Stihl BG 85 Parts Manual PDF

The Stihl BG 85 is a professional-grade backpack blower designed for demanding commercial and residential use. This parts manual provides detailed diagrams, part numbers, and ordering information for the complete BG 85 system, including the engine, fan housing, throttle controls, fuel system, carrying harness, and all associated hardware. Below are key sections for identification, engine components, blower assembly, fuel system, controls, harness, and maintenance parts.

Introduction & Model Identification

This manual covers the Stihl BG 85 Backpack Blower. Verify your model using the serial number plate located on the blower housing. Key assemblies: Engine (2-stroke), Blower Tube, Harness System, and Controls.

Component Group	Description
Engine Assembly	Complete power unit including crankcase, cylinder, and mounting points
Blower Housing	Fan shroud and impeller assembly for airflow generation
Fuel System	Tank, cap, lines, filter, and carburetor
Air Filtration	Air filter cover, pre-filter, and foam element
Starter Assembly	Rewind starter with rope, pulley, and spring
Muffler	Spark-arresting muffler and heat shield
Throttle Controls	Throttle lever, cable, and trigger on handle
Carrying Harness	Padded shoulder straps, waist belt, and frame
Blower Tube	Main tube and nozzle for directing airflow
Fasteners & Decals	All screws, nuts, washers, and identification labels

Engine Assembly & Crankcase

The crankcase forms the foundation of the engine. It houses the crankshaft, bearings, and seals.

1. Crankcase Halves: Left and right magnesium alloy halves. Includes gasket surface and mounting bosses.
2. Crankshaft: Forged steel shaft with integrated counterweights and bearing journals.
3. Main Bearings & Seals: Ball bearings and crankshaft seals to maintain crankcase pressure.
4. Mounting Studs & Bushings: Threaded studs for cylinder attachment and vibration dampeners.

WARNING! Always replace crankcase seals when rebuilding the engine to prevent air leaks and engine damage.

Cylinder, Piston & Ignition System

Components responsible for compression, combustion, and spark generation.

1. Cylinder: Aluminum with Nikasil plating. Includes intake, transfer, and exhaust ports.
2. Piston & Rings: Aluminum piston with two compression rings and wrist pin.
3. Cylinder Head & Gasket: Combustion chamber cover with spark plug thread.
4. Ignition Module (Coil): Generates spark for the plug. Includes stop switch wire.
5. Spark Plug: Standard resistor plug (e.g., Bosch WSR6F).

CAUTION! Match piston size (A, B, C) to cylinder marking for correct clearance.

Fuel System & Carburetor

• Fuel Tank: Polyethylene tank with integrated mounting points.
• Fuel Cap: Venting cap with retaining chain.
• Fuel Line & Filter: Tygon fuel line and in-tank sintered bronze filter.
• Carburetor: Zama or Walbro diaphragm carburetor. Includes gaskets, diaphragms, metering lever, and adjustment screws (H, L, LA).
• Impulse Line: Connects crankcase to carburetor pump chamber.
• Primer Bulb: For easy starting (if equipped).

Air Filtration & Cooling System

Protects engine from debris and manages operating temperature.

Air Filter Assembly: Cover, pre-filter (foam), main filter element (felt/fabric), and retaining clip.

Cooling Fan & Shroud: Plastic fan mounted on crankshaft and metal/plastic shroud directing air over cylinder fins.

Intake Manifold: Connects carburetor to crankcase. Includes gasket and mounting clamp.

Blower Housing & Impeller

The blower assembly generates high-velocity air output.

1. Turn off engine and allow to cool before disassembly.
2. Remove housing screws to access impeller.
3. Impeller is keyed to the crankshaft; inspect for cracks or damage.
4. Select air direction via tube rotation (straight or angled output).

Tip: Ensure impeller is clean and balanced for smooth, vibration-free operation.

Throttle Linkage & Control Handle

Supports precise throttle control and operator comfort.

1. Throttle Lever/Cable: Cable connects handle trigger to carburetor throttle arm.
2. Control Handle: Main handle with throttle trigger, lock-out lever, and mounting clamp.
3. Throttle Lock: Cruise control feature for sustained high RPM.
4. Linkage Springs: Return springs for throttle and stop switch.
5. Stop Switch: Grounds ignition to stop engine. Wire connects to handle and coil.

WARNING! Ensure throttle cable moves freely and returns fully to idle position for safe operation.

Carrying Harness & Frame

Ergonomic system for comfortable extended use.

Harness Frame: Metal or plastic frame that attaches to engine housing.

Shoulder Straps: Padded, adjustable straps with quick-connect buckles.

Waist Belt & Strap: Stabilizing belt with padding and adjustment.

Mounting Hardware: Bolts, washers, and clips for securing harness to blower unit.

Starter Assembly & Rewind

Manual recoil starting system.

1. Starter Housing: Plastic cover containing rewind mechanism.
2. Rewind Spring & Pulley: Spring provides rewind force; pulley guides rope.
3. Starter Rope & Handle: Braided nylon rope with ergonomic grip.
4. Pawl & Spring: Engagement dogs that catch the engine fan for cranking.
5. Mounting Screws: Secures starter to the blower housing.

CAUTION! Wear gloves when handling rewind spring to prevent injury from sudden uncoiling.

Muffler & Exhaust System

Reduces noise and directs exhaust gases.

Symptom	Possible Cause	Corrective Action
Loss of power, excessive smoke	Clogged spark arrestor screen	Remove muffler, clean screen with wire brush.
Exhaust leak	Damaged gasket or loose bolts	Replace cylinder exhaust gasket and tighten bolts to spec.
Muffler rattling	Internal baffle broken or loose	Replace entire muffler assembly.
Overheating	Restricted exhaust flow	Ensure spark arrestor is not melted or blocked.

Note: The spark arrestor screen is required for use in forested areas.

Fasteners, Decals & Miscellaneous Parts

Includes all hardware and identification labels.

• Screws & Bolts: Various metric thread sizes (M5, M6) with different lengths and head types (Phillips, Hex).
• Nuts, Washers, Lock Washers: Nylock nuts, flat washers, and split lock washers.
• Vibration Dampeners: Rubber bushings and grommets for harness and handle mounts.
• Decals: Warning labels, model identification, throttle pictograms, and mixture ratio (50:1) stickers.
• Clamps & Bands: Hose clamps for fuel lines, band clamps for blower tube.

Service: For genuine Stihl parts, contact an authorized Stihl dealer or visit www.stihlusa.com.