Pin Bore Dimensions and Maintenance on the 1986 JCB 1400B Extradig Arm

The bucket pin bore on a backhoe’s dipper arm is a critical wear point where the bucket connects to the arm via steel pins and bushings. On the 1986 JCB 1400B with an Extradig arm, this interface is subject to high loads, frequent articulation, and abrasive contamination. The bore diameter must match the pin precisely to ensure proper fit, minimize slop, and prevent accelerated wear.

While the exact static bore diameter for the 1400B Extradig arm is not universally published, field measurements and parts catalogs suggest a nominal bore size of approximately 2.00 inches (50.8 mm) for the bucket pin. However, wear, bushing type, and aftermarket modifications may alter this slightly.

Common Bore Configurations and Tolerances

Typical configurations include:

• Bare bore (no bushing): Machined directly into the dipper arm steel. Rare in modern machines due to wear concerns.
• Press-fit bushing: Hardened steel or bronze sleeve inserted into the bore. Allows easy replacement when worn.
• Greased pin with seal rings: Reduces friction and contamination. Requires regular maintenance.

Standard tolerances:

• Bore diameter: 2.000" ± 0.005"
• Pin diameter: 1.998" to 1.999" for clearance fit
• Bushing wall thickness: ~0.125" depending on design

Field Measurement and Inspection Techniques

To determine actual bore diameter:

• Use a telescoping bore gauge and micrometer for precision
• Clean bore thoroughly before measurement
• Measure at multiple depths and orientations to detect ovality
• Compare with new pin or bushing specs

If the bore is worn beyond tolerance, options include:

• Installing oversized bushings
• Line boring and welding to restore diameter
• Replacing the dipper arm (rare and costly)

One operator in Ohio reported restoring a 1400B bore using a portable line boring rig and custom bushings machined from 4140 steel. The repair held up for over 1,000 hours of trenching work.

Extradig Arm Considerations

The Extradig variant of the 1400B features a sliding inner dipper that extends the reach of the backhoe. This adds complexity to the bucket linkage, as the geometry changes during extension. The pin bore must accommodate dynamic loads and maintain alignment across the full stroke.

Challenges include:

• Increased side loading during extension
• Higher wear rates due to longer leverage
• Difficulty accessing bore for repair without full disassembly

Operators often reinforce the Extradig arm with gussets or switch to heavier-duty pins when working in rocky soil.

Historical Context and Legacy Maintenance

The JCB 1400B was a popular model in the 1980s and early 1990s, known for its mechanical simplicity and robust steelwork. However, parts availability has declined, and many machines now rely on custom fabrication for wear components.

In one case, a municipality in Saskatchewan maintained a fleet of 1400Bs for snow removal and trenching. Their maintenance crew developed a catalog of custom bushings and pin kits, allowing continued operation decades after OEM support ended.

Final Thoughts

The bucket pin bore diameter on a 1986 JCB 1400B Extradig arm is a small but vital specification that affects performance, longevity, and repair strategy. While nominally around 2 inches, actual dimensions must be verified in the field due to wear and variation. With proper inspection, bushing selection, and maintenance, even aging machines like the 1400B can continue to serve reliably in demanding conditions. The key is precision, patience, and a willingness to adapt when factory specs are no longer available.