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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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Summarization of Contents

Professional Shop Manual
Chapter 1: Introduction - Manual Scope and Basics
Outlines the manual's purpose, fastener details, assembly guidelines, and engine identification.
Chapter 1: Introduction - Maintenance and Fuel Systems
Covers spark plug service, oil specifications, changes, fuel requirements, and filter maintenance.
Chapter 1: Introduction - Valve Lash and Engine Cleaning
Details valve lash adjustment procedures and recommendations for cleaning the engine.
Chapter 1: Introduction - Specifications and Charts
Provides general torque specifications, maintenance schedules, and key engine specifications.
Chapter 2: Basic Troubleshooting - Fundamentals and Problem Definition
Defines troubleshooting, diagnosis, and outlines initial steps for identifying engine problems.
Chapter 2: Basic Troubleshooting - Symptom Analysis and Tests
Correlates symptoms like blockages, smoke, noises with faults, and covers diagnostic tests.
Chapter 2: Basic Troubleshooting - Repair and Test Interpretation
Covers repair steps, prime tests, leak-down tests, and interpreting compression readings.
Chapter 3: Air Intake System - Heat Box and Carburetor Service
Explains the heat box's role and covers carburetor and insulator removal/installation procedures.
Chapter 4: The Fuel System and Governor - Fuel and Carburetor Service
Details fuel inspection, testing, tank vent, filter, lines, and carburetor inspection.
Chapter 4: The Fuel System and Governor - Governor System
Explains governor operation and procedures for governor arm and shaft removal, installation, and adjustment.
Chapter 5: Lubrication - Oil and PCV System Service
Covers oil specifications, level checks, dipstick tube removal, and PCV valve service.
Chapter 6: Starter and Charging Systems - Starter Service
Details recoil starter removal, rope replacement, starter pulley/spring service, and electric starter replacement.
Chapter 6: Starter and Charging Systems - Charging System
Describes charging system components (stator, rotor, rectifier) and provides testing procedures.
Chapter 7: Ignition System - Troubleshooting and Stop Switch
Outlines ignition troubleshooting, testing stop switches, and verifying engine shutdown functionality.
Chapter 7: Ignition System - Module, Flywheel, and Spark Plug Service
Covers ignition module service, flywheel inspection, and spark plug removal/installation procedures.
Chapter 8: Exhaust - Muffler Service
Provides steps for removing and reinstalling the muffler, including gasket replacement.
Chapter 9: Cylinder Head - Head Removal, Installation, and Valve Service
Comprehensive guides for cylinder head removal, installation, and servicing engine valves.
Chapter 10: Crankshaft, Piston, and Connecting Rod - Disassembly and Inspection
Details engine disassembly, component removal, and inspection procedures for crankshaft, piston, and rod.
Chapter 10: Crankshaft, Piston, and Connecting Rod - Reassembly and Specifications
Covers engine reassembly steps, specifications, and torque values for all components.
Chapter 11: Failure Analysis - Causes and Symptoms
Explains failure analysis and details abrasive ingestion causes, symptoms, and mechanisms.
Chapter 11: Failure Analysis - Lubrication, Overspeed, and Overheating
Describes how insufficient lubrication, engine overspeed, and overheating lead to component damage.
Chapter 11: Failure Analysis - Mechanical Issues and Detonation
Covers mechanical failures from wear/abuse and detonation/preignition causes and resulting damage.

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