How To Repair Trimmer Head That Will Not Turn

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If the trimmer engine runs, but the trimmer head does not spin when the throttle is engaged, the clutch may be broken. The clutch prompts the drive shaft to start rotating once a certain rotational speed is reached and allows the engine to run without always rotating the drive shaft. If the clutch is broken or the springs are not tensioned properly, the clutch may not engage at all. Disassemble the engine housing to gain access to the clutch, and check for any damage. To protect the trimmer during this repair, remove the spark plug and feed a piece of scrap starter rope into the combustion chamber, as this will stop the piston from moving while the clutch is removed. Check your user manual for the proper part number if your clutch is broken and needs replacing.

Cable or Shaft

If your trimmer head will not spin and the engine is running as usual, the problem may be the drive cable or shaft. The cable or shaft connects the crankshaft from the engine at the back end of the unit to the trimmer head at the opposite side. The crankshaft attaches to the drive cable (sometimes referred to as the shaft), and connects to a gear box which allows the head of the trimmer to spin. If the drive cable is broken or detached, the trimmer head will not spin. To inspect the drive cable, remove the engine assembly from the shaft and look to see if the cable is in its proper place. Reinstall the cable if it has slipped from its place. If the cable is damaged or broken, it should be replaced altogether. Refer to your user manual for the proper replacement part number if a new drive cable is required.


The most common issue with gearboxes is the failure of the teeth on the gearing. This can happen over many years due to normal wear or can happen quickly if the trimmer is overloaded or abused. Lack of lubrication can also be an issue. Lack of lube alone won’t cause the gearbox to seize but damage caused to the gears from the lack of lube will. In other words you can’t just add lube to a gearbox that is not working and have it work again. The lack of lube will cause damage to the gearing which will then need to be replaced. Remove the trimmer head assembly to access the gearbox. If the gearbox is broken and still will not function properly, it will need to be replaced.

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