How to Inspect Undercarriage on Used Excavators

Why Undercarriage Inspection Is Critical for a Used Excavator

The undercarriage represents up to 50% of a machine’s maintenance costs over its lifespan. On a used excavator, hidden wear or damage can lead to unexpected downtime, poor stability, and expensive repairs. A thorough inspection helps you avoid buying a machine with shortened track life, misaligned components, or structural cracks. For contractors and equipment buyers, mastering undercarriage evaluation is the key to making a profitable purchase.

Tools You Will Need Before Starting

Having the right equipment ensures accurate measurements and safety. Prepare the following items before approaching the excavator:

• Digital caliper or track pitch gauge – for measuring link wear and bushing diameter.
• Steel ruler (1m / 39 inch) or measuring tape – to check track sag and grouser height.
• Straight edge / wear gauge – for roller flange and idler wear.
• Flashlight and inspection mirror – to see seals and inner faces.
• Safety gloves, hard hat, safety shoes – the machine may be on unstable ground.
• Grease gun (if allowed) – to test track tensioner function.
• Camera & notebook – record wear measurements for comparison.

Pro tip: Always park the excavator on a flat, firm surface, lower the attachment to the ground, shut off the engine, and engage safety locks before inspection.

Step-by-Step Undercarriage Inspection Guide

Each component of the undercarriage wears at different rates and requires specific checks. Follow this systematic approach to identify hidden damage and estimate remaining life.

1. Inspect Track Links & Bushings

The track chain links and bushings experience the highest load and abrasion. Excessive “link stretch” leads to poor engagement with the sprocket and increases risk of chain breakage.

How to measure link pitch (chain stretch)

Measure the distance between four or five link pins. For standard excavator chains (e.g., 203mm pitch), stretch beyond 5% (≈213mm over 4-pin span) indicates immediate replacement needed. Use a caliper to measure bushing outer diameter—if bushing OD is worn more than 6–8mm from original spec, the chain is at end of life.

What to look for

Check for cracked or missing link plates, rust jacking (swollen links due to corrosion), and excessive pin protrusion. Any significant lateral movement between links is a red flag.

2. Examine Track Shoes (Grousers)

Track shoes provide traction and protect the chain. Worn grousers reduce digging force and increase track slippage.

Measuring grouser height

Grouser height typically starts around 25–35mm (1–1.4 inches) for medium excavators. When height drops to 40% of original (approx 10–14mm), replace shoes. Also check for bent, cracked, or missing bolts (track shoe bolts). Loose bolts cause shoe separation and accelerate component wear.

Special note for used excavators

Look for signs of asymmetric wear on outer shoe edges – this often indicates misaligned track frames or prior operation on slopes without proper maintenance.

3. Check Track Rollers & Carrier Rollers

Bottom rollers (track rollers) support the machine’s weight. Carrier (top) rollers guide the return track. Worn rollers cause vibration, poor tracking, and increase internal pin wear.

Visual & physical inspection

Inspect each roller for:

• Flange wear – sharp edges or step wear indicates replacement. Acceptable flange width reduction ≤ 3mm.
• Leaking oil seals – grease or oil around the roller suggests bearing failure.
• Flat spots or uneven rotation – spin each roller by hand (if safe). Stiffness or noise means worn bearings.
• Side wear on the roller tread – uneven contact pattern signals track misalignment or worn pivot bushings.

Replace any rollers with end play >2mm or visible metal debris near seals.

4. Inspect Sprockets and Front Idlers

The drive sprocket engages the track chain bushing; the idler maintains tension and redirects the track. Their condition directly affects travel power and chain life.

Sprocket wear indicators

Look at tooth profile: new sprockets have symmetrical, curved teeth. Wear stages: slightly hooked teeth (acceptable), sharp or “knife-edge” teeth (must replace). Measure radius reduction at tooth tip – if more than 20% worn, replace both sprockets and consider replacing the chain at the same time to avoid accelerated wear.

Idler inspection

Check idler tread for scoring, pitting, or diameter reduction (more than 10% wear requires replacement). Inspect the idler yoke and sliding frame for cracks. Also verify that the idler guard (if present) is not bent into the track.

5. Measure Track Tension & Sag

Proper track tension prevents derailment and reduces power loss. Too tight causes extra wear on sprockets, rollers and final drive; too loose leads to track throwing (derailment).

How to check sag on standard excavators

Lift the track with a blade or bucket so that the track hangs freely. Measure the distance between the bottom of the track frame and the top of the track shoe. Sag should be approximately 20–40mm (0.8–1.6 inches) for most medium-sized excavators, or as specified by manufacturer. On rubber-tracked models, follow specific tension values.

Testing the tensioner function

Locate the grease fitting on the recoil spring housing. Apply a small amount of grease (if allowed) and observe if the idler extends. If no movement or audible grease bypass, the tensioner seal is blown – a costly repair.

Caution: Do not over-grease; high pressure can cause injury. Consult operation manual for exact procedure.

6. Check Final Drive and Track Motor Seals

Final drive housings contain planetary gears. Leaks or contamination lead to catastrophic failure of travel motors and gears.

Inspection points

Check for gear oil leaks around the face seal (between sprocket and final drive). Any drip of heavy oil or visible wetness suggests seal failure. Listen for grinding or knocking when moving the track (if operable). Also check the track motor mounting bolts – loose bolts cause misalignment and sheared bolts.

For used machines without power, rotate sprocket manually (with safety lock) to detect abnormal play (backlash). Excessive backlash >15 degrees indicates internal gear wear.

Wear Limits & Replacement Benchmarks (Quick Reference)

Use this summary table as a quick field guide when evaluating a used excavator’s undercarriage remaining life. Values are typical for 15–30 ton excavators; refer to OEM specs for exact tolerances.

• Track chain stretch – max 5% over original pitch → replace chain.
• Bushing outer diameter wear – more than 7mm from original → end of life.
• Grouser height – less than 40% of original (e.g., from 30mm to ≤12mm) → replace shoes.
• Sprocket tooth wear – sharp, hooked teeth or >20% radius reduction → replace sprocket.
• Bottom roller flange wear – step wear deeper than 3mm or leakage → replace roller.
• Idler tread diameter – wear more than 10% of original diameter or visible grooving → replace idler.
• Track sag (empty condition) – 20–40mm except special applications → adjust if outside range.
• Carrier roller wear – flat spots or more than 2mm side wear → replace.

If multiple components are near their wear limits, the entire undercarriage may require overhaul. Always combine measurements for better negotiation on used equipment price.

Common Undercarriage Red Flags – What Hidden Defects Look Like

Some damage is subtle but costly. Watch for these signs when inspecting a used excavator:

• Asymmetric track wear (one side significantly more worn): Indicates track frame misalignment, bent track link, or operator abuse during counter-rotation turns.
• “Railroad track” noise when walking: Usually caused by seized track roller bearings or a kinked chain.
• Track idler not centered in the track chain: The idler guide guards are worn; the track may derail.
• Hard, cracked grease at tensioner fitting: Suggests lack of maintenance – the tensioner might be stuck.
• Oil seepage near sprocket face seal combined with track chain rust in one area: Final drive internal leakage.
• Worn track shoe bolt holes & loose shoes: Danger of shoe separation during transport.

If any of these symptoms appear, consider professional inspection or factor major repair costs into the offer.

Pro Tips for Buying a Used Excavator – Undercarriage Negotiation

Understanding undercarriage wear allows you to estimate remaining hours and cost to replace. Use these guidelines:

• Request service records: track replacement date, hours on current undercarriage, and tension adjustments.
• Measure track sag and link stretch on both left and right tracks – differences > 8% indicate poor maintenance.
• Take photos of wear measurements and share with an independent mechanic for a second opinion.
• Budget for undercarriage replacement: new chain groups cost $5,000–$15,000 depending on size. Use wear % to estimate deductions.
• If the seller refuses to let you lift the track or remove inspection covers, treat as high-risk.
• Always test drive (if possible): listen for clicking from sprockets, feel for pulsing in travel levers.

A thorough undercarriage inspection gives you powerful negotiation leverage and protects your investment.

Need Expert Advice or High-Quality Used Excavators? Contact Rich Reach

At Rich Reach, we specialize in supplying certified used excavators with transparent undercarriage inspections. Our team provides detailed wear reports, component life estimates, and genuine maintenance support. Whether you are buying your first machine or expanding your fleet, we help you avoid costly mistakes.

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Sales & General Inquiries:
sales-01@richreach.cn
amy@richreach.cn

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Address: Approx. 150m east of Baogong Ave & Dazhong Rd intersection, Longgang Comprehensive Economic Development Zone, Yaohai District, Hefei, Anhui, China (about 250m east of Poly Luolan Spring).
Our showroom offers multiple brands with fully inspected undercarriages. We welcome international buyers — export documents, shipping coordination, and warranty support provided.

Why Rich Reach? Transparent reports, competitive pricing, and after-sales assistance. Every used excavator we sell undergoes a rigorous 150-point inspection, including detailed undercarriage measurements with digital reports sent before purchase. Ask us for inspection photos and wear data.

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