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String Trimmer Maintenance

A well-tended lawn sometimes requires more than a mower. A string trimmer keeps areas a mower can't reach tidy and manicured — as long as it's working well. There are some simple steps you can take to keep your trimmer running well and performing its best for your landscaping work.

String Trimmer Cutting Grass.

Tools & Materials

Materials

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Maintenance Preparation

Work in a well-ventilated area. Before you begin, spread a drop cloth over the work area to make cleanup easier. Maintenance practices may vary between different string trimmer models. There are some general procedures below, but read the documentation that came with your trimmer before beginning work and always follow the manufacturer's instructions for use, maintenance and safety. Contact the manufacturer with any questions. Your device documentation may also provide a maintenance schedule to help you keep your trimmer in top shape.

Before performing any maintenance, cleaning or inspections on your trimmer, turn it off and let all moving parts come to a stop. On a gasoline-powered trimmer, remove the spark plug wire from the spark plug. Disconnect an electric trimmer from its power supply. Follow any pre-maintenance procedures the manufacturer specifies.

Replacing the Trimmer Line

Replacing the Trimmer Line.

Regardless of the type of string-trimmer you have, you'll need to replace the trimmer line it at some point. There are several different methods for replacing line, depending on whether your trimmer is a single- or dual-line model and whether you use precut pieces of line, use a pre-wound spool or wind the line yourself. Follow the manufacturer's instructions for your model and use the specified trimmer line.

While you're replacing the line, it's a good time to clean the cutting shield and the area around the trimmer head. Also inspect the area for damage and wear. You may be able to replace some damaged parts yourself, but some require professional attention. Use only approved replacement parts.

Good to Know

Have extra line available so you don’t have to stop in the middle of the job to buy more.

Good to Know

Your trimmer may accept different types of line or spools that make changing the trimming line easier.

Electric vs. Gasoline-Powered String Trimmers

Aside from replacing the trimmer line, the maintenance you perform depends on whether you have an electric or a gasoline-powered string trimmer.

Electric trimmers require very little additional maintenance. Clean away dirt and debris as instructed by the manual and inspect the device for wear and damage. If you have a cordless trimmer, make sure you follow the proper procedures for battery care.

Gasoline-powered trimmers require more attention. The information below applies to these models.

Fueling a Gasoline-Powered String Trimmer

Proper fueling is an important part of caring for a gasoline-powered string trimmer. Use only the type of fuel and additives the trimmer manufacturer specifies. Use fresh fuel — standard pump gasoline can degrade over time. Store gasoline in an airtight container designed for gasoline.

Check and Replace the Air Filter

A clean air filter is important for good engine performance and for avoiding unnecessary engine wear.

Step 1

Make sure the trimmer is off and that all moving parts are stopped.

Step 2

Remove the spark plug wire from the spark plug.

Step 3

Follow any pre-maintenance procedures the manufacturer specifies.

Step 4

Remove the air filter cover and air filter.

Step 5

Inspect the filter for dust, debris and damage.

Step 6

Replace the filter with a new one as needed. Some air filters are reusable. If you have a reusable air filter, refer to your manual for cleaning instructions and directions on whether or not you should apply oil to the filter before reinstalling. Paper filters typically require replacement.

Step 7

Install the filter and attach the air filter cover.

Adjust the Idle Speed

If the engine stalls when the trimmer is idling, you may need to adjust the idle speed. Some manufacturers also specify that if the cutting attachment rotates while the trimmer is idling, you must adjust the idle speed so that the attachment no longer rotates. Some trimmers have a single idle adjustment screw while others have multiple screws. Follow the instructions for your specific model to use the adjustment screw(s) to set the idle speed.

The idle speed adjustment procedure is the only time during maintenance when you should have the spark plug wire connected. You'll need to have the trimmer running, so wear protective gear.

Caution

Do not run a gasoline-powered trimmer indoors or in an area that does not have proper ventilation.

Clean or Replace the Spark Plug

A dirty or damaged spark plug may make the trimmer difficult to start or cause the engine to run poorly.

Step 1

Turn the trimmer off and make sure all moving parts are stopped.

Step 2

Follow any pre-maintenance procedures the manufacturer specifies.

Step 3

Remove the spark plug cover or boot and wire from the end of the spark plug.

Step 4

Clean the area around the spark plug to prevent debris from falling into the engine’s combustion chamber when you remove the plug.

Step 5

Use a spark plug wrench (or a socket wrench and spark plug socket) to loosen and remove the spark plug.

Step 6

Visually inspect the spark plug for damage and condition. The tip should be intact and gray, not covered with oil.

Step 7

If the spark plug is dirty, you can clean it. If the spark plug is worn or severely damaged, get an approved replacement.

Step 8

Check the gap distance on the end of the spark plug with a spark plug gap tool or feeler gauge and adjust as needed, following the trimmer manufacturer’s instructions.

Step 9

Install the spark plug and tighten it until the plug is snug. Do not over-tighten.

Step 10

Reconnect the spark plug cover or boot and wire.

Check and Add Oil (4-Cycle Engines)

A string trimmer with 4-cycle engine does not use combined fuel and oil like one with a 2-cycle engine. In addition to the previous maintenance steps, a 4-cycle engine requires that you check the oil before every use.

Step 1

Make sure the trimmer is off and that all moving parts are stopped.

Step 2

Remove the spark plug wire from the spark plug.

Step 3

Follow any pre-maintenance procedures the manufacturer specifies.

Step 4

Set the trimmer level on a workbench, allowing the cutting head to hang over the edge.

Step 5

Check the oil level. Your trimmer may have an oil level window. On some models, the oil fill plug has a dipstick to indicate the oil level. Or, you may need to use a flashlight to check the oil level inside the reservoir. If you need to remove the oil fill plug, clean debris from around the plug first.

Caution

The engine, muffler and oil may be hot.

Step 6

Add the recommended oil type to the correct level. Don't overfill the reservoir.

Step 7

Make sure the O-ring is correctly seated on the oil fill plug and replace the plug.

Change the Oil (4-Cycle Engines)

Since a 4-cycle engine does not use combined fuel and oil, you will need to change the oil periodically. It's best to change oil after the engine has run for 1 to 2 minutes and the oil is slightly warm. The oil will drain more quickly from the engine and remove impurities more easily.

Caution

Do not run a gasoline-powered trimmer indoors or in an area that does not have proper ventilation.

Step 1

Turn the trimmer off and make sure that all moving parts are stopped.

Step 2

Remove the spark plug wire from the spark plug.

Step 3

Follow any pre-maintenance procedures the manufacturer specifies.

Step 4

Wipe away debris from around the oil fill plug.

Step 5

Remove the plug.

Step 6

Tip the trimmer and drain the oil into a used-oil container.

Caution

The engine, muffler and oil may be hot.

Step 7

Once the oil compartment is empty, wipe off any residue from the engine and clean up any spills in the work area.

Caution

Contact your local recycling center for oil disposal instructions and dispose of the oil properly.

Step 8

Set the trimmer level on a workbench, with the cutting head hanging over the edge.

Step 9

Refill the reservoir with the specified oil.

Step 10

Verify that the O-ring is in place on the oil fill plug and replace the plug.

Other String Trimmer Maintenance

Other maintenance procedures may include:

  • General cleaning
  • Verifying proper lubrication of the angle / bevel gear
  • Maintaining the drive shaft
  • Checking and replacing the fuel filter (if equipped)

Storing Your String Trimmer

Storage is an important part of taking care of your string trimmer. Here are some general practices:

  • Allow the trimmer to cool before storage.
  • Brush off any clippings or debris.
  • Store in a well-ventilated, dry place where any fumes or leakage will not come into contact with an open flame or spark.
  • Store out of the reach of children.
  • For long-term storage, manufacturers may instruct you to run the fuel system dry or to store the equipment with the tank full of fuel mixed with a fuel stabilizer.