Greasing the Bucket Main Pin When No Zerk Is Present

[MikePhua]

The Role of Grease in Excavator Joint Longevity
In hydraulic excavators, the bucket main pin is one of the most stressed pivot points. It endures constant rotation, side loading, and exposure to abrasive materials. Proper lubrication is essential to prevent galling, seizure, and accelerated wear. Most machines are equipped with grease fittings—commonly called zerks—that allow pressurized grease to reach the bearing surfaces. However, in some cases, the zerk may be missing, broken, or never installed due to aftermarket pin replacement or design oversight.
When the bucket main pin lacks a grease fitting, operators face a dilemma: allow metal-on-metal contact to continue or attempt a retrofit. Drilling for a zerk is possible but must be done with precision to avoid damaging the pin, bushing, or surrounding structure.
Terminology Annotation

• Zerk Fitting: A small, threaded grease nipple that allows grease to be injected into a bearing or bushing under pressure.
  
• Bucket Main Pin: The central pivot pin connecting the bucket to the stick or linkage, transmitting digging force and motion.
  
• Bushing: A replaceable sleeve that provides a bearing surface between the pin and the housing.
  
• Gall: A form of adhesive wear caused by metal surfaces seizing and tearing under pressure.
  

Assessing the Pin and Bushing Condition
Before drilling, inspect the pin assembly:

• Check for visible wear, scoring, or discoloration.
  
• Measure pin diameter and compare to spec—more than 0.5 mm wear may require replacement.
  
• Rotate the bucket manually to feel for binding or rough spots.
  
• Look for signs of heat damage or metal transfer.
  

If the pin is seized or the bushing is dry and worn, drilling a zerk may not restore function. In such cases, disassembly and replacement are recommended.
Drilling and Installing a Zerk Fitting
If the pin is in good condition and the goal is to add a grease point:

• Identify the center of the pin housing where grease would best distribute.
  
• Use a center punch to mark the drill point—avoid edges or welds.
  
• Drill a pilot hole with a 3 mm bit, then enlarge to match the zerk thread (typically 6 mm or 1/4").
  
• Tap the hole using a matching thread tap—ensure clean threads and no burrs.
  
• Install a high-quality zerk fitting rated for heavy equipment use.
  
• Pump grease until resistance is felt or it begins to purge from the pin ends.
  

Use molybdenum-based grease for high-pressure joints. Avoid over-greasing, which can rupture seals or attract abrasive debris.
Alternative Greasing Methods Without Drilling
If drilling is not feasible due to design or risk:

• Remove the pin and manually apply grease during reassembly.
  
• Use a needle adapter to inject grease between the pin and bushing edge.
  
• Apply anti-seize compound during installation to reduce initial wear.
  
• Schedule frequent inspections and manual lubrication intervals.
  

In one case from a quarry operation, a Komatsu excavator had a non-greaseable bucket pin. The crew removed the pin every 300 hours and applied high-pressure grease manually. Though labor-intensive, this method extended pin life by over 2,000 hours.
Preventive Maintenance and Long-Term Solutions
To avoid future lubrication issues:

• Replace pins with greaseable versions during overhaul.
  
• Use sealed bushings with internal grease reservoirs if available.
  
• Inspect zerks monthly—replace missing or clogged fittings immediately.
  
• Train operators to recognize dry joint symptoms—squeaking, binding, or heat.
  

Keep spare zerks, taps, and grease guns in the field kit. Document all lubrication points and intervals in the maintenance log.
Recommendations for Technicians and Fleet Managers

• Standardize pin types across machines to simplify greasing routines.
  
• Retrofit older machines with grease ports during rebuilds.
  
• Use color-coded grease guns to match lubricant types.
  
• Monitor pin wear with calipers and replace before tolerance exceeds spec.
  

Closing Reflections
A missing zerk may seem minor, but in the world of heavy equipment, it can lead to major downtime. The bucket main pin is a silent workhorse—bearing the brunt of every dig, curl, and dump. Whether through careful drilling or creative greasing, restoring lubrication is a must. With the right tools and a steady hand, even a dry joint can be brought back to life—keeping the bucket swinging and the job moving forward.