Overview
A failing gear head announces itself with excess vibration, grease leaks, and rough operation. This replacement gear head and blade is machined to OEM dimensions and arrives pre-greased, ready to bolt onto your trimmer shaft. A cutting blade is included, making this a complete kit for brush-clearing tasks. It is a straightforward fix that restores smooth, quiet cutting.
Key specifications
- Type: aftermarket replacement gear head
- Pre-greased: yes
- Material: die-cast aluminum housing with steel gears
- Includes: brush-cutting blade
Compatibility
This gear head fits Stihl Series FS91 FS91R FS111R FS131 FS131R FS111RX and similar models that share the same shaft interface. Always verify your trimmer’s model and part number against the full compatibility list to make sure the housing mount and drive splines align.
Installation notes
Remove the cutting attachment and unbolt the old gear head from the shaft tube. Inspect the drive shaft splines for damage before installing the new head. Slide the replacement onto the shaft, ensuring the splines engage fully, and secure the clamp bolts. Mount your preferred cutting attachment, start the trimmer at low RPM, and check for unusual vibration or noise.
Common questions
Q: Will this 4180 640 0114 gear head and 9” x 20T blade fit my Stihl FS91R, or is it only for the FS111 and FS131 models?
Yes, this assembly is listed as compatible with the Stihl FS91, FS91R, FS111, FS111RX, FS111R, FS131, FS131R, FSA135, and FSA135R. If your machine is one of those models and uses the matching brush cutter setup, this gear head and 9-inch 20-tooth chainsaw tooth blade should fit correctly.
Q: Does the 9” x 20T chainsaw tooth blade work well for heavy brush, and what kind of material is it best for?
The 9-inch 20-tooth blade is designed for aggressive cutting in thick weeds, brambles, saplings, and dense brush where standard trimmer line struggles. It is best used on woody growth and overgrown areas, but you should avoid striking rocks, fence wire, or hard stumps to prevent tooth damage and excess wear on the gear head.
Q: What should I check when installing and maintaining this gear head on a Stihl FS131R or FS111RX?
When installing it, make sure the gear head is fully seated, the blade is mounted in the correct cutting direction, and all locking hardware is tightened to the trimmer’s specifications. For maintenance, regularly inspect the gearbox for play, keep the blade sharp and balanced, and grease the gear head at the recommended service intervals so it runs cooler and lasts longer.
