Stihl MS660 or 066 Piston & Rings Installation: A Complete Guide

Introduction

This tutorial provides a comprehensive guide on how to install piston rings and perform a top-end rebuild on a Stihl MS660 or 066 chainsaw. Whether you're looking to save money by doing it yourself or simply want to understand the process better, this guide will walk you through each crucial step of the rebuild, including the use of aftermarket and OEM parts.

Step 1: Gather Tools and Parts

Before starting the rebuild, ensure you have the following tools and parts:

Tools Needed

• T27 Torx bit
• Long reach 3/8 drive ratchet
• Pressure washer or cleaning solution
• Hemostats or needle-nose pliers
• Torque wrench
• Piston ring compressor (plastic preferred)
• Screwdrivers (various sizes)
• Shop air compressor

Parts Needed

• Aftermarket or OEM piston kit
• New spark plug (if applicable)
• Gaskets and seals (check for wear)
• Fuel filter

Step 2: Prepare the Work Area

• Clean your work area thoroughly to prevent dirt from entering the crankcase.
• Disassemble the chainsaw carefully to access the cylinder and piston. Remove the carburetor, spark plug, and any covers as necessary.

Step 3: Clean the Components

• Use a pressure washer to clean the engine block and surrounding parts. This prevents debris from contaminating the crankcase during the rebuild.
• Inspect all components for wear or damage, particularly the intake manifold boot and fuel filter.

Step 4: Remove the Old Piston and Cylinder

• Take off the cylinder by removing the four T27 screws.
• Detach the piston by removing the clips that hold the wrist pin in place. Use a small screwdriver to pry them out, ensuring you don’t lose them.

Step 5: Install the New Piston

• Before installing the new piston, ensure it's lubricated with two-cycle oil.
• Place the new piston rings onto the piston, aligning the notches with the locating pins.
• Use a piston ring compressor to compress the rings and insert the piston into the cylinder, ensuring the arrow on the piston points toward the exhaust.

Step 6: Reattach the Cylinder

• Carefully align the new cylinder over the piston and ensure the gasket is in place.
• Secure the cylinder with the T27 screws, tightening them in a cross pattern to ensure even pressure. Torque to 150 inch-pounds.

Step 7: Reassemble Other Components

• Reattach the manifold boot and carburetor. Ensure all connections are secure and leak-free.
• Install the safety brake and any other covers that were removed during disassembly.

Step 8: Perform a Leak Down Test

• Use a pressure tester to check for leaks in the crankcase. Block off the intake and exhaust ports to ensure no air escapes.
• If the air pressure drops, inspect for leaks around the gaskets and seals. Use soapy water to identify any leaks.

Step 9: Final Checks and Clean Up

• After confirming everything is sealed, recheck the carburetor settings and clean the air filter.
• Replace the fuel filter in the tank to ensure clean fuel reaches the engine.
• Reassemble the chainsaw carefully, ensuring all screws and clips are securely fastened.

Conclusion

You've now successfully installed new piston rings and completed a top-end rebuild on your Stihl MS660 or 066 chainsaw. Regular maintenance and cleaning can help prevent future issues, ensuring your chainsaw operates smoothly for years. If you encounter problems, don't hesitate to consult a professional or refer back to this guide for troubleshooting tips. Happy cutting!