Replacing a saw blade on a trimmer: step-by-step guide with photos and advice from professionals

A trimmer is an indispensable assistant in the fight against weeds and lawn grass, but even the most reliable tool requires regular maintenance. One of the most common procedures is cutting tool replacement, be it a fishing line, a knife or a circular saw. If this is your first time encountering this task, it is important to understand: incorrect installation will not only reduce work efficiency, but can also lead to trimmer breakdown or injuries.

In this article we will look at how to change the saw on any type of trimmer - from household electric to professional gasoline. You'll learn what tools you'll need, how to choose the right cutting blade, and what hidden nuances often missed even by experienced users. We will also reveal secrets on how to extend the life of the saw and avoid common mistakes when replacing.

When is it time to change the saw on the trimmer: 5 obvious signs

Many trimmer owners wait until the tool stops doing the job, but this risks overloading the engine and accelerating wear of parts. You can determine that it’s time to replace the saw based on several signs:

• 🔹 Visible damage: cracks, chips or deformation of disc teeth. Even a small defect increases the load on the shaft and bearings.
• 🔹 Decreased performance: The trimmer "burns" the grass instead of cutting it cleanly. This is a sign of dull teeth.
• 🔹 Vibration and noise: If unusual knocking or vibration occurs during operation, this may indicate an imbalance of the disc due to wear.
• 🔹 Engine overheating: a dull saw causes the engine to work at the limit, which leads to overheating (especially true for gasoline models).
• 🔹 Getting stuck in thick grass: If your trimmer keeps getting stuck in weeds, it's likely that the cutting edge has lost its sharpness.

Manufacturers recommend inspecting the saw after each 10-15 hours of work (for household models) or 50-80 hours (for professionals). But these figures are relative: when mowing on rocky soil or dry wood, wear occurs 2-3 times faster.

⚠️ Attention: Never attempt to “rebuild” a circular saw using a grinder or file. Even the slightest imbalance can lead to disc failure at high speeds and injury.

Which saw to choose for a trimmer: comparison of types and materials

Not all saws are suitable for every trimmer. The choice depends on engine power, type of vegetation and even climatic conditions. Let's look at the main types of cutting tools:

Saw type	Material	Suitable for	Service life	Price (average)
Toothed disc	Steel, hard alloys	Dense grass, young shrubs (∅ up to 15 mm)	50-100 hours	800-2500 ₽
Milling disc	Tungsten carbide	Hard grass, dead wood, thin branches (∅ up to 25 mm)	100-200 hours	1500-4000 ₽
Line (cord)	Nylon, polypropylene	Soft grass, lawns	5-20 hours	100-500 ₽
Plastic knives	Impact resistant plastic	Young grass, lawn trimming	20-40 hours	300-1200 ₽

For petrol trimmers with power from 1.5 hp Steel and carbide wheels are suitable. Electric and battery models (up to 1 kW) are usually equipped with plastic knives or fishing line - the use of metal saws can lead to overheating of the engine.

When choosing, pay attention to:

• 🔧 Bore diameter: must match the diameter of the trimmer shaft (standard dimensions: 20 mm, 25.4 mm, 30 mm).
• 🔧 Disc thickness: thin saws (1-1.6 mm) suitable for soft grass, thick (2-3.5 mm) - for tough vegetation.
• 🔧 Number of teeth: the more of them, the cleaner the cut, but the higher the load on the engine. Optimally - 40-80 teeth for household tasks.

Preparing the trimmer to replace the saw: tools and safety precautions

Before you start replacing, make sure you have everything you need. Minimum set of tools:

• 🔨 Wrench (usually comes with a trimmer) or a head of a suitable size.
• 🔨 Screwdriver (flat or cross - depends on the model).
• 🔨 Cloth or gloves (so as not to cut yourself on the sharp teeth).
• 🔨 Vise or clamp (to fix the shaft when unscrewing the nut).
• 🔨 WD-40 or similar lubricant (if the nut is stuck).

Protect yourself and your tool:

1. Unplug the trimmer (for electric models) or remove the spark plug (for gasoline models).
2. Make sure that the cutting tool has cooled completely - hot metal may become deformed during dismantling.
3. Wear gloves: even a dull saw can cut your hands.
4. If the trimmer is gasoline, drain the fuel or turn off the fuel valve to avoid leaks.

⚠️ Attention: On some models (eg Husqvarna 128R or STIHL FS 55) the saw fastening nut has left-hand thread. This means that you need to unscrew it clockwise, and not against it, as usual. Check the instructions for your model!

Step-by-step instructions: how to remove an old saw from a trimmer

The process of dismantling the old cutting tool is the same for most models, but there are nuances depending on the type of fastening. Let's consider a universal algorithm:

1. Shaft fixation. To prevent the shaft from spinning when unscrewing the nut, use one of the following methods:

   • 🔧 Insert a screwdriver into the hole on the shaft (if provided for by the design).
   • 🔧 Clamp the shaft in a vice through soft spacers (rag, rubber).
   • 🔧 On some models (for example, Echo SRM-22GES) there is a special locking bolt - tighten it.

Unscrewing the nut. Use the wrench that came with the trimmer. If the nut does not budge:

• 🔧 Process the thread WD-40 and wait 5-10 minutes.
• 🔧 Tap a hammer through a soft pad (wood, plastic).
• 🔧 Apply leverage (extend the key with a pipe), but without excessive force.

• Removing the old saw. After unscrewing the nut, remove the washer (if there is one) and carefully pull the disc off the shaft. Please note tooth direction - this will help you install the new saw correctly.

• Cleaning the shaft and gearbox. Remove dirt and grass from the seat, check the integrity of the splines. If there is severe wear, the splines may be “licked” - in this case, the shaft will need to be replaced.

If, when unscrewing the nut, you feel the key “slipping,” this is a sign of broken edges. In this case:

• 🔧 Try using adjustable wrench or pliers.
• 🔧 Put it on the nut rubber belt (from the car's generator) and try to unscrew it with its help.
• 🔧 As a last resort, cut the nut with a grinder, but be careful not to damage the shaft.

What to do if the nut is “stuck” tightly?

If standard methods do not help, try heating the nut with a hair dryer (up to 100-150°C) - this will expand the metal and weaken the connection. Alternative: Use a rust remover (such as Liqui Moly Rostloser) and leave for 1-2 hours.

Installing a new saw: procedure and common mistakes

Installing a saw is easier than removing it, but there are some pitfalls. Follow this algorithm:

1. Compatibility check. Make sure that:

   • 🔹 The mounting hole of the saw coincides with the diameter of the shaft.
   • 🔹 The direction of rotation of the disk (indicated by the arrow on the saw) coincides with the direction of rotation of the shaft.
   • 🔹 The thickness of the saw does not exceed the maximum allowable for your model.

Installing washers. Most trimmers use a set of washers:

• 🔹 Spring washer (grower) - prevents the nut from self-unscrewing.
• 🔹 Flat washer — protects the bearing from distortion.
• 🔹 Special washer (with a projection) - centers the disk on the shaft.
Important: Don't confuse the installation order! Typical scheme: shaft → centering washer → saw blade → flat washer → spring washer → nut.

• Tightening the nut. Tighten the nut firmly 20-25 Nm (for most household models). There is no need to overtighten - this may damage the gearbox bearings. If you don't have a torque wrench, tighten it all the way, then tighten it 1/4 turn.

• Balance check. After installation, rotate the saw by hand. If you feel a beating or the disk stops in one position, it means that it is installed crookedly or there is an imbalance. In this case, reinstall the saw or check it on a special balancing stand.

Typical installation errors:

• ❌ Skewed saw — leads to vibration and accelerated wear of bearings.
• ❌ No washers — the nut may unscrew itself during operation.
• ❌ Rotation direction mismatch — the saw will “slow down” the engine and overheat it.
• ❌ Using non-original nuts - may lead to thread failure.

💡

Always check that the washers are present and in the correct position! Their absence or incorrect installation order is the main reason for self-unscrewing of nuts and gearbox failures.

Running in the trimmer after replacing the saw: why is it important

Many people skip this step, but running in a new saw - the key to her long service. The fact is that during the first start, the teeth are “grinded in” and the balancing is optimized. How to roll in correctly:

1. First launch. Start the trimmer and let it run 1-2 minutes at idle. This will allow the oil to be evenly distributed in the gearbox.

2. Test cut. Start mowing soft grass (not dead wood!) on 1/3 maximum speed. Duration - 5-10 minutes.

3. Heating test. After the test, touch the gearbox and shaft. If they hot (and not warm), means:

   • 🔥 The saw is installed crookedly and creates increased friction.
   • 🔥 There is not enough lubrication in the gearbox.
   • 🔥 The engine power is not enough for this type of saw.

Final setup. If everything is fine, gradually increase the load. A complete break-in takes 1-2 hours of work.

For gasoline trimmers, after replacing the saw, it is also recommended carburetor check. The fact is that a new saw may change the load on the engine, and adjustments will be required idle speed (screw T on the carburetor).

Saw care: how to extend its service life by 2-3 times

Even the most expensive saw will not last long if it is not properly cared for. Here 5 rulesthat will help you save on replacement:

• 🛠️ Cleaning after work. Remove grass and dirt from the saw plastic scraper (not metal!). Store the disc in a dry place - moisture causes corrosion.
• 🛠️ Lubrication. Once every 10-15 hours of work apply to the shaft and threads of the nut lithol or gear lubricant (for example, Husqvarna Grease).
• 🛠️ Sharpening. Blunt teeth increase the load on the engine by 30-40%. Sharpen the disc diamond file or on a machine, maintaining the winding sharpening angle.
• 🛠️ Balancing. After each sharpening, check the balancing of the saw on a special stand or by hanging the blade on a nail - the overweight is more 5 grams unacceptable.
• 🛠️ Wear monitoring. If the tooth thickness has decreased by more than 30% from the original, the disk must be replaced.

What not to do:

• ❌ Mow along rocky soil - this quickly grinds down the teeth.
• ❌ Hit with a saw hard objects (stumps, metal, concrete).
• ❌ Store the trimmer with the saw, downward - this deforms the disk.
• ❌ Use gasoline or kerosene for cleaning - they destroy the protective coating.

FAQ: Answers to frequently asked questions about replacing the saw blade on a trimmer

Is it possible to install a saw with a larger diameter on the trimmer than indicated in the instructions?

No, it's dangerous! Increasing the saw diameter leads to:

• 🔸 Increased load on the engine and gearbox (risk of overheating).
• 🔸 An increase in centrifugal force, which can lead to disk destruction.
• 🔸 Loss of warranty (if the trimmer is under warranty).

The exception is if you have upgraded the engine (increased power) and installed a reinforced shaft.

How often should you change the saw blade on your trimmer?

Service life depends on intensity of use and type of vegetation:

• 🔸 Household models (line/plastic knives): every 20-50 hours.
• 🔸 Semi-professional (steel wheels): every 80-150 hours.
• 🔸 Professional (carbide discs): every 200-300 hours.

When mowing on abrasive soil (sand, dust) or dead wood, wear accelerates 2-3 times.

What should I do if the trimmer vibrates after replacing the saw?

Vibration is a sign of one of the problems:

• 🔸 Saw installed crooked or skewed.
• 🔸 Missing balancing (especially after sharpening).
• 🔸 Damaged gear bearings.
• 🔸 Fastening nut understretched or overtightened.

First check the fastening of the saw and washer. If the vibration remains, remove the disk and check its balancing on a bench or in a service center.

Can I use a grinder to sharpen a trimmer saw?

Technically possible, but highly not recommended. Bulgarian:

• 🔸 Overheats the metal, which leads to steel release and rapid dulling.
• 🔸 Removes too much material, violating the geometry of the tooth.
• 🔸 Does not ensure uniform sharpening of all teeth.

Better to use diamond file or a special sharpening device for trimmer saws.

Why does a new saw get dull quickly?

Reasons for rapid wear:

• 🔸 Mowing sand, stones, asphalt.
• 🔸 Using a saw not for the intended purpose (for example, cutting branches thicker than allowed).
• 🔸 Absence grease on the shaft (leads to overheating and accelerated wear).
• 🔸 Low quality metal (especially for cheap “no-name” saws).

To extend service life, use saws with carbide brazing (for example, Oregon 25-075 or STIHL 263 40-02).