WhatsApp Online Chat !
Tel : +86 18876548025/+8613906095209
0%

Table of Contents

So, what exactly does a Hitachi EX120, EX200, EX300, or EX400 track roller do? Basically, it’s a heavy-duty undercarriage part that carries a good chunk of the excavator’s weight. It sits under the track chain and helps keep things moving smoothly over dirt, gravel, and whatever uneven mess a jobsite throws at it. Inside, you’ve got hardened steel, bearings, seals, and lubricating oil all working together under constant load. And yeah—small design differences can matter more than people think.

Lots of buyers type in “Hitachi Ex120/Ex200/Ex300/Ex400 Track Roller As” when they’re replacing worn undercarriage parts. That “AS” bit might mean an assembly or just some supplier-specific label, so don’t assume—confirm it. Model names alone won’t always guarantee a correct fit, either. Production year, track frame design, bolt spacing, roller width, flange profile, and even serial number can all affect compatibility. The reliable way to check? Compare the old roller against technical drawings and actual measured dimensions.

Keep an eye out for oil leaks, damaged seals, abnormal side play, uneven flange wear, and flat spots on the running surface. These usually show up before serious track instability starts. And don’t ignore strange noise—it’s telling you something.

From practical maintenance experience, a roller that looks clean can still have worn bearings inside. On the flip side, a little surface rust doesn’t always mean it’s about to fail. That’s where careful judgment comes in. A professional supplier should give you material info, inspection records, warranty terms, and clear installation guidance. Hitachi equipment deserves parts picked for its real working conditions, not just its model label. This guide walks through how EX120, EX200, EX300, and EX400 track rollers work, how they differ, and what to check before you buy or install.

What Is a Hitachi EX120 EX200 EX300 EX400 Track Roller?
Table of Contents [Hide]
1 Track Roller Basics: Role in a Crawler Excavator Undercarriage
2 Hitachi EX120–EX400 Models by Nominal 12-, 20-, 30- and 40-Ton Classes
3 Track Roller Construction: Shell, Shaft, Bushings, Seals and Lubricant
4 Single- and Double-Flange Rollers: How Flanges Guide the Track Chain
5 Load, Wear and Alignment Factors Affecting Track Roller Service Life
6 Track Roller Inspection: Measuring Wear, Oil Leakage and Operating Clearance
7 CAT349, CAT352 & CAT355 Excavator Track Lower Roller Assembly 399-5056 by CQCTRACK

Track Roller Basics: Role in a Crawler Excavator Undercarriage

A track roller is a steel wheel mounted beneath a crawler excavator’s track frame. It supports the machine’s weight and guides the track chain along the undercarriage. Excavators in the 120, 200, 300, and 400 size classes use rollers built for different loads and frame dimensions.

The roller shell contacts the track links while internal bearings carry rotating force. A sealed, oil-filled design helps reduce friction and protects moving parts from dust and water. During field inspections, technicians often check for oil leakage, uneven wear, cracked flanges, and unusual heat. A dry roller can still turn, but damage may already be developing.

Track rollers work under constant shock from digging, travel, and uneven ground. Poor track tension increases side loading and accelerates flange wear. Excessive tension is not safer. It can overload bearings and reduce service life. I have seen operators focus on the track chain while overlooking rollers hidden under mud. That habit can become expensive.

Clean the undercarriage regularly, especially after working in clay or crushed rock. Measure roller diameter against service limits instead of judging wear by appearance alone. Listen for grinding during slow travel. A small leak matters. Replacement quality, correct installation, and proper track adjustment all affect undercarriage reliability. Even experienced teams sometimes miss one damaged roller during a busy inspection.

Hitachi EX120–EX400 Models by Nominal 12-, 20-, 30- and 40-Ton Classes

A track roller supports an excavator’s lower frame and carries the machine’s weight across the track chain. In the EX120, EX200, EX300, and EX400 ranges, the numbers generally reflect nominal 12-, 20-, 30-, and 40-ton classes. They are useful starting points, not exact operating weights. Attachments, counterweights, boom configuration, and site equipment can change the real load.

The 12-ton class usually needs a compact roller with accurate flange spacing and strong sealing. A 20-ton machine demands greater shell thickness and dependable bearing support.

In the 30-ton class, impact resistance becomes more important, especially on rocky ground. The 40-ton class places heavier and more frequent loads on the roller assembly, so heat control, shaft hardness, and seal quality deserve close inspection.

From field maintenance experience, leakage often appears before obvious roller damage. Check for oil around the seal, uneven flange wear, rough rotation, and abnormal track noise. Measure wear instead of judging by appearance alone. Weight class helps, but mounting dimensions must match precisely. A similar-looking roller may still fail early.

Not every failure is a parts problem. Incorrect track tension, packed soil, or misalignment can destroy a sound roller. I have seen clean replacements wear quickly because installation checks were skipped. That lesson is easy to overlook. Always compare bolt pattern, width, shaft diameter, and lubrication requirements with the machine’s service data.

Track Roller Construction: Shell, Shaft, Bushings, Seals and Lubricant

A track roller supports an excavator’s lower structure while guiding the track chain across uneven ground. In EX120, EX200, EX300, and EX400 class machines, its shell carries radial load and repeated shock. The shaft stays fixed inside the roller frame, while internal bushings allow controlled rotation. Clearances matter. A few tenths of a millimeter can change oil-film strength and heat generation.

Seals protect the bushing area from clay, water, and abrasive dust. The lubricant reduces metal contact and carries heat away. ISO 281 uses a 90% reliability basis for bearing-life calculations, but field conditions are harsher than laboratory assumptions. A 2024 Off-Highway Research review reported that Asia-Pacific accounted for more than half of global construction-equipment demand, highlighting the severe duty cycles common in wet and dusty sites. Inspection should check shell scoring, shaft grooves, seal lips, and side play. Fresh lubricant is not enough. Contamination may already have damaged the bushing surface. That is easy to miss.

A practical service check is simple: lift the track safely, rotate the roller, and listen for grinding or tight spots. Measure looseness instead of judging it by hand. The exact limit depends on the roller design and service manual. Some failures begin quietly. Others appear after one long shift. A better design can still fail when installation torque, seal seating, or lubricant quantity is wrong. Scrap records and operating hours should guide replacement decisions, although many maintenance teams record too little.

What Is an Excavator Track Roller? - Track Roller Construction: Shell, Shaft, Bushings, Seals and Lubricant

Component or Data Dimension Typical Construction or Value Primary Function Practical Service Notes
Track roller assembly Sealed steel roller containing a shell, fixed shaft, internal bushings, thrust surfaces, floating seals and lubricant Supports the machine’s lower frame and guides the track chain The correct roller must match the undercarriage geometry, mounting pattern and track-chain dimensions
Roller shell Forged or machined alloy steel; commonly induction-hardened on the running surface Contacts the track links and carries radial loading Typical surface hardness is approximately 50–60 HRC, depending on steel grade and heat treatment
Roller shaft High-strength alloy steel shaft, fixed to the track frame with retaining hardware Provides the stationary support around which the roller rotates Shaft wear, scoring or looseness can cause oil leakage, abnormal noise and roller wobble
Bushings Hardened steel or wear-resistant bearing sleeves installed between the shaft and shell Reduces friction and maintains controlled radial clearance Insufficient lubrication or contaminated oil accelerates bushing wear and increases internal clearance
Thrust washers or thrust surfaces Hardened steel contact surfaces, sometimes combined with wear rings Controls lateral movement of the roller Excessive side play may indicate worn thrust parts, bent components or incorrect assembly
Floating seals Pair of hardened seal rings with elastomeric O-rings, commonly made from nitrile rubber or comparable seal material Retains lubricant and prevents entry of water, soil and abrasive particles Oil around the roller end face is a common sign of seal damage or improper seal installation
Internal lubricant Sealed oil bath, normally filled with gear or extreme-pressure lubricating oil specified for the assembly Lubricates bushings and thrust surfaces while carrying heat away from the bearing area Do not mix incompatible oils; the correct oil grade and fill quantity should follow the equipment service specification
Roller diameter Approximately 180–400 mm for many compact and medium crawler excavator applications Determines contact geometry, load capacity and track travel height The actual dimension varies with machine operating weight, track pitch and undercarriage design
Roller face width Often approximately 70–180 mm, excluding mounting and shaft features Provides the running surface for the track links Incorrect width can create track misalignment, flange interference or uneven wear
Mounting configuration Single-flange or double-flange roller; mounting may use a central shaft, bracket or frame bolts Positions the roller accurately beneath the track chain Verify bolt spacing, shaft diameter, flange arrangement and overall width before replacement
Operating load Designed for repeated radial and impact loads generated by the machine weight and ground conditions Transfers machine weight from the track frame to the track chain Rocky ground, high travel speed, overloading and poor track tension can significantly reduce service life
Inspection indicators Oil leakage, shell cracking, deep grooves, flat spots, excessive side play, noise or abnormal heat Shows potential damage to the shell, shaft, bushings, seals or lubricant system Inspect regularly, keep the undercarriage clean and maintain track tension according to the machine service manual

Note: Dimensions and material descriptions are typical engineering ranges for crawler excavator track rollers. Exact specifications vary by machine size, undercarriage design and operating conditions.

Single- and Double-Flange Rollers: How Flanges Guide the Track Chain

A track roller supports the excavator’s lower track chain and transfers machine weight to the ground. It must rotate smoothly while working through mud, gravel, and repeated shock loads. The roller’s flange design controls how the chain travels across the undercarriage.

A single-flange roller has one raised guide edge. It is commonly used where the track chain needs moderate lateral control. The flange contacts the chain sides and helps prevent excessive drift during straight travel. A double-flange roller has raised edges on both sides. It offers stronger guidance and keeps the chain more centered during turning, slope work, and uneven loading. However, more guidance does not always mean better performance. Incorrect roller placement can create unnecessary contact and accelerate wear.

Inspect the flange edges for sharp scoring, cracks, or polished areas. These marks can reveal misalignment before the problem becomes obvious. Check for oil leakage around the seals and compare roller rotation from one side to the other. A healthy roller should turn without grinding, tight spots, or unusual noise. Small differences matter.

Field inspection is not perfect. Mud can hide early damage, and a loose track may imitate a roller fault. I have seen operators replace one roller when the real issue was incorrect track tension. Service records, measured wear, and operating conditions should guide the decision. The correct single- or double-flange arrangement depends on the undercarriage layout, chain design, and manufacturer specifications.

Single- and Double-Flange Track Roller Comparison

A track roller supports the machine’s weight and uses raised flanges to help keep the track chain aligned.

A single-flange roller has one raised flange, while a double-flange roller has two. The additional flange provides guidance from both sides of the roller and can improve track-chain control. Actual undercarriage designs may combine roller types and use different arrangements depending on the machine and track-frame design.

Load, Wear and Alignment Factors Affecting Track Roller Service Life

A track roller supports the excavator’s lower frame while guiding the track chain. On EX120, EX200, EX300, and EX400 class machines, roller life depends on load, wear, and alignment. Larger machines create higher contact pressure. Heavy digging, rock, and frequent travel increase shell and flange stress.

Field maintenance reports often place undercarriage costs near 50% of total tracked-machine maintenance spending. The 2023 Off-Highway Research maintenance review also identifies abrasive soil as a major life-reduction factor. Dry sand can enter seals, while mud keeps abrasive particles against the roller face. A worn flange may then push the track sideways. Misalignment accelerates uneven wear, even when the roller still turns smoothly. That detail is easy to miss.

Tips

Check oil leakage, abnormal heat, and flange polishing during every 250-hour inspection. Measure roller diameter and flange wear against the service manual, not visual judgment alone. Keep track tension within the manufacturer’s specification. Over-tight tracks increase bearing load and power loss. Loose tracks can derail and damage adjacent components. ISO 14224 recommends recording operating hours, failure mode, and repair time. This creates useful local evidence. I have seen clean-looking rollers fail early. Inspection is never perfect. Recheck alignment after frame repairs, hard impacts, or repeated work on slopes.

Track Roller Inspection: Measuring Wear, Oil Leakage and Operating Clearance

A track roller supports the machine’s lower track chain and guides it across the ground. On crawler excavators, its condition affects travel stability, undercarriage life, and operator confidence. Inspection should begin with the machine parked on firm ground, the attachment lowered, and the track cleaned. Dirt can hide cracks, worn flanges, or a damaged seal.

Measure the roller’s tread diameter and flange profile with calipers. Compare each reading with the manufacturer’s service limit, not with appearance alone. Uneven wear often points to incorrect track tension, misalignment, or packed soil. Check for oil leakage around the end seals. A light oily film may be old residue, but fresh oil collecting beneath the roller needs attention. Wipe the area clean, run the track briefly, and inspect it again. This simple retest prevents many wrong conclusions.

Operating clearance also deserves careful measurement. Use a dial indicator to check axial movement while applying controlled side force. Excessive play may indicate worn bushings, bearings, shafts, or retaining components. The exact limit depends on the roller design and service specification. I have seen technicians replace a roller too quickly after noticing noise. Noise matters, but it can come from the track chain or a nearby roller. Temperature, load, and working surface can change the result. One reading is never the whole story. Record measurements, leakage location, operating hours, and track tension before deciding on repair.

CAT349, CAT352 & CAT355 Excavator Track Lower Roller Assembly 399-5056 by CQCTRACK

The 399-5056 excavator track lower roller assembly is designed for crawler excavators in the 349, 352, and 355 size ranges, providing stable track support and smooth movement across demanding working conditions. Manufactured through a forging process, the roller features a black surface finish and hardened working areas rated at HRC 52–60, with a hardened depth of 10–12 mm. Its robust construction is suitable for heavy-duty undercarriage applications, helping reduce wear and maintain reliable machine mobility.

With an approximate weight of 100 kg per piece, this undercarriage component is available for OEM and ODM requirements. The standard warranty is 12 months or 2,000 operating hours, whichever comes first, and production can be completed within 20 days after the contract is established. Quality management follows ISO 9001:2015 standards. FOB pricing from Xiamen Port is approximately US$25–100 per piece, with payment options including T/T, L/C, and Western Union. Video technical support and online after-sales assistance are also available for installation and service guidance.

Caterpillar CAT349 / CAT352 / CAT355 DF Excavator Track Lower Roller Assembly (P/N: 399-5056) – Specialized Manufacturer of Components for Heavy-Duty Rotary Blast-Hole Drills and Crawler Excavator Undercarriages. Manufactured by CQCTRACK

FAQS

What does a track roller do on a crawler excavator?

It supports the excavator’s weight and guides the track chain beneath the track frame. The roller shell contacts the links, while internal bearings support rotation. Small wheel, heavy duty.

Why are sealed, oil-filled track rollers important?

Sealed oil-filled rollers reduce friction and protect bearings from dust and water. A roller may still turn after losing oil. Damage could already be developing.

Which signs suggest a track roller needs inspection?

Look for oil around the seals, uneven wear, cracked flanges, rough rotation, or unusual heat. Listen for grinding during slow travel. Check carefully under the mud.

Does excavator weight determine the correct roller?

Weight class provides a useful starting point, but it does not decide everything. Attachments, counterweights, and working conditions can change actual loading. Mounting dimensions must match precisely.

What measurements should be checked before installing a replacement roller?

Compare roller width, flange spacing, shaft diameter, bolt pattern, and lubrication requirements with service data. Similar-looking parts may still fail early. Measure, do not guess.

What is the difference between single- and double-flange rollers?

A single-flange roller provides moderate lateral guidance for the track chain. A double-flange roller offers stronger centering during turns, slopes, and uneven loading. More guidance is not always better.

Can incorrect track tension damage a good roller?

Yes. Excessive tension overloads bearings, while loose tension increases side loading and flange wear. Neither setting is automatically safer. Adjustment matters.

How should track rollers be maintained in muddy or rocky conditions?

Clean the undercarriage regularly after working in clay, gravel, or crushed rock. Measure roller diameter against service limits. Inspect for packed soil, leaks, and sharp flange scoring.

Can one damaged roller be mistaken for another undercarriage problem?

Yes. Loose tension, packed soil, and misalignment can imitate roller faults. Busy inspections sometimes miss one damaged roller. Service records and measured wear can improve decisions.

How does operating ground affect roller life?

Rocky ground creates repeated impact, while slopes and turning increase lateral loading. Frequent travel also raises heat and bearing stress. Real conditions matter more than a simple size label.

Conclusion

A Hitachi Ex120/Ex200/Ex300/Ex400 Track Roller As a key undercarriage component supports the crawler excavator’s weight and helps the track chain move smoothly across different working surfaces. These rollers are commonly associated with nominal 12-, 20-, 30-, and 40-ton machine classes. Depending on the undercarriage design, a roller may use a single or double flange to guide the track chain, maintain alignment, and reduce the risk of derailment during travel and digging operations.

Typical construction includes a hardened outer shell, central shaft, bushings, seals, and internal lubricant. Service life depends on operating load, ground conditions, track tension, alignment, lubrication quality, and maintenance practices. Regular inspection should check shell wear, flange damage, abnormal clearance, oil leakage, loose movement, and uneven contact patterns. Measuring roller dimensions and operating clearance can help identify deterioration before it causes broader undercarriage damage. Replacing worn rollers at the appropriate time supports smoother travel, better track alignment, and more predictable maintenance costs.

Blog Tags:

Finn
Updated:
Finn

Finn

Finn is a dedicated marketing professional at Heli Machinery Manufacturing Co., Ltd., a company that has been a significant player in the machinery manufacturing sector since its establishment in 2000. With extensive expertise in excavators and bulldozer undercarriage parts, Finn is well-versed in......
Previous How to Choose a Quanzhou CQC Undercarriage Parts Manufacturer?