1970s–1980s Husqvarna 50 / 50 Special / 51 / 55 Chainsaw Workshop Manual (P/N 531 03 00-76)

Husqvarna Workshop Manual 531 03 00-76 covers repair of the 1970s–1980s 50, 50 Special, 51, and 55 chainsaws, with model-specific engine, fuel system, and chain drive information.

Workshop Text Search and PDF Page Detail

Search, bookmarks, and legibility: Much of the workshop text is searchable, but some headings and text within illustrations are not. Bookmarks open only the additional front page and the manual start. Text and artwork overlap at the bottom of PDF p. 38 in the carburetor section.

The download is one printable, English-language 59-page PDF, including 58 manual pages (the cover, introduction, and 56 numbered pages) and one additional front page.

Engine Overhaul, Carburetor Diagnosis, and Chain Brake Service

Beyond the selected repair topics below, the manual covers bar stud replacement and spark plug connector spring installation.

• Engine repair: Step-by-step procedures for cylinder and piston removal, piston ring replacement, crankcase splitting, crankshaft bearing installation, and crankshaft seal replacement.

• Fuel system: Walbro WA and WT carburetor disassembly, pressure testing, reassembly, and adjustment, plus fuel tank ventilation testing and fuel filter replacement.

• Ignition and starting: Electronic ignition diagnosis, flywheel removal and timing alignment, ignition module air gap adjustment, and recoil starter repair.

• Clutch and lubrication: Centrifugal clutch inspection and reassembly, rim and spur sprocket checks, and automatic oil pump disassembly and assembly.

• Safety equipment: Inertia and manual chain brake function checks, brake band replacement, throttle trigger lockout repair, chain catcher inspection, and anti-vibration element replacement.

• Diagnostic references: Troubleshooting charts, crankcase/cylinder leakage test data, carburetor cross-section schematics, exploded assembly drawings, and component-specific service specifications.

This manual is suited to mechanics familiar with two-stroke engine repair and equipped for pressure testing and crankshaft service.

Walbro Carburetors and Fuel System Diagnosis

The 50 and 50 Special use the Walbro WA82; the 51 and 55 use the WT170. The fuel chapter distinguishes their fuel circuit plate and Welch plug arrangements, fuel inlet lever settings, and the choke-operated fast idle system on the 51 and 55.

Carburetor overhaul: Carburetor Operation cutaways explain the metering, mixing, and pumping sections. Diaphragm and gasket exploded views accompany the assembly text, and pressure-test illustrations show the test equipment connections. The manual warns that damage to internal fuel passages and seats can make carburetor replacement necessary.

Intake manifold coverage includes the fuel pump pulse passage, its seal, and the rubber intake tube. The installation and adjustment sections address throttle and choke linkages, basic mixture settings, and final running adjustment. Pressure gauge P/N 5025038-01 and tachometer P/N 5027114-01 are identified for these checks.

Fault isolation: The two-page Trouble-shooting Chart connects starting, idle, acceleration, deceleration, and high-speed symptoms with possible fuel, air, metering, and circuit plate faults. It provides a way to narrow a running complaint before choosing which components to inspect.

Flywheel Variants and Ignition Testing

For Model 50, serial number 9250857 marks changes in flywheel construction and service-tool application. The ignition chapter describes the cast-in flywheel key as well as removable-key and dual-keyway arrangements, including the timing alignment for dual-keyway flywheels.

The spark-checking section addresses the stop switch, short-circuit wire, high-tension lead, and ignition module. Rewind starter procedures cover the rope and spring cassette; flywheel service also includes starter pawl and spring inspection.

Cylinder, Crankcase, and Crankshaft Repair

The Cylinder & Piston fault/remedy table addresses seizure marks, damaged cylinder coatings, and stuck piston rings. Crankcase bearing procedures describe bearing removal and installation using heated bearing seats.

Crankshaft inspection distinguishes connecting-rod axial movement from radial play and explains when the crankshaft assembly requires replacement. The illustrated procedures identify crankcase separation tool P/N 5025161-01 and seal installation tool P/N 5025079-01.

The seal replacement section also warns that careless removal can scratch or damage the crankshaft.

Chain Brake, Clutch, and Oil Pump Service

Brake band and clutch shoe inspections include wear limits. Assembly sections provide the corresponding flywheel, clutch, and crankcase torque specifications.

Oil pump service covers the drive gear, pump piston and cylinder, pickup filter, and oil tank vent. The exhaust section explains how a restricted spark arrester screen can cause overheating and damage the piston or cylinder.

Keep in mind that this is an informational overview. Use the complete manual for service procedures, particularly work on the tensioned chain brake and rewind springs.

Carburetor Pressure and Brake Band Limits: A Preview

Carburetor leakage testing is specified at 50 kPa (7.2 psi), with no air leakage permitted. This check accompanies the carburetor inspection and reassembly material.

The chain brake section lists an original brake band thickness of 0.80 mm (0.031 in.). Its replacement threshold is 0.65 mm (0.026 in.) or less anywhere along the band.