Master Pin Removal and Track Service on the Hitachi EX100-2

[MikePhua]

The EX100-2 and Its Undercarriage Design
The Hitachi EX100-2 is a mid-size hydraulic excavator introduced in the early 1990s, built for general construction, trenching, and light forestry work. With an operating weight around 10 metric tons and powered by a 4-cylinder Isuzu diesel engine, the EX100-2 is known for its mechanical simplicity and durable undercarriage. The track system uses sealed chains with a master pin to allow disassembly and reassembly during maintenance.
Terminology annotation:

• Master pin: A removable track pin that allows the track chain to be separated for service or replacement.
  
• Track chain: A continuous loop of links and bushings that forms the excavator’s undercarriage.
  
• Sealed and lubricated track (SALT): A track system where pins and bushings are sealed to retain grease and reduce wear.
  

The EX100-2’s track chain is built with a single master pin per side, typically located near the sprocket or idler. This pin is pressed in during assembly and may be retained with a clip, plug weld, or interference fit depending on the chain manufacturer.
Identifying and Accessing the Master Pin
Locating the master pin can be challenging, especially on older machines with worn or repainted chains. Signs of a master pin include:

• Slightly different coloration or finish
  
• Absence of plug welds on one end
  
• Raised or recessed center mark
  
• Alignment with factory punch marks on adjacent links
  

Recommendations:

• Rotate the track until the suspected master pin is accessible at the top of the sprocket or idler
  
• Clean the area thoroughly to expose welds or retaining clips
  
• Use a caliper to measure pin diameter—master pins may be slightly oversized
  
• Mark the pin and adjacent links before removal to preserve alignment
  

In Alberta, a contractor used a magnetic particle inspection wand to locate the master pin on a heavily rusted EX100-2 chain. The pin showed a distinct magnetic signature due to its different metallurgy.
Removing the Master Pin Safely
Master pin removal requires force, precision, and safety precautions. Common methods include:

• Hydraulic press with custom jigs
  
• Pin press tool with threaded ram
  
• Sledgehammer and drift punch (only for field emergencies)
  
• Induction heating to expand the link and reduce interference
  

Steps:

• Support the track on cribbing or blocks to prevent movement
  
• Align the master pin horizontally and secure adjacent links
  
• Apply penetrating oil and allow time to soak
  
• Use a press or hammer to drive the pin out slowly
  
• Catch the pin with a soft surface to prevent damage
  

Safety tips:

• Wear face shield and gloves during hammering
  
• Never stand directly behind the pin during removal
  
• Use heat only on the link—not the pin—to avoid tempering
  

In New Zealand, a forestry crew built a portable hydraulic press using a bottle jack and steel frame. They removed both master pins in under 30 minutes without damaging the bushings.
Reinstalling the Master Pin and Track Chain
After servicing the undercarriage, reinstalling the master pin requires alignment and lubrication. Steps include:

• Clean the pin and bore with solvent
  
• Apply anti-seize compound or light grease
  
• Align the chain using pry bars or excavator boom
  
• Press or hammer the pin in evenly
  
• Install retaining clip or weld plug if applicable
  

Recommendations:

• Use a torque wrench if the pin includes threaded retainers
  
• Check track tension after installation—should allow 1–1.5 inches of sag between carrier rollers
  
• Run the machine slowly to verify smooth rotation and seating
  

In Texas, a land-clearing operator used a laser alignment tool to ensure the master pin was centered. This reduced bushing wear and improved track life over the next 1,000 hours.
Preventative Maintenance and Track Longevity
To extend the life of the EX100-2’s undercarriage:

• Inspect track tension weekly and adjust as needed
  
• Grease idler and carrier roller bearings every 250 hours
  
• Monitor pin and bushing wear with calipers or wear gauges
  
• Replace track pads if bolt holes elongate or pads crack
  
• Rotate chains side-to-side every 1,500 hours to balance wear
  

Use ISO VG 68 hydraulic oil for track adjusters and avoid over-tensioning, which accelerates link wear. Keep the undercarriage clean of mud and debris to prevent abrasive damage.
In British Columbia, a contractor added track guards and debris deflectors to his EX100-2. Over three seasons, his chain wear rate dropped by 40%, and master pin service intervals doubled.
Conclusion
Master pin removal on the Hitachi EX100-2 is a critical step in undercarriage maintenance. With proper identification, safe extraction, and precise reinstallation, operators can maintain track integrity and avoid costly downtime. Whether in the shop or the field, understanding the mechanics behind the master pin ensures that the machine stays productive and the chain keeps rolling—link by link, hour by hour.