String Trimmer Safety And Maintenance

Richard L. Parish  |  12/11/2004 12:46:05 AM

As with any power tool, string trimmers (Figure 1) are capable of causing injury if not used in a safe manner. String trimmers will last longer and give more trouble-free service if used and maintained properly.

Fuel Safety
Gasoline is highly flammable and must be treated with care. Always store gasoline in an approved gasoline storage container, and keep it sealed. Never pour gasoline into a hot engine; always allow the engine to cool first. Take a break; get a drink; let the engine cool! You should also avoid getting fuel on your skin. Never store fuel (or gasoline engines) in a storeroom or utility room with a gas-fired water heater, clothes dryer, etc. The pilot light can ignite the gasoline.

Fuel Storage and Protection
It is best to buy fuel in relatively small quantities so you can use it up promptly. If stored for very long, the more volatile components of gasoline can evaporate, leaving only the heavier, harder to burn components. If you must store gasoline, use a gasoline stabilizer at the recommended rate. Note that you must add the stabilizer when the gasoline is fresh; the stabilizer will not rejuvenate gasoline that has already deteriorated.
Keep your fuel clean and in a closed, approved container. Store the containers in a shady place, out of the sun. Since most string trimmers have 2-cycle engines, you will need to mix oil with the gasoline. It is best to add the correct amount of oil to the empty container, and then add 1 gallon of gasoline from the service station pump. Shake thoroughly before each use.

Protective Clothing
When using a string trimmer, always wear long trousers and sturdy shoes. Tall boots are best. The string can really sting if you allow it to contact bare legs or feet. Always wear safety glasses, goggles or a face shield when using a string trimmer. It can throw objects with considerable force. Keep bystanders away, also. Hearing protection is desirable since the trimmer engine is very close to your ear. Gloves are useful to damp out vibrations when using a string trimmer. Even with gloves, you may find your hands tingling after spending some quality time with your string trimmer.

Brush-cutting Head
A brush blade is far more dangerous than plastic line and must be treated with great respect. Use a brush blade only with a heavy-duty trimmer having a "bicycle-type" handle (Figure 2) and keep both hands on the handle. Be sure no bystanders are nearby. Don’t try to cut trees larger than recommended by the operator’s manual.

Cutting Head Maintenance and Safety
Straight-shaft trimmers have a gearbox on the head. This gearbox contains grease and must be checked and refilled occasionally. Check your operator’s manual for timing and instructions. Most trimmers use a centrifugal clutch to allow the head to stop when you idle the engine down. Don’t trust it!
Centrifugal clutches are notoriously unreliable. Always shut the engine off before servicing the head.

Engine Maintenance
As with most small engines, the primary maintenance considerations on the engine are the air filter, the spark plug and the fuel filter. String trimmers can kick up a lot of dust, so the air filter can get dirty rapidly. Inspect your air filter often, and clean or replace it (according to the operator’s manual) whenever it looks dirty.
You will need to clean and gap, or better yet replace, your spark plug every year or two in homeowner use. Consult the operator’s manual for gap and torque (it is very easy to over-torque a spark plug and strip the threads). You will need to replace the fuel filter every two to three years in typical homeowner service.
An often-overlooked engine maintenance item is the muffler. You may need to clean out carbon buildup in the muffler or on the spark suppressor, if so equipped. It is also important to blow out the cooling fins on the engine occasionally. If the cooling fins are plugged with dirt or trash, the engine will overheat.

Replacement Line
Your operator’s manual will tell you what size of line to use. You have a choice of round line, square line or X-shaped line. Round line is generally more abrasion-resistant, and it wears longer, but the square and X-shaped lines are more aggressive and cut tough weeds better. When winding new line onto the trimmer’s spool, be sure to wind it the right way or it won’t feed properly; consult your operator’s manual. It is possible to purchase a new head with pre-wound line, but this is much more expensive than rewinding your head with line you buy in bulk.

A string trimmer can be a useful tool, but it must be maintained properly, especially if it has a gasoline engine. String trimmers (unless equipped with a brush blade) are not as dangerous as lawnmowers or chainsaws, but they can injure if not used correctly. Be sure to wear protective clothing and glasses.

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