0458-759-8221-C
2
English 
1 Introduction
Thank you for your purchase. The information contained in 
this manual will help you receive maximum performance and 
satisfaction from your STIHL chain saw and, if followed, 
reduce the risk of injury from its use.
SAVE THIS MANUAL!
Have your authorized STIHL servicing dealer show you how 
to operate your chain saw. All safety precautions that are 
generally observed when working with an axe or a hand saw 
also apply to the operation of chain saws. Observe all 
applicable federal, state and local safety regulations, 
standards and ordinances.
Do not lend or rent your chain saw without this instruction 
manual. Allow only persons who have the proper training 
and fully understand the information in this manual to 
operate the chain saw.
For further information, or if you do not understand any of 
the instructions in this manual, please go to www.stihl.ca or 
contact your authorized STIHL servicing dealer.
2.1 Signal Words
This manual contains safety information that requires your 
special attention. Such information is introduced with the 
following symbols and signal words:
20  Storing
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20.1 Storing the Chain Saw
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21  Cleaning
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21.1 Cleaning the Chain Saw
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21.2 Cleaning the Guide Bar and Saw Chain
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21.3 Cleaning the Air Filter
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21.4 Cleaning the Spark Plug
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22  Inspection and Maintenance
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22.1 Inspection and Maintenance Chart
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22.2 Inspecting and Maintaining the Chain Saw
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22.3 Inspecting and Maintaining the Chain Sprocket
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22.4 Inspecting and Maintaining the Guide Bar
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22.5 Inspecting, Maintaining and Sharpening the Saw 
Chain
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23  Troubleshooting Guide
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23.1 Chain saw
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23.2 Clearing the Combustion Chamber
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24  Specifications
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24.1 CEPA
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24.2 STIHL MS 661 C-M
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24.3 Chain Sprockets
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24.4 Minimum Groove Depth of Guide Bars
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24.5 Depth Gauge Setting
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24.6 Symbols on the Chain Saw
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24.7 Engineering Improvements
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25  CSA Standard
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25.1 Chain Saw Class
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25.2 Definition of the Chain Saw Classes according to 
CSA Z62.1
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26  Combinations of Guide Bars and Saw Chains
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26.1 STIHL MS 661 C-M
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27  Replacement Parts and Equipment
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27.1 Genuine STIHL Replacement Parts
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28  Disposal
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28.1 Disposal of the Power Tool
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29  Emission Control Warranty
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29.1 STIHL Limited Federal Emission Control 
Warranty Statement
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1 Introduction
Because a chain saw is a high-speed wood-
cutting tool, special safety precautions must be 
observed to reduce the risk of personal injury.
Read this instruction manual thoroughly before 
use and periodically thereafter. Follow all safety 
precautions. Careless or improper use of the 
chain saw can cause serious or fatal injury.
2 Guide to Using this Manual