Comprehensive Guide to Converting Cat CB Linkage Buckets to C Linkage Using Bushings and Shims

[MikePhua]

Introduction to Cat CB and C Linkage Differences
Caterpillar excavator bucket linkages come in various styles, with the commonly encountered CB (Cat B) and C linkages having distinct dimensions and pin sizes that prevent direct interchangeability. The CB linkage uses larger pins and wider internal spacing compared to the C linkage, making conversion challenging without modification.
Understanding these dimensional differences and available solutions such as bushings and shims is crucial for operators who want to fit more readily available C-linkage attachments onto CB-equipped machines, enabling greater attachment versatility and compatibility with quick couplers like Hendrix systems.

Key Differences Between Cat CB and C Linkages

• Pin Diameter:
  • CB linkage pins measure approximately 90 mm in diameter.
    
  • C linkage pins are smaller, around 80 mm in diameter.
    
• Internal Ear Spacing:
  • CB linkage has an internal ear spacing of about 388 mm.
    
  • C linkage has a narrower ear spacing of approximately 351 mm.
    
• Pin Center-to-Center Spacing:
  • Both CB and C linkage share the same pin center-to-center distance of approximately 485 mm.
    

These disparities mean that while the general layout remains similar, key fitting dimensions prevent direct use of C linkage attachments on CB linkages without adaptation.

Approaches to Converting CB Linkage Buckets to C Linkage

• Bushing and Shim Inserts:
  • By machining or installing bushings/shims to reduce the 90mm pin bores on the CB linkage attachment down to 80mm, it becomes possible to fit the smaller C linkage pins.
    
  • Similarly, shims can adjust internal ear spacing to accommodate reduced dimensions.
    
  • This method preserves the base structure without weakening pins by turning down their diameter.
    
  • Off-the-shelf CB-to-C linkage bushing/shim inserts are not commonly available; users often fabricate custom inserts or seek assistance from machinists.
    
• Pin Modification Considerations:
  • Machining a 90mm pin down to 80mm where the quick coupler grips is a suggested alternative but has drawbacks:
    • It removes hardened steel surface, potentially weakening pin strength and durability.
      
    • Precision machining is required to maintain pin integrity and fitment.
      
• Custom Fabrication and Machining:
  • Many operators rely on skilled machinists to fabricate bushings or sleeves that can be inserted into the bucket linkage ears to safely reduce pin hole size.
    
  • This requires precise tolerance control, material selection for wear resistance, and sometimes heat treatment to maintain durability.
    

Practical Recommendations and Solutions

• Work with Experienced Machinists:
  • Custom bushings or shims should be designed and fabricated by professionals who understand load-bearing requirements.
    
• Avoid Weakening Pins:
  • Opt for modifying attachment ear hole sizes rather than pin diameter reduction to preserve pin strength.
    
• Use High-Quality Materials:
  • Bushings should be made from hardened steel or equivalent wear-resistant materials to handle heavy loads and reduce wear.
    
• Precision Measurements:
  • Accurately measure all relevant dimensions (pin diameter, ear inside width, pin spacing) before modifications.
    
• Maintain Proper Clearance:
  • Ensure bushings and shims allow for correct pin fit with minimal play to avoid accelerated wear and operational looseness.
    
• Consult Attachment Manufacturer or Experts:
  • Before modifications, seek advice or approval from attachment manufacturers or experienced heavy equipment technicians to ensure safety and compatibility.
    

Terminology Explained

• Linkage Pins: Hardened steel pins that connect loader arms to bucket ears, enabling bucket movement.
  
• Ears: The side plates on bucket linkage where pins are inserted.
  
• Bushings: Cylindrical sleeves inserted into linkage ears to reduce pin bore size and serve as wear surfaces.
  
• Shims: Thin pieces of material used to adjust internal spacing or alignment between linkage parts.
  
• Quick Coupler: An attachment interface system allowing rapid bucket/tool changes on excavators.
  
• Internal Ear Spacing: The distance between the inner faces of bucket ears where pins fit.
  
• Pin Center-to-Center Spacing: Distance between the centers of the pivot pins on the linkage.
  

Real-World Examples and Stories

• One excavator operator shared frustration finding scarce C-linkage attachments for their Cat 325BL equipped with CB linkage. They found it easier to modify bucket ears with custom bushings to fit the commonly available 80mm C linkage pins, thereby expanding attachment options without risk to pin strength.
  
• A retired machinist offered advice about turning down 90mm pins to fit smaller couplers, but concerns about significantly weakening the pins led to choosing bushing inserts instead.
  
• Heavy equipment technicians emphasize the importance of preserving pin hardness and geometry, as worn or weakened pins can lead to costly failures and dangerous situations on job sites.
  
• Custom bushing inserts have proven successful in rental fleets, allowing machines to be compatible with a wider array of bucket types without expensive linkage replacements.
  

Additional Tips and Solutions

• Maintain a clear maintenance schedule to inspect bushings and linkage pins for wear after modification.
  
• Use grease fittings and proper lubrication to extend the life of bushings and pins post-conversion.
  
• Document modifications thoroughly for future service and inspection records.
  
• When operating converted attachments, monitor for any unusual play or noises indicative of wear or fitting issues.
  

Summary
Converting a bucket with Cat CB linkage to fit C linkage pins involves overcoming differences in pin diameters and ear spacing. The preferred and safest method is installing custom bushings or shim inserts to adapt the 90mm CB linkage ear holes to 80mm C linkage pins while preserving pin integrity and function. Machining pins down is generally discouraged due to potential weakening.
This approach enables operators to access a larger market of C linkage attachments and compatible quick couplers without compromising machine safety or performance. Close attention to measurements, materials, and professional fabrication ensures a reliable modification.
Real-world experiences confirm that careful modification and maintenance extend attachment versatility and machine uptime, allowing operators to adapt to various job requirements effectively.
This guide provides owners, operators, and technicians with detailed insights and practical recommendations on converting Cat CB linkage buckets to C linkage safely using bushings and shims.