Stihl Chainsaw Bar 20 Inch (5 Pro Tips for Perfect Tension)

(Image: A split image. On one side, a chainsaw bar is visibly drooping with excessive slack in the chain. On the other, the same bar shows perfect tension, with the chain taut but flexible, and a slight “snap” when lifted.)

Stihl Chainsaw Bar 20 Inch: 5 Pro Tips for Perfect Tension

As a seasoned woodcutter, I’ve spent countless hours in the field, felling trees and processing timber. And let me tell you, nothing’s more frustrating – and potentially dangerous – than a chainsaw with improperly tensioned chain. It’s like trying to drive a car with flat tires; you’re going nowhere fast, and you risk a serious blowout. The 20-inch bar is a real workhorse, a sweet spot for many tasks, but only if you keep it properly tensioned. That’s why I’m sharing my top five pro tips to ensure your Stihl chainsaw bar is always perfectly tensioned, maximizing its performance, lifespan, and, most importantly, your safety.

Why Proper Chain Tension Matters: More Than Just Cutting Faster

Before we dive into the how-to, let’s understand the why. Chain tension isn’t just about cutting speed; it’s about the overall health and safety of your chainsaw operation.

• Safety First: A loose chain can derail during operation, becoming a dangerous projectile. A chain that’s too tight can snap, also posing a risk. I once saw a chain break on a job site, and thankfully, no one was hurt, but it was a stark reminder of the potential dangers.
• Performance: A properly tensioned chain cuts more efficiently, reducing strain on the engine and bar. This translates to faster cutting times and less fuel consumption. A loose chain will bounce and vibrate, making it harder to control the saw and resulting in uneven cuts.
• Longevity: Consistent improper tension accelerates wear and tear on the chain, bar, and even the sprocket. Replacing these components can be costly and time-consuming. I’ve learned the hard way that preventative maintenance is always cheaper than repairs.
• Bar Oil Efficiency: Correct tension helps the chain properly distribute bar oil, reducing friction and extending the life of the bar. A loose chain might not effectively pick up and distribute oil, leading to premature wear and overheating.

Tip #1: The “Snap Test” – Your Quick and Dirty Tension Gauge

The “snap test” is my go-to method for quickly checking chain tension in the field. It’s simple, reliable, and requires no tools.

1. Safety First: Always wear gloves when handling the chain. Engage the chain brake.
2. Locate the Midpoint: Find the midpoint of the bar on the underside.
3. Lift the Chain: Using a gloved hand, gently pull the chain away from the bar at the midpoint.
4. The “Snap”: You should be able to pull the chain out far enough to see about half of the drive links. When released, the chain should “snap” back against the bar.
5. Adjust Accordingly: If the chain hangs loosely or doesn’t snap back, it’s too loose. If you can barely pull it away from the bar, it’s too tight.

Why this works: The “snap test” provides a tactile assessment of the chain’s slack. The slight play allows for thermal expansion during operation, preventing the chain from becoming too tight as it heats up. I’ve found that aiming for that distinct “snap” sound is the key to getting it right.

Data Point: A study by the Oregon State University Extension Service found that chainsaws with properly tensioned chains experienced up to 20% less wear on the bar and chain over a 6-month period compared to saws with inconsistent tension.

Tip #2: Mastering the Side-Mounted Chain Tensioner – A Step-by-Step Guide

Most modern Stihl chainsaws feature a side-mounted chain tensioner. This design makes adjustments significantly easier and safer than older front-mounted systems. Here’s how to use it effectively:

1. Safety First: Turn off the chainsaw and engage the chain brake.
2. Loosen the Bar Nuts: Using the appropriate wrench (usually included with the saw), loosen the bar nuts that hold the side cover in place. Don’t remove them completely; just loosen them enough so the bar can move freely.
3. Locate the Tensioning Screw: The tensioning screw is usually a small screw or dial located on the side of the chainsaw, near the bar nuts.
4. Tighten or Loosen: Turning the screw clockwise tightens the chain; turning it counter-clockwise loosens it. Make small adjustments, checking the tension after each turn.
5. The Sweet Spot: Aim for the “snap test” result described in Tip #1. The chain should be snug against the bar but still able to be pulled away slightly.
6. Tighten the Bar Nuts: Once you’ve achieved the correct tension, tighten the bar nuts securely.
7. Final Check: After tightening the nuts, double-check the chain tension. It may change slightly when the nuts are fully tightened.

Personal Story: I remember once struggling with a particularly stubborn chain. No matter how much I tightened the tensioning screw, the chain remained loose. After closer inspection, I discovered that the bar was worn, causing the chain to sit too low. Replacing the bar solved the problem instantly. This taught me the importance of inspecting all components, not just focusing on the chain tensioner.

Technical Requirement: Stihl recommends checking chain tension after every refueling or approximately every 15-20 minutes of continuous use.

Tip #3: The Temperature Factor – Adjusting for Expansion and Contraction

Temperature plays a significant role in chain tension. As the chain heats up during operation, it expands. Conversely, when it cools down, it contracts. Therefore, it’s crucial to adjust tension based on the current temperature and expected operating conditions.

• Cold Weather: In cold weather, set the chain slightly looser than normal. This allows for contraction without making the chain too tight.
• Hot Weather: In hot weather, set the chain slightly tighter than normal. This allows for expansion without making the chain too loose.
• New Chains: New chains tend to stretch more than used chains. Check and adjust the tension frequently during the first few hours of use. I usually adjust a new chain after every other cut when initially breaking it in.

Practical Example: I once worked on a logging project in the mountains where the temperature fluctuated dramatically throughout the day. I learned to adjust the chain tension several times a day to compensate for these changes, ensuring optimal performance and safety.

Data Point: A study published in the “Journal of Forestry Engineering” found that chain tension can change by as much as 1/8 inch (3.175 mm) for every 20°F (11.1°C) change in temperature.

Tip #4: Bar Maintenance – The Foundation of Proper Tension

The chainsaw bar is the foundation upon which proper chain tension rests. A damaged or worn bar can make it impossible to achieve and maintain correct tension. Regular bar maintenance is essential.

• Cleaning: Regularly clean the bar groove with a bar groove cleaner or a flathead screwdriver. Debris buildup can prevent the chain from seating properly.
• Filing: File down any burrs or damage on the bar rails. These imperfections can cause the chain to bind and wear unevenly.
• Bar Rotation: Rotate the bar periodically (usually after each chain sharpening). This ensures even wear on both sides of the bar.
• Bar Inspection: Inspect the bar regularly for wear, damage, or bending. Replace the bar if it’s significantly worn or damaged.

Technical Requirement: Stihl recommends replacing the chainsaw bar after every two to three chain replacements, or sooner if signs of wear or damage are present.

Material Specifications: Chainsaw bars are typically made from hardened steel alloys, such as chromium-molybdenum steel, to withstand the high stresses and temperatures generated during operation.

Tip #5: The “Chain Stretch” Test – Recognizing When to Replace

Even with proper tensioning and maintenance, chainsaw chains eventually wear out and stretch beyond their usable limit. Recognizing when to replace the chain is crucial for safety and performance.

• Excessive Slack: If you find yourself constantly adjusting the chain tension, and it continues to loosen quickly, it’s likely stretched beyond its limit.
• Drive Link Wear: Inspect the drive links for wear. If they’re significantly worn or damaged, the chain needs to be replaced.
• Cutter Damage: Check the cutters for damage or excessive wear. If they’re chipped, broken, or too short to sharpen effectively, replace the chain.
• Chain Pitch Mismatch: Ensure the chain pitch matches the sprocket and bar pitch. Using the wrong pitch can damage the chain and saw.

Case Study: In one of my firewood processing projects, I noticed that a chainsaw chain was constantly loosening, even after multiple adjustments. Upon closer inspection, I discovered that the drive links were significantly worn, and the chain had stretched beyond its usable limit. Replacing the chain immediately improved cutting performance and reduced the risk of chain derailment.

Safety Codes: OSHA (Occupational Safety and Health Administration) regulations require that chainsaw operators inspect their equipment daily and replace any worn or damaged components.

The Chain Stretch Test – Detailed Steps:

This test isn’t a formal scientific measurement but a practical gauge for field use.

1. Visual Inspection: Lay the chain flat on a clean surface. Observe the spaces between the links. If the gaps appear significantly larger than when the chain was new, it indicates stretching.
2. Bar Alignment: Mount the chain on the bar with the tension adjusted to what you consider “normal.” If the chain can be easily pulled further out of the bar groove than usual, the stretch is excessive.
3. Drive Link Engagement: Examine how well the drive links engage with the sprocket. Excessive stretching will cause the drive links to sit loosely or even skip on the sprocket teeth. This is a clear sign of replacement.
4. Sharpening Limits: If you’ve sharpened the chain multiple times and find that the cutters are becoming too short or the rakers (depth gauges) are difficult to maintain at the correct height, the chain is nearing the end of its life. This indirectly indicates stretching as the metal wears away from each sharpening.

Data Point: A study conducted by a leading chainsaw chain manufacturer indicated that a chain stretched beyond 3% of its original length should be replaced to maintain optimal cutting performance and safety.

Bonus Tip: The Importance of a Sharp Chain

While this guide focuses on tension, remember that a sharp chain is just as crucial for efficient and safe cutting. A dull chain requires more force, increasing the risk of kickback and putting unnecessary strain on the saw. Learn how to sharpen your chain properly or take it to a professional.

Specifications and Technical Requirements Summarized

Here’s a breakdown of the specifications and technical requirements discussed in this guide, presented in a clear and organized manner:

| Chain Tension | “Snap Test” | Chain should pull out slightly from the bar midpoint (approx. half the drive link visible). Should snap back when released.

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