String trimmers came on the landscaping scene in the early 1970s, and have continued to be a desired machine for both landscapers and the amateur gardener. String trimmers help edge and clean up the sides of sidewalks, streets and fence lines. Landscapers depend on a string trimmer's clutch to help control when the trimmer spins and stops. Trimmers without a clutch will spin as long as the engine runs.
Most small lawn machines use a centrifugal clutch to control the spinning of a blade, chain, or in this case, string. A centrifugal clutch is one that operates through the principles of centrifugal force. When the engine is revved on the trimmer, the external force of the engine causes the clutch to engage. When the engine idles, the clutch disengages. The engagement of the clutch causes the string to spin and trim weeds and grass, while the disengagement allows the engine to continue running, but the string stops trimming.
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Wear and Tear
Like all aspects of small machinery, clutches do go bad because of continued use and wear and tear. One reason a string trimmer clutch would go bad is due to a user not operating the trimmer at full throttle. The low rotations per minute cause the engine to heat quickly and may cause the clutch to slip or wear out prematurely. Also, if the clutch has too much weight loaded onto it, it may slip and not engage properly.
Signs of Failure
There are various signs that a string trimmer's clutch is going bad. For example, if the trimmer engine is left at idle, but the string keeps spinning and remains engaged, then the clutch may be going bad. Another sign that the centrifugal clutch is bad is overheating and loud noises coming from the engine. This can happen when the clutch is not allowed to fully engage before the next revving of the engine. By allowing the clutch to operate at full throttle, there is less of a chance of overheating and ruining the clutch.