Machinery Insights: 16 Excavator Parts You Need to Know

Understanding the components of your excavator is crucial—not only for operating the machine efficiently but also for ensuring long-term maintenance and effective troubleshooting. While operators don't necessarily need the in-depth expertise of a mechanic, having a basic grasp of the machine's main parts is highly advantageous.

Despite the differences in brands and models, most excavators share a common set of core components. These are generally divided into two main sections: the upper structure and the lower structure. In this article, we’ll focus on breaking down these essential elements to help you better understand, operate, and maintain your excavator.

Lower Structure of a Track Excavator

The lower structure, also known as the undercarriage, forms the base of the excavator. It is the part that makes contact with the ground and allows the machine to move. In this section, we’ll concentrate on track excavators (also referred to as crawler excavators) and examine the five key components that make up the undercarriage:

1. Tracks and Track Pads
2. Rollers
3. Idlers
4. Sprockets
5. Swing Drive/Slewing Ring

By understanding these parts, you can better navigate the operational and maintenance aspects of your equipment, ultimately extending its life and improving performance.

1. Tracks and Track Pads
Tracks are the foundation of a crawler excavator’s mobility. Constructed from reinforced steel, they are made up of track pads or shoes, which vary in size depending on the machine’s application. The outer edges of the pads, called grousers, provide traction and help the excavator grip the ground. Track bolts hold these pads together, forming a continuous loop known as the crawler system. This system is mounted to the excavator through a track frame, functioning similarly to an axle. Within the track assembly, a track chain connects the tracks to the sprockets and idlers, ensuring coordinated movement.

2. Rollers
Rollers are durable metal wheels located on the undercarriage. Their primary job is to guide the track chain between the sprocket and idler. There are two main types: bottom rollers, which support the weight of the machine, and top rollers, which help maintain chain alignment. Some rollers are fitted with rock guards to prevent damage from debris and rough terrain.

3. Idlers
Idlers are larger than rollers and serve as crucial guiding components. Positioned at one end of the undercarriage, they work alongside rollers and sprockets to keep the tracks properly tensioned and aligned. Their strategic placement and size play a vital role in ensuring smooth, efficient track movement.

4. Sprockets
Sprockets resemble oversized bicycle gears and are responsible for driving the track chain. They engage with the chain links to move the tracks, propelling the excavator forward or in reverse. Properly maintained sprockets are essential for efficient power transfer and machine performance.

5. Swing Drive / Slewing Ring
The swing drive and slewing ring allow the upper structure of the excavator to rotate independently of the lower undercarriage. These components are driven by hydraulic motors and are vital for directional control. To ensure consistent and reliable operation, they require regular lubrication and maintenance.

Upper Structure of a Track Excavator

The upper structure—often referred to as the "house" of the excavator—is where the machine's power, control, and primary functionality are concentrated. It integrates the carbody with the boom-and-arm assembly, housing key systems for operation, hydraulics, and operator control. This section rotates on top of the lower structure, allowing full 360-degree movement.

1. Counterweight
The counterweight plays a critical role in stabilizing the excavator during operation. It prevents the machine from tipping over while digging or lifting heavy loads. The weight of the counterweight is designed in proportion to the excavator’s total operating weight. For example, a CAT 395 with a 94-ton operating weight includes a 15.5-ton counterweight, while a Komatsu PC400, weighing 43.3 tons, features a 9.2-ton counterweight.

2. Engine Compartment
More than just a space for the engine, the engine compartment houses several key components:

• Fuel Tank – Stores diesel fuel.
• Engine – Usually located near the cab for ease of maintenance, it powers the entire machine.
• Hydraulic Oil Tank – Supplies fluid necessary for the hydraulic systems.
• Main Control Valve – Connects the engine to hydraulic components and manages oil pressure distribution.

3. Cabin
The cabin is the operator’s control hub, equipped with visibility-enhancing features and safety systems. Most modern cabins rotate 360 degrees to offer maximum situational awareness. Key features include:

• Main Control Interface – Varies by model, typically includes joysticks and displays.
• ROPS (Rollover Protective Structure) – Protects the operator in case of a rollover.
• FOPS (Falling Object Protective Structure) – Shields against falling debris.

4. Boom Cylinder
This hydraulic cylinder connects the boom to the carbody and is responsible for raising and lowering the boom.

5. Boom
A critical extension that links to the cab, the boom supports the arm and facilitates vertical movement during digging.

6. Arm Cylinder
This cylinder controls the extension and retraction of the arm, connecting it to the boom.

7. Arm (Dipper or Stick)
The arm connects to the boom and holds the bucket. It plays a central role in reaching and positioning the bucket during excavation.

8. Boom/Arm Linkage
A set of pins and bushings that connect the boom to the arm. These components require regular greasing for smooth, noise-free operation.

9. Bucket Cylinder
This hydraulic cylinder controls the motion of the bucket, enabling it to dig and dump material.

10. Arm/Bucket Linkage
The joint mechanism that connects the arm to the bucket, facilitating synchronized movement.

11. Bucket
The bucket is the main working tool at the end of the arm. While standard excavators are equipped with buckets, other attachments can be installed, using the same mechanical linkage.

To enhance your understanding, we’ve created a detailed infographic showcasing all the discussed components on a medium-sized KOBELCO SK350 track excavator. This visual reference highlights both lower and upper structure elements for comprehensive learning.

FAQs About Excavator Parts

What is the most commonly replaced part of an excavator?
The most frequently replaced parts are typically the tracks and track pads. These components experience continuous wear and tear due to constant contact with the ground and the demands of movement.

How often should the hydraulic oil be changed in an excavator?
Hydraulic oil should generally be changed every 1,000 operating hours. However, it’s always best to follow the maintenance schedule recommended in the manufacturer’s manual for your specific model.

Can the bucket of an excavator be replaced with other attachments?
Yes. Excavators are designed to be versatile machines and can accommodate a range of attachments beyond the standard bucket. Common alternatives include hydraulic breakers, grapples, and augers, depending on the task.

What’s the purpose of the counterweight in an excavator?
The counterweight is essential for maintaining stability. It offsets the weight of the boom and arm during lifting and digging operations, helping to prevent the machine from tipping over.