Start repairs or maintenance by locating the *AV model reference sheet*–a detailed breakdown of each mechanical piece is available in the manufacturer’s official documentation. If the original manual is missing, obtain the exploded view PDF from authorized service centers, which list assembly codes alongside visual references. Avoid third-party replicas unless verified by an OEM supplier; generic schematics often omit critical tolerances or material specifications.
Key assemblies where breakdowns frequently occur include the crankcase, *cylinder block*, and carburetor linkage. The *piston ring set*–often labeled as part #1120 120 0600–requires precise measurements (0.5mm gap) during installation; deviations produce scoring or compression loss. For the ignition module, use only the prescribed *flywheel magneto* (part #1130 400 0200) to maintain spark timing; aftermarket coils may cause misfires.
When replacing the clutch drum, note the direction of the *drive sprocket* tab before dismounting–misalignment strips the spline groove. The anti-vibration mounts (part #1112 200 0700) degrade after 300–400 hours; premature failure leads to excessive handle vibration and potential bearing damage. Tools needed: a 19mm socket for crankshaft tightening, a feeler gauge for choke calibration, and Loctite 243 for securing bolts above 15 Nm torque.
Order replacements through certified distributors only–counterfeit air filters, for example, lack the dual-stage cellulose layer, reducing engine life by 40%. Keep a printed copy of the component matrix on-site for quick cross-referencing; digital versions can be unreliable in remote areas. Store spare gaskets in low-humidity conditions–paper-based seals warp within weeks if exposed to moisture.
Finding and Using Your Chainsaw Model AV Schematic
Locate the serial plate first–it’s riveted near the crankcase under the muffler shroud. Write down every digit; discrepancies in numbers like “028AV-Super” versus “028AV” change component compatibility. Cross-reference this data with the official exploded view PDF from the manufacturer’s service portal; third-party copies often omit revisions like emission-compliant carburetors or updated clutch springs introduced in 2003.
Label each screw, spring, and gasket before disassembly using painter’s tape and a fine-tip marker. Store them in modular tackle boxes sorted by sub-assembly–flywheel housing, piston group, throttle linkage. Below is a snapshot of typical fastener specs to prevent thread damage during reinstallation:
| Component | Size | Thread Pitch (mm) | Torque (Nm) |
|---|---|---|---|
| Cylinder base screws | M6 | 1.0 | 8.5–9.5 |
| Flywheel cover bolts | M5 | 0.8 | 5.0–6.0 |
| Exhaust port nuts | M8 | 1.25 | 15–17 |
Replace every o-ring if you break down the crankcase even once; micro-fractures invisible to the naked eye cause compression leaks. Use aviation-grade grease on needle bearings; lithium-based multipurpose greases lack shear stability under 8,000 RPM loads. After sealing the casing, pressurize with ether-free starter spray and watch for bubbles at seams–this confirms integrity before firing the unit.
Finding Critical Elements in Your Chainsaw’s Exploded Schematic
Begin with the carburetor assembly, typically positioned near the center of the schematic. Look for components labeled with numbers in the 110–130 range, as these identify the throttle valve, diaphragm, and gaskets. Cross-reference these with the official service manual’s section on fuel system adjustments to confirm their exact location.
Locate the ignition module by tracing the spark plug wire backward. The magneto, flywheel, and coil will appear clustered in the upper-left quadrant of the diagram, often marked with codes like 210–230. Verify the module’s condition by checking for cracks or corrosion–common failure points in older models.
The guide bar mounting area is found in the lower-right section. Key elements include the clutch drum, sprocket, and chain tensioner, usually coded between 300 and 350. Pay attention to the small washers and retaining rings; misplacement during reassembly can lead to premature wear.
To identify the air filtration system, focus on the top-right corner. The housing, filter element, and intake cover are grouped together, frequently numbered 400–420. Note the orientation of the filter–installing it backward restricts airflow, causing engine strain.
Examine the crankcase assembly near the middle-left of the schematic. Pistons, rings, and bearings fall under codes 500–550. Check for wear on the piston skirt and cylinder walls; scoring here indicates poor lubrication or debris ingestion.
Verifying Small but Vital Components
Shift focus to the recoil starter mechanism, typically in the upper-right. Springs, pulleys, and the starter rope are labeled 600–630. Test the spring tension before disassembly–weak tension often requires replacement of the entire unit.
The muffler and exhaust ports appear in the lower-left, often coded 700–730. Carbon buildup here is inevitable; remove the spark arrestor screen carefully to avoid tearing its mesh. Soak the muffler in solvent if clogged to restore proper exhaust flow.
Step-by-Step Process for Breaking Down the MS 260 Chainsaw Using Its Schematic
Locate the spark plug wire and disconnect it first to prevent accidental starts. Store it in a secure position away from the engine housing. This eliminates ignition risks during disassembly.
Remove the bar and chain by loosening the side cover nuts using a 13mm socket. Set the cover aside, then lift the bar off the mounting studs. Clean debris from the oil port and guide slot to avoid contaminating internal components later.
Extract the air filter by releasing the latch beneath the top cover. If the filter is clogged, tap it gently against a hard surface to dislodge sawdust or wash it with soapy water. Let it dry completely before reinstallation.
Accessing the Crankcase and Piston
Unscrew the starter cover fasteners–typically four Torx T25 bolts–then lift the cover. Detach the recoil spring carefully; tension can cause it to snap back unexpectedly. Inspect the spring for fatigue or rust.
Rotate the flywheel until the piston reaches top dead center. This aligns the piston with the cylinder ports, simplifying removal. Remove the cylinder head bolts in a cross pattern to avoid warping the mating surface. Lift the cylinder off; if stuck, tap lightly with a rubber mallet.
Check the piston rings for scoring or excessive wear. Gently pry them off using a bent wire if replacement is needed. Clean carbon buildup from the piston crown and cylinder walls with a brass brush–avoid steel wool to prevent scratching.
Final Component Separation
Disconnect the carburetor by removing two mounting screws and the fuel line. Label the lines if multiple hoses are present. Inspect the intake manifold for cracks, as leaks can cause hard starting.
Separate the crankcase halves by removing the final bolts around the perimeter. Use a plastic wedge to pry them apart–metal tools can damage gaskets. Note the orientation of the crankshaft seals; they must face the correct direction during reassembly.
Key Components for the Stihl AV Chainsaw and Their Reference Codes
Replace the air filter (part #1123-020-1002) every 25 operating hours under dusty conditions. Clean it with warm soapy water, rinse, and dry thoroughly before reinstalling. Avoid compressed air–it can damage the filtering material. The foam pre-filter (#1123-020-1001) should be checked weekly, especially in high-debris environments.
Spark plugs (#4137-020-2103 for the NGK BPMR7A) degrade faster if the saw runs on low-quality fuel. Inspect every 10 hours: gaps should measure 0.5mm. If electrodes show wear or carbon buildup, replace immediately–faulty plugs cause hard starts and uneven idling. Keep a spare in the toolkit; original equipment lasts longer than aftermarket alternatives.
Critical Drive and Cutting System Elements
Rim sprocket wear directly affects chain performance. The 7-tooth sprocket (#1123-180-3806) should be swapped when teeth thin to 50% of original width–typically after 3-4 chains. Ignoring this accelerates bar wear and increases kickback risk. Pair replacements with a new chain (#3610-005-6700 for 3/8″ pitch) for optimal grip.
- Bar rails (#1123-640-0500 for 16″): File grooves when they deepen beyond 0.5mm to prevent chain derailment.
- Drive links: Measure calibration marks every 5 refuels. If links stretch beyond 0.5mm per segment, replace the entire chain.
- Clutch drum (#1123-020-2600): Inspect pawls for smooth engagement. Replace if springs lose tension–symptoms include erratic chain movement.
Fuel system failures often trace to the diaphragm (#1123-020-0700). If the saw floods or cuts out during operation, peel the gasket from the carburetor housing–distorted diaphragms starve the engine. The intake cover (#1123-120-8100) seals this component; inspect its O-ring (#1123-120-8130) during each disassembly for cracks.
Where to Locate Part Numbers
- Engraved on components: Rim sprockets, bars, and clutch drums carry numbers near mounting points.
- Original manual: The exploded view on page 12 lists all OEM codes with arrows pointing to physical locations.
- Authorized dealers: Printed parts lists at service centers include cross-references to compatible third-party alternatives.
- Online databases: Stihldealers.com hosts downloadable schematics with searchable text layers.
Prioritize components exposed to friction or combustion byproducts: chains, filters, and ignition elements fail predictably. Log replacement dates in the saw’s service booklet–patterns emerge after 150-200 hours, allowing preemptive stocking of wear items. Avoid mixing brands for pressure-sensitive parts like diaphragms; material consistency prevents leaks.