Decisions on tensioning and replacing the track chain (commonly known as the undercarriage chain) are directly tied to equipment safety, travel performance and cost control. Make a scientific judgment by following this three-step method:

Step 1: Precisely Measure Wear (Establish a Basis with Quantification)

This is the core of judgment, requiring the measurement of two key metrics:

1. Tension check: On a flat, hard surface, measure the sag at the middle of the track shoe between the idler wheel and the first top roller. Compare with the standard value (20–50 mm for most common models) to determine if adjustment is needed.

2. Track link pitch check: This is the gold standard for deciding replacement. Measure the total length of 10 consecutive links (from the outer edge of one bushing to the outer edge of the last) – record this as the new length L0. If the elongation rate exceeds 3% (i.e., the measured length of 10 links > 1.03 x L0), or the pitch of individual links is significantly uneven, the chain is worn beyond the limit due to bushing wear and must be replaced.

   
   

Step 2: Observe Wear Patterns & Associated Components (Identify Correlations via Visual Inspection)

Local wear / Adjustable condition

• The chain has uniform overall wear and is only loose due to normal wear, with no pitch overrun.

• Tensioning the cylinder can restore the sag to the standard range, with no abnormal noise or derailment tendency.Conclusion: Only tension the chain and continue use.

Overall wear / Non-adjustable condition

• The chain is severely stretched (pitch exceeds the limit), with excessive sag even when tensioned to the maximum.

• Teeth jumping (poor meshing with the drive sprocket) and track scuffing (abnormal contact with the edges of idler wheels/track rollers) occur.

• Severe uneven wear, cracking or missing parts are found on track pins, bushings and track plates.

• The tips of the drive sprocket teeth are worn down and thinned simultaneously.Conclusion: The chain has reached the end of its service life and must be replaced immediately. It is highly recommended to inspect or replace the drive sprocket at the same time – otherwise, the new chain will suffer rapid abnormal wear with the worn drive sprocket.

Step 3: Make Decisions Based on Working Conditions & Costs (Calculate the Economic Trade-off)

Tensionable but near the wear limit

If the chain pitch is close to but not yet over the limit, it can be temporarily tensioned for light-load, short-duration projects. However, increase the inspection frequency and budget for the upcoming replacement.

Replacement is mandatory in the following cases:

1. Safety first: Any chain with fracture risks (cracked track plates) or frequent derailment risks must be replaced, regardless of wear metrics.

2. Efficiency priority: If excessive chain looseness causes huge travel resistance, slow speed, a sharp surge in fuel consumption and project delays, replacement is more economical than forced continued use.

3. Prevent chain-reaction damage: An excessively worn chain acts like sandpaper, accelerating wear on idler wheels, track rollers, top rollers and even travel motor reducers, leading to a multiplicative increase in maintenance costs. Replacement is the most cost-effective option in this case.

Final Decision Mnemonic

• Loose only, not stretched → Tension, don’t replace: Adjust the chain if it is merely loose with no pitch overrun.

• Loose and stretched → Replace, no cost cutting: Replace the chain immediately if it is both loose and has an overrun pitch.

• Inspect the full undercarriage when replacing → Save costs and ensure safety: When replacing the chain, conduct a systematic inspection of the "Three Wheels and One Sprocket" (idler wheel, track roller, top roller, drive sprocket) and decide on simultaneous replacement based on their wear to achieve the longest overall service life.

Adhering to this three-step method avoids accelerated wear from over-tensioning and greater losses from forced use, achieving a balance between safety and cost control.