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The E120 and Its Mechanical Legacy
The Caterpillar E120 hydraulic excavator was introduced in the late 1980s as part of CAT’s push into mid-size, globally distributed machines. With an operating weight around 27,000 lbs and a bucket capacity of roughly 0.8 cubic yards, the E120 was designed for utility trenching, site prep, and light demolition. It featured a robust undercarriage, a two-piece boom, and a mechanical simplicity that made it popular in developing markets and rental fleets.
Though no longer in production, the E120 remains active in many regions, especially where parts support and rebuild culture keep older machines alive. One of the most common service tasks on these units involves replacing worn bushings and pins in the boom, stick, and bucket linkage.
Understanding Bushing Fitment and Wear Points
Bushings in the E120 serve as wear surfaces between moving components—primarily where pins rotate under load. These include:
While exact dimensions vary slightly depending on production year and linkage type, common bushing sizes for the E120 include:
Recommended tolerances:
To replace bushings correctly:
Common Pitfalls and Field Solutions
Frequent mistakes include:
To extend bushing life:
The CAT E120 excavator remains a workhorse in many fleets, and its bushing system is central to maintaining tight, responsive linkage movement. Understanding proper dimensions, fitment tolerances, and installation techniques ensures long-term reliability and smooth operation. Whether trenching in clay or lifting pipe, a well-maintained bushing and pin system keeps the E120 performing like it was built to—strong, precise, and dependable.
The Caterpillar E120 hydraulic excavator was introduced in the late 1980s as part of CAT’s push into mid-size, globally distributed machines. With an operating weight around 27,000 lbs and a bucket capacity of roughly 0.8 cubic yards, the E120 was designed for utility trenching, site prep, and light demolition. It featured a robust undercarriage, a two-piece boom, and a mechanical simplicity that made it popular in developing markets and rental fleets.
Though no longer in production, the E120 remains active in many regions, especially where parts support and rebuild culture keep older machines alive. One of the most common service tasks on these units involves replacing worn bushings and pins in the boom, stick, and bucket linkage.
Understanding Bushing Fitment and Wear Points
Bushings in the E120 serve as wear surfaces between moving components—primarily where pins rotate under load. These include:
- Boom-to-base pivot
- Boom-to-stick joint
- Stick-to-bucket linkage
- Bucket cylinder rod end
- Stick cylinder base end
- Bushing: A cylindrical sleeve, often made of hardened steel or bronze, that provides a replaceable wear surface.
- Pin: A solid steel shaft that passes through bushings to connect two components, allowing rotation.
- Interference Fit: A tight press-fit between bushing and housing to prevent movement.
- Clearance Fit: A small gap between pin and bushing to allow lubrication and rotation.
- Grease Groove: Internal channel in the bushing to distribute lubricant evenly.
While exact dimensions vary slightly depending on production year and linkage type, common bushing sizes for the E120 include:
- Boom base bushing: ~90 mm OD, ~65 mm ID, ~80 mm length
- Boom-to-stick bushing: ~85 mm OD, ~60 mm ID, ~75 mm length
- Stick-to-bucket bushing: ~80 mm OD, ~55 mm ID, ~70 mm length
- Bucket linkage bushing: ~70 mm OD, ~50 mm ID, ~65 mm length
Recommended tolerances:
- Interference fit: 0.1–0.2 mm between bushing OD and bore
- Clearance fit: 0.05–0.15 mm between pin and bushing ID
- Surface hardness: 50–60 HRC for bushings, 55–65 HRC for pins
- Lubrication: Lithium-based grease with molybdenum additive
To replace bushings correctly:
- Remove old bushings with a press or bushing driver
Avoid hammering, which can distort the bore.
- Clean and inspect bore for scoring or ovality
Use a bore gauge to confirm roundness. Re-machine if out of spec.
- Chill new bushings before installation
Freezing bushings contracts the metal slightly, easing press-fit.
- Use a hydraulic press or threaded installer
Apply even pressure to avoid tilting or galling.
- Align grease holes and grooves
Ensure proper orientation for lubrication flow.
- Install new pins with anti-seize or assembly grease
Torque locking bolts to spec and verify free movement.
Common Pitfalls and Field Solutions
Frequent mistakes include:
- Installing bushings dry without lubrication
- Using mismatched pin and bushing sizes
- Ignoring bore wear or distortion
- Failing to align grease grooves
- Reusing worn pins with new bushings
- Always replace pins and bushings as a matched set
- Use precision measuring tools (micrometer, bore gauge)
- Document bushing specs and source from reputable suppliers
- Consider bronze bushings for high-load, low-speed joints
- Use locking compound if bore is slightly oversized
To extend bushing life:
- Grease pivot points daily during heavy use
- Inspect for play or noise monthly
- Replace seals and dust caps to prevent contamination
- Avoid side loading the bucket during excavation
- Monitor pin rotation and wear patterns
- Install grease fittings with check valves
- Use hardened pins with chrome plating
- Add wear indicators or shims for early detection
- Retrofit with sealed bushings in high-contamination zones
The CAT E120 excavator remains a workhorse in many fleets, and its bushing system is central to maintaining tight, responsive linkage movement. Understanding proper dimensions, fitment tolerances, and installation techniques ensures long-term reliability and smooth operation. Whether trenching in clay or lifting pipe, a well-maintained bushing and pin system keeps the E120 performing like it was built to—strong, precise, and dependable.
