When repairing a mid-range professional chainsaw, the exploded view chart is the most reliable reference. This schematic breaks down each piece by number, grouping assemblies like the powerhead, guide bar, and clutch system for precise identification. Always cross-check part codes with the serial number stamped on the saw’s housing–variations between production years may affect compatibility.
Start disassembly at the top cover. Remove the air filter housing first, as it often conceals screws securing the recoil starter. Note the orientation of the spring-loaded pawl inside the starter–incorrect reassembly leads to kickback failure. Below, the flywheel should lift cleanly once the retaining nut is loosened; if stuck, a rubber mallet applied sharply to the crankshaft end frees it without damage.
The piston-cylinder group requires special attention. Clean the crankcase interior thoroughly before replacing rings or bearings–debris as small as 0.1mm can score surfaces. Measure piston diameter at three points: just below the wrist pin, mid-skirt, and skirt edge. Tolerances tighter than 0.03mm indicate wear that necessitates a full rebuild kit, not just individual rings.
For clutch replacement, heat the drum evenly to 120°C (248°F) before attempting removal. Cold disassembly risks splintering the aluminum hub. Secure the crankshaft end with a holder tool–using a screwdriver point risks keyway damage. The needle cage bearing inside the drum must align perfectly with the drive shaft tangs; misalignment causes erratic engagement.
Refer to the oil pump section if chain lubrication is inadequate. Remove the bar mount to access the pump–it’s cam-driven, so timing the gears to the crankshaft marks ensures proper flow. Replace the inlet valve if the plunger shows more than 0.05mm play, as even minor leakage reduces feed pressure to near zero.
Always compare new components against the old. Wear patterns on bar rails should match; uneven depth signals misaligned chain tension or worn sprocket teeth. File guides and depth gauges to exact manufacturer specifications–deviations of 0.2mm in gauge height alter cutting efficiency by up to 30%.
Exploded View for the MS 260 Chainsaw: Key Components and Maintenance Tips
Begin by locating the air filter assembly (position 12 in most schematics) to prevent debris buildup. Clean or replace it every 10 operating hours using compressed air or a mild solvent–never exceed 30 psi to avoid damaging the pleated paper. A clogged filter reduces engine efficiency by up to 20%, increasing fuel consumption and wear on the piston rings (item 28).
The carburetor (part 34) demands precise adjustments. Use a tachometer to set the idle speed to 2,800 RPM (H-screw) and the high-speed screw (L-screw) to 13,500 RPM, turning clockwise until resistance is felt, then back 1/4 turn. Incorrect settings lead to overheating or incomplete combustion, identifiable by blackened spark plugs (component 15).
| Component | Manufacturer Part # | Lifespan (Hours) | Replacement Signs |
|---|---|---|---|
| Piston Rings | 1123-120-0603 | 300–500 | Excessive smoke, loss of compression |
| Spark Plug | 4140-020-0600 | 100 | Fouling, electrode erosion |
| Clutch Assembly | 1125-020-3400 | 400 | Slipping, inconsistent engagement |
| Drive Sprocket | 1128-007-1000 | 200 | Teeth wear, chain skipping |
Inspect the chain brake band (ref. 50) for cracks or glazing every 5 hours of use. Replace if wear exceeds 0.5mm thickness–the band’s failure can result in uncontrolled chain rotation, posing severe injury risk. Lubricate the brake mechanism with SAE 10W-30 oil to maintain smooth operation, avoiding heavy greases that attract sawdust.
Bar maintenance hinges on the oil pump (item 77) and grooving. Check for burrs along the bar rails with a depth gauge: grooves deeper than 0.6mm require bar replacement. Clean the oil ports (0.5mm diameter) weekly using a wire brush–clogs disrupt lubrication, causing chain binding and premature dulling. For optimal performance, alternate bar usage to distribute wear evenly.
When disassembling the flywheel (component 18), mark its position relative to the crankshaft keyway (item 22) to ensure precise reassembly. A misaligned flywheel alters ignition timing, reducing power output by 15%. Use a flywheel puller specific to the 0.8mm thread pitch–generic tools may strip the shaft. Check the woodruff key for deformation; replace if bent to prevent rotational imbalance.
Fuel system integrity relies on the fuel filter (part 45) and line condition. Replace the filter every 25 hours or when flow resistance is detected. Use ethanol-free gasoline (≤10% ethanol) to prevent corrosion of the diaphragm (item 36), which swells and restricts fuel flow. Drain the tank overnight if storing the saw for over 30 days to avoid varnish buildup.
Track wear on the needle bearings (ref. 25) via operational noise–grinding or rattling indicates failure. These bearings, preloaded to 0.2–0.3mm, support the crankshaft and tolerate no lateral play. Replace as a pair using a bearing puller with a 12mm adapter, ensuring equal torque on the crankcase bolts (6Nm). Over-tightening distorts the housing, compromising seal integrity.
For spring-loaded components like the recoil starter (item 1), stretch-test the return spring every 50 hours. A spring elongated beyond 3% of its free length loses tension, causing slow pull-cord retraction. Coat the spring with lithium grease during reassembly to prevent corrosion. Check the pawl engagement (item 6) for chipping–replace if teeth are worn below 2mm depth to avoid starter slippage.
Locating Authorized Schematics for Your Professional Chainsaw Model
Download official exploded views directly from the manufacturer’s regional portal by filtering for your tool’s serial number–EU users visit *stihl.eu*, US customers use *stihlusa.com*, and Australian owners navigate to *stihl.com.au*. Each microsite hosts downloadable PDFs under “Service & Support” > “Manuals & Diagrams,” where you’ll input the last seven digits of your unit’s ID plate to retrieve precise schematics. Avoid third-party repositories; authorized schematics include tolerance specs, material codes, and torque values absent in replicas.
For immediate access without downloads, certified dealers maintain printed binders of these blueprints–request them during in-person visits. Dealer locators on the same portals pinpoint nearby service centers stocking these references, often accessible same-day for urgent repairs.
Critical Elements of the MS 260 Carburetor Breakdown
Start by locating the diaphragm assembly–its thin, flexible membrane regulates fuel flow under varying engine loads. Inspect for cracks or warping, as even minor damage disrupts pressure balance, leading to hard starts or erratic idling. Replace with a factory-spec component if deformation exceeds 0.1mm, measured using calipers at three equidistant points.
Next, examine the metering lever and pivot pin. The lever’s contact point must sit flush against the diaphragm with 0.3–0.5mm clearance; adjust using the built-in eccentric screw. Lubricate the pin with two drops of 2-stroke oil before reassembly to prevent galling. Misalignment here causes fuel starvation at high RPMs.
- Needle valve: Ensure the tapered tip sits precisely in the seat without visible grooves. Test seal integrity by blowing through the fuel inlet–air should pass freely only when the throttle is open.
- Throttle shaft: Check for play exceeding 0.2mm; replace bushings if wear is evident. A loose shaft distorts airflow maps, causing 20–30% power loss.
- Choke mechanism: Verify the bimetallic spring’s tension; it should snap back within 3 seconds after cooling from 80°C. Slow response indicates thermal fatigue, requiring spring replacement.
Calibration Checks
After reassembly, reset the idle mixture screw (clockwise to seat, then back out 1.5 turns). Run the engine at 2,800 RPM for 5 minutes; if hesitation occurs, fine-tune the screw in 1/8-turn increments. Use a tachometer–guesswork leads to carbon fouling within 10 operating hours.
Maintenance Pitfalls
Avoid silicone gasket sealers on the diaphragm cover–they swell and clog fuel passages within 50 hours. Use only the OEM paper gasket or pre-cut fiber substitute. Never reuse the inlet screen; particles as small as 5 microns (invisible to the naked eye) disrupt fuel atomization. Replace every 200 hours or if filter mesh appears distorted.
Locating Correct Components for Your Chainsaw Model
Begin by matching the exploded view illustration with the corresponding assembly numbers printed directly on the engine housing or bar mount. Each sub-assembly–such as the carburetor cluster, ignition module, or sprocket cover–carries a three-digit prefix (e.g., 112, 134, 420) followed by a unique suffix. Cross-reference this stamp against the numerical sequence on the breakdown chart; discrepancies over ±2 digits typically signal an incompatible variant. Store manuals from 2001 onward group compatible revisions under color-coded tabs–green for OEM, yellow for aftermarket–eliminating guesswork.
Key Areas to Inspect Before Ordering
Check wear patterns to avoid ordering duplicate fixes: needle bearings near the flywheel often display pitting, while piston rings show radial scoring. The crankcase gasket’s silhouette–a raised ridge compared to the flat flange–distinguishes genuine replacements from generic shims. For fuel system upgrades, compare venturi diameters; models with 26 mm throttle bores use different jets than 28 mm variants outlined in the same schematic block. Keep a micrometer set within 0.05 mm tolerance to verify O-ring grooves on the clutch drum.
Installers often overlook subtle revisions: early production runs featured hexagonal drive links requiring metric pitch chains, whereas later units switched to semi-chisel cutters with offset tie straps. The catridge air filter’s internal baffle–absent on economy kits–redirects airflow differently, affecting fuel trim. Scan the barcode sticker beneath the recoil housing; the last four digits encode the build week, correlating with part revisions listed in appendix B of the guide.