Track Tensioners on the Caterpillar 315 Excavator

[MikePhua]

Understanding Track Tensioners and Their Role
On the Caterpillar 315 excavator, the track tensioner plays a critical role in maintaining the correct tension of the track chain (undercarriage). Proper tension ensures the track stays engaged with the sprocket and idlers, reduces the risk of derailment, and helps avoid excessive wear on track links, rollers, and idlers.
The track tensioner assembly typically comprises a cylinder (or spring-package), a grease or hydraulic adjuster, and associated seals and relief valves.
Common Symptoms of Tensioner Problems
While working on 315 series machines, operators and technicians have reported several recurring issues tied to the tensioner assembly:

• The track slack increases over time, even though it had been correctly tensioned.
  
• Lubricant (grease) leaks from the track adjuster housing or around the idler-frame area.
  
• The tensioner does not respond when grease is pumped in—i.e., the track cannot be tightened further.
  
• The guard or protective cover over the grease-fitting is obstructive, making access difficult and maintenance delayed.
  

Typical Causes of Failure or Malfunction
Several root causes tend to underlie tensioner problems on the 315:

• Seal failure or casing damage: When the adjuster cylinder or grease block’s seals fail, grease bleeds out and pressure is lost, resulting in slack track.
  
• Blockage or improper access to grease fitting: The design of the guard and limited clearance can prevent proper greasing, causing undervaluation of maintenance.
  
• Spring-package fatigue (in spring type adjusters): Over time, the spring loses its preload and cannot maintain proper tension under track load.
  
• Hydraulic or grease relief valve stuck open: If the relief valve allows fluid or grease to escape too easily, the adjuster cannot maintain pressure. Reference material from Caterpillar describes this procedure for checking track tension, including releasing grease to loosen the track when too tight.
  

Diagnostic & Maintenance Steps
When inspecting and repairing the track tensioner on a 315, consider the following procedural steps:

• Park the machine on level ground, lower the bucket to lock the undercarriage, apply parking brake.
  
• Remove debris from the idler and tensioner area to gain access to the grease fitting or adjuster chamber.
  
• Attempt to add grease (or hydraulic oil depending on design) via the tensioner’s fitting; if there is no response (track remains slack), suspect seal or cylinder failure.
  
• Inspect the adjuster cylinder and idler housing for visible leaks of grease fluid or hydraulic oil. Leaks are a red-flag.
  
• If equipped with a relief valve, check the setting and operation: the valve should hold pressure—that is, minimal escape of grease when properly tensioned.
  
• Check track sag according to the manual’s spec (for example, gap between sprocket and idler). Caterpillar documents: loosen relief valve to allow tension to release if too tight.
  
• Remove the idler if necessary to access internal adjuster components (bearing seals, spring pack). Some user-reports on forum recall this for older 315 machines.
  

Solutions and Recommendations
Depending on findings, recommended actions include:

• Replace the grease adjuster block or complete tensioner cylinder if seals are damaged or the mechanism is seized.
  
• Replace the guard or reposition the grease fitting if access is chronically obstructed, to ensure proper greasing schedule.
  
• If using spring-package style, replace worn springs and preload as per specifications.
  
• After service, properly tension the track: pump in grease until the correct sag is achieved, then operate machine slightly to seat components and re-check sag. Too much tension can cause undue wear; too little causes derailment risk.
  
• Include the tensioner in scheduled preventative maintenance: check for leaks, verify grease condition, and ensure adjuster is responsive.
  

Conclusion
The track tensioner system in the Caterpillar 315 excavator is a relatively simple but critical component of the undercarriage. When functioning correctly it ensures the machine operates smoothly and undercarriage wear is minimised. Failure to maintain this component can lead to track loosening, premature wear, or even derailing of the track. By proactively inspecting for leaks, ensuring grease fittings are accessible and functional, and following correct tensioning procedures, operators can extend the life of the undercarriage and avoid costly downtime.