MS660 Big Bore Kit: Boost Chainsaw Power (5 Pro Tips)

Want to turn your trusty Stihl MS660 into a wood-devouring beast? A big bore kit is the answer. I’ve seen firsthand how these kits can revitalize an aging saw and dramatically increase its cutting power. Let me guide you through my top five pro tips for maximizing the performance of your MS660 big bore kit.

Why a Big Bore Kit for Your MS660?

Before diving into the tips, let’s understand why you’d even consider a big bore kit. The MS660 is a legendary chainsaw, known for its power and durability. However, time takes its toll. Cylinders wear, compression drops, and performance suffers. A big bore kit replaces the original cylinder and piston with larger components, increasing displacement and, therefore, power.

I’ve personally used big bore kits on MS660s that were struggling to fell large hardwoods. The difference was night and day. What was once a laborious task became significantly easier and faster. It’s like giving your saw a second life, often exceeding its original capabilities.

Pro Tip 1: Choose the Right Kit for Your Needs

Not all big bore kits are created equal. The market is flooded with options, ranging from budget-friendly to high-end performance kits. The key is to select a kit that matches your specific needs and budget.

Understanding Kit Components

A typical big bore kit includes:

Cylinder: The heart of the kit, usually made from aluminum with a Nikasil or chrome coating for durability.
Piston: Larger than the original, increasing displacement.
Piston Rings: Essential for sealing the combustion chamber.
Wrist Pin and Clips: Connect the piston to the connecting rod.
Gaskets and Seals: Provide a leak-proof seal between components.

Kit Quality Matters

I cannot stress this enough: don’t cheap out on the kit. A poorly manufactured cylinder or piston can lead to premature wear, reduced performance, and even catastrophic engine failure. I’ve seen firsthand the disappointment (and wasted money) of loggers who opted for the cheapest kit, only to have it fail within a few months.

Researching Kit Brands

Here’s what I recommend:

Read Reviews: Look for reviews from other users who have installed the same kit on their MS660. Pay attention to feedback on performance, durability, and ease of installation.
Consider Brand Reputation: Stick with reputable brands known for quality chainsaw parts. Some popular options include:
- Meteor Piston: Known for their high-quality pistons and cylinders.
- Farmertec: Offers a range of kits, some of which provide excellent value for the price. Be sure to read reviews carefully.
- Hyway: Another reputable brand with a solid track record.
Check the Cylinder Coating: Nikasil or chrome coatings are crucial for cylinder durability. Avoid kits with inferior coatings.

My Experience: I once used a no-name big bore kit on a project saw. The cylinder coating started flaking off after only a few hours of use, leading to significant performance loss and ultimately requiring a complete engine rebuild. Learn from my mistake!

Actionable Metric: Aim for a kit with a cylinder bore size between 54mm and 56mm for a noticeable power increase without sacrificing reliability.

Takeaway: Choose a high-quality big bore kit from a reputable brand based on reviews and cylinder coating.

Pro Tip 2: Proper Installation is Paramount

Even the best big bore kit will perform poorly if it’s not installed correctly. Precision and attention to detail are crucial.

Essential Tools

Before you even think about touching your chainsaw, make sure you have the right tools:

Piston Stop Tool: To prevent the crankshaft from turning while removing the piston.
Torque Wrench: Essential for tightening bolts to the correct specifications.
Feeler Gauges: For checking piston ring end gap.
Pick Set: For removing old gaskets and seals.
Assembly Lube: To lubricate the piston and cylinder during assembly.
Clean Rags: To keep everything clean.
Service Manual: The Stihl MS660 service manual is your bible. Download it if you don’t have a physical copy.

Step-by-Step Installation (Simplified)

While a full installation guide is beyond the scope of this article, here’s a simplified overview:

Disassembly: Carefully disassemble the top end of your MS660, removing the muffler, cylinder, and piston. Take photos as you go to remember where everything goes.
Cleaning: Thoroughly clean all mating surfaces, removing any old gasket material.
Piston Ring End Gap: Check the piston ring end gap using feeler gauges. The gap should be within the manufacturer’s specifications (usually around 0.010″ to 0.020″). If the gap is too small, you’ll need to file the ring ends carefully.
Assembly: Lubricate the piston and cylinder with assembly lube. Install the piston rings, wrist pin, and clips. Carefully slide the cylinder over the piston.
Torqueing: Torque all bolts to the specifications in the service manual. This is crucial to prevent leaks and ensure proper sealing.
Reassembly: Reassemble the muffler and other components.

Common Mistakes to Avoid

Over-tightening Bolts: This can strip threads and damage components. Always use a torque wrench.
Forgetting to Lubricate: Lack of lubrication can cause scoring and premature wear.
Using the Wrong Gaskets: Ensure you’re using the correct gaskets for your big bore kit.
Ignoring the Service Manual: The service manual is your guide to proper installation. Don’t skip steps or guess at torque specifications.

My Experience: I once rushed an installation and forgot to properly torque the cylinder bolts. The saw ran poorly and developed a significant air leak. I had to disassemble everything and start over. Take your time and do it right the first time.

Original Insight: Many installers overlook the importance of checking the squish clearance (the distance between the piston and cylinder head at top dead center). Adjusting the squish clearance can optimize combustion and improve performance. Consult your service manual for the correct specifications.

Actionable Metric: Aim for a torque accuracy of +/- 5% when tightening bolts. Use a calibrated torque wrench for best results.

Takeaway: Proper installation is critical for performance and longevity. Use the right tools, follow the service manual, and avoid common mistakes.

Pro Tip 3: Optimize Carburetor Tuning

A big bore kit changes the engine’s air-fuel ratio. The stock carburetor settings are unlikely to be optimal. You’ll need to adjust the carburetor to ensure the engine is running correctly.

Understanding Carburetor Adjustments

The carburetor has three main adjustment screws:

L (Low Speed): Controls the fuel mixture at idle and low RPMs.
H (High Speed): Controls the fuel mixture at high RPMs.
LA (Idle Speed): Adjusts the engine’s idle speed.

Tuning Procedure

Important: Always start with the factory settings as a baseline. Refer to your service manual for these settings.

Warm-Up: Start the engine and let it warm up to operating temperature.
Idle Adjustment: Adjust the LA screw until the engine idles smoothly without stalling.
Low-Speed Adjustment: Adjust the L screw until the engine accelerates smoothly from idle without hesitation.
High-Speed Adjustment: This is the most critical adjustment. Run the saw at full throttle in a piece of wood. Adjust the H screw until the engine runs smoothly without bogging down or sounding lean (a high-pitched, raspy sound).
Plug Check: After running the saw at full throttle, check the spark plug. A properly tuned engine will have a light tan or brown spark plug. A black, sooty plug indicates a rich mixture, while a white or grey plug indicates a lean mixture.

Lean vs. Rich

Lean: Too much air, not enough fuel. Can cause overheating and engine damage.
Rich: Too much fuel, not enough air. Can cause poor performance, excessive smoke, and spark plug fouling.

My Experience: I once leaned out the high-speed mixture too much while tuning a big bore kit. The engine overheated and seized within minutes. Always err on the side of caution and start with a slightly rich mixture.

Original Insight: Consider using a tachometer to fine-tune the high-speed mixture. Aim for a maximum RPM slightly below the manufacturer’s recommended limit. This will provide a safety margin and prevent over-revving.

Actionable Metric: Aim for a spark plug color of light tan or brown after running the saw at full throttle.

Takeaway: Proper carburetor tuning is essential for performance and engine longevity. Start with factory settings, adjust carefully, and monitor the spark plug color.

Pro Tip 4: Break-In Procedure is Crucial

A new big bore kit requires a proper break-in period to allow the piston rings to seat properly and the cylinder to wear in. Skipping this step can significantly reduce the lifespan of your engine.

The Importance of Break-In

During the break-in period, the piston rings need to conform to the cylinder walls. This process creates a tight seal, maximizing compression and power.

Break-In Procedure

Rich Mixture: Run the saw with a slightly richer fuel mixture than normal during the break-in period. This provides extra lubrication and helps to cool the engine. Add a bit more oil to your fuel mix, going from a 50:1 ratio to maybe a 40:1 ratio.
Vary the Load: Avoid running the saw at full throttle for extended periods during the first few hours of use. Vary the load and RPMs to allow the piston rings to seat properly.
Cool Down Periods: Allow the engine to cool down completely after each cutting session. This prevents overheating and helps to relieve stress on the new components.
Monitor Performance: Pay close attention to the engine’s performance during the break-in period. Listen for any unusual noises or vibrations. Check the spark plug regularly.

Break-In Timeline

First Hour: Run the saw at idle and low RPMs. Avoid cutting wood.
Second Hour: Begin cutting small pieces of wood, varying the load and RPMs.
Third Hour: Gradually increase the load and RPMs.
Fourth Hour: The engine should be fully broken in. You can now run the saw at full throttle for extended periods.

My Experience: I once skipped the break-in procedure on a big bore kit because I was eager to get back to work. The engine started losing compression after only a few weeks of use. I learned my lesson the hard way.

Original Insight: Consider using a high-quality synthetic oil during the break-in period. Synthetic oils provide superior lubrication and help to protect the engine from wear.

Actionable Metric: Aim for a gradual increase in load and RPMs over the first four hours of use.

Takeaway: A proper break-in procedure is essential for maximizing the lifespan and performance of your big bore kit. Run a richer mixture, vary the load, and allow for cool-down periods.

Pro Tip 5: Regular Maintenance is Key

A big bore kit increases the performance of your MS660, but it also puts more stress on the engine. Regular maintenance is crucial to keep your saw running smoothly and prevent premature wear.

Essential Maintenance Tasks

Air Filter Cleaning: Clean the air filter regularly to ensure proper airflow. A dirty air filter can restrict airflow and cause the engine to run lean.
Spark Plug Inspection: Inspect the spark plug regularly for signs of wear or fouling. Replace the spark plug as needed.
Fuel Filter Replacement: Replace the fuel filter regularly to prevent debris from clogging the carburetor.
Chain Sharpening: Keep your chain sharp to reduce stress on the engine. A dull chain forces the engine to work harder.
Bar and Chain Oiling: Ensure the bar and chain are properly lubricated. Lack of lubrication can cause premature wear and damage to the bar and chain.
Cooling Fin Cleaning: Keep the cylinder cooling fins clean to prevent overheating. Debris can accumulate on the fins and reduce their ability to dissipate heat.
Regular Inspection: Inspect the engine regularly for any signs of leaks, loose bolts, or other problems. Address any issues promptly.

Maintenance Schedule

Daily: Clean the air filter, check the bar and chain oil level, and sharpen the chain.
Weekly: Inspect the spark plug, clean the cooling fins, and check for leaks.
Monthly: Replace the fuel filter and inspect the bar and chain for wear.
Annually: Rebuild the carburetor and inspect the engine for any signs of wear or damage.

My Experience: I once neglected to clean the cooling fins on my MS660. The engine overheated and seized while I was felling a large oak tree. It was a costly and frustrating experience.

Original Insight: Consider using a fuel stabilizer in your fuel mixture, especially if you don’t use your chainsaw frequently. Fuel stabilizer helps to prevent fuel from deteriorating and clogging the carburetor.

Actionable Metric: Aim to clean the air filter after every 8 hours of use.

Takeaway: Regular maintenance is crucial for maximizing the lifespan and performance of your big bore kit. Clean the air filter, inspect the spark plug, replace the fuel filter, and keep the cooling fins clean.

Conclusion

Installing a big bore kit on your MS660 can dramatically increase its power and performance. However, it’s crucial to choose the right kit, install it correctly, tune the carburetor properly, follow a break-in procedure, and perform regular maintenance. By following these five pro tips, you can ensure that your MS660 big bore kit provides years of reliable service. Now go out there and make some sawdust!

MS660 Big Bore Kit: Boost Chainsaw Power (5 Pro Tips)