Kubota KX121-3S Mini Excavator – Parts, Specs & Serial Number Guide

Description:

The Kubota KX121-3S is a premium 4-ton mini excavator with powerful digging capabilities, a smooth hydraulic system, and a deluxe cab option for all-day comfort. Known for its durability and versatility, the KX121-3S is ideal for utility work, trenching, demolition, and general construction tasks. The "S" model includes enhanced features such as an adjustable auxiliary flow valve and proportional thumb control, making it more productive with attachments.

Key Specifications:

Engine:

• Model: Kubota V2203-M

• Type: 4-cylinder, liquid-cooled diesel

• Displacement: 134.1 cu in (2.2 L)

• Gross Power: 45.2 hp (33.7 kW) @ 2,350 rpm

Transmission & Travel:

• Travel Speed: Low: 1.6 mph (2.6 km/h), High: 2.9 mph (4.6 km/h)

• Drive Motors: Hydraulic piston motors with planetary gear reduction

Hydraulic System:

• Pump Capacity: 37.4 + 37.4 + 19.0 l/min (triple pump system)

• Auxiliary Flow: 17.5 gpm (66.2 l/min)

• Max Hydraulic Pressure: 3,135 psi (216 bar)

• Auxiliary Hydraulic Adjustment: Proportional thumb-operated flow control (S model only)

Dimensions:

• Operating Weight: 9,250 lbs (4,196 kg)

• Max Digging Depth: 11 ft 6 in (3.5 m)

• Max Reach at Ground Level: 18 ft 2 in (5.55 m)

• Tail Swing Radius: 4 ft 4 in – conventional tail swing

Performance:

• Bucket Breakout Force: 9,861 lbf (43.9 kN)

• Arm Digging Force: 4,977 lbf (22.1 kN)

Maintenance & Common Parts:

Routine Maintenance Schedule:

• Engine oil/filter: Every 250 hours

• Hydraulic oil: Every 500 hours

• Inspect pins, bushings, and track tension weekly

• Clean radiator and oil cooler screens every 50 hours

Frequently Replaced Parts:

• KX121-3S Hydraulic Cylinder Seal Kits

• Final Drive Motors

• Rubber Tracks & Undercarriage Parts

• Thumb and Coupler Attachments

• Filters (Fuel, Oil, Air)

Common Issues & Quick Fixes:

• Thumb not functioning properly: Typically a worn auxiliary valve or misadjusted flow setting—adjust or replace with compatible thumb control kits.

• Track slipping or de-tracking: Usually due to under-tensioned or worn-out tracks—replace with OEM-fit rubber tracks and sprockets.

• Hydraulic oil overheating: Often caused by clogged coolers—flush the system and clean the radiator thoroughly.

Pro Tips:

• Make use of the auxiliary flow adjustment knob (standard on KX121-3S) when switching between attachments with different flow demands.

• Store with bucket lowered to relieve hydraulic system pressure and prevent drift.

• Use genuine Kubota filters and fluids to preserve pump and engine longevity.

Serial Number Location:

• Located on a metal plate welded to the right side of the front frame, near the boom pivot or inside the cab near the control console.

• Always verify the serial number before ordering parts from our KX121-3S parts collection.