 23 10 Gently rock the crank case cover until it seats fully against the cylinder block 11 Install the crank case cover bolts and tighten to a torque of 80 106 in lbs 9 12 Nm NOTE Use a star torque pattern to tighten the cover bolts 12 Install the cylinder head by following the steps described in Chapter 9 Cylinder head 13 Install the muffler by foll
64. ions issues Disassembly and rebuilding the carburetor l Bowl vent channel Clamp off the fuel line to prevent fuel spillage then disconnect the fuel line from the carburetor NOTE lf the carburetor is equipped with a primer disconnect the primer hose Remove the carburetor by following the steps described in Chapter 3 Air Intake and Filter NOTE An insulator separates the carburetor from the cylinder head A bowl vent port is in a recessed passage on the end of the carburetor that faces the insulator A second passage in the insulator supple ments the passage on the carburetor Gaskets separate the insulator from the cylinder head and the carburetor from the insulator e A port in the carburetor to insulator gasket ties the bowl vent passages together Bowl vent port Figure 4 THE FUEL SYSTEM AND GOVERNOR Remove the bowl bolt using a 10mm wrench See Figure 4 15 Figure 4 15 NOTE From this point an assessment can be made about the viability of rebuilding the carbu retor If extensive corrosion is evident replace the car buretor If varnish build up is too extensive to clean replace the carburetor When inverted the float should rest in a level position See Figure 4 16 Float valve Figure 4 16 THE FUEL SYSTEM AND GOVERNOR Remove the pin that the float hinges on to remove the float NOTE The float is not adjustable Spring ten sion against the float valve begin
65. ispose of drained fuel in a safe and responsible manner 28 THE FUEL SYSTEM AND GOVERNOR The fuel tank To remove the fuel tank 1 Drain the tank 2 Disconnect the fuel line from the tank by follow ing the steps described in the fuel filter section of Chapter 1 Introduction Remove the dip stick 4 Remove the dip stick tube cover by removing the two screws See Figure 4 5 ba ae Eo Dip stick tube cover Ra 2 if 1 A il a Figure 4 5 5 Remove the two nuts from the fuel tank studs See Figure 4 6 Remove these nuts Figure 4 6 THE FUEL SYSTEM AND GOVERNOR NOTE On snow engines with electric start the starter switch mounting bracket is bolted to the fuel tank and will come off with the tank If replacing the tank make sure to remove the bracket from the old tank and mount it on the new one See Figure 4 7 Figure 4 7 6 Remove the bolt securing the fuel tank mounting tab to the cylinder block See Figure 4 8 A ty l UET R Remove this bolt M N m Figure 4 8 7 Install the fuel tank by following the above steps in reverse order Choke MTD engines are equipped with a choke a primer or both If equipped with a manual choke it must be closed to start the engine The choke should be opened when the engine starts This can be a source of starting issues w
66. issues Typical dam age from this kind of over heating is a dropped valve seat A dropped exhaust valve seat combined with coked oil in the cylinder head would be sure indicators of an over heated engine FAILURE ANALYSIS Mechanical Breakage Wear Sometimes an engine fails because a part breaks There are generally three causes of a broken part out side of the previously discussed engine failures They are abuse wear and manufacturing defects A very common way to abuse an engine is a bent crank shaft Crank shafts bend when they or something bolted to them hits something A prime example of this is when a mower blade hits a rock See Figure 11 12 Benkblade Cr S N g m Figure 11 12 As the engine runs there is friction between the mov ing parts This friction wears down the parts Lubrica tion slows the process but wear can not be prevented Over time the parts wear to the point they break or fail in some way Car tires are a good example of wear A tire will only last for so many miles before all the rubber is worn off and the tire goes flat Bushings are another example they are designed to wear so that the wear of other parts will be minimized Vibration issues have a chicken and the egg relation ship to mechanical failures Which came first Bent crankshafts and imbalanced implements will cause vibration issues However a vibration issues such as a over speed or loose mounting bolts on the engine
67. ith customers who are not familiar with manual chokes The choke is operated by either a knob or a lever at the carburetor depending on the application If the choke plate fails to close fully the engine will be difficult or impossible to start when cold See Figure 4 9 Choke knob 2 Choke lever Figure 4 9 NOTE Engines with a choke lever do not have any choke linkages The choke lever is mounted on the carburetor and directly connected the choke plate See Figure 4 10 e Ay 4 5 o x 1 choke lever Figure 4 10 Choke linkage The rod connecting the choke knob to the choke plate on the carburetor can be bent slightly to facilitate adjustment To access it il Remove the choke knob and the engine shroud by following the steps described in Chapter 3 Air Intake Systems 2 Rotate the choke knob shaft to verify full choke movement See Figure 4 11 i l r Ch ok linkage Choke knob shaft Figure 4 11 3 the choke plate does not open fully or close fully adjust the choke linkage NOTE When adjusting the choke linkage make small bends and recheck the movement of the choke plate Repeat this step until full movement is achieved 4 Reassemble by following step 1 in reverse order 5 Test run the engine before returning to service 30 THE FUEL SYSTEM AND GOVERNOR Primers MTD engines use a dry bulb primer This means that ther
68. move the cylinder head 1 Disconnect and ground the spark plug high ten sion lead 2 Remove the spark plug using a 13 16 or 21mm wrench 3 Rotate the crankshaft until it is at TDC of the compression stroke by following the steps described in the valve lash section of Chapter 1 Introduction 4 Remove the carburetor and insulator plate by following the steps described in Chapter 3 Air Intake Systems 5 Disconnect the throttle stop switch See Figure 9 1 Disconnect switch Figure 9 1 6 Remove the throttle lever by removing the two screws using a 8mm wrench See Figure 9 2 Figure 9 2 7 Remove the muffler by following the steps described in Chapter 8 Exhaust 8 Remove the heat baffle See Figure 9 3 Remove these screws E Figure 9 3 CYLINDER HEAD 9 10 12 Remove the four screws securing the valve cover using a 10mm wrench See Figure 9 4 Figure 9 4 Loosen the jam nuts and fulcrum nuts that secure the rocker arms using a 10mm wrench and a 14mm wrench See Figure 9 5 Figure 9 Pivot the rocker arms aside or remove them completely and remove the push rods NOTE Once broken in the rocker arm should be kept with its corresponding valve NOTE The intake and exhaust push rods are identical and interchangeable It is preferable but not absolutely necessary to return the same push rods to their original locations on engine with substantial gt 100 hours op
69. n lead from the spark ro ee 07 plug and ground it well away from the spark plug lt 20 Most likely a stuck valve or hole 1 38 Bar too tight of a valve lash pro e Remove the spark plug using a 13 16 or 21mm oe the E rope pulls wrench A flexible coupling or wobbly exten with normal effort sion may help 20 35 Valve seat damage or piston Pull the starter rope several times to purge any 1 38 2 4 Bar ring and or cylinder wear fuel or oil from the combustion chamber 35 95 Normal readings NOTE Air compresses readily liquid does not Liquid in the combustion chamber will result in 2 4 6 5 Bar an artificially high compression reading 95 Excessive valve lash a partial 1 Install a compression gauge in the spark plug gt 6 5 Bar hydraulic lock a bad cam or a hole bad automatic compression 2 Confirm that the gauge is zeroed then pull the relief starter rope repeatedly until the needle on the gauge stops rising See Figure 2 2 Compression gauge 3 Reading 40 PSI Figure 2 2 17 PCV testing The PCV valve is located in the valve cover and allows the crankcase pressure to escape Leakage and blockage are the two failure modes for a PCV system Either mode will cause crankcase pres sure to build up though the effects of a blocked PCV are generally more dramatic Increased case pressure will result in oil entering the combustion chamber 1 The PCV chamber is vented to t
70. nation A spark plug that is wet with fuel indicates that fuel is present in the combustion chamber but it is not being ignited IGNITION SYSTEM Spark plug removal 1 2 Disconnect and ground the spark plug wire Remove the spark plug using a 13 16 or 21mm wrench A flexible coupling or wobbly exten sion may help See Figure 7 17 13 16 spark plug ay r 4 a 2 sock 7 z a l a n l 1 00 0 6 8 Figure 7 17 Gap a new spark plug to 024 032 60 80 mm Install the new spark plug and tighten to a torque of 15 18 ft los 20 25 Nm 57 EXHAUST CHAPTER 8 EXHAUST The exhaust system is a frequently overlooked compo nent of an engine It is important to make sure the muf fler is in good condition and free of debris and or insects NOTE A blocked muffler will result in poor per formance If a muffler is completely blocked the engine may not start Summer engines One of the main differences between the summer and the snow engines is the exhaust system Because of this they will be addressed separately Spark arrestor The spark arrestor should be checked and or cleaned every month NOTE The spark arrestor also serves to keep blockages out of the exhaust system Typical blockages include insect nests built during the dormant season The spark arrestor can be inspected by shining a flash light into the muffler See Figure 8 1
71. nect the black lead of a digital multimeter to a good ground on the engine 3 Connect the red lead of the multimeter to the yellow wire in the charger harness See Figure 6 14 TRER LT Figure 6 14 4 Set the multimeter to read AC voltage Start the engine and run it at full throttle The multimeter should read a voltage of 13 18Vac 7 Set the multimeter read DC voltage STARTER AND CHARGING SYSTEMS 8 Move the red to the red wire of the charger Stator harness See Figure 6 15 To remove replace the stator 1 Remove and ground the spark plug wire 2 Remove the flywheel by following the steps described in Chapter 7 Ignition System 3 Remove the baffle that covers the charger har ness using a 10mm wrench 4 Remove the two screws that secures the stator with a 10mm wrench and lift the stator off of the engine See Figure 6 16 i Remove these Screws Figure 6 15 9 The multimeter should read 17 26Vdc 10 Ifthe results do not match what is listed above replace the stator Figure 6 16 5 Install the stator by following the above steps in reverse order 6 Test run the engine in a safe area and retest the voltage output before returning to service Rotor Rotor failures are extremely rare To check the rotor Confirm that the magnets are firmly attached to the flywheel Hold a screwdriver or a similar tool made of fer rous metal within a 1 4 of each magnet
72. ngine to run rich as the fuel in the tank heats and expands forcing it s way past the float valve in the carburetor A cap that maintains vacuum will cause the engine to run lean as the fuel is depleted and no air comes in to replace it The two conditions may both be present but the symptoms vary with fuel fuel level and operat ing conditions Usually presents as a Runs and quits scenario The fuel filter The fuel filter is located in the fuel tank nipple It can be removed and cleaned with a can of carb cleaner or it can be replaced See Figure 4 4 NOTE If cleaning a filter back flush it by spray ing the carb cleaner through the barb end and out of the screen Also make sure the fuel tank is clean Figure 4 4 To replace the fuel filter follow the steps described in Chapter 1 Introduction Inspect the fuel lines Are they cracked Are they clogged Are they brittle NOTE If the answer to any of the above is yes replace the fuel lines When replacing fuel lines low permeable fuel line must be used in order to meet EPA and CARB standards NOTE The nipple has a sharp edge that will damage the inner lining of the fuel line Replace the fuel line every time it is removed from the carburetor fuel nipple CAUTION When working around the fuel sys tem do not bring any sources of heat spark or open flame near the work area Drain the fuel tank before starting work to pre vent spillage D
73. ore Figure 10 13 NOTE The measurements can be made using telescoping gauges inside micrometers or dial indicating bore gauge See Figure 10 14 Measuring the cylinder bore using a dial indicating bore gauge 4 2 gS eee SS p 1 ae a i 3 CRANKSHAFT PISTON AND CONNECTING ROD 2 Compare the measurements to those that are Bearings 2 There are two bearings to inspect a bearing in the 3 Inspect the cylinder cross hatch crank case cover and one in the cylinder block To inspect the bearings NOTE The cross hatch is important because it helps hold oil on the cylinder walls 1 Remove the crank case cover and cylinder block oil seals using a seal puller See Figure 10 15 NOTE If the cross hatch is polished off that is a sign of dirt ingestion The cylinder can not be re honed because replacement piston rings are not available The engine must be short blocked Figure 10 15 2 Inspect the bearing surface for galling scratches metal transfer or any other signs of damage 2 Measure the inside diameter of the bearings and compare to the chart at the end of this chapter 4 If the crankshaft journal is with in specifications slide it into the bearing and check for movement in the bearing that would indicate that the bear ing is worn out NOTE The bearing can not be serviced If they are bad the engine must be short blocked 72 CRANKSHAFT PISTON AND CONNECTING ROD Reassembly
74. owing the steps described in Chapter 8 Exhaust 14 install the fuel tank by following the steps described in Chapter 4 Fuel systems and Gov ernor 15 Install the carburetor by following the steps described in Chapter 3 Air Intake and Filters 16 Install the flywheel and module by following the steps described in Chapter 7 Ignition system 17 Install the blower housing and starter by follow ing the steps described in Chapter 6 Starter and Charging Systems 18 Install the engine on the application by following the steps described in the application s service manual 19 Install the spark plug by following the steps described in Chapter 7 Ignition system 20 Fill the engine with oil and fuel by following the steps described in Chapter 1 Introduction 21 Test run the engine in a safe area and make any carburetor and governor adjustments needed 75 CRANKSHAFT PISTON AND CONNECTING ROD CRANKSHAFT PISTON AND CONNECTING ROD Engine specifications chart Table 1 Crank journal flywheel end Min diameter 0 0 970 24 879mm 0 970 24 879mm 879mm 0 0 970 24 879mm 0 970 24 879mm 879mm 0 0 970 24 879mm 0 970 24 879mm 879mm Crank journal PTO end 0 970 24 879mm 0 970 24 879mm 0 970 24 279mm min diameter Crank pin min diameter 1 02 24 849mm 1 168 29 942mm 1 168 29 942mm Connecting rod max ID Connecting rod max ID crank side side Conn
75. owly turn the crank shaft while watching the dial indicator NOTE Stop the crank shaft before the dial indi cator hits the keyway 5d Compare the reading on the dial indicator to the specification listed at the end of this chapter 5e Repeat the above steps on the other end of the crank shaft CRANKSHAFT PISTON AND CONNECTING ROD Piston Inspection 1 Clean the piston and remove all carbon from the rings and ring groves N Clean the cylinder bore and remove all carbon g Insert one ring into the cylinder Push it down about one inch from the top See Figure 10 9 7 7 p N i i 4 H 5 4 4 a 14 a 1 p Ey hh al F Ti a 4 Measure the end gap with a feeler gauge and compare to the chart at the end of this chapter See Figure 10 9 5 Repeat steps 3 and 4 on the other rings Figure 10 9 NOTE Piston rings are not available as service parts If any of the end gaps are out of spec the engine must be short blocked 6 Install rings back onto the piston 70 NOTE Typically there is a top and bottom profile to compression rings But the compression rings on the MTD are symmetrical See Figure 10 10 Top piston ring Middle piston ring 3 piece oil ring t C Figure 10 10 7 Measure the distance between the ring and the ring land using a feeler gauge and compare the measurement to the chart at the end of this chapter See F
76. ped to 024 032 60 80 mm See Figure 1 1 Figure 1 1 NOTE Champion RN14YC or NGK BPR4ES are physically similar but do not match the F6RTC in heat range This difference in heat ranges will effect performance and emissions It is recommended that only the torch FERTC plug be used in MTD engines INTRODUCTION Wear rate will vary somewhat with severity of use If the edges of the center electrode are rounded off or any other apparent wear dam age occurs replace the spark plug before oper ating failure no start occurs Cleaning the spark plug NOTE MID does not recommend cleaning spark plugs 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 damage to ceramic insulator or leave blast media in the recesses of the spark plug When the media comes loose during engine operation severe and non warrantable engine damage may result Inspection of the spark plug can provide indica tions of the operating condition of the engine Light tan colored deposits on insulator and elec trodes is normal Dry black deposits on the insulator and elec trodes indicate an over rich fuel air mixture too much fuel or not enough air Wet black deposits on the insulator and elec trodes indicate the presence of oil in the com bustion chamber Heat damaged melted electrodes cracked insulator
77. plug using a 13 16 or 21mm wrench A flexible coupling or wobbly exten sion may help See Figure 1 7 Spark plug Muffler y Valve cover High tension lead Figure 1 7 4 Disconnect the breather hose from the valve cover See Figure 1 8 Breather hose Figure 1 8 INTRODUCTION 5 Remove the four bolts that secure the valve cover using a 10mm wrench and remove the valve cover from the engine NOTE If care is taken not to damage the valve cover gasket it can be re used 6 Slowly pull the starter rope until air can be heard coming out of the spark plug hole 7 Confirm that the piston is at Top Dead Center on the compression stroke See Figure 1 9 Probe to confirm piston is at top of travel Valves closed A ae a 7 Figure 9 The compression stroke can be distinguished from the overlap stroke by the presence of air pressure at the spark plug hole and the fact that neither of the valves should move significantly on the compression stroke There is an automatic compression release mechanism that bumps the exhaust valve as the piston rises on the compression stroke At TDC the exhaust valve should be fully closed 8 Check valve lash between each valve stem and rocker arm using a feeler gauge Chapter 1 INTRODUCTION 9 Intake valve lash carburetor side should be 13 Double check the clearance after tightening the 003 005 10 02mm Se
78. r cup Apply a small amount of thread locking com pound such as Loctite 242 blue to the threads of the shoulder screw and install the screw Tighten it to a torque of 71 89 in lb 8 10 Nm Install the starter rope by following the steps described in the previous section of this chapter Install the starter and tighten the starter nuts to a torque of 53 71 in lbs 6 8 Nm Electric starter The electric starter is only available on the snow engine It is powered by an extension cord that is plugged into household 120 volt AC current The starter and switch assembly are one piece and are not serviceable To replace the starter assembly 1 2 Disconnect the extension cord Remove the two screws that secures the switch box to the engine See Figure 6 10 rhe 2 p 2 Tt 4 5 pe 1 eas x 60 6 1056 screws Figure 6 10 Remove the starter by removing the two screws that hold it to the engine block using an 8mm wrench See Figure 6 11 PORTA ay To PRODUC INF ORM A THON nonu ue WO a 1 Hy 2 a Figure 6 11 STARTER AND CHARGING SYSTEMS NOTE Before condemning a starter make sure to bench test it To bench test a starter A Remove the starter from the engine B Plug the extension cord into the switch housing C Hold the starter down and press the starter button If the starter works on the bench confirm that the eng
79. r cylinder head indicates that it has been over heated See Figure 11 10 Figure 11 10 Another sign of an overheat failure is warped parts As metal parts heat up they expand In an engine a cer tain amount of expansion is expected Engines are built so that when parts are at operating temperature the parts will expand to be within the tolerances needed for the engine to run A problem occurs when the parts are over heated They expand more than they were designed to Some parts are mounted firmly like cylin der heads the hottest part of the engine As they try to expand they fight against the head bolts The head bolts will not move to allow the expansion so the head warps to allow the expansion 82 FAILURE ANALYSIS This warping of the head allows the head gasket to leak A leaking head gasket allows the compressed gases in the engine to escape lowering the compres sion in the engine and hurting engine performance As the cylinder head cools it shrinks back down to its nor mal size but there will still be some warpage of the head See Figure 11 11 Figure 11 11 Localized over heating will leave localized hot spot indications such as discoloration Rapid over heating of a cylinder like when there is a cooling air flow obstruction may cause hot spots and metal transfer between the piston skirt and the cylinder wall Over heating of the cylinder head maybe caused by lack of air flow or exhaust system
80. r filter tappia Note on air filter Dirt may be shaken or tapped out of the air filter but compressed air is not to be used for cleaning Do not wash or oil paper filter element Note on pre filter Foam pre filter may be washed in water and mild 8 Check clean spark arrestor Change o Note on oil Change oil after first 5 hrs of use and before prolonged storage Change air fiter ae See ae Note on air filter Air filter and pre filter life vary dramatically with operating conditions Drain or preserve fuel Before prolonged storage Fog or lube cylinder Before prolonged storage Rotate engine to TDC Before prolonged storage BASIC TROUBLESHOOTING CHAPTER 2 BASIC TROUBLESHOOTING Definitions Troubleshooting The act gathering information by pre forming 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 upon several factors First and most importantly is a good understanding of how the engine works The second is skills that have 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 p
81. r than a problem with the governor 36 THE FUEL SYSTEM AND GOVERNOR Governor arm To remove the governor arm from the governor shaft 1 Remove the fuel tank by following the steps described in the Fuel Tank section of this chap ter 2 Unhook the governor spring NOTE Mark which hole the spring was in to ensure it goes back in the same hole 3 Unhook the governor linage and throttle return spring 4 Loosen the nut and through bolt See Figure 4 26 Spread here h Tae 4 et lt a ay Loosen nut Figure 4 26 Carefully spread open the seam on the arm Carefully slide the Governor arm off of the gov ernor shaft 7 Install the governor arm by rotating the governor shaft clockwise until it stops 8 Slide the arm onto the shaft The flat on the top of the shaft should be roughly perpendicular to the arm See Figure 4 26 NOTE There is a hairpin clip that keeps the gov ernor shaft from sliding into the engine It may be necessary to hold the shaft while sliding the arm on to prevent it from going into the engine 9 Tighten the nut on the clamp bolt to secure the arm 10 Attach the governor linkage and spring 11 Adjust the governor to maintain top no load speed as described in a previous section of this chapter THE FUEL SYSTEM AND GOVERNOR Governor shaft To remove or replace the governor shaft 1 Remove the engine from the equipment that
82. reform while troubleshooting CAUTION The first two rules in troubleshooting is to cause no further harm to the engine and prevent injuries Always make sure to check the oil for level and condition before starting an engine Also 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 trouble shooting the MTD engine The technician does not necessarily have to follow them as described in this chapter 10 Define the problem The first step in troubleshooting is to define the prob lem Crankshaft will not turn a Hard to pull rope steady pressure b Rope jerks back 6 Rope will not pull at all Crankshaft turns no start e Starts runs poorly a Starts then dies b Runs with low power out put c Makes unusual smoke when running Black smoke usually heavy ll White smoke usually heavy Ill Blue smoke usually light d Makes unusual sounds when running Knock Il Click Ill Chirp IV Unusual exhaust tone There are tools that the technician can use in order to define the problem such as 1 Interview the customer 1a 1b Get a good description of their complaint it is an intermittent problem verify what conditions aggravates the problem as best as possible 1c Get an accurate service history of the equip ment 1d Find out how the customer uses and
83. s publication are for reference use only and may not depict actual model and component parts Copyright 2007 MTD Products Inc All Rights Reserved MTD Products Inc Product Training and Education Department FORM NUMBER 769 04015 04 2008 Table of Contents Chapter L E EEES EEEa 1 Protessional Shop Manualinte it ererninnie a 1 1 Maen cea cela neone 3 7 3 0 4 We and CAD ACY ssc lh hesss dk hae set T ens ate ieee tae ae toe eesaeas 5 6 1 asi onctasatsa sncasieins waa ue vas seca E 5 0 T E E E A 6 6 Valve laS ieas e E N 7 8 6 0 Renta ruk cated a atau 8 General tordue to iiuancve cuore tedden ds siuens 9 9 Chapter 2 10 wcmmumemneven emia te oer A E A reece ene ea ge 10 mere rane er rer ne nrr noe EE mry erent ter ter errr rere rere 10 Steps TO AOU IES ROOTING ia a a a a euuaonesdaacespeedsed 10 Derme 10 Identify factors that could cause the problem cccccceessssssecceceeceeeeeeeeeeseceeeeeeeeaaeenees 1 0 the 10 session vusearachacentss Adaiarenedeeda a a a aa iadaateanisibsdatienstaaneieeats 15 PEO We 0 ohh Ata tile 15 Ne AI LO 16 97 17 0 talia 18 Chapter Air Intake systems sssr eentenari 19 19 FG AON r area tiger ae a ae es arene a ea ee rete ia 19 MOPS CN SINE aaae a SEO A E aia nueeucten caaataomantsemreniadads 21 0 21 Air fil
84. s to build from the horizontal position putting progressively more pressure between the tip of the valve and the seat See Figure 4 17 Figure 4 17 NOTE Because the float valve is crucial to the functioning of the carburetor and the viton tip of the valve is subject to wear technicians should replace the valve and spring any time the carbu retor is disassembled for cleaning A square cross section gasket seals the bowl to the body of the carburetor 33 Remove the main jet using a narrow shank straight blade screwdriver See Figure 4 18 Figure 4 18 NOTE Fuel enters the central column through a port about 1 2 1cm from the bottom to help prevent the ingress of any residue in the bottom of the bowl NOTE The orifice in the main jet meters fuel into the central column NOTE Air from the main jet emulsion port enters the central column near the top then gets bubbled through the emulsion tube into the metered fuel flow to promote atomization THE FUEL SYSTEM AND GOVERNOR 8 Carefully pry out the metering plug using a small screwdriver See Figure 4 21 NOTE The main jet secures the emulsion tube in the central column of the carburetor z gt See Figure 4 19 i Figure 4 21 Figure 4 19 9 Examine the metering plug See Figure 4 22 Leese Ce BREE sag He 7 The throttle stop screw has a large pliable lip Air a Endview 7 7 around the head of the screw That lip secures
85. soline leaking out of the intake and exhaust ports Install the cylinder head by following the steps described earlier in this chapter set the valve lash by following the steps described in Chapter 1 Introduction Test run the mower in a safe area before return ing it to service Check all safety features CYLINDER HEAD Push rod bushings The MTD engine has bushings for the push rods that need to be replaced from time to time An indication that the bushings are worn is that the valve lash loos ens up This is because the push rods start moving side to side which opens up the valve lash To replace the push rod bushings le Disconnect and ground the spark plug high ten sion lead 2 Remove the spark plug using a 13 16 or 21mm wrench 3 Rotate the crankshaft until the piston is at TDC of the compression stroke by following the steps described in the valve lash section of Chapter 1 Introduction 4 Remove the valve cover Remove the jam and fulcrum nuts 6 Remove the rocker arms and push rods See Figure 9 15 Figure 9 15 66 7 Remove the rocker studs See Figure 9 15 o Lift the push rod bushing plate out of the cylinder head See Figure 9 16 Push rod bushing plate Figure 9 16 NOTE When installing a push rod bushing plate make sure the bushings extend away from the cylinder head See Figure 9 17 This side points up towards the valve cover Figure 9 17 9 Install
86. speed the vibrations change resonance Parts that can not handle the new resonance will crack This may result in parts flying off of the engine which is an unsafe condition such as when a flywheel shat ters pieces of it fly off of the engine The vibration can also lead to fasteners loosen ing up Evidence of this could be elongated mounting holes The area around the mounting holes may be polished due to the two surfaces rubbing against each other 3 When an engine overspeeds the moving parts can not pull the oil in between them This allows metal to metal contact Because of this signs of inadequate lubrication will show 4 When trying to diagnose an overspeed failure look at all the pieces Individually the lack of lubrication piston position and condition of the connection rod will usually indicate separate fail ures Collectively they would indicate an over speed failure Overheated The MTD engines are air cooled engines Because of this cleanliness of the engine is very important to the life of the engine Dirt grass and sludge all form an insulating layer on the engine This will trap the heat in the engine and cause it to over heat As metal parts heat up enough to change their proper ties they will take on a yellowish or blue cast As oil is heated to the point that it evaporates black deposits are left behind This is called coking An engine with lots of coked oil deposits inside the crank case o
87. ssembly by following the steps described in Chapter 6 Starter Remove the blower housing Disconnect the lead that runs from the module to the stop switch o 7 Remove the module using a 10mm wrench mF So Figure 7 12 NOTE Flash over voltage will vary with spark plug condition and gap NOTE Pull over speed may vary from operator to operator NOTE Failure of the magnets in the flywheel is exceedingly rare To test the magnets simply hold an item made of ferrous metal roughly 1 4 635cm away from the magnets in the flywheel It should be drawn to the flywheel A wrench or screwdriver is suitable for this test 54 IGNITION SYSTEM Installing the module and setting the air gap 10 11 NOTE If just setting the air gap loosen the module mounting screws first then follow the same steps as described below Rotate the flywheel so that the magnets are away from where the module is mounted Install the module Do not tighten the module down Place a non ferrous feeler gauge between the module and the flywheel NOTE The air gap should be 008 016 2 4mm Rotate the flywheel so that the magnets align with the legs of the module while holding the feeler gauge in place See Figure 7 14 Figure 7 14 Tighten the module mounting screws to a torque of 80 106 9 12 Nm Rotate the flywheel to remove the feeler gauge Install the blower housing and starter
88. stantial case pressure A leaky PCV system will allow the engine to ingest contaminants through the system accel erating engine wear A blocked PCV system will allow crankcase pressure to build very rapidly Noticeable oil fumes will be evident in the exhaust within sev eral minutes of normal operation AIR INTAKE SYSTEMS CHAPTER 3 AIR INTAKE SYSTEMS MTD builds horizontal crank engines for snow blowers and chore performers The differences between snow engines and chore engines are the muffler and the air intake system Therefore the air intake system for the snow and chore engines will be discussed separately as will the mufflers in a later chapter Snow engines One of the big differences between the snow engine and the chore engine is that the air intake of the snow engine does not have an air filter because air filters freeze and cut off air flow The snow engine however does have a heat box to preheat the intake air which the chore engines do not have Heat box To remove replace the heat box 1 Drain the fuel out of the fuel tank into an approved safety fuel can 2 Remove the muffler shroud by taking off the six screws the hold the muffler shroud in place using a 10 mm wrench See Figure 3 1 Remove these screws Figure 3 1 3 Disconnect the breather hose from the valve cover 19 4 Pull off the choke and throttle knobs See Figure 3 2 Pull off the throttle 4 and choke knobs 4 Figur
89. stores the equipment 2 Direct observation 2a Do not take it that the customer is correct with their description of the problem Try to duplicate the problem 2b Check the general condition of the equip ment visually BASIC TROUBLESHOOTING Cleanliness of the equipment will indi cate the level of care the equipment has received Make sure the engine and attach ments are securely fastened The tune up factors NOTE Most hard starting and poor running con ditions 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 exhaust system block age or cooling system blockage Broken starter rope 3a Usually means the engine was hard to start 3b Makes it impossible to confirm any running or hard starting symptoms by direct obser vation 3c Some inference can be made from checking other factors of he general condition of the equipment 11 Identify factors that could cause the problem This is the second step in the troubleshooting process 1 Crankshaft will not turn a Hard to pull rope steady pressure This usually indicates a mechanical bind of some sort the likely suspects are l A slightly bent crankshaft in some cas
90. t the person using this manual is uncomfortable with any procedures they encounter they should seek the help of a qualified technician Fasteners Most of the fasteners used on the MTD engine are metric Some are fractional inches For this reason wrench sizes are frequently identified in the text and measurements are given in U S and metric scales a fastener has a locking feature that has worn replace the fastener or apply a small amount of releasable 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 inter nal cotter pins hairpin clips may be reused if they do not show signs of wear or damage This manual leaves that decision to the judgement of the technician Assembly Torque specifications may be noted in the part of the text that covers assembly They may also be summa rized 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 The level of assembly instructions provided will be determined by the complexity of reassembly and by the potential for unsafe conditions to arise from mis takes made in
91. t top dead center the engine will rotate when com pressed air is introduce to the combustion cham ber 1 Find top dead center by following the steps described in the valve lash section of Chapter 1 Introduction 2 Thread the leak down tester adapter into the spark plug hole See Figure 2 1 Figure 2 1 16 BASIC TROUBLESHOOTING Connect tester to compressed air Adjust the regulator knob until the needle on the gauge is in the yellow or set area of the gauge Connect the tester to the adapter NOTE If the engine rotates it was not at top dead center Check the reading on the gauge Compare the results to the following chart See Table 1 Table 1 Air escaping from Worn cylinder or piston the breather rings Possible blown head gasket Air escaping from Leaking exhaust valve the exhaust Air escaping from Leaking intake valve the carburetor Gauge reading low Cylinder and piston rigs are in good condition Gauge reading There is some wear in moderate the engine but it is still usable Gauge reading high excessive wear of cylin der and or piston rings Engine should be short blocked or it could be a blown head gasket BASIC TROUBLESHOOTING Compression test 3 Interpreting compression readings To perform a compression test Table 2 NOTE Compression should be in the range of 40 60 PSI 2 81 4 1 Bar Readings in psi Possible causes Disconnect the high tensio
92. ter base and intake 6 OW sersscacusecausvauccsustletaiondimuss inte a a 22 CarOUrelOr 07 oie Mabie tice ata ecue ian Matte A ed 23 Chapter 4 The Fuel System and Governor 02 2 2 00 07 26 0 26 0 ua amie epee ues 26 iiecite 27 27 27 Inspect the Tuel 0 28 0 28 0 29 0 E Serene eee 30 0 sen ie etree ae iced 30 SAF UEC LORS esre Gnesi sSsandenndussu ved diandtansch sited shen denn tusutasdiandanssieeesiens 31 Inspecting the Carburetor 31 Disassembly and rebuilding the Carburetor ccccccccccssssseseeeceeeeeeeeeeeeseeeceeeeeeaueeeeeees 32 CON ON aa a e A cue ate eae eerie anaes 36 Governor 8 36 Govemors AE saa e E E sand uuainetiid on nse daawiemmenieonycea Paws 37 Governor cup and the governor Tear scores a E teewotadeueawaws 38 Chapter 5 ccsecccocss cocstiscstecccsscuecsssevicceass seas aere arara Erea aaao rosis 39 and goant 0 39 OPIN GLI UN EE sais pacts ean I AA EEE EAE nas dean oun EE EE aan Sessa aoc 39 Dip SUCK TUDE TEMIOY allcctaices cause esos asses saaaed pee ea a teed 40 SEIN ceca a Sst sae eect nds ecard enc meget 4 Positive crankcase ventilation Val Vex Sciaasines setter a A eves 42 Chapter 6 Starter and Charging Systems scccccccssssssssssssssssccccccssssssssssccccssccsssssssees 43 Reco Staticr 0 lanai iceman 43 Sater CO naa AE 43 Sre RODE siatiernindvaiedonanivabedusheniaied A a etieanlatios ce
93. the lubrication system is probably not the cause As an example a piston skirt shows metal trans fer to the cylinder wall The connecting rod and wristpin show some signs of excessive heat The main bearings and camshaft are not damaged This would indicate that the problem was proba bly related to cylinder temperature FAILURE ANALYSIS The hall mark of a lubrication failure is the pres ence of discoloration and or metal transfer on all friction surfaces within the engine See Figure 11 8 Figure 11 8 An important thing to note is that just because there are signs of insufficient lubrication that does not mean that was the cause of the failure It may only be a symptom of the real cause of the failure Larger size abrasive particles can render the lubricants ineffective leading to an engine failure An overheated engine can cause the oil to break down leading to a failure In an engine overspeed the oil is pushed away from the bearing surface leading to a failure In all three of the above cases the signs of insufficient lubrication are symptoms not the cause There will also be signs of heat or discoloration around the parts affected by the lack of lubrication See Figure 11 9 0 1 ae 7 o g d 7 A aai 7 i 0 5 TEA 2 4 Pig TEES 5 weet oi s oe J gt om 4 Fi Discolorati 19 N AS Eis 0 S
94. ther material Install a new gasket Install the muffler and tighten the muffler nuts to a torque of 13 16 ft lbs 18 22 Nm Test run the engine before returning to service Snow engines Unlike the summer engines the snow engines are not equipped with spark arrestors To remove replace the muffler 1 Remove the muffler shroud by taking off the six screws that hold the muffler cover in place using a 10mm wrench See Figure 3 6 Muffler shroud Remove these screws Figure 3 6 2 Remove the four screws securing the muffler shield using a 10mm wrench and lift it off of the engine See Figure 8 7 ea 7 a oe 8 g a AD mt muffler shield 7 134 9 i 24 Figure 8 7 a 60 EXHAUST 3 Remove the two muffler nuts using a 13mm wrench and lift the muffler off of the engine See Figure 8 8 Figure 8 8 4 Clean all of the gasket material off of the cylinder head and the muffler if reusing the muffler NOTE The MID engine uses a graphite exhaust gasket It is not reusable and must be replaced every time the muffler nuts are loos ened Install a new gasket Install the muffler and tighten the muffler nuts to a torque of 13 16 ft lbs 18 22 Nm 7 Test run the engine before returning to service CYLINDER HEAD CHAPTER 9 CYLINDER HEAD The Cylinder head of the MTD engine can be removed without removing the engine from the piece of equip ment To re
95. uaaet 44 Starter pulley and 000 Spine 4 seseswasie taut e uated ancameeeiadvace wate reloiondieusaselauss 45 Electes ONE orrena na nn E adie E aati aarnne 47 Charo mo Syste aenea R ences cucas 48 O 70 Uren er 49 RO 7 5 650 E E A 49 Chapter 7 Tenition 8 50 Troubleshooting the ignition system eeneesssssssoeerssssssssserrressssssssecteesssssssseerrssssssseeees 50 S T E enn yee tury errr 51 Remote Stop Sw ieh wena irieints ate E 32 Ehe TNR 53 54 Installing 55 55 2 PIUS 0 56 Clan CSO ARO recen ected is aaa canara erates camera anal wua mena deena aeeanseuredist 56 IMIS PSCHOM OL TNC Sal QS aeii ucssistaenc sd atnco se avmend destined esaaae dures Lanne aaeeaadaawess 56 SPAK Pll TEMOV Al csc advescenetanseaiedesanssaaesd a a ai 97 Chaper s FE XMAUSE unian a EE 58 58 SPAK ALN CSU OR wins e cnc eetipe wets ahaa besa eatin weetss ake eac eesaah sees aa wows aap mena aa 58 TO PEMOVE TEPlaCe EMS muer ona a a a AA 59 60 Chapter 9 Cylinder Head assosierer ro a araire ake Sa Aa E resisait 61 WIV E sae foie E tay hace tans ace ete at eae Ee ea rola het tute eco analy 64 0 6 Chapter 10 Crankshaft piston and Connecting 110610 67 Crank shalt MSPeCliON seuctuae heared a ie ae uate a tne ths A eet eee ne aloes 69 Piston TS CAO IM gatos wassac tee seen rent ata eacetaa sda rncaieaterneinsts ae ate eects ose aa tater cate acaba 70 Connecting TOG msp arene A aneteta ier Raed esa e
96. ure 5 6 5 Inspect the O rings on the dip stick and the dip stick tube Replace if damaged A 6 Install by following the above steps in reverse Figure 5 4 order 3 Remove the screw at the bottom of the dip stick tube See Figure 5 5 Fuel tank Figure 5 5 40 Lubrication system MTD uses a splash lube system for it s horizontal shaft engines The connecting rod has a dipper on it that splashes oil around the inside of the engine See Figure 5 7 4 Sa Ji Ris Figure 5 7 NOTE The cam and tappets were removed for better visualization of the lubrication system The splashing action will also atomize or change the oil into a mist There are two oil passages that run along the engine cylinder The one on the top side of the engine is the oil supply passage The oil mist will flow through this passage to the cylinder head See Figure 5 8 he A gt OY 6 3 Oil supply passage x ia Oil return i 7 Figure 5 8 41 LUBRICATION The second oil passage runs along the bottom side of the cylinder This is the oil return passage As the name implies it allows the oil collecting in the cylinder head to return to the sump The return passage is the tiny hole that is in between the two tappet passages NOTE Because these engines use splash lubri cation the type of oil and the oil level is critical for proper operation of the engine If the oil level is too low the dipper on the
97. y on the market are not pure gas Today s fuels have alcohol and other additives in them to reduce emissions The fuel make up can vary sea sonally and geographically Fuel with alcohol added to it is sometimes referred to as oxygenated fuel The extra oxygen carried by the ethanol increases the oxidation of the fuel This speeds up the process that causes the fuel to go bad Excessive alcohol in fuel creates a lot of problems for gasoline engines One of the biggest problems is that alcohol attracts and holds water This corrodes the metal components of the fuel system especially the carburetor Alcohol also does not produce as much heat as gasoline when burnt This results in less power for the engine A 10 alcohol mix E10 is acceptable for MTD engines Anything higher than that will result in perfor mance issues NOTE E85 and E20 fuels are not to be used in any MTD engines 1 Use clean fresh fuel with a pump octane rating of 87 or greater Stale or out of date fuel is the leading cause of hard starting issues Pump octane ratings beyond 87 will not improve engine performance Fuel filters Dirty fuel can clog the carburetor and introduce abra sive materials into the engine To help prevent that MTD engines are equipped with a fuel filter The fuel fil ter is part of the fuel tank nipple See Figure 1 5 fuel filter Figure 1 5 To replace the fuel filter NOTE On snow blower engines the
98. ylinder occurring at the right time 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 Fuel correct type and grade of fresh gasoline in sufficient quantity atom ized tiny droplets and in correct fuel air proportions Elow 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 2b Isolate the ignition system and compression from the fuel system by preforming a prime test Burns prime and dies This would indi cate a fuel system issue Does not burn prime Not a fuel sys tem issue Check for an ignition com pression or flow problem 2c Compression or ignition problem VI VI Check the engine stop and or ignition switch Test the ignition system using a proper tester Replace the spark plug with a new one or a known good one Check compression or leak down Check valve lash Check valve timing actuation Check exhaust 12 BASIC TROUBLESHOOTING 3 Starts runs poorly 3a Starts then dies 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 same time the eng

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