Symptoms
- Strong vibration only when the metal blade is attached
- Blade appears to wobble visibly when spinning
- Blade edge looks nicked or bent
- Mounting bolt feels loose
Likely causes
- CommonBent or damaged bladeHitting a rock or fence wire can bend the blade slightly, throwing off its balance.
- CommonLoose mounting bolt or missing washerImproper installation without the correct retaining washer allows play at the mount.
- PossibleUneven sharpening of blade edgesSharpening one side more than the other unbalances the blade.
- PossibleWorn gearbox bearingPlay in the gearbox output shaft can cause wobble independent of the blade itself.
- Less commonCracked blade near the center holeStress cracks near the mounting hole can cause dangerous wobble and should stop use immediately.
What to do
- Shut off the engine and let the blade stop completely before inspecting it.
- Remove the blade and check for visible bends, nicks, or cracks, especially around the center mounting hole.
- Confirm all washers and the retaining nut are installed in the correct order per the manual, since missing a washer causes wobble.
- Check that the blade was sharpened evenly on both edges; uneven filing causes imbalance.
- Reinstall the blade with the mounting nut torqued to the correct tightness, not overly loose or excessively tight.
- Spin the gearbox output shaft by hand (blade removed) to check for play or grinding in the bearing.
- Replace any cracked or significantly bent blade immediately rather than continuing to use it.
Tools and parts
- Wrench set
- File (for sharpening)
Brush cutter bladeSearch: “brush cutter metal blade replacement”
Blade mounting hardware kitSearch: “trimmer blade washer nut kit”
When to call a pro
If the gearbox bearing shows play, have a small-engine shop service or replace the gearbox.
Safety
Use caution
Never use a cracked or significantly bent metal blade; a blade failure at speed can cause serious injury.