The Stihl FS 120 is a professional-grade trimmer/brushcutter designed for demanding clearing and maintenance work. This parts manual provides detailed diagrams, part numbers, and ordering information for the FS 120 model, including the engine assembly, cutting head, drive shaft, handle assembly, fuel system, ignition system, and all associated components. Below are key sections for identification, assembly groups, exploded views, and ordering.
Key identifiers: Engine type, serial number location, power output.
| Feature | Description |
|---|---|
| Model Designation | FS 120 |
| Engine Type | 2-stroke, single cylinder, air-cooled |
| Displacement | Approx. 30.1 cm³ (1.84 cu. in.) |
| Power Output | Approx. 1.3 kW (1.8 hp) |
| Fuel/Oil Mix Ratio | 50:1 (STIHL HP Ultra or equivalent) |
| Idle Speed | 2,800 rpm |
| Max. Engine Speed | 12,500 rpm |
| Drive System | Flexible drive shaft |
| Cutting Attachment | STIHL PolyCut head, circular saw blade, etc. |
| Weight (without attachment) | Approx. 6.2 kg (13.7 lbs) |
Always refer to the original instruction manual for safe operation. Use genuine STIHL parts.
WARNING! Never operate a power tool with damaged, missing, or improperly assembled parts. Disconnect the spark plug boot before performing any maintenance.
Includes cylinder, piston, crankshaft, bearings, seals, and crankcase halves.
Note: Torque specifications must be followed during assembly. Use sealant on crankcase mating surfaces as specified.
Components for spark generation and engine stop.
Ignition Module (Coil) (1140 400 1001): Includes spark plug boot and wire.
Spark Plug (Bosch WSR 6 F or equivalent): Electrode gap 0.5 mm (0.020 in).
Stop Switch (1140 792 2000): Handle-mounted kill switch assembly.
Wiring Harness: Connects stop switch to ignition module.
Flywheel & Magneto (1140 400 0801): Includes flywheel, key, and fan.
Transmits power from the engine to the cutting attachment.
Tip: Lubricate the gearbox with STIHL Gear Oil (or approved grease) during assembly and periodic maintenance.
Supports various STIHL cutting heads and blades.
WARNING! Always use the correct guard for the cutting attachment. Ensure the blade or head is securely fastened and balanced.
Includes handlebar, throttle trigger, lockout, and mounting hardware.
| Part | Part Number | Description |
|---|---|---|
| Loop Handle | 4118 792 4700 | Main handle with throttle housing |
| Throttle Trigger | 1130 850 2000 | Trigger and spring assembly |
| Throttle Cable | 1130 850 2100 | Control cable from handle to carburetor |
| Handle Mounting Clamp | 4118 792 4800 | Clamp to secure handle to shaft tube |
| Lockout Lever | 1130 850 2200 | Safety lever that must be engaged to press throttle |
| Handle Grip | 1130 850 2300 | Rubber grip for comfort |
External covers and shrouds.
CAUTION! Ensure all covers are securely fastened to maintain proper cooling and prevent debris ingress.
Screws, nuts, washers, clips, and small hardware.
Common Fasteners: M5 x 25mm flange screws, M6 nuts, lock washers, E-clips, circlips.
Vibration Dampeners: Rubber bushings and mounts throughout the assembly.
Decals & Labels: Warning labels, model identification stickers, and instructional decals.
Starter Assembly (1140 791 2001): Complete starter pulley, rope, and handle.
Muffler (1128 140 0501): Spark-arresting muffler with gasket.
Use exploded view diagrams to identify parts and corresponding numbers.
| Symptom / Need | Reference Document | Action |
|---|---|---|
| Identify a specific part | Exploded View Diagram (Group 1-11) | Locate the part number from the diagram corresponding to the assembly group. |
| Order parts | Genuine STIHL Parts List | Provide the part number to an authorized STIHL dealer. |
| Assembly guidance | STIHL Repair Manual | Refer to the official repair manual for torque specs and procedures. |
| Part not available | Dealer Support | Your STIHL dealer can check superseded part numbers or kit availability. |
| Verify model compatibility | Serial Number | Always provide the unit's serial number to ensure correct parts. |
Reset: N/A for parts manual.
Service & Support: Contact an authorized STIHL servicing dealer. For dealer locator: www.stihlusa.com