All 533 pages of this Yanmar B50-2 service manual PDF are built around one machine family: the B50-2 and B50-2A compact excavators, with factory-level coverage from engine block to hydraulic circuit to electrical panel. You get a complete hydraulic system section covering pump teardown, control valve service, swing motor, travel motor, and full circuit schematics for every attachment circuit, boom through dozer. Inside: a full troubleshooting section spanning machine, engine, and electrical panel faults, plus wiring diagrams and page after page of tightening torque tables backed by exploded views. Set cylinder head bolt torque to 8.7 kgf-m on the M10x1.5 fasteners, then torque swing bearing M16 bolts to 27-31 kgf-m with Loctite 262 applied. Your machine is down. Search any spec by keyword, jump straight to the section you need, and get the right answer on the first try.
What's Inside This Yanmar B50-2, B50-2A Manual
| System | Pages | Key Topics |
|---|---|---|
| General Cautions for Maintenance Work | 12-22 | Correct Work, Safety Precautions, Preparations, Cautions for Disassembly and Reassembly, Cautions for Attaching and Detaching Hydraulic Equipment |
| Technical Data | 24-36 | Specifications, External Drawings and Working Ranges (Canopy Type Specifications, Cabin Type Specifications), Weight of Main Parts, Lifting Capacities |
| Servicing Standards | 38-56 | Machine Performance, Undercarriage (Rubber Track Specifications, Steel Track Specifications, Steel & Rubber Track Common Specifications), Control Devices |
| Engine | 58-183 | Cylinder Block, Cylinder Head, Piston and Piston Pin, Connecting Rod, Crankshaft and Main Bearing, Camshaft and Tappets, Timing Gear, Service Data |
| Hydraulic System | 184-413 | Outline, Circuit Schematic, Hydraulic Pump, Control Valve, Pilot Valve, Swing Motor, Travel Motor, Pressure Adjustment |
| Adjustment Procedures for Each Equipment | 414-477 | Electrical Equipment of the Machine (Arrangement of Electrical Equipment and Names of Parts, Monitor and Alarm Systems) |
| Periodic Inspection and Servicing | 478-481 | List of Periodic Inspection and Servicing |
| Fuel, Lube Oil and Grease Recommended | 482-484 | Fuel Specifications, Lube Oil Specifications, Grease Specifications, Cooling Water |
| Troubleshooting | 486-523 | Non-Breakdowns, Machine & Engine, Electrical Equipment on Panel |
| Reference Data | 524-533 | Steel Track Exchange, Rubber Track Exchange |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Hydraulic hose length change at high pressure | +2% to -4% | p. 17 |
| Swing bearing to lower frame tightening torque | 27 ~ 31 kgf-m | p. 54 |
| Swing bearing to turning frame tightening torque | 27 ~ 31 kgf-m | p. 54 |
| Cylinder head bolt torque (M10x1.5) | 8.7 kgf-m | p. 56 |
Yanmar B50-2, B50-2A Common Problems This Manual Covers
Yanmar B50-2 upper structure drifts after swing stop, machine won't hold position on slopes p. 449
Check swing bearing axial clearance with a dial gauge under 200 kgf load. Standard range is 0.05~0.25 mm; replace the bearing if worn past 0.55 mm, per the spec on page 449. When reinstalling, torque M16 swing bearing bolts to 27~31 kgf-m using Loctite 262 per torque specs on page 54.
Manual Section: Swing System TroubleshootingWork implement moves slowly or stops mid-cycle under load, bucket digging force noticeably weak
Verify pilot valve function and inspect control valve spools for contamination. Trace flow restrictions using the hydraulic schematic. Measure relief pressure and compare to servicing standards on page 38. When replacing any hoses, leave slack to accommodate the +2% to -4% length change under full working pressure, per page 17.
Manual Section: Work Implement TroubleshootingEngine won't start or cranks slowly in cold weather, glow plugs suspected
Verify battery charge and test the starter circuit against the wiring diagram. Check that engine oil viscosity matches cold-weather recommendations from page 482. Inspect glow plug operation and clean battery terminals. Follow the troubleshooting sequence on page 496 for starter motor and battery charging faults before condemning any single component.
Manual Section: Electrical System TroubleshootingMachine veers to one side during travel or won't move forward and reverse in both tracks p. 486
Inspect travel motor pilot supply circuits and verify hydraulic oil level against the capacity specs on page 484. Confirm neither left nor right travel spool is sticking or worn. Check track tension and undercarriage condition per servicing standards on page 38. Use the troubleshooting section starting on page 486 to isolate motor, valve, or supply faults.
Manual Section: Travel System TroubleshootingWater temperature warning lamp stays lit or charge lamp illuminates at normal operating temperature
Trace monitor and alarm wiring against the diagram. Check coolant level, test alternator output voltage, and inspect sensor connector pins for corrosion or moisture. Verify the maintenance schedule on page 480 is current, as low oil or coolant pressure trips multiple lamps simultaneously. Check for chafed harness wires near the engine compartment.
Manual Section: Electrical System TroubleshootingEngine emits black smoke under load and loses power at full throttle p. 496
Check air cleaner condition and inspect for intake restriction first. Verify coolant level and radiator core airflow against the fluid specs on page 484. Inspect injection nozzle condition and fuel quality per recommendations on page 482. Follow the engine output and smoke diagnostics on page 496 to isolate fuel delivery, injection timing, or air supply as the root cause.
Manual Section: Engine Troubleshooting (General)Frequently Asked Questions
What are torque specs for hydraulic cylinder bolts on Yanmar B50-2A?
The tightening torque for hydraulic cylinder bolts varies by position. For the rod nut (position ⑧) on the Boom (Cabin spec.) cylinder, the tightening torque is 190~200 kgf-m. For the Arm cylinder, the rod nut (position ⑧) requires 145~155 kgf-m.
Can I use a cylinder with a smaller inner diameter on Yanmar B50-2A?
The manual provides standard inner diameters and wear limits for hydraulic cylinders. For example, the Boom (Cabin spec.) cylinder has a standard inner diameter of 700 mm. If the inner diameter wears down to 670 mm, it is at its wear limit. The manual does not recommend using a cylinder with an inner diameter smaller than the specified standard or wear limit, as it would suggest a worn or incorrect part.
What are the replacement specifications for swivel box / swing assembly components?
For swivel box/swing assembly components, seals and O-rings should be replaced if they show flaws, distortion, or hardening. For example, floating seals should be replaced if there are abnormal flaws, wear, or seizure on the moving surface. O-rings should be replaced if they show flaws or distortion or are not hardened.
What are the replacement specifications for hydraulic seals?
Hydraulic seals, including floating seals and O-rings, should generally be replaced with new ones after any disassembly. Specifically, floating seals should be replaced if they show abnormal flaws, wear, or seizure. O-rings should be replaced if they have flaws, distortion, or are not hardened. Oil seals should be replaced if their lip surface shows flaws, distortion, or abnormal wear.
What format is this manual in?
Immediate download of the complete 533-page searchable Service Manual. Access it on any device, from a laptop at your desk to a phone in the field.
Can I print this manual?
There are no print restrictions. The PDF is DRM-free — print whatever sections you need for the shop. Standard letter or A4 paper works.
Can I find wiring schematics in this Yanmar B50-2, B50-2A manual?
Yes, this Yanmar B50-2, B50-2A Service Manual includes complete electrical wiring diagrams, wire routing, and connector pinouts.
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