CAT 311B Track Tensioner Maintenance and Troubleshooting Guide

[MikePhua]

Maintaining proper track tension is critical for the performance and longevity of tracked machinery like the CAT 311B excavator. The track tensioner system ensures the tracks are neither too loose nor too tight, preventing premature wear and operational issues. This article explains the fundamentals of the CAT 311B track tensioner, common problems, maintenance tips, and practical troubleshooting, complemented with terminology and real-life insights.
Understanding the Track Tensioner System
The track tensioner on the CAT 311B is a hydraulic or grease-actuated mechanism designed to keep the undercarriage tracks at the correct tension. Proper tension minimizes track derailment, uneven wear, and damage to sprockets and rollers.
Key Terminology

• Track Tensioner: The device applying force to adjust the track’s tightness.
  
• Grease Cylinder: A cylinder filled with grease that pushes the idler forward to tighten the track.
  
• Idler: A wheel at the front of the track frame that guides the track and maintains tension.
  
• Track Sag: The amount of looseness or slack in the track.
  
• Track Roller: Supports the weight of the machine and guides the track.
  
• Derailment: When the track comes off the sprockets or rollers.
  
• Track Link: Individual sections of the track chain linked together.
  

Common Symptoms of Track Tension Problems

• Excessive track sag leading to derailment or noise.
  
• Overly tight tracks causing accelerated wear on rollers, sprockets, and the track itself.
  
• Difficulty in adjusting tension or loss of pressure in the tensioner.
  
• Visible grease leaks from the tensioner cylinder.
  
• Uneven track wear or damaged track links.
  

Track Tension Adjustment Procedure

• Park the machine on a flat surface and safely secure it.
  
• Clean the area around the tensioner to prevent contamination during adjustment.
  
• Release pressure in the tensioner system by loosening the grease fitting or valve.
  
• Adjust track tension by adding grease to the tensioner cylinder or hydraulic fluid as specified.
  
• Check track sag by measuring the vertical distance between the track and the bottom rollers, usually around 25-40 mm (1-1.5 inches).
  
• Add or release tension accordingly, avoiding over-tightening.
  
• Re-tighten grease fittings or valves to maintain system integrity.
  

Maintenance and Inspection Tips

• Regularly check for grease leaks around the tensioner cylinder seals.
  
• Inspect idler wheels for wear and damage.
  
• Monitor track sag monthly or after heavy usage.
  
• Replace worn track components such as links and rollers promptly.
  
• Lubricate grease fittings as per the manufacturer’s maintenance schedule.
  

Real-World Example
An operator of a CAT 311B reported frequent track derailment during excavation work in uneven terrain. Upon inspection, the grease tensioner had lost pressure due to a leaking seal, causing excessive track sag. The mechanic replaced the seal, re-greased the cylinder, and adjusted the tension to the recommended specification. Following the repair, track derailment ceased, and machine performance improved.
Preventive Measures and Best Practices

• Avoid excessive track tension; it can cause strain on the undercarriage and reduce component life.
  
• Keep the tensioner clean and free of dirt to prevent seal damage.
  
• Use manufacturer-recommended grease types to ensure proper function.
  
• Incorporate track tension checks into daily pre-operation inspections.
  

Summary of Track Tension Checkpoints

• Measure track sag regularly.
  
• Inspect for hydraulic or grease leaks.
  
• Confirm idler and rollers are in good condition.
  
• Adjust tension using grease or hydraulic methods.
  
• Replace faulty parts promptly.
  

Conclusion
The track tensioner on the CAT 311B plays a pivotal role in maintaining undercarriage health and overall machine reliability. Proper understanding, routine inspections, and timely maintenance prevent costly breakdowns and extend equipment life. Operators and technicians should prioritize track tension checks as part of standard operating procedures to ensure smooth and safe excavator performance across diverse working conditions.