Komatsu D21P Tracks Too Tight

[MikePhua]

The Komatsu D21P is a compact bulldozer designed for precise grading and light construction tasks. Owners occasionally report issues with tracks being too tight, which can affect performance, accelerate wear, and increase fuel consumption. Understanding track tension, causes, and corrective measures is crucial for maintaining optimal operation.

Machine Background

• Komatsu is a leading Japanese manufacturer of construction and mining equipment, established in 1921.
  
• The D21P model is part of the D21 series, a small crawler dozer line with approximately 60–70 hp engines, designed for landscaping, light grading, and farm work.
  
• The D21P features a hydrostatic or mechanical drive depending on the production year, with track assemblies optimized for maneuverability in tight spaces.
  

Symptoms of Overly Tight Tracks

• Excessive wear on sprockets, rollers, and track links.
  
• Difficulty steering or turning; the machine may “push” when trying to pivot.
  
• Higher than normal fuel consumption due to increased rolling resistance.
  
• Vibrations or jerky motion while driving on uneven surfaces.
  

Common Causes

1. Improper Track Adjustment During Maintenance
   • Track tension is typically adjusted via a grease-filled idler assembly. Over-tightening can occur if the idler is over-extended during installation or after maintenance.
     
2. Track Stretch or Sagging Compensation
   • As tracks wear, they naturally stretch. New or recently replaced tracks can be over-tightened to compensate, leading to excessive tension.
     
3. Hydraulic or Mechanical Idler Malfunction
   • The idler cylinder or mechanical spring may apply too much tension if seals fail or spring preload is too high.
     
4. Debris Between Track Links or Under Idler
   • Rocks, mud, or compacted dirt can interfere with normal track movement, giving the impression of “tight” tracks.
     
5. Temperature-Related Changes
   • Metal expansion in hot conditions can increase tension, particularly if tracks were set tightly in cooler environments.
     

Diagnostic Steps

• Inspect track sag: Measure the vertical deflection at the midpoint of the track span. Recommended sag for a D21P is usually around 25–30 mm (1–1.2 in).
  
• Check idler grease pressure or mechanical spring tension: Excess pressure indicates over-tightening.
  
• Examine rollers, sprockets, and links for abnormal wear or damage caused by excessive tension.
  
• Look for debris trapped in the track assembly, which can increase resistance.
  

Correction and Adjustment

• Loosen Idler Tension: Gradually release grease from the idler assembly or reduce spring preload until proper sag is achieved.
  
• Check Track Alignment: Ensure the track is centered on rollers and sprockets to prevent uneven tensioning.
  
• Inspect Components: Replace any damaged or excessively worn rollers, sprockets, or track links.
  
• Clean Track Assembly: Remove rocks, dirt, and debris to allow normal articulation.
  
• Regular Monitoring: Check track tension periodically, especially after maintenance or long idle periods.
  

Preventive Recommendations

• Avoid over-tightening tracks during installation or post-maintenance adjustments.
  
• Keep a maintenance log including track tension measurements.
  
• Use manufacturer-recommended grease and adjustment procedures.
  
• Train operators to recognize signs of track stress, such as increased vibration or unusual steering resistance.
  

Technical Terms Explained

• Track Sag: The vertical drop of the track midway between the sprocket and idler; a measure of proper tension.
  
• Idler Assembly: A wheel at the front of the track that allows adjustment of tension through spring preload or hydraulic pressure.
  
• Track Stretch: The natural elongation of a track over time due to wear and link articulation.
  

Conclusion
Overly tight tracks on a Komatsu D21P can significantly affect machine performance and longevity. Proper inspection, adjustment, and periodic monitoring are essential. By ensuring correct track sag, maintaining idler assemblies, and keeping the track assembly clean, operators can optimize efficiency and reduce wear. For any persistent issues, consulting a qualified technician or referring to the official service manual is advised to avoid irreversible damage.