Removing Broken Bottom Roller Bolts with Heat and Precision

[MikePhua]

The Challenge of Undercarriage Repairs
In tracked equipment like dozers and excavators, bottom rollers are critical for distributing weight and guiding the track chain. These rollers are bolted to the track frame, often with countersunk or recessed bolts that endure years of vibration, mud, and corrosion. When bolts shear off or seize, removing them becomes a test of patience and technique. Torch work, drilling, and extraction tools all play a role—but each method carries risks to the frame, threads, and surrounding components.
One operator working on a mid-size dozer encountered broken bottom roller bolts that refused to budge. After trying extractors and reverse drills, he turned to heat—a time-tested method in heavy equipment repair.
Torching Techniques and Safety Considerations
Using an oxy-acetylene torch to remove broken bolts requires finesse. The goal is to heat the bolt shank enough to expand and break the rust bond, or to melt the bolt out without damaging the threaded bore. In recessed bolt holes, torch access is limited, and slag buildup can complicate cleanup.
Best practices include:

• Use a fine-tip torch for precision flame control
  
• Heat the bolt gradually to avoid warping the frame
  
• Shield surrounding components with heat blankets or wet rags
  
• Wear fire-resistant gloves and eye protection
  
• Keep a fire extinguisher nearby in case of flare-ups
  

One technician shared that he heated the bolt stub until it glowed cherry red, then let it cool slightly before striking it with a punch. The thermal expansion and contraction cracked the rust seal, allowing the stub to spin free.
Drilling and Thread Preservation
If torching fails or access is limited, drilling becomes the next option. The challenge is centering the drill on a broken bolt without damaging the threads. Using a pilot bit followed by a left-hand drill can sometimes spin the bolt out during drilling.
Steps for safe drilling:

• Center punch the bolt stub to guide the bit
  
• Start with a small pilot hole (⅛ inch or 3 mm)
  
• Use left-hand cobalt bits for hardened bolts
  
• Apply cutting oil to reduce heat and wear
  
• Stop frequently to check depth and alignment
  

If the bolt does not back out, the hole can be tapped for a thread insert or helicoil. In extreme cases, the hole may need to be bored oversize and welded shut before re-tapping.
Alternative Methods and Field Innovations
Some operators use weld-on extraction techniques. By welding a nut or washer onto the broken bolt stub, they create a grip point for a wrench. The heat from welding also helps break the rust bond.
Another method involves using a plasma cutter to remove the bolt flush, followed by a carbide burr to clean the hole. This approach is faster but requires skill to avoid gouging the frame.
In one logging operation, a mechanic used a portable induction heater to remove seized bolts without flame. The magnetic field heated the bolt internally, loosening it without damaging paint or seals.
Preventive Measures and Bolt Selection
To avoid future bolt failures:

• Use grade 8 bolts with anti-seize compound
  
• Torque bolts to spec using a calibrated wrench
  
• Inspect roller mounts during routine service
  
• Replace bolts showing signs of stretch or corrosion
  

Some shops install stainless bolts or zinc-coated fasteners for added corrosion resistance. Others use thread lockers to prevent vibration loosening, though this can complicate removal later.
Recommendations for Undercarriage Work
When dealing with broken bottom roller bolts:

• Assess bolt access and choose the least invasive method
  
• Use heat cautiously and protect surrounding components
  
• Drill only when confident in alignment and depth
  
• Consider extraction tools like spiral flutes or weld-on nuts
  
• Document bolt grade, torque, and installation date for future reference
  

For fleet managers, training technicians in bolt removal techniques can reduce downtime and prevent frame damage. Investing in quality tools—torches, drills, extractors—pays off when facing stubborn fasteners.
Conclusion
Removing broken bottom roller bolts is a rite of passage in heavy equipment maintenance. Whether using heat, drills, or creative welding, the goal is the same: restore the undercarriage without compromising the frame. With patience, precision, and the right tools, even the most stubborn bolts can be defeated—one glowing stub at a time.