The Bobcat 331 is a compact excavator you'll see trenching services, digging footings, loading trucks, and doing farm utility work. The service manual is what a shop mechanic or field tech grabs when the machine's out of warranty and something heavier than "check the fuses" is going on. You're using it when you need teardown steps, hydraulic test specs, wiring logic, and how it all goes back together, same way we use Cat or Deere books in the shop.
What this manual helps you do
- Diagnose hydraulic problems, check pressures, and trace weak or dead functions in the boom, arm, bucket, and travel.
- Follow step-by-step teardown and reassembly on the upperstructure, swing motor, travel motors, cylinders, and final drives.
- Troubleshoot engine and fuel system issues on the small diesel, including hard-start, low power, and stalling complaints.
- Trace and repair electrical faults using wiring diagrams, connector callouts, and harness routing info.
- Adjust, set, and verify control linkages, pilot controls, and relief settings after repairs or component replacement.
Who this is for
This manual is for shop mechanics, small contractors with their own 331, rental fleets, and owner-operators who actually wrench on their equipment. If you only want basic operating tips, safety, and daily checks, you want the operator's handbook instead, not this service manual.
FAQ
Q: Is this a searchable PDF with readable wiring diagrams?
A: Most copies of this book are clear, searchable PDFs and the wiring diagrams are usually legible when you zoom in and print on full-size paper.
Q: How do I know if it covers my exact 331?
A: Check your serial plate. This manual is for 331 excavators in the 512911001-512912999 serial range. If your number is outside that, you need a different book.
Q: Is this the right document for doing real repairs?
A: Yes. This is the workshop service manual, not a parts book or operator's manual, and it's what you'd use for real diagnostics and component rebuilds.
If your 331's serial number falls in 512911001-512912999 and you're doing your own repairs, this is the manual you want. If your serial doesn't match, skip it.
📘 Show Index
Table of Contents:
- MAINTENANCE SAFETY
- ALPHABETICAL INDEX
- CONTENTS
- FOREWORD
- SAFETY INSTRUCTIONS
- SERIAL NUMBER LOCATIONS
- HYDRAULIC EXCAVATOR SERIAL NUMBER
- ENGINE SERIAL NUMBER
- DELIVERY REPORT
- HYDRAULIC EXCAVATOR IDENTIFICATION
- MACHINE SIGNS TRANSLATIONS (DECALS)
- PREVENTIVE MAINTENANCE
- SERVICE SCHEDULE (S/N 11001–11999)
- SERVICE SCHEDULE (S/N 12001 & Above)
- PREVENTIVE MAINTENANCE
- LIFTING AND BLOCKING THE EXCAVATOR
- TRANSPORTING THE EXCAVATOR
- ENGINE COVER
- AIR CLEANER
- Servicing the Air Cleaner (S/N 11001–11999)
- Servicing the Air Cleaner (S/N 12001–12999)
- Servicing the Air Cleaner (S/N 13001 & Above)
- FUEL SYSTEM
- Fuel Specification
- Filling the Fuel Tank
- Fuel System Service
- Fuel Filter
- Removing Air from the Fuel System
- ENGINE LUBRICATION SYSTEM
- Checking Engine Oil
- Replacing Oil and Filter
- COOLING SYSTEM
- Coolant Level
- Ethylene Glycol
- Propylene Glycol
- Coolant Replacement
- HYDRAULIC SYSTEM
- Checking and Adding Fluid
- Replacing the Hydraulic Filter (S/N 11001–11999)
- Replacing the Hydraulic Filter (S/N 12001 & Above)
- Return Line Filter Service (S/N 12240 & Above)
- Hydraulic Reservoir
- Diagnostic Couplers
- USING A BOOSTER BATTERY (Jump Starting)
- Procedure (S/N 11001–11999)
- Procedure (S/N 12001 & Above)
- SPARK ARRESTOR MUFFLER
- Cleaning Spark Arrestor Muffler (S/N 11001–11999)
- Cleaning Spark Arrestor Muffler (S/N 12001 & Above)
- LUBRICATION OF THE EXCAVATOR
- Procedure (S/N 11001 – 11999)
- Procedure (S/N 12001 & Above)
- FINAL DRIVE CASE
- Checking Oil Level
- Draining Final Drive Case
- HEATER AIR FILTER SERVICE
- HYDRAULIC SECTION
- HYDRAULIC SCHEMATICS
- HYDRAULIC SYSTEM TROUBLESHOOTING
- HYDRAULIC SERVICE INFORMATION (S/N11001–12999)
- MAIN RELIEF VALVES (S/N 11001–12999)
- Description
- Checking Dual Pressure Relief Valves
- Checking Single Pressure Relief Valve
- Dual Pressure Relief Valve Adjustment (6–Spool Valve)
- Single Pressure Relief Valve Adjustment (3–Spool Valve)
- HYDRAULIC SERVICE INFORMATION (S/N 13001 &Above)
- MAIN RELIEF VALVE (Adjustable) (S/N 13001 & Above)
- Checking the Main Relief Valves
- Testing the Blade, Boom Swing, Arm and Boost Circuit Relief Valves
- Testing the 4050 PSI (27925 kPa) Circuit Relief
- Testing the Auxiliary and Bucket Circuit Relief Valve
- Testing the Left Hand Travel Circuit Relief Valve
- Testing the Right Hand Travel Circuit Relief Valve
- Testing the Boom Circuit Relief Valve
- HYDRAULIC PUMP
- Checking the Hydraulic Pump
- Removal and Installation
- Parts Identification
- Disassembly
- Assembly
- HYDRAULIC CONTROL VALVE (6–Spool) (S/N 12999 & Below)
- Removal and Installation
- Parts Identification
- Disassembly
- Assembly
- Right Hand Travel Section Disassembly and Assembly
- Boom, Bucket and Arm Section Disassembly and Assembly
- Auxiliary Section Disassembly and Assembly
- Left Hand Travel Section Disassembly and Assembly
- End Cover Disassembly and Assembly
- HYDRAULIC CONTROL VALVE (3–Spool) (S/N 12999 & Below)
- Description
- Removal and Installation
- Parts Identification
- Disassembly
- Assembly
- Housing Swing Section Disassembly and Assembly
- Blade and Boom Swing Section Disassembly and Assembly
- End Cover Disassembly and Assembly
- HYDRAULIC CONTROL VALVE (5–Spool) HUSCO VALVE (S/N 13001 & Above)
- Left Travel, Right Travel, Boom, Bucket and Auxiliary
- Removal and Installation
- Parts Identification
- Disassembly
- Outlet Sections Disassembly
- Outlet Sections Assembly
- Mid Inlet Section Disassembly
- Mid Inlet Section Assembly
- Left Travel, Right Travel and Auxiliary Disassembly
- Left Travel, Right Travel and Auxiliary Assembly
- Boom and Bucket Disassembly
- Boom and Bucket Assembly
- Assembly
- PORT RELIEF VALVES AND MAIN RELIEF VALVES (S/N 13001 & Above)
- Parts Identification
- Port Relief Valve Pressure Setting
- Disassembly
- Assembly
- MAIN RELIEF VALVES (Adjustable) (S/N 13001 & Above)
- Parts Identification
- Assembly
- Disassembly
- Assembly
- Adjusting the Main Relief Valves
- HYDRAULIC CONTROL VALVE (5–Spool) HUSCO VALVE (S/N 13001 & Above)
- Boost, Arm, Boom Swing, Blade and Swing Section
- Description
- Removal and Installation
- Parts Identification
- Disassembly
- Inlet Section
- Arm, Boost and Swing Motor Disassembly
- Arm, Boost and Swing Motor Assembly
- Boom Swing Disassembly
- Boom Swing Assembly
- Blade Disassembly
- Blade Assembly
- Assembly
- ACCUMULATOR (S/N 12999 & Below)
- Adjustment
- Pressure Reducing Valve
- Testing
- Removal and Installation
- Parts Identification
- Disassembly
- Assembly
- Setting the Safety Relief Valve
- Charging
- ACCUMULATOR (S/N 13001 & Above)
- Removal and Installation
- Parts Identification
- AUXILIARY SELECTOR VALVE
- Removal and Installation (S/N 12999 & Below)
- Removal and Installation (S/N 13001 & Above)
- Disassembly and Assembly
- TWO SPEED VALVE (S/N 12999 & Below)
- Removal and Installation
- Parts Identification
- Disassembly
- Assembly
- TWO SPEED SWITCH (S/N 13001 & Above)
- PORT BLOCK
- Removal and Installation (S/N 12999 & Below)
- Removal and Installation (S/N 13001 & Above)
- OIL COOLER
- Removal and Installation (S/N 11001 – 11999)
- Removal and Installation (S/N 12001 & Above)
- HYDRAULIC RESERVOIR AND FUEL RESERVOIR
- HYDRAULIC FILTER ASSEMBLY
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001 & Above)
- BOOM CYLINDER
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001 & Above)
- Parts Identification
- ARM CYLINDER
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001 & Above)
- Parts Identification
- BUCKET CYLINDER
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001 & Above)
- Parts Identification
- BLADE CYLINDER
- Removal and Installation
- Parts Identification
- BOOM SWING CYLINDER
- Removal and Installation
- Parts Identification
- HYDRAULIC CYLINDER
- JOYSTICK CONTROL CHANGE
- ISO to STANDARD Control Pattern (S/N 12999 & Below)
- STANDARD to ISO Control Pattern (S/N 12999 & Below)
- ISO to STANDARD Control Pattern (S/N 13001 & Above)
- STANDARD to ISO Control Pattern (S/N 13001 & Above)
- DRIVE SECTION
- LEFT CONSOLE (S/N 12999 & Below)
- Lockout Valve Removal and Installation
- Cylinder Removal and Installation
- Removal and Installation
- LEFT CONSOLE (S/N 13001 & Above)
- Control Lock Micro–Switch Removal and Installation
- Cylinder Removal and Installation
- Removal and Installation
- LEFT CONSOLE RELEASE HANDLE (S/N 13001 & Above)
- Removal and Installation
- Adjustment
- JOYSTICK (S/N 12999 & Below)
- Removal and Installation
- Parts Identification
- Disassembly and Assembly
- JOYSTICK (S/N 13001 & Above)
- JOYSTICK (S/N 13001 & Above)
- Parts Identification
- Disassembly
- Assembly
- Troubleshooting
- RIGHT CONSOLE
- Removal and Installation (S/N 12999 & Below)
- Removal and Installation (S/N 13001 & Above)
- RIGHT CONSOLE COVER
- SPEED CONTROL LEVER
- Low Idle Adjustment
- High Idle Adjustment
- Removal and Installation
- BLADE CONTROL LEVER AND CABLE
- STEERING LEVERS AND PEDALS
- Removal and Installation
- Adjusting Linkage Rods
- UPPER WORKS AND SWING SECTION
- ENGINE COVER
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001 & Above)
- SEAT AND SEAT MOUNT
- FLOORMAT AND FLOOR PLATE
- REAR FLOOR PLATE
- SWING MOTOR COVER
- INSPECTION COVER (S/N 11001–11999)
- TOOL BOX
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001 & Above)
- LEFT HAND SIDE COVER
- Removal and Installation (S/N 11001–11999)
- Removal & Installation (S/N 12001 & Above)
- RIGHT HAND SIDE COVER
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001 & Above)
- RIGHT HAND CORNER POST
- LEFT HAND CORNER POST
- COUNTERWEIGHTS
- FRONT ENGINE COVER
- BUCKET
- BUCKET TEETH
- ARM
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001 & Above)
- BOOM
- BOOM SWING BRACKET
- Removal and Installation
- Hose Installation
- SWING BRACKET BUSHING
- Bushing Removal
- Bushing Installation
- BOOM PIVOT BUSHING
- Bushing Removal
- Bushing Installation
- SWING MOTOR
- Removal and Installation (S/N 11001–11056)
- Removal and Installation (S/N 11057–12999)
- Disassembly (S/N 11001–12999)
- Assembly (S/N 11001–12999)
- CROSS PORT RELIEF VALVE (S/N 11001–11056 S/N 13001 & Above)
- Disassembly
- Assembly
- Description
- Testing
- COUNTERBALANCE VALVE (S/N 11057–12999)
- Description
- Removal and Installation
- Disassembly
- Assembly
- SWING GEAR BOX
- Parts Identification (S/N 11001–12999)
- Disassembly (S/N 11001–12999)
- Assembly (S/N 11001–12999)
- SWING MOTOR
- Removal and Installation (S/N 13001 & Above)
- SWING MOTOR DRIVE CARRIER (S/N 13001 & Above)
- Removal and Installation
- Parts Identification
- Disassembly
- Assembly
- UPPERSTRUCTURE AND SWING CIRCLE GEAR
- Removal and Installation
- Swing Bearing Removal
- Swing Bearing Installation
- Alignment Pins (Not Threaded)
- CENTER SWIVEL JOINT
- Removal and Installation (S/N 12999 & Below)
- Removal and Installation (S/N 13001 & Above)
- Parts Identification
- Disassembly
- Assembly
- ROPS CANOPY
- CAB
- Removal and Installation
- Front Window Removal and Installation
- Front Lower Window Removal and Installation
- Front Upper Window Removal and Installation
- Door Removal and Installation
- Door Window Removal and Installation
- Left Hand Side Window Removal and Installation
- Right Hand Side Window Removal and Installation
- Right Hand Window Assembly Removal and Installation
- Rear Window Removal and Installation
- CAB/CANOPY REAR COVER
- MAIN FRAME AND TRACKS
- BLADE
- TRACK
- Track Lug Height
- Track Tension Adjustment
- Rubber Track Clearance
- Steel Track Clearance
- Adjustment (S/N 512912999 & Below)
- Adjustment (S/N 512913001 & Above)
- Rubber Track Removal and Installation
- Steel Track Removal and Installation
- TRACK FRAME
- Disassembly and Assembly (S/N 512912999 & Below)
- Disassembly and Assembly (S/N 512913001 & Above)
- TRAVEL MOTOR
- Testing
- Removal and Installation
- (S/N 512911001–512913404)
- Parts Identification
- Disassembly
- Assembly
- (S/N 512913405 & Above)
- Parts Identification
- Disassembly
- Assembly
- TRACK DAMAGE IDENTIFICATION
- Cutting Of Steel Cords
- Abrasion Of Embedded Metals
- Separation Of Embedded Metals
- Separation Of Embedded Metals Due To Corrosion
- Cuts On The Lug Side Rubber
- Cracks Of The Lug Side Rubber Due To Fatigue
- Lug Abrasion
- Cracks And Cuts On The Lug Side Rubber
- Abrasion Of The Track Roller Side
- Cuts On The Edges Of Track Roller Side
- ELECTRICAL SYSTEM
- ELECTRICAL SCHEMATICS
- TROUBLESHOOTING
- ELECTRICAL SYSTEM
- Description
- Fuses
- Fuse Arrangement
- Electrical System Service
- BATTERY
- Check the Battery
- Removal and Installation (S/N 11001–11999)
- Removal & Installation (S/N 12001 & Above)
- ALTERNATOR
- Belt Adjustment
- Removal and Installation
- Parts Identification
- Disassembly and Inspection
- Stator Continuity Test
- Stator Ground Test
- Rotor Continuity Test
- Rotor Ground Test
- Rectifier Continuity (Diode) Test
- Assembly
- STARTER
- Removal and Installation
- Disassembly and Assembly
- Cleaning and Inspection
- Part Identification
- FUEL LEVEL SENDER
- Removal and Installation
- Checking
- INSTRUMENT PANEL
- GAUGES
- GAUGE LIGHTS
- CAB ELECTRICAL
- ENGINE SERVICE
- TROUBLESHOOTING
- VALVE CLEARANCE
- ENGINE COMPRESSION
- GLOW PLUGS
- Removal and Installation
- Checking the Glow Plug
- FUEL SHUT–OFF SOLENOID
- Adjustment
- Removal and Installation
- Timer Module Removal and Installation
- FUEL INJECTION PUMP
- Checking the Injection Pump
- Removal and Installation
- Timing the Injection Pump
- FUEL INJECTOR NOZZLES
- Removal and Installation
- Checking the Injector Nozzle
- FAN GUARD
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001 & Above)
- RADIATOR
- Removal and Installation (S/N 11001 – 11999)
- Removal and Installation (12001 & Above)
- MUFFLER
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001 & Above)
- AIR CLEANER
- Removal and Installation (S/N 11001–11999)
- Removal and Installation (S/N 12001–12999)
- Removal and Installation (S/N 13001 & Above)
- ENGINE
- ENGINE FLYWHEEL
- Removal and Installation
- Flywheel Ring Gear
- CYLINDER HEAD
- Removal and Installation
- Disassembly and Assembly
- Servicing the Cylinder Head
- Top Clearance
- VALVE, VALVE SEAT AND GUIDE
- Checking the Valve Guide
- Reconditioning the Valve and Valve Seat
- Valve Spring
- ROCKER ARM AND SHAFT
- TIMING GEARCASE COVER
- IDLER GEAR AND CAMSHAFT
- Removal and Installation
- Servicing the Camshaft
- Servicing the Idler Gear and Shaft
- TIMING GEARS
- FUEL CAMSHAFT
- Removal and Installation
- Governor
- CRANKSHAFT GEAR
- OIL PUMP
- Removal and Installation
- Oil Pump Service
- ENGINE COMPRESSION
- Checking Engine Oil Pressure
- Relief Valve
- PISTON AND CONNECTING ROD
- Removal and Installation
- Servicing the Piston and Connecting Rod
- Connecting Rod Alignment
- CRANKSHAFT AND BEARINGS
- Removal and Installation
- Servicing the Crankshaft and Bearings
- CYLINDER BORE
- Checking the Cylinder Bore
- WATER PUMP
- Removal and Installation
- Disassembly and Assembly
- SPECIFICATIONS
- EXCAVATOR SPECIFICATIONS
- Machine Dimensions (S/N 11001–11999)
- Machine Dimensions (S/N 12001 & Above)
- Lifting Capacity
- OPERATIONS & PERFORMANCE
- ENGINE
- HYDRAULIC SYSTEM
- SWING SYSTEM
- HYDRAULIC CYLINDERS
- DRIVE SYSTEM
- BRAKES
- UNDERCARRIAGE
- STD TRACK SHOES
- REFILL CAPACITIES
- DIGGING FORCE
- Machine Dimensions (S/N 13001 & Above)
- Lifting Capacity
- WEIGHTS
- CONTROLS
- ENGINE
- ELECTRICAL
- HYDRAULIC SYSTEM
- CYLINDER CYCLE TIME
- SWING SYSTEM
- HYDRAULIC CYLINDERS
- DRIVE SYSTEM
- BRAKES
- UNDERCARRIAGE
- STD TRACK SHOES
- REFILL CAPACITIES
- DIGGING FORCE
- ENGINE SPECIFICATIONS
- Fuel Injection Nozzles
- Fuel Injection Pump
- Cylinder Head
- Valves
- Valve Springs
- Valve Timing
- Rocker Arms
- Camshaft
- Tappet
- Piston Rings
- Pistons
- Connecting Rod
- Oil Pump
- Crankshaft
- Timing Gear
- Thermostat
- Engine Bolt Torque
- Crankshaft Re–Grind Data
- Torque For General Metric Bolts
- FUEL, COOLANT AND LUBRICANTS
- ENGINE OIL SPECIFICATIONS
- Description
- Ethylene Glycol
- Propylene Glycol
- DECIMAL AND MILLIMETER EQUIVALENTS
- U.S. TO METRIC CONVERSION
- SERVICE MANUAL REVISION
- 331-1
- 331-2
- 331-3
- 331-4
- 331-5
- 331-6
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