Removing the Track Grease Fitting on a CAT 320

[MikePhua]

The CAT 320 and Its Undercarriage Design
The Caterpillar 320 series excavator has been a cornerstone of medium-duty earthmoving since its introduction in the early 1990s. With operating weights ranging from 20 to 23 metric tons and engine outputs around 150–165 horsepower, the 320 is widely used in roadwork, utility trenching, and general construction. Caterpillar, founded in 1925, has sold tens of thousands of 320 units globally, with strong adoption in Asia, North America, and the Middle East.
The undercarriage of the CAT 320 is built around a sealed and lubricated track system. Each track assembly includes an idler, sprocket, rollers, and track tensioning mechanism. The tension is maintained by a hydraulic grease cylinder, which uses a grease fitting—commonly referred to as a grease nipple—to inject grease and extend the cylinder, pushing the idler forward and tightening the track.
Understanding the Grease Fitting and Its Role
The grease fitting is a small threaded port located on the tensioning cylinder. It allows grease to be pumped into the cylinder, increasing pressure and extending the piston. This system is simple, effective, and widely used across tracked machines.
Terminology clarification:

• Grease nipple: A threaded fitting that allows grease to be injected under pressure.
  
• Track tensioner: A hydraulic cylinder that adjusts track slack by pushing the idler forward.
  
• Idler: The front wheel of the track assembly that guides and supports the track chain.
  
• Zerk fitting: Another term for grease nipple, named after its inventor Oscar Zerk.
  

Over time, the grease fitting may become damaged, clogged, or need removal for servicing the tensioner. However, due to its location and exposure to dirt, rust, and pressure, removal can be challenging.
Common Challenges During Removal
Operators and technicians often encounter the following issues:

• Fitting is seized due to corrosion
  
• Threads are stripped or cross-threaded
  
• Grease hardened inside the fitting, preventing flow
  
• Fitting breaks during attempted removal
  
• Access is limited due to track guards or frame geometry
  

In a 2019 case in Queensland, a contractor attempted to remove a seized grease nipple on a CAT 320D. After multiple failed attempts with wrenches, the fitting snapped off flush with the cylinder. The team used a left-hand drill bit and extractor to remove the remnants without damaging the threads.
Recommended Removal Procedure
To safely and effectively remove a grease fitting from a CAT 320 track tensioner, follow these steps:

1. Clean the Area Thoroughly
   Remove all dirt, rust, and hardened grease around the fitting using wire brushes and solvent.
   
2. Apply Penetrating Oil
   Soak the fitting with a high-quality penetrating oil (e.g., Kroil or PB Blaster) and allow it to sit for several hours.
   
3. Use the Correct Tool
   Use a six-point socket or box-end wrench that fits snugly. Avoid adjustable wrenches or pliers.
   
4. Heat the Surrounding Area
   If the fitting is seized, apply heat with a torch to the cylinder body—not the fitting itself—to expand the metal and break the bond.
   
5. Attempt Removal with Steady Pressure
   Avoid jerking or over-torquing. If resistance is high, stop and reassess.
   
6. Use Extractor if Broken
   If the fitting snaps, drill a pilot hole and use a screw extractor. Ensure the drill bit is centered and does not damage the threads.
   
7. Inspect Threads and Replace
   Clean the threads with a tap if needed. Install a new grease fitting with thread sealant or anti-seize compound.
   

Preventive Measures and Maintenance Tips
To avoid future removal issues:

• Apply anti-seize compound during installation
  
• Grease fittings monthly to prevent hardening
  
• Use protective caps to shield from mud and debris
  
• Replace damaged fittings promptly
  
• Keep a spare fitting and extractor in the field kit
  

In a 2022 fleet audit in Ontario, machines with capped grease nipples showed 60% fewer removal failures compared to uncapped units, especially in winter conditions.
Conclusion
Removing a track grease fitting on a CAT 320 may seem minor, but it requires precision and patience. The fitting plays a critical role in maintaining track tension, and improper removal can lead to downtime or costly repairs. With the right tools, preparation, and technique, even a seized or broken nipple can be extracted cleanly. In the world of tracked equipment, small fittings carry big responsibilities—and knowing how to handle them keeps the machine moving forward.