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The new B Series track feller bunchers feature smoother hydraulic performance, increased engine HP, a more comfortable operator station and better right side operator visibility. The Cat 521B Series are zero tail swing machines designed for medium to high production clear cut and or select cut on rough terrain. These machines perform in a variety of small through larger tree size applications. A robust undercarriage utilizes proven components, customized for demanding forestry conditions. The unique boom design provides industry leading lift capacity throughout full reach range, a benefit in large timber.


Gross Power 303.0 hp 226.0 kW Less

Hydraulic System

Pumps Dedicated variable displacement pump for travel circuit - 200 cc Dedicated variable displacement pump for travel circuit - 200 cc Less
Pumps Dedicated variable displacement pump for boom and implement functions - 200 cc Dedicated variable displacement pump for boom and implement functions - 200 cc Less
Pumps Electric hydraulic oil fill pump Electric hydraulic oil fill pump Less

Operating Specifications

Max Reach w/ Head 32.5 ft 9.9 m Less

Service Refill Capacities

Cooling System 10.8 gal 41.0 L Less
Engine Oil 10.3 gal 39.0 L Less
Hydraulic System 118.0 gal 448.0 L Less
Swing Drive 2.6 gal 10.0 L Less
Fuel Capacity 226.0 gal 856.0 L Less


Operating Weight w/o Head 59450.0 lb 26966.0 kg Less


Cab Cab meets FOPS/OPS/ROPS/WCB/OR-OSHA requirements Cab meets FOPS/OPS/ROPS/WCB/OR-OSHA requirements Less


Pitch 8.5 in 215.9 mm Less
Size 330 EX (D7) 330 EX (D7) Less

Power Train

Displacement 537.0 in3 8.8 L Less
Engine Model Cat® C9 ACERT™ Cat® C9 ACERT™ Less
Gross Power 303.0 hp 226.0 kW Less
Gross Power @ 1,800 rpm 303.0 hp 226.0 kW Less
Rated Power @ 2,100 rpm 282.0 hp 210.3 kW Less

Boom System

Track Harvester Configuration - Lift over front of tracks: Bare Pin Lift @ Maximum Reach (without head) 4000 kg @ 9.8 m (8,800 lb @ 32 ft 5 in) 4000 kg @ 9.8 m (8,800 lb @ 32 ft 5 in) Less
Track Harvester Configuration - Lift over front of tracks: Maximum Reach (with head) 32.5 ft 9.9 m Less

Operating Weights (without heads, standard counterweight)

Track Harvester Configuration - 521B 59450.0 lb 26966.0 kg Less

Track Gauge

521B 102.0 in 2591.0 mm Less

Track Length

Track Length 191.1 in 4855.0 mm Less

Ground Clearance

Ground Clearance 35.0 in 889.0 mm Less

Tractive Effort

521B 70500.0 lb 31978.0 kg Less

Power Train

Built for power, reliability, low maintenance, fuel efficiency and low emissions.

Hydraulic Packages

Powerful hydraulic system combined with a powerful boom and stick maximize productivity.

Operator Station

Superior comfort and visibility.


Heavy duty forestry undercarriage.

Boom and Stick

Maximum reach and lift capacity.


Maximum efficiency and productivity while conserving natural resources.


Easy servicing and extended service intervals.

Customer Support

Count on your Cat dealer.

521B Standard Equipment

  • 24 volt electrical system
  • Two 12 volt maintenance free batteries with 950 CCA
  • 95 Amp alternator
  • IQAN programmable controls
  • MD3 monitor display screen

  • Hydraulically actuated hinged engine enclosure with warning alarm
  • Engine fan guard
  • Bottom guards
  • Isolation mounted cab and engine
  • Heavy duty radiator guard door

  • OPS/FOPS/ROPS/WCB/OR-OSHA certified cab
  • Dual joystick control
  • Reverse slope windshield
  • Air ride seat
  • Skylight - alternate escape hatch
  • Top escape hatch
  • 76.2 mm (3 in) retractable seat belt
  • DIN mount radio ready with speakers
  • Operator sound suppression to standards
  • Travel alarm
  • Cup holders (2)
  • Two 12 volt and one 24 volt power outlets
  • Front window, 32 mm (1.25 in) thick Margard
  • Positive filtered ventilation, pressurized cab with bi-level air conditioner, heater and defroster with manual control
  • Left side fresh air window with screen
  • Forced air fan
  • Washable floor mat
  • Neutral lever (lockout) for all controls

  • C9 ACERT engine meets U.S. EPA emission standards
  • Variable travel speed (3 ranges)
  • Under hood primary air filter
  • 43° C (109° F) degree ambient temperature cooling package: - Aluminum core ATAAC and side-by-side radiator and oil cooler - Removable debris screen - Swing out A/C condenser
  • Electric fuel priming pump
  • Fuel water separator

  • Track roller guards with access holes
  • Hydraulic track adjusters
  • Double flange track rollers
  • GFT80 Lohmann final drives
  • Cat 330 size undercarriage components
  • Nine (9) track rollers and two (2) carrier rollers per side
  • Welded, non-leveling carbody

  • Dedicated fixed displacement pilot pump
  • Dedicated variable displacement pumps for track and implement functions
  • 325 EX swing drive and swing motor
  • Electric hydraulic oil fill pump
  • 265 L (70 gal) hydraulic tank

  • 50% concentration extended life coolant

  • Heavy duty hood enclosure
  • Flexxaire fan
  • Vandalism protection
  • Spare hose storage area
  • Grease gun bracket and storage area
  • 856 L (226 gal) fuel tank

521B Optional Equipment

  • Harvester Long
  • Omission - Linkage

  • Harvester

  • 610 mm (24 in) SG pads, clipped corners, with mud/snow reliefs
  • 711 mm (28 in) SG pads, clipped corners, with mud/snow reliefs
  • 711 mm (28 in) DG pads, clipped corners, with mud/snow reliefs
  • 914 mm (36 in) Tri-track, clipped corners, with mud/snow reliefs
  • Star Carrier Rollers
  • Standard Carrier Rollers

  • Lighting Gp-HID, replaces certain standard lights
  • Heavy Counterweight
  • Starting Aid, Cold Weather - includes two additional batteries
  • Starting Aid, Arctic - includes engine and hydraulic oil Arctic heater

  • Skylight, peaked, removable

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