Komatsu PC 120-6 Boom and Stick Replacements: A Comprehensive Guide

[MikePhua]

The Komatsu PC 120-6 is a widely used hydraulic excavator that has built a strong reputation for reliability and performance. However, like all heavy machinery, it requires regular maintenance and occasional repairs to ensure it continues to perform at its best. One of the more significant repair tasks that owners of the PC 120-6 may encounter is the replacement of the boom and stick. These components are crucial for the machine’s lifting, digging, and reaching capabilities, so when they are damaged or worn out, they must be addressed promptly.
This guide will explore the process of replacing the boom and stick on a Komatsu PC 120-6, common issues related to these components, and tips for a successful replacement.
Understanding the Boom and Stick of the Komatsu PC 120-6
Before diving into the replacement process, it is important to understand the role that the boom and stick play in the overall operation of the Komatsu PC 120-6.

• Boom: The boom is the large, hydraulic arm of the excavator that extends from the base of the machine. It provides the reach and height required to lift and lower the bucket. The boom is essential for a variety of tasks, such as digging, lifting heavy materials, and reaching areas that are difficult to access.
  
• Stick: The stick, also known as the arm, connects to the boom and is responsible for extending the excavator’s reach further. It allows the bucket to dig deep into the earth, providing the necessary movement to carry out tasks like trenching or digging into uneven terrain.
  

Both of these components are subject to significant wear and tear due to the constant forces they are subjected to. Over time, they may experience cracks, bending, or severe wear, which can reduce the machine’s efficiency and safety.
Common Causes for Boom and Stick Replacement
The replacement of the boom and stick is typically due to one or more of the following reasons:

1. Cracking or Fractures
   Over time, the stress and strain of heavy work can cause the boom and stick to develop cracks or fractures. These cracks can be a result of overloading, improper use, or natural wear. If not addressed, they can lead to catastrophic failure, making replacement the only viable option.
   
2. Severe Wear
   Extended use in tough conditions, such as digging in rocky or abrasive soils, can wear down the boom and stick. The joints and connections, including the bushings and pins, can wear out, causing the components to lose their integrity and efficiency.
   
3. Bent Components
   The boom and stick are designed to withstand considerable pressure, but in cases of misuse or accidents, these components can become bent. A bent boom or stick will negatively affect the performance of the excavator, often resulting in costly repairs or replacements.
   
4. Accidental Damage
   Accidents, such as impact with hard objects (e.g., rock, concrete, or other machinery), can result in significant damage to the boom and stick. Such damage can be immediate and severe, requiring the components to be replaced.
   
5. Corrosion
   Exposure to harsh environmental conditions, such as salty air or moisture, can lead to rust and corrosion on the boom and stick. Corrosion weakens the metal and can lead to the failure of these components.
   

Symptoms of Boom and Stick Problems
Recognizing when the boom and stick need to be replaced is crucial to maintaining the functionality and safety of the Komatsu PC 120-6. Here are some common signs that indicate a problem with these components:

• Unusual Noises: If you hear popping, cracking, or grinding sounds when operating the boom or stick, it’s a sign that there may be significant damage or wear within the components. This is often a precursor to failure.
  
• Inconsistent Movement: If the boom or stick moves erratically or doesn’t extend/retract as smoothly as it should, it may be due to bent components or worn hydraulic parts.
  
• Visible Cracks or Fractures: Inspect the boom and stick regularly for visible cracks, fractures, or bends. Any visible signs of damage should be addressed immediately.
  
• Hydraulic Leaks: Leaking hydraulic fluid around the boom or stick area can indicate problems with the seals or hydraulic components. These issues can cause the excavator to lose power or efficiency.
  
• Loss of Strength or Capacity: If the excavator is struggling to lift or dig as effectively as before, the boom and stick may have lost some of their structural integrity, affecting the overall performance of the machine.
  

Step-by-Step Process for Replacing the Boom and Stick
Replacing the boom and stick on the Komatsu PC 120-6 can be a complex task that requires the right tools and knowledge. Below is a general guide for replacing these components:

1. Prepare the Excavator
   Ensure the excavator is parked on level ground, and the engine is turned off. Use appropriate safety equipment, such as gloves and goggles. Disconnect the battery to avoid any accidental electrical issues.
   
2. Support the Boom
   Using a crane or hoist, lift the boom slightly off the machine. This will allow for easier removal of the stick and the hydraulic connections.
   
3. Remove the Hydraulic Lines
   Carefully remove the hydraulic hoses or lines connected to the boom and stick. These lines control the movement of the excavator’s arm and must be disconnected before you can remove the components. Make sure to have a catch container to collect any hydraulic fluid that may leak out.
   
4. Remove the Stick
   Unbolt the stick from the boom, taking care not to damage the pins or bushings. Depending on the wear and age of the machine, this may require some force or a hydraulic press. If the stick is bent or cracked, it will need to be replaced.
   
5. Detach the Boom
   Once the stick is removed, you can proceed to remove the boom. This usually involves removing bolts or pins that secure the boom to the rest of the machine. Use a hoist or lifting equipment to remove the boom from the machine.
   
6. Install the New Boom and Stick
   Once the old boom and stick are removed, it’s time to install the new components. Carefully lift and position the new boom and stick, ensuring that they are properly aligned with the machine.
   
7. Reattach Hydraulic Lines
   Reconnect the hydraulic lines to the new boom and stick. Make sure the connections are secure and that there are no leaks.
   
8. Test the New Components
   Once everything is reattached, conduct a thorough test to ensure that the boom and stick are functioning properly. Check for smooth movement, hydraulic pressure, and correct operation under load.
   

Choosing the Right Replacement Parts
When replacing the boom and stick on the Komatsu PC 120-6, it is essential to use high-quality, compatible parts. Some key factors to consider when selecting replacement parts include:

• OEM Parts vs. Aftermarket Parts: Original Equipment Manufacturer (OEM) parts are typically preferred because they are designed specifically for your machine. However, high-quality aftermarket parts can also be a viable option if they meet the necessary specifications.
  
• Durability: Choose parts made from durable materials that can withstand the demanding conditions in which the excavator will operate.
  
• Compatibility: Ensure that the new boom and stick are compatible with the existing hydraulic system and other components of the PC 120-6.
  
• Cost vs. Quality: While it may be tempting to go for cheaper options, investing in higher-quality parts can save money in the long run by improving the machine’s reliability and lifespan.
  

Conclusion
Replacing the boom and stick on the Komatsu PC 120-6 is a significant repair that requires careful attention to detail and proper procedures. By understanding the common causes of failure, symptoms to look out for, and following the correct steps for replacement, operators can extend the life of their machine and ensure that it continues to perform at optimal levels. Regular maintenance, proper operation, and timely repairs are key to avoiding costly breakdowns and maximizing the productivity of your excavator.