MTD 478 Series Professional Shop Manual
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MTD 478 Series Professional Shop Manual

MTD 478 Series Professional Shop Manual

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Professional Shop Manual
478/483/490 Series Horizontal Shaft Snow Engines
NOTE: These materials are for use by trained technicians who are experienced in the service and repair of outdoor power
equipment of the kind described in this publication, and are not intended for use by untrained or inexperienced individuals.
These materials are intended to provide supplemental information to assist the trained technician. Untrained or inexperi-
enced individuals should seek the assistance of an experienced and trained professional. Read, understand, and follow all
instructions and use common sense when working on power equipment. This includes the contents of the product's Oper-
ators Manual, supplied with the equipment. No liability can be accepted for any inaccuracies or omission in this publication,
although care has been taken to make it as complete and accurate as possible at the time of publication. However, due to
the variety of outdoor power equipment and continuing product changes that occur over time, updates will be made to these
instructions from time to time. Therefore, it may be necessary to obtain the latest materials before servicing or repairing a
product. The company reserves the right to make changes at any time to this publication without prior notice and without
incurring an obligation to make such changes to previously published versions. Instructions, photographs and illustrations
used in this publication are for reference use only and may not depict actual model and component parts.
© Copyright 2009 MTD Products Inc. All Rights Reserved
MTD Products Inc - Product Training and Education Department
FORM NUMBER - 769-04951
05/2009

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Summary of Contents for MTD 478 Series

  • Page 1 Instructions, photographs and illustrations used in this publication are for reference use only and may not depict actual model and component parts. © Copyright 2009 MTD Products Inc. All Rights Reserved MTD Products Inc - Product Training and Education Department...

  • Page 3: Table Of Contents

    Table of Contents Chapter 1: Introduction ......................1 Professional Shop Manual intent ......... . 1 Assembly .
  • Page 4 Governor arm ............34 Governor shaft .
  • Page 5 Chapter 11: Failure Analysis ................... 81 Abrasive Ingestion ........... . 81 Insufficient lubrication .

  • Page 7: Chapter 1: Introduction

    • In no event shall MTD or Cub Cadet be liable for poor text interpretation or poor execution of the procedures described in the text. • If the person using this manual is uncomfortable with any procedures they encounter, they should seek the help of a qualified technician.
  • Page 8 S n o w /N o ta n k L o g s p litte r T ille r (s lo w re v e rs e ) S n o w T ille r V e rtic u tte r MTD Engine Serial Numbers 1P65FH/0510271A0023 Model number Year Month Date Engine ...

  • Page 9: Model And Serial Number

    NOTE: Please refer to Chapter 7: Ignition for the Front of engine complete service instructions on spark plugs. The spark plug used in the MTD engine is a Torch model F6RTC gapped to .026”-.030” (0.65 - 0.75 mm). See Figure 1.2.

  • Page 10: Oil Type And Capacity

    • 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. •...

  • Page 11: Changing The Oil

    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- Oil drain ter is part of the fuel tank nipple. See Figure 1.5.
  • Page 12 Chapter 1: INTRODUCTION To replace the fuel filter: Remove the fuel line from the fuel tank nipple: 3a. Squeeze the tabs on the fuel line clamp with To avoid personal injury or prop- ! W A R N IN G ! W A R N IN G a pair of pliers while sliding the clamp down erty damage, use extreme care in...

  • Page 13: Valve Lash

    INTRODUCTION Valve lash Remove the five bolts that secure the valve cover using a 10mm wrench. Remove the valve Valve lash is the clearance between the top of the cover from the engine. valve stem and the rocker arm. The valve lash should be checked after the first 25 hours of use and every NOTE: If care is taken not to damage the valve 100 hours after that.

  • Page 14: Cleaning The Engine

    Chapter 1: INTRODUCTION Intake valve lash (carburetor side) should be Double-check the clearance after tightening the .004”-.006” (0.10 - 0.15mm). See Figure 1.11. jam nut, to confirm that it did not shift. Re-adjust if necessary. .006” feeler Rotate the engine through several compression gauge cycles: •...

  • Page 15: General Torque Specifications

    INTRODUCTION General torque specifications size size Grade in-lbs ft-lbs Nm 1.2 10.5 21.7 36.6 in-lbs ft-lbs Nm 1.7 13.6 27.1 47.5 in-lbs ft-lbs Nm 2.9 24.4 47.5 82.7 10.9 in-lbs ft-lbs Nm 4.1 33.9 66.4 116.6 12.9 in-lbs ft-lbs 16.5 40.7 81.4 139.7...

  • Page 16: Frequently Used Specifications

    Chapter 1: INTRODUCTION Frequently used specifications Minimum Maximum Intake valve lash 0.004 0.10 0.006 0.15 0.004 0.10 0.006 0.15 0.004 0.10 0.006 0.15 Exhaust valve lash 0.006 0.15 0.008 0.20 0.006 0.15 0.008 0.20 0.006 0.15 0.008 0.20 Spark plug gap 0.026 0.65 0.030...

  • Page 17: Chapter 2: Basic Troubleshooting

    NOTE: The steps and the order of the steps that preforming tests and direct observations. follow are a suggested approach to trouble- shooting the MTD engine. The technician does Diagnosis - Developing and testing theories of what the not necessarily have to follow them as described...

  • Page 18: Identify Factors That Could Cause The Problem

    BASIC TROUBLESHOOTING Direct observation: Identify factors that could cause the problem 2a. Do not automatically accept that the cus- This is the second step in the troubleshooting pro- tomer is correct with their description of the cess. problem. Try to duplicate the problem. Crankshaft will not turn.
  • Page 19 BASIC TROUBLESHOOTING V. Internal binding, crankshaft, connect- Starts, runs poorly ing rod or piston (unrepairable) 3a. Starts, then dies Crankshaft turns, no start. Run the engine with a spark tester in- 2a. Most gasoline engine diagnosis involves iso- line between the spark plug wire and lating problems in the four critical factors an the spark plug or use an oscilloscope engine needs to run properly:...
  • Page 20 BASIC TROUBLESHOOTING VI. Flow blockage ping. It can also be caused by leaky carburetor float valve, if A Exhaust blockage, usually accompanied by there is a down-hill path from the an unusual exhaust sound. carb. to the intake port. Check oil •...
  • Page 21 BASIC TROUBLESHOOTING • Advanced ignition timing E Engine over-speed • Low octane fuel a. Continual over-speed • Over-heating engine (check for • Binding or damaged external gov- blocked cooling air flow) ernor linkage or carburetor throttle. • Carbon build-up in cylinder: glow- •...

  • Page 22: Repairing The Problem

    BASIC TROUBLESHOOTING Repairing the problem Leak-down test The third step in the troubleshooting process is to A leak-down test is the preferred method to test the repair the problem. This step consists of: engine’s ability to compress the charge. It will also show where pressure is leaking from.

  • Page 23: Compression Test

    BASIC TROUBLESHOOTING Connect tester to compressed air. Compression test Adjust the regulator knob until the needle on the To perform a compression test: gauge is in the yellow or set area of the gauge. NOTE: Compression should be in the range of Connect the tester to the adapter.

  • Page 24: Pcv Testing

    BASIC TROUBLESHOOTING Interpreting compression readings. PCV testing The PCV (Positive Crankcase Ventilation) valve is Table 2: located in the valve cover and allows the crankcase pressure to escape. Readings in Possible causes Leakage and blockage are the two failure modes for a PCV system.
  • Page 25 BASIC TROUBLESHOOTING 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 substantial case pressure. • A leaky PCV system will allow the engine to ingest contaminants through the system, accel- erating engine wear.
  • Page 26 BASIC TROUBLESHOOTING...

  • Page 27: Chapter 3: Air Intake System

    AIR INTAKE SYSTEM CHAPTER 3: AIR INTAKE SYSTEM Heat box Disconnect the wire from the ignition switch and the primer line from the primer button. One of the big differences between snow engines and all other small engines is that the air intake of the Slide the breather hose out of the heat box.

  • Page 28: Carburetor And Insulator

    AIR INTAKE SYSTEM Carburetor and Insulator 3b. Disconnect the fuel line from the fuel tank. See Figure 3.4. NOTE: Drain the fuel tank before starting work to prevent spillage. To avoid personal injury or prop- erty damage, use extreme care ! WARNING ! WARNING in handling gasoline.
  • Page 29 AIR INTAKE SYSTEM NOTE: The carburetors are not inter-changeable NOTE: An insulator block separates the carbu- from one engine model to another. To help pre- retor from the cylinder head. There is a gasket vent carburetor mix-ups, the engine model num- on each side of the insulator.
  • Page 30 AIR INTAKE SYSTEM...

  • Page 31: Chapter 4: The Fuel System And Governor

    NOTE: Fuel is the maintenance item most often overlooked by consumers. A lot of fuel systems A 10% ethanol (E10) mix is acceptable for MTD problems are caused by bad gas or too much engines. Anything higher than that will result in perfor- alcohol in it.

  • Page 32: Fuel Tank Vent

    THE FUEL SYSTEM AND GOVERNOR Generally these kits involve mixing a measured To test the cap vent amount of water and gas together and seeing were the Remove the fuel cap. boundary layer is. See Figure 4.2. Clean off the vent. Blow air into the vent hole.

  • Page 33: Inspect The Fuel Lines

    THE FUEL SYSTEM AND GOVERNOR Inspect the fuel lines The fuel tank • Are they cracked? To remove the fuel tank: • Are they clogged? Drain the tank. • Are they brittle? Remove the four screws that secure the fuel tank using a 12 mm wrench.

  • Page 34: Choke

    The choke rod can be bent slightly to facilitate adjustment. To access it: MTD snow engines are equipped with a choke and a primer. Both must be used to start the engine. The Remove the choke knob and the engine shroud choke should be opened when the engine starts.

  • Page 35: Primers

    THE FUEL SYSTEM AND GOVERNOR Primers Carburetors MTD engines use a dry bulb primer. This means If diagnosis indicates a fuel problem, inspect the that there is no fuel in the primer bulb. The primer carburetor. This is important even if problems are iden- works by pushing air into the float chamber of the car- tified elsewhere in the fuel system.

  • Page 36: Disassembly And Rebuilding The Carburetor

    THE FUEL SYSTEM AND GOVERNOR Disassembly and rebuilding the carburetor Remove the bowl bolt using a 10mm wrench. See Figure 4.12. Clamp-off the fuel line to prevent fuel spillage, then disconnect the fuel line from the carburetor. Float bowl Disconnect the primer hose. Remove the carburetor by following the steps Drain bolt described in Chapter 3: Air Intake and Filter.
  • Page 37 THE FUEL SYSTEM AND GOVERNOR Remove the pin that the float hinges on to Remove the main jet using a narrow-shank remove the float. straight blade screwdriver. See Figure 4.15. NOTE: The float is not adjustable. Spring ten- Main jet sion against the float valve begins to build from the horizontal position, putting progressively more pressure between the tip of the valve and...
  • Page 38 THE FUEL SYSTEM AND GOVERNOR Carefully pry out the metering plug using a small screwdriver. See Figure 4.18. NOTE: The main jet secures the emulsion tube in the central column of the carburetor. Throttle stop See Figure 4.16. screw Emulsion air port: pilot jet Metering Emulsion tube plug...
  • Page 39 THE FUEL SYSTEM AND GOVERNOR Start the engine and check the idle RPM using a tachometer. NOTE: The pilot screw regulates how much of this pre-mixed fuel/air emulsion is allowed to Check the top no load speed of the engine. enter the throat of the carburetor, to atomize NOTE: The top no-load speed of the engine is down-stream of the throttle plate.

  • Page 40: Governor

    THE FUEL SYSTEM AND GOVERNOR Governor Governor arm The engine speed is controlled by a balance To remove the governor arm from the governor shaft: between the force applied by a spring (pulling the throt- Remove the fuel tank by following the steps tle open) and a flyweight mechanism within the engine described in the Fuel Tank section of this chap- applying force to the governor arm (pushing the throttle...

  • Page 41: Governor Shaft

    THE FUEL SYSTEM AND GOVERNOR To install the governor arm: Governor shaft Rotate the governor shaft clockwise until it To remove or replace the governor shaft: stops. Remove the engine from the equipment that it Slide the arm onto the shaft. The flat on the top powers.

  • Page 42: Governor Cup And The Governor Gear

    THE FUEL SYSTEM AND GOVERNOR Governor cup and the governor gear Governor adjustment The Governor gear and cup are located inside the To adjust the governor: crankcase cover. See Figure 4.25. Remove the fuel tank by following the proce- dures described in the fuel tank section of this Governor gear chapter.

  • Page 43: Chapter 5: Lubrication

    • 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.

  • Page 44: Dip Stick Tube Removal

    Dip stick tube removal Lubrication system To remove/replace the dip stick tube: MTD uses a splash lube system for its horizontal shaft engines. The connecting rod has a dipper on it Remove the upper screw that secures the dip that “splashes” oil around the inside of the engine.

  • Page 45: Positive Crankcase Ventilation Valve

    LUBRICATION The second oil passage runs along the bottom side Positive crankcase ventilation valve of the cylinder. This is the oil return passage. As the The PCV valve is located inside the valve cover. name implies, it allows the oil collecting in the cylinder The function and test procedures for the PCV valve is head to return to the sump.
  • Page 46 LUBRICATION 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 torque of 62 - 79.7 in-lbs.

  • Page 47: Chapter 6: Starter And Charging Systems

    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- wheel. Remove the three nuts that secure the recoil assembly to the engine using a 8mm wrench.

  • Page 48: Starter Rope

    STARTER AND CHARGING SYSTEMS Install a starter cup: Starter Rope • Place the starter cup on the flywheel, with the The most common failure mode for most recoil three dimples on the bottom of the starter cup assemblies is a broken rope. into the dimples in the flywheel NOTE: If the spring was not damaged when the •...

  • Page 49: Starter Pulley And Recoil Spring

    STARTER AND CHARGING SYSTEMS Install the handle and handle insert on the loose Starter pulley and recoil spring end of the rope, again using a double half-hitch. The recoil spring is nested within the starter pulley See Figure 6.5. and both parts are sold as a single part number. Eye protection should be worn if the starter pulley is to be removed.
  • Page 50 STARTER AND CHARGING SYSTEMS Inspect the pawls and torsion springs for wear and damage. See Figure 6.8. NOTE: If 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 Torsion springs the outer lip of the recess of the pulley and wind the spring into the recess in a counter-clockwise...

  • Page 51: Electric Starter

    STARTER AND CHARGING SYSTEMS Electric starter NOTE: The rolled end of the pawl fits in the The electric starter is only available on the snow recess in the starter pulley. The hooked end engine. It is powered by an extension cord that is engages the starter cup.

  • Page 52: Charging System

    STARTER AND CHARGING SYSTEMS Pull back on the starter approximately 1/2”. Then Charging system angle it away from the engine while sliding it out Description of the engine. See Figure 6.13. Some engines are equipped with a charging system. The charging system consists of: Pull back and angle the starter away while •...
  • Page 53 STARTER AND CHARGING SYSTEMS Testing The multimeter should read a voltage of 13 - 18Vac. The charging system will produce AC and DC volt- ages. The rectifier for the DC voltage is inside of the Set the multimeter read DC voltage. stator and is not serviceable.

  • Page 54: Stator

    STARTER AND CHARGING SYSTEMS Stator Rotor To remove/replace the stator: Rotor failures are extremely rare. To check the rotor: Remove and ground the spark plug wire. • Confirm that the magnets are firmly attached to the flywheel. Remove the flywheel by following the steps described in Chapter 7: Ignition System.

  • Page 55: Chapter 7: Ignition System

    IGNITION SYSTEM CHAPTER 7: IGNITION SYSTEM Troubleshooting the ignition system Never remove the spark plug and hold it against the cylinder head to ! CAUTION ! CAUTION The purpose of the ignition system is to provide a test for spark. The fuel/air mix spark in the combustion chamber at the proper time to coming out of the spark plug hole ignite the fuel/air mixture.

  • Page 56: Stop Switch

    When the throttle is all the way to the right (stop), the multimeter should read at or near All MTD horizontal engines that are in use in North 0.0Ω, indicating continuity. See Figure 7.3. America have a stop switch built into the throttle lever assembly.

  • Page 57: Remote (Ignition) Stop Switch

    IGNITION SYSTEM Remote (ignition) stop switch • With the key removed, the meter should show continuity. See Figure 7.7. To test the remote stop switch: Remove the engine shroud by following the pro- Key removed cedures described in Chapter 3: Air Intake Sys- tem.

  • Page 58: Test For Ignition That Won't Turn Off

    Test for ignition that won’t turn off Repeat steps 6 - 8 on the other wire. See Figure 7.9. MTD engines are turned off by removing the spark from the engine. This is accomplished by shorting the primary windings of the coil to ground.

  • Page 59: The Module

    IGNITION SYSTEM The module • At operating speed, the ignition should produce voltage approaching 12,000. The coil in this ignition system is an inductive dis- charge magneto, contained in a single module. • At pull-over speed (~ 600 RPM), voltage should be at least 10,000V.

  • Page 60: Module Removal

    IGNITION SYSTEM Module removal Installing the module and setting the air gap Unplug the spark plug. NOTE: If just setting the air gap, loosen the module mounting screws first then follow the Remove the engine shroud by following the same steps as described below. steps procedures in Chapter 3: Air Intake Sys- tems.

  • Page 61: Flywheel

    See Figure 7.14. A sheared flywheel key will throw off the ignition tim- ing. Sheared keys are uncommon on MTD engines. If one is found, check the crankshaft and flywheel for damage. To Remove and/or inspect the flywheel and key: Remove the blower housing.

  • Page 62: About The Spark Plug

    IGNITION SYSTEM Inspect the key, keyway, and tapered mating sur- About the spark plug faces of the flywheel and crankshaft. • The spark plug is a Torch model F6RTC, gapped NOTE: If the key is damaged, it must be to .026”-.030” (0.65-0.75 mm). replaced.

  • Page 63: Spark Plug Removal

    IGNITION SYSTEM Spark plug removal 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 7.15. 13/16” spark plug socket Muffler Valve cover Figure 7.15 Gap a new spark plug to .026”-.030”...
  • Page 64 IGNITION SYSTEM...

  • Page 65: Chapter 8: Exhaust

    EXHAUST CHAPTER 8: EXHAUST The exhaust system is a frequently overlooked Remove the screw that holds the heat shield to component of an engine. It is important to make sure the cylinder head using a 10 mm wrench. the muffler is in good condition and free of debris and/ See Figure 8.2.
  • Page 66 Clean all of the gasket material off of the cylinder head and the muffler (if reusing the muffler) 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.

  • Page 67: Chapter 9: Cylinder Head

    CYLINDER HEAD CHAPTER 9: CYLINDER HEAD Cylinder head removal Remove the heat baffle. See Figure 9.2. The Cylinder head of the MTD engine can be removed without removing the engine from the piece of equipment. To remove the cylinder head: Disconnect and ground the spark plug high ten- sion lead.
  • Page 68 CYLINDER HEAD Remove the five screws securing the valve Remove the cylinder head bolts using a 12mm cover using a 10mm wrench. See Figure 9.4. wrench. See Figure 9.5. Cylinder head bolts Remove valve cover Figure 9.5 Figure 9.4 Loosen the jam nuts and fulcrum nuts that NOTE: The 490 engine has an over sized bolt secure the rocker arms using a 10mm wrench with a Belleville washer in the number 4 position.

  • Page 69: Cylinder Head Installation

    See Figure 9.7. See Figure 9.8. NOTE: Make a visual inspection of the valves NOTE: MTD uses graphite head gaskets that and cylinder bore to confirm the initial diagnosis. have a bead of silicon on them. They are not reusable.

  • Page 70: Valves

    CYLINDER HEAD Insert the push rods. Valves Install the rocker arms. The valves and valve seats can be serviced by grinding and lapping or the head can be replaced. Adjust the valve lash by following the steps Depending on local machine and labor costs, it is prob- described in Chapter 1: Introduction.
  • Page 71 CYLINDER HEAD Inspect the valve seat. See Figure 9.13. NOTE: The exhaust valve has a cap called an “adjuster” on it. The cap needs to be pulled off before the keeper can be removed. See Figure 9.11. .028-.035” Seat angle is 45 margin Seat contact...
  • Page 72 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.

  • Page 73: Chapter 10: Crankshaft, Piston And Connecting Rod

    CRANKSHAFT, PISTON AND CONNECTING ROD CHAPTER 10: CRANKSHAFT, PISTON AND CONNECTING ROD The exact procedure a technician uses to disas- Align the timing marks to allow easier removal of semble an engine depends on the type of repairs the cam shaft and to help protect the compres- needed.
  • Page 74 CRANKSHAFT, PISTON AND CONNECTING ROD Remove one of the piston pin retaining rings. See Figure 10.5. NOTE: The valve tappet should be kept riding against their original lobes. Once broken in, switching the tappets to run on different cam lobes will cause rapid tappet and cam wear. Remove the valve tappets.

  • Page 75: Crankshaft Inspection

    CRANKSHAFT, PISTON AND CONNECTING ROD Remove the piston rings from the piston using a Crankshaft inspection pair of piston ring pliers. See Figure 10.7. Inspect the crankshaft journals and the crank pin for galling, scoring, pitting or any other form of damage.

  • Page 76: Piston Inspection

    Piston Inspection Install rings back onto the piston. Clean the piston and remove all carbon from the NOTE: The compression rings on the MTD rings and ring groves. engine have different profiles. It is important that the proper profiled ring is on the right grove.
  • Page 77 CRANKSHAFT, PISTON AND CONNECTING ROD Measure the gap between the ring and the ring Measure the piston pin at the center and the land using a feeler gauge and compare the mea- ends using a micrometer or a vernier caliper. surement to the chart at the end of this chapter.

  • Page 78: Connecting Rod Inspection

    CRANKSHAFT, PISTON AND CONNECTING ROD Connecting rod inspection Cylinder inspection Inspect the connecting rod for cracks or any Clean and inspect the cylinder, inside and out. signs of damage. NOTE: If there is any sign of damage, especially Install the rod cap and tighten to a torque of 106 cracked cooling fins, short block the engine.

  • Page 79: Balance Shaft (483 & 490)

    (the piston, piston pin and one-third of the con- of the crankshaft, and the reciprocating motion of the necting rod). The crankshafts on MTD engines are not piston. See Figure 10.17. balanced. Extra weight is added to the crankshaft...

  • Page 80: Reassembly

    CRANKSHAFT, PISTON AND CONNECTING ROD Reassembly 5a. Compress the piston rings using a piston ring compressor. Install the governor shaft. 5b. Pre-lube the cylinder wall with clean 10W- NOTE: The governor shaft MUST be installed 30 motor oil before the crankshaft is installed. 5c.
  • Page 81 CRANKSHAFT, PISTON AND CONNECTING ROD 6c. Insert the balance shaft while aligning the Gently rock the crank case cover while rotating timing marks. See Figure 10.22. the crankshaft until it seats fully against the cylin- der block. Timing marks Install the crank case cover bolts and tighten to a torque of 80 - 106 in-lbs (9 - 12 Nm).

  • Page 82: Engine Specifications Chart

    CRANKSHAFT, PISTON AND CONNECTING ROD Engine specifications chart Specification New Min New Max Service Limit Bore (digit 2&3 of the model number) 3.071 78.02 3.072 78.03 3.080 78.23 3.268 83.02 3.269 83.03 3.277 83.24 3.544 90.02 3.544 90.03 3.553 90.26 Crank pin min.
  • Page 83 CRANKSHAFT, PISTON AND CONNECTING ROD Specification New Min New Max Service Limit Intake lobe height 1.248 31.70 1.252 31.80 1.237 31.42 1.281 32.54 1.285 32.64 1.269 32.24 1.281 32.54 1.285 32.64 1.269 32.24 Exhaust lobe height 1.248 31.70 1.252 31.80 1.237 31.52 1.261...
  • Page 84 CRANKSHAFT, PISTON AND CONNECTING ROD Specification New Min New Max Service Limit Balance shaft bearing max. ID (cylinder block) 0.591 15.00 0.591 15.00 0.592 15.03 0.591 15.00 0.591 15.00 0.592 15.03 Compression ring to land max. clearance 0.001 0.02 0.002 0.06 0.008 0.20...
  • Page 85 CRANKSHAFT, PISTON AND CONNECTING ROD Minimum Maximum Intake valve lash 0.004 0.10 0.006 0.15 0.004 0.10 0.006 0.15 0.004 0.10 0.006 0.15 Exhaust valve lash 0.006 0.15 0.008 0.20 0.006 0.15 0.008 0.20 0.006 0.15 0.008 0.20 Spark plug gap 0.026 0.65 0.030...

  • Page 86: Engine Torque Values Chart

    CRANKSHAFT, PISTON AND CONNECTING ROD Engine torque values chart Fastener Torque Blower housing 80-106 in-lbs (9-12 Nm) 80-106 in-lbs (9-12 Nm) 80-106 in-lbs (9-12 Nm) Carburetor drain bolt 80-106 in-lbs (9-12 Nm) 80-106 in-lbs (9-12 Nm) 80-106 in-lbs (9-12 Nm) Carburetor mounting nuts 80-106 in-lbs (9-12 Nm) 80-106 in-lbs (9-12 Nm)

  • Page 87: Chapter 11: Failure Analysis

    FAILURE ANALYSIS CHAPTER 11: FAILURE ANALYSIS A properly maintained engine will provide years of Abrasive Ingestion service. Occasionally an engine will fail. An important Abrasive Ingestion is when hard particles are intro- part of working on engines is finding out why they duced into the engine.
  • Page 88 FAILURE ANALYSIS Particles that enter the intake system travel at Other sources of abrasives that get into the engine great speed and act like sand blasting media includes carbon that builds up on the top side of the inside the engine. This causes wear to the parts piston, metal shavings from the wear of engine parts or affected.

  • Page 89: Insufficient Lubrication

    FAILURE ANALYSIS Because the oil absorbs the abrasive particles, Insufficient lubrication the engine components that are immersed in oil The bearing surfaces in an engine are not smooth. will show definite signs of abrasive ingestion As a result of the machining processes to make the especially around the connecting rod and main engine parts, there are little peaks and valleys that are bearing journals.

  • Page 90: Engine Overspeed

    Metal to metal On most engines that would be about an inch transfer 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 Figure 11.7...

  • Page 91: Overheated

    This warping of the head allows the head gasket to leak. A leaking head gasket allows the compressed The MTD engines are air cooled engines. Because gases in the engine to escape, lowering the compres- of this, cleanliness of the engine is very important to sion in the engine and hurting engine performance.

  • Page 92: Mechanical Breakage/ Wear

    FAILURE ANALYSIS Mechanical Breakage/ Wear Detonation/preignition Sometimes an engine fails because a part breaks. Detonation is the undesirable condition of the fuel There are generally three causes of a broken part, out- spontaneously combusting the combustion chamber side of the previously discussed engine failures. They prior to the spark plug firing.

This manual is also suitable for:

490 series483 series

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