Tools and Materials
Tools
Materials
- 2-Cycle or 4-Cycle Engine Oil
- Fuel Stabilizer
- Trimmer Line
- Spark Plug
- Air Filter
Fuel Filter (If Equipped)
- Nitrile Gloves
Product costs, availability and item numbers may vary online or by market.
How Does a String Trimmer Work?
Knowing how a string trimmer works helps you understand what maintenance is necessary and why. Here are the basics of how a string trimmer works:
- A gas engine or electric motor provides power. The engine on a gas string trimmer requires the right fuel as well as a clean air filter and spark plug to create the combustion that drives the engine. The motor on a cordless or corded string trimmer needs a healthy, charged battery or an extension cord connected to an outdoor outlet.
- The engine or motor turns a metal cable running down the shaft to the trimmer head.
- At the trimmer head, a cable spins a reel of trimmer line at a high rate of speed.
- The trimmer line cuts grass and weeds but is flexible enough to pass over hard surfaces such as concrete or edging stones without the damage a mower blade would cause.
- The reel dispenses more line as needed, either automatically or when the user bumps the head against the ground.
- A debris guard on the head helps protect the user from stones, clippings, etc.
Before You Load a String Trimmer or Perform Maintenance
Maintenance varies between string trimmer models. There are some general procedures below, but read the documentation that came with your trimmer and follow the instructions for use, maintenance and safety. Your device documentation also has a maintenance schedule to keep your trimmer in top shape.
Before you start any maintenance on a string trimmer there are things you need to do.
Prepare the Work Area
- Set up in a well-ventilated area when working with fuel.
- Have protective equipment ready. If you’re working with the fuel or oil wear nitrile gloves or chemical protection gloves. If you’re adjusting the idle speed, you need safety glasses and hearing protection.
- Keep children and pets clear of the area.
Prepare the String Trimmer for Maintenance
Prevent accidental start-ups. Before any maintenance or inspections — before you even replace trimmer string:
- Turn the trimmer off and let all moving parts come to a stop.
- On a gasoline-powered trimmer, disconnect the spark plug wire from the spark plug and ensure it can’t contact the plug. Disconnect the battery or power cord from an electric trimmer.
- Follow any additional pre-maintenance procedures the manufacturer specifies.
How to Replace String Trimmer Line
For any type of string trimmer, you need to know how to load a string trimmer or replace the trimmer string. Check the manual or the existing reel for the line diameter and purchase line that works with your trimmer. There are different steps for replacing trimmer string or line, depending on your trimmer model.
We’ve got steps on how to restring a string trimmer for several types of trimmer heads, but always rely on the instructions for your model when learning how to load a string trimmer.
Replacing the Trimmer Line
Other String Trimmer Maintenance
Aside from replacing the trimmer line, maintenance depends on whether you have an electric or a gasoline-powered string trimmer.
Electric Trimmer Maintenance
Electric trimmers require little additional maintenance. Clean away dirt and debris and inspect the device for wear and damage. If you have a cordless trimmer, follow the proper procedures for battery care to get the longest life and most power possible from your battery. You might need to:
- Recharge the battery before it’s fully discharged.
- Take the battery off of the charger once it’s fully charged.
- Remove the battery when you store the trimmer.
- Store the battery in a warm location over winter.
Gas Trimmer Maintenance
Gasoline-powered trimmers need more attention, including air filter changes, spark plug cleaning and, for some models, an oil change.
Fuel a Gasoline-Powered String Trimmer Correctly
Proper fueling helps keep the engine running smoothly, reduces buildup in the fuel system and gives you the most life from your trimmer. Use only the fuel and additives the manufacturer specifies. If you have a 2-cycle engine, mix the fuel and 2-cycle oil to the correct ratio.
Use fresh fuel (less than 30 days old) or treat the fuel with a stabilizer. Premixed power equipment fuel with a longer shelf life is also an option. Take a look at our Small Engine Fuel and Gasoline Guide for tips on fueling your trimmer the right way.
Check the String Trimmer Air Filter
A clean air filter allows the engine to get the air it needs for maximum performance and reduces excess engine wear. Your manual tells you how often to clean or replace the filter, for example, after every 10 hours of operation.
Inspecting the Trimmer Air Filter
Adjust the Idle Speed
If the engine stalls during use or the trimmer head turns when you release the throttle, you need to adjust the idle speed. This is the only time you should have the spark plug wire connected during maintenance. You need to have the trimmer running, so move the trimmer outside and wear protective gear.
Don’t run a gasoline-powered trimmer indoors, in a garage or in an area that doesn’t have proper ventilation.
Increasing or Decreasing the Idle Speed
Clean or Replace the Spark Plug
A dirty or damaged spark plug makes the trimmer difficult to start and causes the engine to run poorly.
Checking the Trimmer Spark Plug
Check the Oil on a 4-Cycle Trimmer Engine
A string trimmer with a 4-cycle engine doesn’t use a fuel and oil mixture like one with a 2-cycle engine. In addition to the previous maintenance steps, if your trimmer has a 4-cycle engine, you need to check the oil before every use.
Checking the Oil Level on a 4-Cycle Trimmer
Change the Oil in a 4-Cycle Trimmer Engine
You need to change the oil in a 4-cycle engine soon after purchase, for example after the first 10 hours of use. For regular maintenance, you might need to change the oil after every 25 to 40 hours of operation, monthly or seasonally depending on how frequently you use the trimmer.
It's best to change the oil after the engine has run for a couple of minutes and the oil is slightly warm so it drains more quickly from the engine.
Don’t run a gasoline-powered trimmer indoors or in an area that doesn’t have proper ventilation.
The engine, muffler and oil may be hot after you run the engine.
Replacing 4-Cycle Engine Oil
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
Proper storage protects your trimmer and helps ensure it’s ready for next job. Check your manual for specifics, but 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 won’t come into contact with an open flame or spark.
- Follow your manual instructions for positioning the trimmer for storage. For example, with a gas trimmer you might need to keep it level or store it vertically with the engine elevated.
- Store out of the reach of children.
- For long-term storage of a gas trimmer, 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. For long term storage of a cordless trimmer, follow the manual instructions for charging and maintaining the battery.