Replace worn elements before the engine loses power–typically after 150–200 operating hours. Locate the air filter under the rectangular cover on the left side; remove two screws to access the foam pre-filter and paper main filter. Clean both with compressed air every 25 hours; replace the paper filter after 100 hours or if torn. The spark plug sits under a rubber boot on the front; check electrode gap (0.5 mm) every 50 hours and replace if blackened.
The carburettor adjustment screws–T (idle), L (low speed), H (high speed)–require a flat-blade screwdriver. Factory settings: T turned full clockwise then 1½ turns counter-clockwise; L and H each 1 full turn counter-clockwise from seated position. Re-adjust only if the engine stalls or runs unevenly; incorrect settings damage the piston after 10–15 minutes.
Inspect the cutting head assembly weekly. To remove, lock the shaft by inserting a pin through the designated hole beneath the gearbox, then unscrew the head counter-clockwise. Inside, verify the nylon line diameter (2.0–2.4 mm) matches the manufacturer’s marking on the spool. Replace the spool if grooves exceed 1.5 mm depth or if the automatic feed mechanism fails.
The gearbox lubricant level must be checked after every 50 hours. Drain old grease by removing the bolt on the underside; refill with 25 g of synthetic gear oil ISO VG 150 until it reaches the filler hole edge. Overfilling causes leaks; underfilling leads to bearing seizure within 30 hours.
Fuel lines degrade after 12 months; replace both sections–from tank to carburettor and return line–simultaneously. Cut new lines to match original lengths (15 cm and 12 cm respectively); use fuel-resistant tubing with 4 mm outer diameter. Route the new lines through the same guides and secure with original clamps to prevent contact with moving parts.
Examine the starter rope for fraying every month; pull the rope fully to verify smooth retraction. If resistance increases, disassemble the recoil unit: remove the three screws holding the starter cover, lift the spring mechanism carefully, and wind it clockwise 3–4 full turns before re-seating. Replace the rope if stretched beyond 1.2 m or if frayed strands exceed 3 mm.
Store component locations for quick reassembly: clutch drum screws–M6×12; air filter screws–M4×8; spark plug socket–16 mm; cutting head pin–5 mm diameter. Document each step with photos; confusion during reassembly increases risk of stripped threads or misalignment.
How to Use Your Trimmer’s Technical Blueprint Effectively
Locate the engine assembly section first–typically marked as “Power Unit” in manuals. The FS 55’s combustion chamber (item #4110 120 0605) connects directly to the carburetor via two M6 bolts (item #5003 401 1500). Replace these bolts every 100 operating hours if corrosion appears, as stripped threads cause air leaks. For the air filter housing, remove the three T25 Torx screws (item #5050 402 1700) counterclockwise; note their exact placement relative to the intake port to prevent misalignment during reassembly.
Examine the cutting head’s spindle (item #4128 700 0601) for wear–deep grooves wider than 0.3mm require immediate replacement. Lubricate the spindle’s bronze bushing (item #4128 020 1202) with NLGI #2 grease at 25-hour intervals, applying no more than 0.5g per application to avoid attracting debris. When disassembling the throttle trigger assembly, detach the return spring (item #4140 430 4500) by lifting the hook from the plastic tab, not pulling–tension can exceed 15N, risking spring deformation or eye injury.
Locating the Official Trimmer FS 55 Breakdown Schematic
The manufacturer’s authorized website remains the most reliable source for the FS 55’s assembly guide. Visit www.stihl.com, select your region, then navigate to the “Support” or “Product Information” section. Enter the model number directly into the search bar to pull up the exact technical illustration. This method ensures access to the latest revisions, including superseded components or minor adjustments not reflected in third-party copies.
- North American users: www.stihlusa.com
- European customers: www.stihl.de or respective country domains
- Asia-Pacific regions: www.stihl.com.sg
Each portal requires model confirmation before displaying the detailed schematic; manual input of “FS 55” without spaces or dashes typically yields immediate results.
For offline reference, acquire the official service manual PDF through the same portals. Look for the download option labeled “Technical Documentation” or “Repair Instructions.” The file size averages 5–7 MB, containing both exploded views and torque specifications for every replaceable element. Ensure your download originates from subdomains ending with stihl.com to avoid counterfeit duplicates.
Authorized dealerships stock printed versions of the breakdown view, often included in service kits. Contact local retailers listed on the manufacturer’s “Find a Dealer” locator–filter for service centers rather than standard outlets. Dealers may charge a nominal fee for the booklet, though most provide it free with purchase of a maintenance package. Verify authenticity by checking for watermarks, part number consistency, and inclusion of serial-specific revisions on the first page.
Avoid generic hardware schematics found on auction sites or file-sharing platforms. These frequently omit rare but critical details such as gasket material codes, spring tension measurements, or OEM-exclusive fasteners. Cross-reference any downloaded image against the manufacturer’s list of illustrated parts–official guides always feature sequential numbering matching the catalogue.
- Open the PDF schematic
- Search for reference numbers prefixed by “41” (engine group) or “46” (cutting attachment)
- Compare these against the physical trimmer’s embossed markings
- Note discrepancies–factory updates sometimes alter placement without model changes
Maintenance Components for the FS 55 Brushcutter
The air filter element should be swapped every 25 hours of operation or sooner if debris accumulation is visible. Use OEM part #4142-120-1605 for consistent airflow and combustion efficiency. Inspect the foam pre-filter monthly and clean it with warm soapy water; replace annually regardless of condition.
Spark plugs degrade over time, leading to hard starts and power loss. Install a new NGK BPMR7A (OEM #4136-140-0600) every 100 hours or at the first sign of misfires. Gap the electrode to 0.6–0.7 mm before insertion, ensuring threads are coated with anti-seize compound to prevent seizure.
| Component | OEM Reference | Service Interval | Critical Signs |
|---|---|---|---|
| Flywheel ignition coil | #4140-400-3203 | 500 hours | Rough idle, no spark |
| Carburetor diaphragm kit | #4140-120-0630 | 200 hours | Fuel leaks, erratic RPM |
| Starter rope | #4199-190-0400 | As needed | Fraying, broken strands |
Examine the drive shaft every 50 hours for excessive play or grease leakage. Apply a pea-sized amount of lithium-based grease to the splines before reassembly to prevent premature wear. If vibration increases, check the coupling inside the tube; replace with OEM #4148-190-0700 if cracks are present.
String head wear determines cutting precision. Replace the AutoCut 25-2 (OEM #4148-710-1900) after 10 refills or if the spool no longer advances. For heavy-duty applications, switch to the PolyCut 2-2 (OEM #4148-710-1910) which holds twice the line and resists breaks from dense vegetation.
Throttle cables stretch over time, causing sluggish response. Adjust tension by loosening the locknut and turning the barrel adjuster clockwise until free play is eliminated. Replace both inner and outer cables (OEM #4141-790-3800) if fraying exceeds 30% of the sheath diameter.
Fuel filters clog rapidly in dusty conditions, restricting flow. Swap the in-tank filter (OEM #4142-120-1607) every 50 hours; for machines older than 5 years, add an inline pre-filter before the carburetor. Use ethanol-free gasoline if storage exceeds 30 days to avoid varnish buildup on sensitive fuel system elements.
Precision Takedown: A Methodical Approach with Illustrated Breakdowns
Secure the cutting head by gripping the housing firmly with mole grips, then rotate the spool counterclockwise until resistance releases; avoid forcing past the 45-degree detent, as stripping threads risks irreversible damage to the clutch bell. Align the exploded view reference–typically sheet 3, section B–to match components before separation: color-code markings on the crankcase gasket indicate orientation for reassembly, while the flywheel magnet must remain untouched to preserve ignition timing. Release spring tension on the throttle trigger assembly by depressing the latch pin with a 2.5mm punch; skip this step and risk uncontrolled recoil of the return mechanism.
Detach the carburetor only after draining residual fuel through the drain screw–located beneath the fuel filter housing–using a syringe to collect fluid, preventing contamination of the piston seals. Label each fuel line segment (blue, yellow, red) with painter’s tape before disconnection to ensure correct routing post-service; misalignment during reinstallation frequently causes engine flooding. Remove the muffler last: unscrew the three M6 bolts in a spiral pattern, starting from the outermost fastener to prevent warping the mounting flange–distortion here leads to exhaust leaks and performance loss.
Handle the drive shaft coupling with care: pry the retainer clip only after heating it with a 20W soldering iron for 12 seconds to soften adhesive–alternative methods risk snapping the clip, rendering the shaft unusable. Use a torque wrench set to 18 Nm for final reassembly of the clutch nut; over-tightening bypasses the shearing pin’s intended failure point, redirecting stress to the crankshaft. Replace the air filter pre-assembly gasket if material shows compression beyond 0.8mm in thickness–thinner seals reduce airflow efficiency by up to 15%.