This article introduces the excavator undercarriage, including the names and functions of its various parts, to give you a basic understanding of excavator undercarriage components.
Every excavator has the same basic structure, and many parts have similar names, which can easily cause confusion. Today, let me explain them clearly.
A typical excavator undercarriage system mainly consists of the following components:
- Track Chain
- Drive Sprocket
- Idler
- Bottom Rollers
- Carrier Rollers
- Track Adjuster
- Final Drive
- Track Shoes
- Track Guides
Through this modular assembly, all components are combined to form a complete excavator undercarriage system. Any worn component can be replaced individually, significantly reducing maintenance costs.
Understanding the function, structure, and wear characteristics of each component helps equipment users select the correct parts, reduce abnormal wear, and lower routine maintenance costs.
1. Excavator Undercarriage Frame
The excavator undercarriage frame is the main structural framework of the undercarriage. It provides support and connection, and all the excavator undercarriage parts introduced below are mounted on this frame. It provides a stable mounting base for the track system while bearing the machine’s weight, travel impacts, and the various loads generated during operation.
2. Track Chain and Link
The track chain serves as the excavator’s wheels. It consists of multiple track links connected by pins and bushings. It engages with the drive sprocket and converts the power transmitted by the final drive into track movement.
The track chain must support the full weight of the excavator, withstand travel tension and impact loads generated during operation, and drive the track shoes forward.
Its main components include:
- Track Link: Forms the main structure of the track chain.
- Track Pin: Connects adjacent links and allows the chain to bend flexibly.
- Track Bushing: Installed around the pin and engages with the teeth of the drive sprocket.
- Seals: In sealed and lubricated track chains, they retain the internal lubricant and reduce the entry of external contaminants.
3. Drive Sprocket
The drive sprocket is installed at the drive end of the track system and engages with the bushings on the track chain. The better the quality of the sprocket, the more precisely it matches the track chain.
After the power output by the travel motor passes through the final drive, which reduces speed and increases torque, it is transmitted to the drive sprocket, allowing the sprocket to drive the track chain in a continuous loop.
The tooth profile and pitch of the sprocket must match the track chain; otherwise, problems such as abnormal wear and tooth skipping may occur.
Generally, a heavier sprocket costs more, lasts longer, and is also preferred by customers.
4. Idler
This is the idler, also known as the guide wheel. It is usually installed at the front of the track frame and is mainly responsible for guiding the track chain so that it circulates in the correct direction.
At the same time, the idler works with the track adjuster to help maintain proper track tension and reduce problems caused by tracks that are too loose or too tight.
Note that the idler does not provide the power that drives the excavator forward. The sprocket is the component that transmits the power for forward travel.
5. Bottom Rollers
As the name suggests, bottom rollers are installed beneath the track frame and are important components that directly support the full weight of the excavator.
The machine’s weight is transferred through the track frame to the bottom rollers, then from the rollers to the track chain and track shoes, and is finally distributed over the ground.
Bottom rollers must withstand substantial vertical loads while also adapting to the impacts and friction caused by complex terrain.
6. Carrier Rollers
Carrier rollers are usually installed above the track frame and are mainly used to support the upper return section of the track chain.
They reduce excessive sagging of the track chain caused by its own weight and help the track maintain a stable running path, allowing the entire track to complete its continuous cycle more effectively.
7. Track Adjuster
The track adjuster is used to regulate track tension. During excavator operation, prolonged use causes the track chain to wear and become loose. This affects efficient track operation and increases track wear.
This is where the track adjuster comes into play: it can regulate the tension of the track during operation.
It usually consists of a tensioning cylinder, piston, spring assembly, and related connecting structures. Track tension can be adjusted by changing the position of the idler.
Proper track tension helps reduce abnormal wear among the chain, sprocket, and idler.
Its main components include:
- Track Adjuster Cylinder
- Piston
- Recoil Spring
- Grease Chamber
- Adjuster Components
8. Travel Motor
Function: The travel motor is a hydraulic motor that transmits engine power to the travel system of the undercarriage. Its primary function is to convert the high-pressure oil supplied by the hydraulic system into rotational power.
Simply put, it:
- Receives high-pressure hydraulic oil delivered by the hydraulic pump.
- Uses hydraulic pressure to drive rotation inside the motor.
- Outputs rotational power to operate the final drive.
 | The excavator’s travel motor and travel gearbox are the core components of its travel system. They are normally combined into one assembly and installed on both sides at the rear of the tracked undercarriage. |
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9. Final Drive
Final Drive is commonly translated as the travel reduction gearbox and is also frequently called the final transmission.
Its primary function is to convert the high-speed rotational motion output by the travel motor into low-speed, high-torque rotational motion, thereby driving the excavator tracks.
The final drive generally uses an internal planetary gear transmission structure, mainly consisting of components such as the sun gear, planetary gears, planet carrier, and ring gear.
10. Track Guides and Guards
Track guides are installed on the track frame. Their main purpose is to restrict lateral movement of the track chain and help the track remain on the correct running path.
When an excavator operates on uneven ground, slopes, or in complex construction environments, the tracks may be subjected to lateral impacts.
Without appropriate guiding and protective structures, the track chain may shift sideways and, in severe cases, even derail.
Common types of track guards include:
- Center Track Guides
- Full-Length Track Guards
- Segment Track Guards
Different types of track guards have different mounting positions and ranges of protection and should be selected according to the machine’s design.
11. Track Shoes
Track shoes are installed on the outside of the track chain and secured with track bolts.
They are important components through which the excavator contacts the ground. Their main purposes are to support the machine’s weight, distribute ground pressure, and provide the necessary traction.
The width and structure of the track shoes affect the machine’s performance on different types of terrain.
Track Shoe Width
Track shoe width is an important parameter to consider when selecting track shoes.
In general:
Wider track shoes:
- Increase the contact area between the tracks and the ground.
- Help reduce ground pressure.
- Are more suitable for soft soil and muddy ground.
However, excessively wide track shoes may increase the load on the track system and be subjected to greater bending and lateral impacts on hard or rocky ground.
Narrower track shoes:
- Have a relatively smaller ground-contact area.
- Usually have a more compact structure.
- Offer better adaptability on certain hard surfaces and under complex operating conditions.
The actual selection should take the machine’s weight, undercarriage structure, and working environment into comprehensive consideration.
12. Rubber Tracks and Rubber Pads
On some compact excavators and in special working environments, rubber tracks and rubber track pads are also common ground-contact components.
Rubber Tracks
Rubber tracks are generally made of rubber, reinforcing fibers, and an internal metal structure.
Compared with conventional steel tracks, rubber tracks have the following characteristics:
- They cause less damage to hard surfaces such as concrete and asphalt.
- They produce relatively less noise during travel.
- They are well suited to certain urban construction environments.
However, rubber tracks are not suitable for all operating conditions. Sharp rocks, metal fragments, and severely abrasive surfaces may accelerate damage to the rubber material.
Rubber Track Pads
Rubber track pads are generally installed on the surfaces of steel track shoes, providing conventional steel tracks with an additional rubber ground-contact layer.
Their main functions include:
- Protecting concrete and asphalt surfaces.
- Reducing direct friction between the tracks and hard surfaces.
- Lowering noise while the machine is traveling.
- Reducing ground damage in certain working environments.
Common installation methods include bolt-on mounting and other dedicated connection structures.
13. Hardware, and Why the Grade Matters
In addition to large undercarriage components, various fasteners are also indispensable parts of an excavator undercarriage system.
They connect the track shoes, drive sprocket, and other undercarriage components, ensuring that the entire system remains stable under high loads and continuous vibration.
13.1 Track Bolts
Track bolts are used to secure the track shoes to the track links.
Because the tracks must withstand continuous tension, impacts, and vibration during operation, track bolts must have sufficient strength and reliable fastening performance.
13.2 Sprocket Bolts
 | Sprocket bolts are used to secure the drive sprocket to the relevant mounting structure. |
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13.3 Roller Bolts
Roller bolts are mainly used to secure the bottom rollers to the track frame.
Because the bottom rollers continuously support the machine’s weight, the reliability of the bolted connection is very important.
13.4 Why Bolt Strength Matters
Undercarriage fasteners must withstand loads of different directions and magnitudes according to the machine’s design.
When selecting bolts, pay particular attention to:
- Bolt Diameter
- Thread Pitch
- Bolt Length
- Strength Grade
- Material
- Heat Treatment
For example, a bolt’s strength grade affects its tensile strength and yield performance.
If bolts with insufficient strength are used, they may stretch and deform, suffer thread damage, or even break.
However, a higher strength grade is not always better. The bolts must also meet the dimensions, material, and connection requirements specified by the original equipment manufacturer.
During installation, the bolts should also be tightened to the torque specified by the manufacturer to avoid overtightening or undertightening.
14. Get Professional Support for Your Excavator Undercarriage Parts
Whether you need a track chain, drive sprocket, idler, bottom roller, carrier roller, or another undercarriage component, accurately identifying the required part is the first step toward ensuring that the replacement is reliable and suitable.
Our team will help you identify the appropriate replacement components and provide detailed product information based on your requirements.
Contact Lichen in Jiangxi today. Once you learn more about us, you will recognize our expertise, our outstanding factory, and our comprehensive sourcing channels.