Komatsu Pins & Bushings Technical Guide
Bucket • Arm • Boom • Bellcrank • Cylinder Pivots
WQ Certified™ Reference
Introduction
Komatsu excavators and wheel loaders rely on hardened pivot pins and precision bushings to transfer breakout force, carry structural load, and control articulation across bucket, arm, and boom assemblies.
This technical guide covers Komatsu bucket, arm, boom, bellcrank and cylinder pivot pins and bushings.
This guide focuses exclusively on:
- Bucket pins and bushings
- Arm (dipper) pins
- Boom foot pins
- Bellcrank (H-link) pivots
- Hydraulic cylinder pivot pins
This guide does not cover undercarriage track pins and bushings, as those operate under entirely different wear conditions.
The purpose of this document is to explain:
- How Komatsu pivot systems function
- Material and hardness requirements
- Clearance tolerances
- Wear limits
- Inspection methods
- Replacement best practices
- WQ Certification standards for aftermarket components
How Komatsu Pivot Systems Operate
Each pivot joint typically consists of:
- A hardened steel pin
- A replaceable bronze or alloy bushing
- Grease passage alignment
- Retention hardware (bolts, snap rings, collars)
- Shim packs where applicable
These joints operate under oscillating motion (not continuous rotation) and are subjected to:
- High breakout force
- Shock loading
- Contamination
- Side-loading during trenching or grading
Wear primarily occurs at:
- Pin outer surface
- Bushing inner diameter
- Bushing outer diameter (if interference fit fails)
- Structural boss bore (if excessive clearance is ignored)
Example Engineering Profile – Mid-Size Excavator
A commonly referenced Komatsu bucket pin used on PC200-class machines is often listed as a flanged pin design with a mid-size pivot diameter and induction-hardened surface treatment.
Example profile (typical reference dimensions):
- Diameter: 70 mm
- Length: 425 mm
- Flange diameter: 100 mm
- Flange thickness: 12 mm
- Induction-hardened surface layer
- Typical hardness reference: HRC 52–56
This illustrates the scale and engineering precision required in mid-size pivot systems. Wheel loader applications (WA mid-range classes) utilize similar hardened pivot configurations operating under comparable load conditions.
Material & Hardness Requirements
For high-load pivot applications, hardened alloy steel is standard.
Premium aftermarket benchmarks commonly include:
- 42CrMo4 alloy steel or equivalent
- Induction hardening
- Surface hardness range: approximately 58–62 HRC
- Deep effective hardening layer
- Precision ground outer diameter
Why hardness depth matters:
- Shallow hardening wears through quickly
- Insufficient case depth can allow core deformation
- Soft pins accelerate bushing and boss wear
Bushings are typically:
- Oil-impregnated bronze (HN type) or split bronze liners
- Precision ground ID and OD
- Designed for controlled interference fit
Clearance Specifications & Wear Limits
Typical New Installation Clearance
Typical new installation clearance is commonly in the range of 0.1–0.2 mm (application dependent). This allows proper grease film formation, free articulation, and load distribution without binding.
Replacement Threshold
Best practice is to schedule replacement when:
- Radial clearance exceeds approximately 0.5 mm
- Visible ovality develops
- Knock or movement is detected under load
- Pin surface scoring becomes evident
Operating beyond this threshold increases risk of boss bore elongation, line boring requirements, and structural fatigue.
Joint-Specific Wear Characteristics
Bucket-to-Link Pins
Highest articulation frequency and direct breakout force exposure. Often the first failure point when lubrication or sealing is poor.
Arm-to-Boom Pins
High static load and side-loading during trenching. Wear accelerates when side clearance increases or grease paths are blocked.
Boom Foot Pins
Carry full attachment weight and are critical to structural integrity. Improper fit can contribute to frame/boss elongation over time.
Bellcrank (H-Link) Pins
High oscillation cycle count. Wear can accelerate in abrasive environments and when grease intervals are missed.
Cylinder Pins
Lower rotation angle but high compressive load. Often neglected in lubrication schedules, leading to premature bushing wear and pin scoring.
Inspection & Measurement Procedure
Tools
- Micrometer (pin OD measurement)
- Dial bore gauge (bushing ID measurement)
- Feeler gauge (side clearance checks)
- Visual inspection (scoring, ovality, grease condition)
Inspection Steps
- Clean grease and debris from the joint area.
- Measure pin diameter (OD) at midspan and at multiple clock positions.
- Measure bushing internal diameter (ID) and check for ovality.
- Calculate clearance: Bushing ID − Pin OD = Radial clearance.
- If clearance approaches or exceeds 0.5 mm, schedule replacement before boss damage occurs.
Replacement Best Practices
- Park the machine on level ground, lower the attachment, and relieve hydraulic pressure.
- Support the boom/arm/bucket safely using stands or blocking as required.
- Remove retaining hardware (bolts, snap rings, collars).
- Press the pin out using proper support (avoid uncontrolled hammering).
- Remove the worn bushing (press/drive out) and clean the housing bore.
- Inspect for boss ovality, scoring, or interference-fit damage.
- Press in the new bushing squarely; align grease holes/grooves where applicable.
- Install the new pin, confirm free articulation and correct endplay.
- Reinstall retainers and torque hardware appropriately.
- Grease thoroughly and cycle the linkage to confirm smooth movement.
Avoid:
- Installing bushings dry
- Hammering pins without proper support
- Ignoring boss ovality
- Reusing severely worn pins with new bushings
Lubrication Discipline
Use a high-pressure, heavy-duty grease appropriate for pivot joints. Grease discipline is the single most controllable factor in pivot life.
- Grease at scheduled intervals based on application severity
- Grease immediately after water exposure or washdowns
- Confirm grease purge at relief points (where designed)
- Keep fittings clean and replace damaged zerks
Manufacturing & Quality Control Framework
WQ Certified™ components are sourced from vetted manufacturing partners operating under structured quality management systems. Where applicable, suppliers maintain ISO 9001:2015 certification, confirming that their production processes are conducted within a documented and independently audited quality management framework.
ISO 9001:2015 certification supports:
- Controlled manufacturing processes
- Material traceability systems
- Inspection and dimensional verification procedures
- Documented quality control checkpoints
- Continuous improvement standards
This certification applies to the manufacturer’s quality management system and does not imply OEM affiliation or product-specific OEM approval.
WQ Certified™ Komatsu Pivot Standard
WQ Certification indicates that a component has been evaluated against internal qualification benchmarks for heavy-duty Komatsu pivot applications. Products may ship under the original manufacturer’s brand. WQ is not affiliated with Komatsu® or any OEM.
WQ-KOM-PIN-01 (Pins)
- Hardened alloy steel (42CrMo4 or equivalent)
- Induction hardened
- Heavy-equipment hardness range (benchmark)
- Deep effective hardening layer (application dependent)
- Precision ground outer diameter
WQ-KOM-BUSH-01 (Bushings)
- Precision ground ID and OD
- Controlled dimensional tolerances
- Suitable for interference-fit pivot housings
- Compatible with high-load articulation environments
Applicable Machine Classes
This guide applies broadly to Komatsu pivot applications including:
- Mid-size excavator classes (example: PC200–PC350)
- Mid-range wheel loader classes (example: WA mid-range series)
- Comparable boom/arm/bucket and cylinder pivot joints
Model-specific dimensional variations exist and should always be confirmed prior to installation.
<p><em>Komatsu® is a registered trademark of Komatsu Ltd. WQ is not affiliated with or endorsed by Komatsu Ltd.</em></p>