Stihl Mist Blower SR 320, SR 400, BR 340, BR 420 Service Manual (P/N 0455 373 0123)

• Official factory publication covering the Stihl BR and SR series blowers and mistblowers (models 320, 340, 400, 420, 430, and 450), provided as a comprehensive PDF (P/Ns 0455 373 0123 & 0455 454 0123).
• Features 47 exploded-view diagrams and 18 technical troubleshooting flow charts.
• Delivers complete step-by-step repair procedures for engine block overhauls, crankcase leakage testing, ignition module diagnostics, and throttle control replacements.
• Covers the teardown and maintenance of the all-position diaphragm carburetor, anti-vibration (AV) system, rewind starter mechanism, mistblower metering unit, and pressure pump.

Component and Assembly Documentation

This comprehensive ~250-page manual serves as the master reference for these production runs. It thoroughly documents the transition from early models utilizing spacer washers to later units with modified crankcase mounting bosses. The specific advantage of this guide for your daily workshop routine is bypassing trial-and-error troubleshooting. By utilizing the exact factory specifications for vacuum and pressure testing—such as holding 0.5 bar to verify crankcase sealing—mechanics can accurately pinpoint air leaks without unnecessarily replacing expensive engine parts.

Inside, you will find extensive documentation detailing the parameters for complete engine overhauls. The text maps out reference data for piston and cylinder removal, crankcase sealing procedures, and ignition system calibration. Mechanics can quickly look up internal engine architecture, including two-part crankshaft assemblies and needle cage bearing specifications. Need the factory tolerances for adjusting carburetors or testing crankcase airtightness? The guide outlines exact vacuum and pressure testing requirements alongside rewind starter component diagrams, illustrated parts list exploded views, torque specification charts, discharge rate tables, carburetor component assembly drawings, and ignition system connection views.

Furthermore, the manual highlights step-by-step instructions for tasks that typically necessitate an expensive trip to the dealer. This includes splitting the crankcase to extract and replace internal oil seals, completely rebuilding the metering and pump diaphragms of the carburetor, and safely tensioning the rewind starter spring without damaging the coil.

When performing complete engine teardowns, technicians often encounter hidden traps that can compromise the rebuild. For instance, attempting to cold-press the crankshaft will cause severe bearing drag; the manual emphasizes that inner bearing races must be pre-heated to exactly 150°C (300°F) so the shaft drops in smoothly, maintaining perfect factory alignment. Additionally, failing to align the hookless piston pin snap ring gap perfectly on the vertical axis is a documented mistake that can lead to the ring vibrating loose and scoring the cylinder wall.

Technical Specification Highlights

Precise reference values are crucial for daily workshop routines. Engine displacement is mapped out clearly: 44.9 cm³ for the 320/340 models, 56.5 cm³ for the 400/420 series, and 63.3 cm³ for the 430/450 units.

You get exact torque values for critical fasteners, highlighting specs like the 25 Nm requirement for the flywheel nut. Electrical system tables list the ignition module coil resistance at 0.8–1.3 ohms for primary circuits. For spraying attachments, detailed fluid flow rates span from 0.13 l/min up to 3.6 l/min depending on the metering knob position and whether the pressure pump is installed.

Working on high-RPM outdoor power equipment requires strict adherence to industry safety standards. Always rely on these documented factory specifications and ensure a qualified technician verifies all system tolerances during hands-on maintenance to prevent equipment failure or personal injury.