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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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Table of Contents
Troubleshooting
Related Manuals for MTD 490 Series
Summarization of Contents
Introduction
Professional Shop Manual Intent
Details the purpose and scope of the shop manual for MTD horizontal shaft engines.
Text Format Conventions
Explains the use of notes, cautions, warnings, and danger signals.
Fastener Specifications
Provides information on metric and fractional inch fasteners and their usage.
Assembly Instructions
Describes how torque specifications and assembly procedures are presented.
Engine Model Designators
Explains the MTD horizontal engine model designation system.
Engine Serial Numbers
Details the format and components of MTD engine serial numbers.
Maintenance Procedures
Covers essential maintenance tasks like spark plug checks and oil changes.
Spark Plug Service
Specifies the correct spark plug, gap, and inspection criteria.
Oil Type and Capacity
Details the recommended oil grade, capacity, and checking procedure.
Changing Engine Oil
Step-by-step guide for draining and refilling engine oil.
Fuel System Information
Discusses fuel types, alcohol content, and their impact on engines.
Fuel Filter Replacement
Instructions for safely removing and replacing the fuel filter.
Valve Lash Adjustment
Procedure for checking and adjusting intake and exhaust valve lash.
Engine Cleaning
Guidance on cleaning the engine for optimal performance and longevity.
Frequently Used Specifications
Summary of common engine specifications for quick reference.
Basic Troubleshooting
Troubleshooting Definitions
Defines key terms used in troubleshooting, such as troubleshooting and diagnosis.
Troubleshooting Steps Overview
Outlines the systematic approach to diagnosing and resolving engine issues.
Defining the Engine Problem
Guide to identifying and categorizing engine operational issues.
Direct Observation Techniques
Methods for visually inspecting the equipment to identify potential causes.
Identifying Problem Causes
Lists potential causes for common engine starting and running problems.
No Start Diagnosis
Troubleshooting steps for engines that turn over but do not start.
Poor Running Diagnosis
Addresses issues like low power, smoke, and unusual sounds during operation.
Flow Blockage Issues
Diagnosing problems related to intake and exhaust flow restrictions.
Smoke Emission Diagnosis
Interpreting engine smoke colors to identify fuel/air mixture or oil consumption issues.
Unusual Noise Diagnosis
Identifying engine issues based on sounds like knocking, clicking, or clatter.
Engine Overspeed Issues
Diagnosing and understanding engine overspeed conditions and their causes.
RPM Surge (Hunting) Diagnosis
Troubleshooting engine speed fluctuations or hunting conditions.
Repairing Engine Problems
Steps for performing repairs, testing, and customer education post-repair.
Prime Test Procedure
Method to isolate fuel system issues by testing with a prime.
Leak-Down Test
Procedure for assessing cylinder sealing using external air pressure.
Compression Test
Steps and interpretation for performing a cylinder compression test.
PCV System Testing
Diagnosing positive crankcase ventilation valve issues and their effects.
Air Intake System
Heat Box Functionality
Explains the role of the heat box in preheating intake air for snow engines.
Heat Box Removal
Procedure for removing and replacing the engine heat box assembly.
Carburetor and Insulator Service
Steps for removing the carburetor and insulator block.
Fuel System and Governor
Fuel Inspection Guidelines
How to inspect fuel for water, dirt, discoloration, and smell.
Alcohol Content Testing
Using test kits to determine alcohol content in gasoline.
Fuel Tank Vent Testing
Procedure to test the fuel cap vent for proper air flow.
Fuel Filter Service
Information on locating, cleaning, or replacing the fuel filter.
Fuel Line Inspection
Checking fuel lines for cracks, clogs, or brittleness.
Fuel Tank Removal
Steps to safely drain and remove the fuel tank.
Choke Operation and Adjustment
How to check and adjust the engine choke linkage.
Primer System Testing
Procedure to test the primer bulb and hose assembly.
Carburetor Inspection
Guidance on inspecting the carburetor for dirt, varnish, or damage.
Carburetor Disassembly
Step-by-step instructions for taking apart the carburetor for cleaning/rebuilding.
Governor System Overview
Explains the function of the governor in controlling engine speed.
Governor Arm Removal
Procedure for removing the governor arm from the governor shaft.
Governor Shaft Removal
Steps to remove the governor shaft from the engine block.
Governor Adjustment Procedure
How to adjust the governor to achieve the correct engine RPM.
Lubrication
Recommended Oil and Capacity
Specifies oil type, API rating, and capacity for the engine.
Checking Oil Level with Dipstick
Step-by-step guide to accurately check the engine oil level.
Dipstick Tube Removal
Instructions for removing and replacing the oil dipstick tube.
Lubrication System Operation
Explanation of the splash lubrication system and oil passages.
Positive Crankcase Ventilation
Details on the PCV valve function and valve cover removal.
Starter and Charging Systems
Recoil Starter Assembly Removal
Procedure for removing the recoil starter from the engine.
Starter Cup Inspection and Replacement
How to inspect and replace the starter cup.
Starter Rope Replacement
Instructions for replacing the recoil starter rope.
Starter Pulley and Spring
Information on the starter pulley, recoil spring, and disassembly.
Electric Starter Replacement
Steps for replacing the electric starter assembly.
Charging System Description
Overview of the charging system components: stator, rotor, and rectifier.
Charging System Testing
Procedure for testing the charging system's AC and DC voltage output.
Stator Removal and Replacement
Instructions for removing and installing the alternator stator.
Rotor Inspection
How to inspect the flywheel rotor magnets for attachment and magnetism.
Ignition System
Ignition System Troubleshooting
General steps for diagnosing ignition system faults.
Spark Tester Usage
How to use a spark tester to check for spark presence and strength.
Stop Switch Testing
Procedure for testing the throttle lever stop switch continuity.
Remote Stop Switch Testing
How to test the remote ignition stop switch for continuity.
Testing Ignition Shut-off
Verifying that the ignition system can be properly shut off.
Ignition Module Function
Explanation of the inductive discharge magneto ignition module.
Module Removal and Air Gap Setting
Steps for removing the ignition module and setting the air gap.
Flywheel Removal and Inspection
Procedure for removing the flywheel and checking for key damage.
Spark Plug Service
Details on spark plug type, gap, cleaning, and inspection.
Spark Plug Removal and Installation
Steps for removing, gapping, and installing the spark plug.
Exhaust
Muffler Service
Instructions for removing, replacing, and inspecting the engine muffler.
Cylinder Head
Cylinder Head Removal
Step-by-step guide to removing the cylinder head from the engine.
Cylinder Head Installation
Procedure for installing the cylinder head with a new gasket.
Valve Service Procedures
Instructions for servicing engine valves, including removal and inspection.
Crankshaft, Piston and Connecting Rod
Engine Reassembly Steps
Comprehensive guide to reassembling the engine short block.
Piston Inspection
Procedure for inspecting pistons, rings, and cylinder bores.
Connecting Rod Inspection
How to inspect the connecting rod for wear and measure clearances.
Cylinder Inspection
Procedure for inspecting the cylinder bore for wear and cross-hatch integrity.
Balance Shaft Operation
Explains the function of the balance shaft in reducing engine vibration.
Failure Analysis
Abrasive Ingestion Failures
Diagnosing engine damage caused by abrasive particles entering the system.
Insufficient Lubrication Failures
Identifying engine damage resulting from inadequate oil supply or quality.
Engine Overspeed Failures
Analyzing engine damage caused by exceeding maximum operating speed.
Overheating Failures
Diagnosing engine damage due to excessive heat buildup.
Mechanical Breakage/Wear
Identifying failures from part breakage, wear, abuse, or manufacturing defects.
Detonation and Preignition
Understanding and diagnosing engine detonation and preignition issues.
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