Machinery Insights: 16 Excavator Parts You Need to Know

7 March, 2024
By Waddah Taweel
Machinery Insights: 16 Excavator Parts You Need to Know

Knowing your excavator's parts is essential, not just for operation but for long-term maintenance and troubleshooting. As an operator, you might not need the detailed knowledge of a mechanic, but a basic understanding of the machine's components is beneficial. Excavators, though varied in makes and models, share many common parts. These can be broadly categorized into two main sections: the upper structure and the lower structure. In this article, we'll break down these essential components, providing you with the insights needed to navigate and maintain your excavator effectively.

Lower Structure of a Track Excavator

The lower structure, or the undercarriage, is the foundational section of an excavator. It's the part that makes contact with the ground and enables movement. We'll focus on track excavators, also known as crawler excavators, and explore the five key elements that make up the undercarriage: tracks and track pads, rollers, idlers, sprockets, and the swing drive/slewing ring.

An Al Marwan Kobelco SK220 on a job site
A view of the Kobelco SK220 crawler excavator's lower structure in action on a job site

1. Tracks and Track Pads

The tracks are the backbone of a crawler excavator's mobility. Made of reinforced steel, they consist of track pads or shoes, which vary in size. The outer edges, known as grousers, help the excavator grip the ground during movement. Track bolts link these plates together, forming the entire crawler system. This system is anchored to the excavator through a track frame, similar to an axle. Inside the crawlers, a track chain connects them to the sprocket and idler, ensuring consistent movement.

2. Rollers

Rollers are metal wheels located on the undercarriage, responsible for guiding the chains between the sprocket and idler. There are two types: bottom and top rollers, each playing a crucial role in chain alignment. Some rollers are equipped with rock guards to protect against debris and rocks.

3. Idlers

Idlers are larger than rollers and serve as major guiding wheels within the undercarriage. They work in tandem with rollers and sprockets to maintain the smooth operation of the tracks. Their size and placement are key to the efficient movement of the excavator.

4. Sprockets

Sprockets, akin to giant bicycle sprockets, engage with the excavator track chain links. Their primary function is to move the chain, propelling the machine forward or backward.

5. Swing Drive/Slewing Ring

The swing drive and slewing ring are crucial for the excavator's rotational movement. They enable the upper structure to pivot relative to the lower structure. These components are hydraulically operated and require regular greasing for smooth operation.

Upper Structure of a Track Excavator

The upper structure, or the "house" of the excavator, combines the carbody with the boom-and-arm mechanism, forming the core of the excavator's functionality. We will explore 11 key components that make up this upper structure, moving from rear to front.

Al Marwan Kobelco SK220 on a construction site
A view of the Kobelco SK220 track excavator's upper structure in action on a job site

1. Counterweight

The counterweight is vital for maintaining balance during operation. It prevents the excavator from tipping over when digging. The weight of the counterweight is proportional to the excavator's operating weight. For instance, a CAT 395 excavator with a 94-ton operating weight has a 15.5-ton counterweight. Similarly, a Komatsu PC400 excavator, weighing 43.3 tons, includes a 9.2-ton counterweight.

2. Engine Compartment

More than just housing the engine, this compartment is a hub for several crucial components:

  • The fuel tank stores the diesel fuel.

  • The engine, typically near the cab for easy maintenance access, is the excavator's powerhouse.

  • The hydraulic fluid or oil tank, essential for the hydraulic mechanisms.

  • The main control valve, connecting the engine to hydraulic devices, controlling oil pressure.

3. Cabin

The cabin is the control center of the excavator, equipped with essential controls and safety features. Depending on the model, cabs can rotate 360 degrees for maximum visibility. The cabin includes:

  • Main control mechanisms vary by model.

  • ROPS (Rollover Protective Structure) for safety in rollovers.

  • FOPS (Falling Object Protective Structure), a reinforced steel structure protecting against falling debris.

4. Boom Cylinder

This component connects the boom to the carbody and controls the boom's vertical movement.

5. Boom

The boom is the forward extension attached to the cab that supports the arm. It's a pivotal part of the digging mechanism.

6. Arm Cylinder

Linking the arm to the boom, the arm cylinder facilitates the arm's extension and retraction.

7. Arm (Dipper or Stick)

The arm, or dipper, connects to the boom and carries the bucket. It's a key component in positioning the bucket for excavation.

8. Boom/Arm Linkage

This linkage, consisting of pins and bushings, connects the boom and arm. Regular greasing is essential for smooth and squeak-free operation.

9. Bucket Cylinder

Connecting the arm to the bucket, this cylinder allows the bucket to perform digging and dumping actions.

10. Arm/Bucket Linkage

This is the joint mechanism that connects the arm and bucket.

11. Bucket

The bucket is the primary earthmoving component at the end of the arm. Standard excavators come with buckets, but even with different attachments, the basic mechanism remains consistent.

To further enhance your understanding of an excavator's anatomy, we've created a detailed infographic. This visual guide neatly outlines all the components we've discussed, both in the lower and upper structures of a medium KOBELCO SK350 track excavator.

Excavator parts infographic - Kobelco SK350
Excavator components: lower and upper structures of a medium KOBELCO SK350 track excavator

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, due to their constant contact with the ground and the wear and tear from movement.

How often should the hydraulic oil be changed in an excavator?

Hydraulic oil should generally be changed every 1000 operating hours, but always refer to the manufacturer's guidelines for the specific model you're using.

Can the bucket of an excavator be replaced with other attachments?

Yes, excavators are designed to accommodate various attachments besides buckets, such as breakers, grapples, and augers, depending on the job requirement.

What's the purpose of the counterweight in an excavator?

The counterweight is crucial for maintaining balance. It counterbalances the weight during digging and prevents the excavator from tipping over.