How to Inspect a Used Excavator Before Buying: Undercarriage, Hydraulics, Engine and Cab — A Complete Checklist

When you buy a used excavator, the brand badge and year on the plate tell you less than the condition of the steel, oil and bearings underneath. Learning how to inspect a used excavator — systematically, component by component — is the single most valuable skill an international buyer can develop. This guide walks you through every major system, gives you measurable wear thresholds, and ends with a used excavator inspection checklist you can print and bring to the yard.

Before you arrive: documentation and hour meter verification

Inspection starts before you touch the machine. Ask the seller for service records, oil analysis reports, and the original paint code or factory delivery documents. Records showing regular oil changes, filter replacements and undercarriage adjustments are worth more than a low hour reading.

Hour meter tampering is real in the used machinery market and not always obvious. Look for scratches around the bezel, mismatched screws, or a flickering display. More importantly, cross-check hours against physical wear: a machine showing 3,000 hours with worn-through track pads, a polished seat and cracked joystick boots has likely seen far more work. We cover this in our guide to machine year and hours verification.

How to inspect a used excavator undercarriage: the single biggest cost factor

On a crawler excavator, the undercarriage accounts for 20 to 30 percent of the machine’s total lifetime maintenance cost. A full undercarriage replacement on a 20-ton excavator — track chains, rollers, idlers, sprockets and shoes — costs USD 8,000 to 15,000 in the Chinese aftermarket, and more with OEM parts, so measure excavator undercarriage wear precisely rather than guess.

Track chain and link wear

The most accurate measurement is track pitch elongation. Measure the centre-to-centre distance across five or ten consecutive links and compare it to the manufacturer’s new-link specification. Per typical manufacturer guidelines, pitch elongation of up to 3 percent is serviceable; beyond 3 percent, the chain is at end-of-life and will accelerate sprocket and roller wear. Some inspection firms flag 5 to 7 percent as "plan for replacement soon" and over 7 percent as "replace immediately."

Also measure track link height (the rail height that runs on the rollers). When link height drops by roughly 20 to 25 percent from new specification, the link loses strength and may crack. Track shoe grouser height is simpler: new pads are typically 20 to 25 mm tall; replace when worn below 10 to 15 mm, as traction and slope stability degrade quickly beyond that point.

Rollers, idlers, sprockets and tension

Inspect bottom rollers for flat spots — run a hand along the tread; a healthy roller is round. Look for oil seepage at the roller end seals; a light film is common, but active dripping means a failed seal. Check the idler for cracks and excessive side play. On the sprocket, look for hooked or pointed teeth rather than the original rounded profile. On level ground, measure track sag between the top rollers and carrier roller — a typical guideline is 20 to 30 mm, varying by model. Finally, inspect the track frame for cracks, bends or repaired welds.

Hydraulic system: pumps, valves and cylinders

The hydraulic system is the heart of an excavator, and hidden internal wear can cost more than visible exterior damage. An excavator hydraulic system check starts with a visual walk-around: inspect every cylinder rod for scoring, pitting or chrome peeling. Even a single deep scratch on a boom cylinder rod will destroy the rod seal and contaminate the oil.

Look for leaks at hose fittings, valve bank connections and the main pump. Seeping — a light oil film that does not drip — is common on older machines and usually acceptable; active dripping indicates a more serious problem. Check the hydraulic tank: oil should be clear amber. Dark, burnt-smelling oil means the system has overheated; a milky appearance means water contamination, and metallic particles on the tank magnet mean internal pump or motor damage. While the engine runs, listen to the main pump — a healthy pump makes a steady, low whine, while a high-pitched whine or rattling indicates wear or cavitation. For context on condition grading, see our four-level delivery condition standards.

How to perform a drift test

The drift test reveals internal seal leakage you cannot see. With the engine at idle, raise the boom to full height, curl the bucket fully in, and extend the stick. Shut the engine off and leave controls in neutral. Watch the boom, stick and bucket for five minutes. Per typical Caterpillar specs for a 20-ton class machine, acceptable drift is approximately 6 mm for the boom cylinder and 10 mm for stick and bucket cylinders (empty bucket); service limits run higher — roughly 11 mm for boom and 30 mm for stick. If the boom drops several centimetres in five minutes, the piston seals are bypassing and the cylinder needs a reseal, typically USD 500 to 3,000 per cylinder.

Engine: start-up, smoke and sound

Insist on a cold start — a pre-warmed engine can hide starting problems and smoke. A healthy diesel fires within a few seconds, settles into a smooth idle, and produces little visible exhaust after the initial puff. Extended cranking, rough idle, or stalling when cold points to glow plug, injector or fuel system issues.

Exhaust smoke colour is diagnostic:

• Blue smoke — the engine is burning oil. Causes include worn piston rings, hardened valve stem seals, or a failed turbo seal. A brief puff on start-up that clears is often valve guide seepage; continuous blue smoke under load is serious.
• Black smoke — incomplete combustion from too much fuel or too little air. Check for a clogged air filter first, then suspect injector wear, turbo boost leak, or fuel pump over-fuelling. Mild, brief black smoke under load is common on older Tier 3 machines.
• White smoke — can be harmless condensation on a cold morning that dissipates as the engine warms. Persistent white smoke, especially sweet-smelling, indicates coolant entering the combustion chamber — a blown head gasket, cracked head, or liner seal failure. One of the most expensive engine repairs.

With the engine idling, open the oil filler cap. Some blow-by vapour is normal; heavy smoke or pressure pushing out indicates worn rings and cylinder liners. Check the dipstick — a milky, frothy appearance means coolant contamination. Inspect belts for cracking, hoses for bulges, and the radiator for bent fins or corrosion. An oil analysis report (particle count, wear metals, viscosity) is the best indicator of internal engine health if available.

Swing system and final drives

The swing bearing (slew ring) is one of the most expensive components to replace — the entire upper structure must be lifted off. To check play, mount a dial indicator on the track frame with the plunger touching the upper carriage, lift the boom and press the bucket down to tilt the machine. Typical acceptable axial play is 1.5 to 3.0 mm depending on machine size; beyond that suggests race wear. Without a dial indicator, use a pry bar between the frames and feel for rocking. Swing slowly through 360 degrees in both directions, listening for grinding, clicking or rhythmic popping — signs of damaged bearing balls or a worn ring gear. Check the grease seal gap: grease should purge evenly; localised purging or oil mixed with grease indicates seal failure. Test the swing brake by stopping mid-rotation — the machine should stop promptly without coasting.

For the final drives (travel motors), inspect behind each sprocket for leaks. Dripping gear oil means the floating face seal has failed; running a drive dry will destroy it within minutes. Check gear oil condition — metal particles on the drain plug magnet indicate internal gear or bearing damage. While driving, listen for grinding or clunking, and compare left and right performance; a weaker side suggests internal leakage through the travel motor.

Cab, controls and electrical

The cab tells you how the machine was treated. Turn the ignition key to the on position (without starting) and watch the dashboard. Every warning light — engine oil, coolant, alternator, hydraulic oil temperature — should illuminate and then go out once the engine starts. A light that stays on, or one that never illuminates (possibly disconnected to hide a fault), needs investigation.

Test gauges against known values: coolant temperature should rise to the normal operating range (typically 85 to 95 degrees Celsius) and stay steady. Check the AC — it should blow cold within a minute on a warm day. Test the heater, wipers, work lights, headlight, beacon and horn. Joystick boots should be intact — torn boots let dust into the pilot valves. Check the seat for structural integrity, the glass for vision-obscuring cracks, and door latches.

Structural integrity: boom, stick, bucket and frame

Structural failures are rare but catastrophic when they occur. Inspect the boom and stick along every weld seam — look for cracks starting at weld toes, especially at the boom foot pivot, the boom-stick joint, and the stick-bucket joint. A repaired crack may be hidden under fresh paint; run your hand along welds to feel for uneven grinding or filler. Pay attention to the boom’s underside, where tensile stress concentrates during digging.

Check pin and bushing play at every joint: boom foot, boom-to-stick, stick-to-bucket, and bucket linkage. With the bucket on the ground, try to move the stick sideways by hand or with a pry bar. Excessive play means worn pins and bushings, causing inaccurate digging and accelerated structural stress. Inspect the bucket: cutting edge should have measurable thickness (replace when worn to half or less), side cutters intact, teeth securely mounted. Check the bucket linkage (H-link or power-latch) for cracks or play, and inspect the main frame and counterweight for cracks, bends, or impact repair.

Test drive: what to do in 15 minutes

No inspection is complete without operating the machine under load. Knowing how to inspect a used excavator means watching it work, not just looking at it parked. Find a clear, level area and set aside 15 minutes:

1. Warm-up (3 min) — Start cold, idle, then run at medium throttle until coolant and hydraulic oil reach operating temperature. Note any unusual noises that appear or disappear.
2. Dig cycle (3 min) — Dig into a pile of soil or gravel with a full bucket. The machine should dig smoothly without stalling, and the engine should maintain RPM. Listen for metallic clunks from the boom, squealing from the pump, or grinding from the swing.
3. Swing test (2 min) — With a full bucket at mid-height, swing 90 degrees left and right repeatedly. The swing should be smooth with no hesitation. Test the swing brake by releasing the lever mid-swing.
4. Track test (3 min) — Drive forward and backward in a straight line, then pivot-turn in both directions. The machine should track straight without pulling. Clunking or grinding from a final drive during a pivot turn is an early warning sign.
5. Lift and hold (2 min) — Raise the boom to full height with a loaded bucket and hold for two minutes. This is a live drift test under load. Note any settling. Test the auxiliary hydraulic circuit if equipped.
6. Shutdown (2 min) — Reduce to idle, run for one minute, then shut off. Check for new leaks that appeared under load, and listen for unusual sounds as components depressurise.

Popular 20-ton machines like the Caterpillar 320D, Komatsu PC200 and SANY SY215C respond well to this test sequence, though cycle times and drift tolerances vary by model.

Used excavator inspection checklist: print and bring to the yard

Print this checklist and bring it to the yard. Mark each item Pass, Fail or Monitor, and note the measurement.

1. Hour meter — reading matches wear patterns, no tampering signs. Pass: consistent with physical condition.
2. Service records — available, show regular oil/filter changes. Pass: records present.
3. Track pitch elongation — measured across 5-10 links. Pass: under 3% per manufacturer spec.
4. Track link and shoe wear — link height above 75% of new, grouser height above 10-15 mm. Pass: both within spec.
5. Rollers and idlers — no flat spots, active leaks, or excessive play. Pass: smooth, dry, firm.
6. Sprocket teeth — rounded profile, not hooked. Pass: original profile visible.
7. Track tension — measured sag. Pass: 20-30 mm (model-specific).
8. Cylinder rods — boom, stick, bucket. Pass: smooth chrome, no scoring.
9. Hydraulic drift test — 5-minute hold, engine off. Pass: boom ~10 mm, stick/bucket ~30 mm max.
10. Hydraulic oil condition — clear amber, no particles or burnt smell. Pass: clean, no contamination.
11. Main pump noise — steady whine, no knocking or high whine. Pass: smooth and consistent.
12. Cold start — fires within seconds, smooth idle. Pass: quick start, stable idle.
13. Exhaust smoke — no continuous blue/black/white after warm-up. Pass: clear or light grey only.
14. Engine blow-by — oil cap check at idle. Pass: light vapour only, no pressure.
15. Swing bearing and operation — play under 1.5-3.0 mm, smooth rotation, brake holds. Pass: quiet, no excessive play.
16. Final drives — no gear oil leaks, no grinding, equal power. Pass: dry, quiet, straight tracking.
17. Boom/stick/frame welds — no cracks or hidden repairs. Pass: intact welds, no grinding evidence.
18. Cab and electrical — all gauges/lights/AC work, no disconnected warnings. Pass: fully functional.

Any item marked Fail should be priced into your offer or used as a negotiation point. For deal-breaking warning signs beyond wear — fraud or catastrophic damage — read our companion guide on 10 red flags when buying used machinery.

What we recommend at Asure

A self-inspection or a local technician’s walk-around is valuable, but nothing replaces a written, signed third-party inspection report received before you pay the balance. When buying used excavator from China, this is especially important because you may not be able to visit the yard. At Asure, every machine goes through our 29-point inspection — a fixed standard of 29 checkpoints across 8 categories, with every item marked Normal or Abnormal and signed by the inspecting technician. Any item marked Abnormal is rectified and re-inspected before release. Read the full methodology in our article explaining the 29-point inspection in detail.

If you cannot travel to China, we also offer live remote video inspections — a technician walks the machine with a camera while you direct what to look at, in real time. Request a written report or live video inspection for any machine you are considering, and use the checklist above to verify what you are shown.

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Wear thresholds and drift tolerances quoted here are typical per manufacturer guidelines and vary by brand, model year, machine size and configuration (Tier 3 vs Tier 4, standard vs long carriage). Always consult the specific service manual for the machine you are inspecting. Repair cost ranges are indicative for the Chinese aftermarket as of 2026 and exclude shipping, duties and labour in the buyer’s country. Sources: Caterpillar service manuals (hydraulic cylinder drift specifications), HeavyDutyYard undercarriage cost guide, BAS World used excavator inspection points, and industry inspection practice.