Caterpillar HH55
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar HH55 is a boom-mounted harvester head built for felling, delimbing, and bucking timber in mechanized cut-to-length harvesting. It attaches to the carrier boom tip through a hydraulic rotator and draws all of its power for the saw, feed rollers, delimb knives, and rotation from the host carrier's own hydraulic circuit; the head has no engine, fuel system, or cooling system of its own. It is built to work on Cat 550/570/580 track harvester carriers, comparable wheel-harvester carriers, and excavator-base carriers set up for harvesting. An optional CABS (Computer Aided Bucking System) electronic control uses a measuring wheel and length sensor to size each stem and help optimize cut length and delimb knife clamping pressure automatically; heads built with this option carry a different serial prefix than the base head.
The HH55 sits in the middle of Caterpillar's HH45/HH55/HH65/HH75 harvester head line, sized above the lighter HH45 used on smaller thinning-focused carriers and below the larger HH65/HH75 heads built for bigger stems. All four share a common design and service platform, so wear parts, rotator layout, and hydraulic architecture carry across the family even as feed and delimb capacity scales up with size. In the used and parts market, a head like the HH55 is judged less on total hours and more on the condition of the rotator, hoses, and feed roller arm pivots, since those components see the heaviest cyclical loading on every grip-cut-rotate cycle. With no engine or driveline to wear out, most of the head's resale and repair economics come down to saw and chain condition, delimb knife wear, and how well the hydraulic hose routing at the head has been kept up.
Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.
Caterpillar HH55 maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 50 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
Servicing the HH55 beyond the schedule
Predictive Maintenance & Fluid Analysis
The HH55 has no engine oil to sample, so predictive care centers on hydraulics. Pull periodic oil samples from the carrier circuit feeding the head and track particle counts instead of waiting for a hose or valve failure. Watch feed roller arm lubrication points for visible oil at the pivots; a dry pivot signals a blocked metering point. Track measuring accuracy over time; gradual drift usually means wheel slippage, bark buildup, or a worn knife/roller before it causes a bad bucking cut.
Corrective & Common Repairs
Most HH55 downtime traces to saw chain and guide bar wear, delimb knife edges going dull, or a hydraulic hose chafing through at the rotator from repeated grip-cut-rotate cycles. Replace the chain and inspect the bar rails before wear reaches the point of throwing chain. Resharpen delimb knives at the correct bevel angle rather than letting them round over, and avoid overheating the edge on the grinder. When a hose fails early, check routing for twist introduced at install rather than assuming a bad hose.
Overhaul & Rebuild Points
Rebuild attention on the HH55 concentrates on the rotator and the feed roller arm pivots. The rotator itself is generally reliable, but its mounting bushings and the hoses feeding it take the most cumulative flex fatigue on the head. At overhaul, check feed roller arm pivot pins and bushings for play against the cam curve specification, inspect the saw motor and drive for wear, and recalibrate the diameter/length measuring system any time a roller, knife, or measuring wheel is replaced.
Seasonal & Environment Servicing
Cold-weather starts call for warming hydraulic oil through low-load head functions before working the saw and feed rollers hard; thick cold oil slows cylinder response and can mask a real fault. Bark, resin, and ice buildup on the measuring wheel are common in wet and freezing conditions and will throw off diameter/length accuracy faster than normal wear; clean the wheel and recheck calibration more often through those seasons. Before winter storage, cycle the head with fresh oil and retract cylinders fully to protect exposed rod surfaces.
HH55 attachments & work tools
Carrier compatibility
The HH55 mounts as a dangle head on Cat 550/570/580 track harvester carriers and comparable wheel-harvester carriers, and it also fits excavator-base carriers set up for harvesting work. Boom hookup and hydraulic tie-in are matched to the specific carrier it is paired with, so exact carrier size class varies by configuration.
Rotator and boom linkage
A factory hydraulic rotator bolts to the head's mounting frame and connects to the carrier's boom-tip bracket, letting the head swing and self-level for felling and delimbing access. Caterpillar introduced an updated rotator design partway through the model's production run; both versions serve the same mounting function.
Saw bar and chain
The head runs a roller-nose guide bar with .404 in pitch harvester-style saw chain sized for its felling and bucking duty. Bar length is chosen per application and varies by configuration.
Diameter sensing configuration
The HH55 can be run with either one or two diameter sensors for stem-size measurement; in the single-sensor setup the second sensor position is simply left unused. This is a factory logic option rather than a mechanical change to the head.
All HH55 assemblies by section
Every catalogued assembly group for the Caterpillar HH55. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Electrical And Starting System
196-4826 Control Ar-Harvester Head -Cabsdos
| 19***26 | Control Ar-Harvester Head; -Cabsdos | 1 |
| 19***28 | Control Group-Harvester Head | 1 |
| 19***30 | Wiring Group-Harvester Head | 1 |
196-1277 Control Ar-Harvester Head
| 19***77 | Control Ar-Harvester Head | 1 |
| 19***78 | Wiring Group-Harvester Head | 1 |
| 19***79 | Control Group-Harvester Head | 1 |
196-4825 Control Ar-Harvester Head -Cabswin
| 19***25 | Control Ar-Harvester Head; -Cabswin | 1 |
| 19***27 | Control Group-Harvester Head | 1 |
| 19***30 | Wiring Group-Harvester Head | 1 |
196-4827 Control Gp-Harvester Head
| 18***01 | Plate As | 1 |
| 19***19 | Box-Control Unit | 1 |
| 19***27 | Keyboard As | 1 |
196-4828 Control Gp-Harvester Head
| 16***25 | Printer Group-Computer | 1 |
| 19***19 | Box-Control Unit | 1 |
| 19***33 | Harness As-Wiring; (Boom) | 1 |
196-1279 Control Gp-Harvester Head
| 19***79 | Control Group-Harvester Head | 1 |
| 19***11 | Harness As-Monitor; (Control Unit) | 1 |
| 19***12 | Harness As-Monitor; (Analog Output Box) | 1 |
198-1402 Module Gp-Monitor Keypad -Rh
| 09***78 | Screw; (Pan Head) | 2 |
| 19***69 | Cover-Front | 1 |
| 19***70 | Cover-Back | 1 |
198-1403 Module Gp-Monitor Keypad
| 09***78 | Screw; (Pan Head) | 2 |
| 19***69 | Cover-Front | 1 |
| 19***70 | Cover-Back | 1 |
198-3434 Printer Gp-Computer
| 19***34 | Printer Group-Computer | 1 |
| 19***35 | Printer Group-Portable | 1 |
| 19***52 | Case-Carrying | 1 |
161-5225 Printer Gp-Computer
| 16***25 | Printer Group-Computer | 1 |
| 17***46 | Paper-Printer | 1 |
198-7017 Sensor Gp-Position -Diameter
| 15***25 | Screw; (M3x45) | 3 |
| 15***12 | Sensor-Pulse; (Knife Position) | 1 |
| 15***60 | Bearing | 1 |
196-1278 Wiring Gp-Harvester Head
| 10***01 | Kit; (Receptacle) (12-Pin) (Includes Receptacle As & Wedge) | 1 |
| 10***03 | Kit; (Receptacle) (3-Pin) (Includes Receptacle As & Wedge) | 2 |
| 13***75 | Wedge-Receptacle Lock | 2 |
196-4830 Wiring Gp-Harvester Head
| 16***85 | Washer | 2 |
| 16***18 | Bracket; (Keypad) | 4 |
| 16***66 | Handle | 2 |
Hydraulic System
184-6473 Bearing Gp-Self-Aligning
| 18***73 | Bearing Group-Self-Aligning | 1 |
| 18***74 | Support-Bearing | 1 |
| 18***75 | Seal-Shaft | 1 |
197-3217 Cover & Mtg Gp-Control Valve
| 15***85 | Washer; (M12) | 4 |
| 15***91 | Spacer | 2 |
| 15***92 | Spacer | 2 |
195-9364 Cylinder & Lines Gp-Delimbing
| 15***85 | Fitting-Adapter | 4 |
| 15***95 | Fitting-Elbow | 2 |
| 15***24 | Hose As | 1 |
195-9363 Cylinder & Lines Gp-Meas & Fdg
| 15***86 | Fitting | 1 |
| 15***95 | Fitting-Elbow | 2 |
| 15***98 | Junction Block | 1 |
195-9362 Cylinder & Lines Gp-Saw
| 15***85 | Fitting-Adapter | 2 |
| 15***95 | Fitting-Elbow | 3 |
| 15***98 | Junction Block | 1 |
228-3394 Cylinder Gp-Delimbing Knife
| 16***45 | Bearing | 2 |
| 21***83 | Kit-Seal; (Delimbing Knife Cylinder) | 1 |
| 22***21 | Piston | 1 |
156-4145 Cylinder Gp-Delimbing Knife
| 15***45 | Cylinder Group-Delimbing Knife | 1 |
| 16***45 | Bearing | 2 |
| 16***55 | Kit-Seal | 1 |
206-2001 Cylinder Gp-Delimbing Knife
| 16***45 | Bearing | 2 |
| 20***01 | Cylinder Group-Delimbing Knife | 1 |
| 21***13 | Kit-Seal; (Delimbing Knife Cylinder) | 1 |
206-2004 Cylinder Gp-Feed Roller Arm
| 16***41 | Bearing | 2 |
| 20***04 | Cylinder Group-Feed Roller Arm | 1 |
| 21***86 | Kit-Seal; (Feed Roller Arm Cylinder) | 1 |
156-3850 Cylinder Gp-Feed Roller Arm
| 15***50 | Cylinder Group-Feed Roller Arm | 1 |
| 16***41 | Bearing | 2 |
| 16***48 | Kit-Seal | 1 |
206-2002 Cylinder Gp-Holding Arm
| 16***41 | Bearing | 2 |
| 20***02 | Cylinder Group-Holding Arm | 1 |
| 22***25 | Piston | 1 |
156-4146 Cylinder Gp-Holding Arm
| 15***46 | Cylinder Group-Holding Arm | 1 |
| 16***41 | Bearing | 2 |
| 16***56 | Kit-Seal | 1 |
156-3852 Cylinder Gp-Measuring Arm
| 15***52 | Cylinder Group-Measuring Arm | 1 |
| 16***42 | Bearing | 2 |
| 16***50 | Kit-Seal | 1 |
206-4594 Cylinder Gp-Measuring Arm
| 09***52 | Ring | 2 |
| 16***42 | Bearing | 2 |
| 20***94 | Cylinder Group-Measuring Arm | 1 |
156-1228 Cylinder Gp-Saw
| 15***28 | Cylinder Group-Saw | 1 |
| 16***52 | Kit-Seal | 1 |
| 6V***75 | Bearing | 2 |
228-3397 Cylinder Gp-Saw
| 09***01 | Bolt-Socket Head; (M8x1.25x40-mm) | 1 |
| 21***85 | Kit-Seal; (Saw Cylinder) | 1 |
| 22***29 | Piston | 1 |
206-2003 Cylinder Gp-Saw
| 20***03 | Cylinder Group-Saw | 1 |
| 21***85 | Kit-Seal; (Saw Cylinder) | 1 |
| 6V***75 | Bearing | 2 |
206-2000 Cylinder Gp-Tilt
| 16***45 | Bearing | 2 |
| 20***00 | Cylinder Group-Tilt | 1 |
| 21***82 | Kit-Seal; (Tilt Cylinder) | 1 |
156-4147 Cylinder Gp-Tilt
| 15***47 | Cylinder Group-Tilt | 1 |
| 16***45 | Bearing | 2 |
| 16***53 | Kit-Seal | 1 |
208-2872 Guard Gp-Saw Motor
| 20***72 | Guard Group-Saw Motor | 1 |
| 20***73 | Guard; (Saw Motor) | 1 |
| 22***22 | Guard As | 1 |
184-6467 Housing Gp-Motor
| 18***67 | Housing Group-Motor | 1 |
| 18***68 | Valve | 1 |
| 18***69 | Kit-Seal | 1 |
194-7954 Hydraulic Ar
| 19***54 | Hydraulic Ar | 1 |
| 19***62 | Cylinder & Lines Group-Saw | 1 |
| 19***63 | Cylinder & Lines Group-Meas & Fdg | 1 |
197-2070 Lines Gp-Hydraulic
| 14***25 | Connector As. | 1 |
| 14***51 | Elbow Group | 1 |
| 19***70 | Lines Group-Hydraulic | 1 |
162-5645 Lubrication Ar -Saw & Feed Roller
| 15***96 | Tank & Lines Group-Lubrication | 1 |
| 15***48 | Pump Group-Lubrication | 1 |
| 16***45 | Lubrication Ar; -Saw & Feed Roller | 1 |
165-4117 Motor Gp-Piston
| 10***58 | Cylinder Group-Piston | 1 |
| 16***97 | Seal-O-Ring | 2 |
| 16***17 | Motor Group-Piston | 1 |
155-9923 Motor Gp-Saw
| 15***23 | Motor Group-Saw | 1 |
| 16***67 | Seal | 1 |
| 16***68 | Plug | 1 |
183-3742 Pump Gp-Lubrication
| 15***95 | Strainer As | 1 |
| 15***79 | Gasket | 1 |
| 15***96 | Fitting | 1 |
156-1248 Pump Gp-Lubrication
| 15***48 | Pump Group-Lubrication | 1 |
| 15***53 | Seal-Ring | 3 |
| 15***12 | Fitting | 1 |
155-8796 Tank & Lines Gp-Lubrication
| 09***52 | Ring | 2 |
| 15***82 | Bolt-Socket Head; (M6x1x40-mm) | 8 |
| 15***96 | Tank & Lines Group-Lubrication | 1 |
196-4833 Valve & Mtg Gp-Main Control
| 13***40 | Locknut; (M8x1.25-Thd) | 3 |
| 15***85 | Washer; (M12) | 2 |
| 15***98 | Washer; (M8x1.25-Thd) | 2 |
224-7578 Valve & Mtg Gp-Main Control
| 13***40 | Locknut; (M8x1.25-Thd) | 3 |
| 15***40 | Washer; (M10) | 2 |
| 15***85 | Washer; (M12) | 2 |
229-9785 Valve Gp-Bank 7
| 16***51 | Kit-Seal | 9 |
| 19***73 | Valve Group-Control; -Pump | 1 |
| 19***76 | Valve Group-Control; -Upper Delimbing Knife | 1 |
214-3508 Valve Gp-Bank 8
| 16***51 | Kit-Seal | 9 |
| 19***73 | Valve Group-Control; -Pump | 1 |
| 19***74 | Valve Group-Control; -Saw | 1 |
194-7118 Valve Gp-Bank 8
| 16***51 | Kit-Seal | 9 |
| 19***18 | Valve Group-Bank 8 | 1 |
| 19***73 | Valve Group-Control; -Pump | 1 |
156-0285 Valve Gp-Breather
| 15***85 | Valve Group-Breather | 1 |
| 15***56 | Fitting | 1 |
| 16***86 | Breather | 1 |
199-8074 Valve Gp-Control -Saw
| 16***84 | Spool As | 1 |
| 17***70 | Valve As-Line Relief | 1 |
| 17***76 | Valve Group-Pilot Relief | 1 |
224-6026 Valve Gp-Control -Oil Manifold
| 19***07 | Valve Group-Pressure Reducing | 2 |
| 22***26 | Valve Group-Control; -Oil Manifold | 1 |
| 23***53 | Manifold | 1 |
211-8770 Valve Gp-Control
| 16***07 | Valve Group-Solenoid; (Medium Pressure) | 1 |
| 16***84 | Spool As | 1 |
| 17***73 | Valve As-Line Relief | 1 |
214-3506 Valve Gp-Control
| 16***84 | Spool As | 1 |
| 17***32 | Kit-Seal | 1 |
| 19***08 | Seal-O-Ring | 2 |
199-8077 Valve Gp-Control -Roller Clamp
| 17***74 | Valve As-Line Relief | 1 |
| 17***75 | Valve As-Line Relief | 1 |
| 17***32 | Kit-Seal | 1 |
199-8080 Valve Gp-Control -End Block
| 19***80 | Valve Group-Control; -End Block | 1 |
| 19***00 | Manifold | 1 |
| 19***07 | Valve Group-Pressure Reducing | 2 |
199-8078 Valve Gp-Control -Lower Delimbing Knife
| 17***74 | Valve As-Line Relief | 1 |
| 17***80 | Valve As-Line Relief | 1 |
| 17***32 | Kit-Seal | 1 |
199-8073 Valve Gp-Control -Pump
| 03***27 | Seal-O-Ring; (19.18mm Id) | 1 |
| 15***40 | Washer; (M10) | 2 |
| 19***73 | Valve Group-Control; -Pump | 1 |
199-8076 Valve Gp-Control -Upper Delimbing Knife
| 17***73 | Valve As-Line Relief | 1 |
| 17***23 | Valve As-Line Relief | 1 |
| 17***32 | Kit-Seal | 1 |
214-3505 Valve Gp-Control
| 16***84 | Spool As | 1 |
| 17***32 | Kit-Seal | 1 |
| 19***08 | Seal-O-Ring | 2 |
199-8079 Valve Gp-Control -Tilt
| 16***41 | Spool As | 1 |
| 17***72 | Valve As-Line Relief | 1 |
| 17***74 | Valve As-Line Relief | 1 |
199-8107 Valve Gp-Pressure Reducing
| 03***27 | Seal-O-Ring; (19.18mm Id) | 1 |
| 03***43 | Seal-O-Ring | 1 |
| 18***27 | Ring-Backup | 2 |
214-3507 Valve Gp-Relief
| 19***06 | Valve Group-Relief | 2 |
| 21***18 | Manifold | 1 |
| 21***07 | Valve Group-Relief | 1 |
Service Equipment And Supplies
169-2759 Film Gp
| 16***59 | Film Group | 1 |
| 16***61 | Film | 2 |
166-9181 Plate & Film Gp
| 13***76 | Film; (Warning) (Universal) (Lh Side Post Inside Cab) | 1 |
| 16***91 | Film-Identification; (Chain Oil) | 1 |
| 16***81 | Plate & Film Group | 1 |
197-5088 Tool Gp-Hand
| 16***53 | Wrench-T-Handle; (6-mm Hex) | 1 |
| 16***56 | Hook As-Cleaning | 1 |
| 16***71 | Wrench-Spanner | 1 |
Work Tools
155-9533 Arm Gp-Feed Roller -Rh
| 09***78 | Pin-Spring | 1 |
| 15***33 | Arm Group-Feed Roller; -Rh | 1 |
| 15***38 | Screw; (M5x0.8x10-mm) | 6 |
155-9531 Arm Gp-Feed Roller -Lh
| 09***78 | Pin-Spring | 1 |
| 15***31 | Arm Group-Feed Roller; -Lh | 1 |
| 15***36 | Guide | 0 |
198-3013 Arm Gp-Grapple
| 15***45 | Fitting-Grease | 0 |
| 15***86 | Arm As-Holding | 1 |
| 15***98 | Washer; (M8x1.25-Thd) | 2 |
155-8781 Arm Gp-Measuring
| 08***73 | Screw-Countersink Head | 3 |
| 09***50 | Ring-Retaining | 1 |
| 13***40 | Locknut; (M8x1.25-Thd) | 1 |
198-3006 Control Ar-Color Marking
| 18***56 | Control Group-Color Marking | 1 |
| 19***06 | Control Ar-Color Marking | 1 |
| 19***13 | Arm Group-Grapple | 1 |
189-1956 Control Gp-Color Marking
| 09***49 | Bolt; (M8x1.25x40-mm) | 2 |
| 14***94 | Guard; (15-cm) | 0 |
| 15***71 | Kit-Connecting Plug; (4-Pin) | 1 |
155-8800 Damper Gp-Harvester Head
| 15***00 | Damper Group-Harvester Head | 1 |
| 15***40 | Body-Damper | 1 |
| 15***41 | Pin As | 1 |
189-5510 Damper Gp-Harvester Head
| 15***41 | Pin As | 1 |
| 15***43 | Washer | 1 |
| 15***44 | Nut | 1 |
196-4835 Frame Ar-Harvester Head
| 15***83 | Yoke Group-Harvester Head | 1 |
| 16***81 | Plate & Film Group | 1 |
| 19***35 | Frame Ar-Harvester Head | 1 |
197-4799 Frame Gp-Harvester Head
| 14***02 | Bolt-Socket Head; (M6x1x10-mm) | 8 |
| 15***40 | Washer; (M10) | 24 |
| 15***97 | Cam-Curve Right | 1 |
197-4797 Frame Gp-Harvester Head
| 12***17 | Bolt-Socket Head; (M24x3x70-mm) | 2 |
| 13***40 | Locknut; (M8x1.25-Thd) | 1 |
| 15***45 | Fitting-Grease | 1 |
194-8101 Head Ar-Harvester
| 15***80 | Roller Group-Feed; -Lh | 1 |
| 15***81 | Arm Group-Measuring | 1 |
| 15***00 | Damper Group-Harvester Head | 1 |
156-5252 Holder Gp-Saw Bar
| 09***60 | Setscrew-Socket; (M6x1x6-mm) | 1 |
| 15***52 | Holder Group-Saw Bar | 1 |
| 15***53 | Kit-Pin; (Contains 10 Pieces) | 1 |
228-3873 Housing Gp-Chain Tensioner
| 08***65 | Bolt; (M3x0.5x8-mm) | 2 |
| 09***19 | Ring-Retaining | 1 |
| 09***73 | Setscrew-Socket | 2 |
219-2535 Measuring Ar-Harvester Head
| 21***34 | Measuring Ar-Harvester Head; (Field Installation) | 1 |
| 21***35 | Measuring Ar-Harvester Head | 1 |
155-8780 Roller Gp-Feed -Lh
| 13***40 | Locknut; (M8x1.25-Thd) | 1 |
| 15***80 | Roller Group-Feed; -Lh | 1 |
| 15***31 | Arm Group-Feed Roller; -Lh | 1 |
155-8803 Roller Gp-Feed -Rh
| 13***40 | Locknut; (M8x1.25-Thd) | 1 |
| 15***03 | Roller Group-Feed; -Rh | 1 |
| 15***33 | Arm Group-Feed Roller; -Rh | 1 |
163-3978 Rotator Gp-Hydraulic
| 12***76 | Bolt; (M10x1.5x130-mm) | 10 |
| 15***42 | Plug | 2 |
| 15***59 | Spring | 12 |
210-1506 Rotator Gp-Hydraulic
| 12***76 | Bolt; (M10x1.5x130-mm) | 10 |
| 15***42 | Plug | 2 |
| 15***59 | Spring | 12 |
162-5698 Saw Ar-Chain
| 15***23 | Motor Group-Saw | 1 |
| 16***98 | Saw Ar-Chain | 1 |
| 18***59 | Saw Group-Chain | 1 |
187-8459 Saw Gp-Chain
| 09***85 | Bolt-Socket Head; (M14x2x30-mm) | 2 |
| 09***87 | Bolt-Socket Head; (M14x2x45-mm) | 2 |
| 09***19 | Ring-Retaining | 1 |
228-3874 Tensioner Gp-Chain
| 09***88 | Setscrew | 3 |
| 15***52 | Holder Group-Saw Bar | 2 |
| 15***81 | Kit-Seal | 1 |
171-4339 Wheel Gp-Feed Roller -Lh
| 15***61 | Screw | 5 |
| 16***09 | Chain; (20m) | 0 |
| 16***32 | Wheel As | 1 |
171-4338 Wheel Gp-Feed Roller -Rh
| 15***61 | Screw | 5 |
| 16***09 | Chain; (20m) | 0 |
| 16***32 | Wheel As | 1 |
155-8783 Yoke Gp-Harvester Head
| 09***70 | Bolt-Socket Hd; (M12 X 1.75 X 45) | 4 |
| 09***28 | Ring-Retaining; (External) | 2 |
| 15***83 | Yoke Group-Harvester Head | 1 |
HH55 serial number reference
The HH55 PIN plate is mounted on the harvester head frame itself, not on the carrier machine, since the head is a separate boom-mounted attachment with its own product identification. The plate shows a 3-character prefix followed by a sequential unit number; the prefix identifies the specific head configuration and production series, while the carrier (wheeled or tracked harvester) has its own separate PIN.
| Prefix | Identifies | Notes |
|---|---|---|
| 3MZ | Base HH55 harvester head, electrical system/schematic coverage (shared manual set with HH45 2JZ, HH65 4RZ, HH75 5WZ) | Tied to HH55 in the shared HH45/HH55/HH65/HH75 harvester head electrical schematic manual, effective from the start of this prefix (1-Up). Sequential prefix pattern across the four models (2JZ/3MZ/4RZ/5WZ) corresponds to model order 45/55/65/75. Confirm with dealer for exact production date range. |
| CFS | HH55 harvester head with CABS (Computer Aided Bucking system) - electronic diameter/length measuring and bucking-optimization control | Tied to HH55 specifically in the dedicated HH55 (CABS) parts manual, effective from the start of this prefix (1-Up). CABS is an electronic measuring/control option on the head, not a physical operator cab (the head itself is a boom-mounted attachment with no cab). Distinct from the base 3MZ prefix; do not merge specs across the two. |
Frequently asked questions
What carrier does the HH55 mount on, and does it have its own engine?
The HH55 is a boom-mounted attachment, not a self-powered machine. It has no engine, fuel tank, or cooling system of its own; every hydraulic function on the head, including the saw, feed rollers, delimb knives, and rotation, runs off the host carrier's hydraulic circuit. It mounts through a hydraulic rotator to the boom tip of Cat 550/570/580 track harvester carriers, comparable wheel-harvester carriers, or an excavator-base carrier set up for harvesting.
What does CABS mean, and how do I tell a base head from a CABS head?
CABS stands for Computer Aided Bucking System, an electronic control that uses a measuring wheel and length sensor to size each stem and help optimize cut length and delimb knife clamping pressure. It is not a physical operator cab; the head has no cab of its own. On the HH45/HH55/HH65/HH75 family the serial prefix tells you which you have: a base HH55 carries the 3MZ prefix, while a CABS-equipped HH55 carries the CFS prefix.
Where does the HH55 sit in Caterpillar's harvester head lineup?
The HH55 is one of four sizes in Caterpillar's harvester head line, HH45, HH55, HH65, and HH75, positioned above the HH45 and below the HH65/HH75 for larger stem work. All four share a common design and service platform. Caterpillar's current production lineup for harvester heads has changed over time, so confirm present-day availability and any successor model with your Cat dealer.
What HH55 owners discuss
What wears fastest on the HH55 saw unit, and how should chain tension be kept?
How should the delimbing knives be maintained, and what is a common mistake?
What feed roller issues come up on a head like the HH55?
How reliable is the rotator, and what should be checked around it?
How accurate is the diameter and length measuring system, and what throws it off?
What are common maintenance mistakes beyond knife sharpening?
What should be checked when buying a used HH55?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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