STIHL BR 550 Service Manual

The STIHL BR 550 is a professional-grade backpack blower designed for demanding commercial and residential applications. This service manual provides detailed instructions for maintenance, troubleshooting, and repair of the BR 550 engine and blower unit. Below are key sections covering safety, specifications, maintenance procedures, fuel system, ignition system, troubleshooting, and parts information.

1. Features at a Glance 2. Safety Precautions 3. Specifications 4. Maintenance Schedule 5. Engine Disassembly & Assembly 6. Fuel System Service 7. Ignition System Service 8. Air Filter & Cooling System 9. Troubleshooting Guide 10. Torque Specifications 11. Parts Diagrams & Ordering

Features at a Glance

Key components: 2-stroke engine, backpack harness, throttle control, anti-vibration system, air filtration system, and fuel tank.

Feature	Description
Engine Type	STIHL 2-MIX 2-stroke engine
Displacement	74.7 cc
Power Output	4.1 kW (5.5 hp)
Fuel Tank Capacity	1.3 L (0.34 US gal)
Air Volume	Up to 1,200 m³/h
Air Speed	Up to 300 km/h (186 mph)
Weight (dry)	10.6 kg (23.4 lbs)
Sound Pressure Level	Typically 112 dB(A)
Vibration Levels	Front/Rear handles: 4.5/3.5 m/s²
Harness System	Padded backpack harness with hip belt

Safety Precautions

Always follow safety procedures when servicing the BR 550.

Work in a well-ventilated area away from sparks or flames.
Allow engine to cool completely before servicing.
Disconnect spark plug wire before performing any maintenance.
Use only STIHL-approved parts and accessories.
Wear appropriate personal protective equipment (PPE).

WARNING! Fuel is highly flammable. Never smoke or work near open flames when handling fuel or servicing fuel system components.

Specifications

Engine: STIHL 2-MIX single cylinder 2-stroke
Bore x Stroke: 50 mm x 38 mm
Compression Ratio: 7.5:1
Ignition System: Electronic, capacitor discharge
Spark Plug: Bosch WSR 6 F or equivalent, gap 0.5 mm
Carburetor: Zama C1Q-S267 or equivalent
Fuel/Oil Ratio: 50:1 with STIHL HP Ultra oil
Idle Speed: 2,800 ± 150 rpm
Maximum Power Speed: 6,800 rpm
Blower Tube Diameter: 63 mm (2.5 in)

Maintenance Schedule

Regular maintenance ensures optimal performance and longevity.

Interval	Service Required
Before each use	Check for loose fasteners, inspect air filter, check fuel system for leaks
Every 25 hours	Clean air filter, check spark plug, clean cooling fins
Every 50 hours	Replace spark plug, clean fuel filter, check carburetor adjustment
Every 100 hours	Replace fuel filter, clean exhaust system, check ignition system
Annually	Replace air filter, check all gaskets and seals, inspect vibration mounts

Note: Service intervals may vary based on operating conditions.

Engine Disassembly & Assembly

Step-by-step procedure for engine service.

Remove blower tube and housing covers.
Disconnect fuel lines and throttle linkage.
Remove cylinder cover and cooling fan.
Remove cylinder head and inspect piston/cylinder.
Remove crankshaft and bearings as needed.
Reassemble in reverse order using new gaskets.

CAUTION! Mark all components during disassembly. Use proper tools to avoid damage.

Fuel System Service

Carburetor adjustment and fuel system maintenance.

Clean fuel tank and replace fuel filter.
Adjust carburetor: LA (idle) 1 turn out, H (high) 1 turn out, L (low) 1 turn out.
Check fuel lines for cracks or deterioration.
Test fuel pump diaphragm and replace if hardened.
Verify proper operation of primer bulb.

Tip: Use only ethanol-free fuel or add fuel stabilizer to prevent carburetor issues.

Ignition System Service

Testing and replacing ignition components.

Check spark plug: Replace if electrode is worn or insulator is cracked.
Test ignition coil: Resistance primary 0.5-1.5 Ω, secondary 8-15 kΩ.
Inspect spark plug wire for cracks or damage.
Check stop switch for proper operation.
Verify flywheel key is not sheared.

WARNING! Always disconnect spark plug wire before testing ignition system.

Air Filter & Cooling System

Maintaining proper airflow and cooling.

Clean air filter: Tap out debris or wash with warm soapy water.
Oil foam filter with STIHL filter oil after cleaning.
Remove debris from cooling fins and fan housing.
Check cylinder fins for damage or clogging.
Inspect fan blades for cracks or damage.

CAUTION! Never operate engine without air filter. This can cause rapid engine wear.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine won't start	No spark, fuel issues, compression	Check spark, fuel delivery, compression (should be 120+ psi)
Engine runs poorly	Clogged filter, carb adjustment	Clean air filter, adjust carburetor, check fuel filter
Loss of power	Exhaust clog, air leak	Clean spark arrestor, check crankcase seals
Excessive vibration	Fan imbalance, mount failure	Check fan blades, replace vibration mounts
Overheating	Clogged cooling fins, lean mixture	Clean cooling system, check carburetor adjustment

Torque Specifications

Critical fasteners and proper torque values.

Component	Torque (Nm)	Torque (ft-lbs)
Cylinder head nuts	20-22	14.8-16.2
Spark plug	25-30	18.4-22.1
Fan housing screws	8-10	5.9-7.4
Carburetor mounting	6-8	4.4-5.9
Muffler bolts	12-15	8.9-11.1

Note: Use a calibrated torque wrench for accurate tightening.

Parts Diagrams & Ordering

Reference diagrams for part identification and ordering.

Cylinder and piston assembly (Part # 1140 020 2001)
Crankshaft assembly (Part # 1140 020 4001)
Carburetor kit (Part # 1140 007 1001)
Ignition module (Part # 1140 400 1301)
Air filter set (Part # 1140 140 6401)
Fuel line kit (Part # 1140 358 7701)

Service Support: Contact STIHL technical support at 1-800-467-8445 or visit www.stihlusa.com for parts and service information.