The Used Excavator Inspection Checklist, Component by Component

A hydraulic excavator is a simple idea built from expensive parts. A diesel engine turns one or more hydraulic pumps; the pumps push oil through a main control valve to cylinders that move the boom, stick and bucket, and to motors that swing the house and drive the tracks. Everything that wears in that chain is either visible, measurable or audible if you know where to stand. This guide is organised the way a good inspector walks a machine, from the ground up, and ends with a checklist you can print.

It applies to crawler excavators from compact units to 40-ton class machines: a Bobcat E40, a Caterpillar 320 or 336, a Komatsu PC210, a Deere 210G. The examples use Caterpillar models because they are the most common on the U.S. used market and because the dealer we profiled listed a 2019 Cat 320 and a 2023 Cat 336.

Before you travel

Ask the seller for five things by email: the full serial number with a photograph of the plate, the current hour reading with a photograph of the monitor, any service records and oil sample reports, the machine’s previous owner type, and a short video of a cold start. A seller who supplies all five has nothing to hide about the basics. Run the serial number through a franchised dealer for the brand, and search for liens under the seller’s legal name, as described in our buying guide.

Bring a tape measure, a straight edge, a flashlight, a rag, a notebook, a camera, and if you can, an undercarriage wear gauge or a set of calipers. Wear boots. Arrange for the machine to be cold when you arrive, and say so explicitly; a machine that has been warmed up “to be ready for you” has already failed one test.

The walk-around and structure

Stand back first. Does the machine sit level? Are both tracks tensioned the same? Is the paint original, or is there fresh paint on one component, which usually means a repair? Then walk the machine clockwise and look at every structural member for cracks, plating and weld repairs: the boom foot, the boom-to-stick joint, the stick tip, the bucket linkage, the car body where the track frames attach, the counterweight mounts and the cab mounts. Weld repairs are not automatically disqualifying; a professional repair with gussets and a documented history is acceptable on an older machine. Cracks radiating from a previous repair are not.

Check the cab’s protective structures. The rollover and falling-object protection should be intact and undamaged, with no cracks at the mounts. Look at the door, glass, mirrors, steps and handrails, both as safety items and as indicators of how the machine was treated.

Undercarriage

The undercarriage is typically the largest single repair cost on a tracked excavator, and the one most often misrepresented. “Tracks are good” means nothing. The components wear together and must be measured separately: track chain (pitch extension and bushing diameter), track shoes (grouser height), rollers (tread diameter), idlers (tread diameter), sprockets (tooth profile) and the track adjuster. Manufacturers publish new and 100-percent-worn dimensions for every model; Caterpillar dealers offer a measured inspection under the Custom Track Service name and will give you a wear percentage per component.

If you cannot measure, you can still look. Sharp, pointed sprocket teeth are worn. Rollers with flat spots or leaking seals are worn. Bushings that have been turned once show a different wear face. Track links with pin bosses worn thin, or chain that sags excessively between rollers at correct tension, are worn. Compare the two sides; uneven wear points to a machine that worked slopes or turned on one track constantly. Ask directly whether the undercarriage has been replaced or turned, and when.

Swing bearing and slew drive

The slewing ring between the undercarriage and the upper structure is a large bearing that carries the whole house, and replacing it is a major job. With the bucket resting lightly on the ground and the machine stable, have an operator rock the house slowly while you watch and listen at the bearing joint. Clunking, visible vertical movement or grinding is bad news. Look at the grease: the bearing should be greased regularly, and old, dry or metallic grease at the seals is a sign of neglect. Then swing the house slowly through 360 degrees in both directions, listening for noise in the swing motor and gearbox and checking that the swing brake holds on a slope.

Boom, stick and bucket pins

Pins and bushings wear from the bucket back. Play at the bucket-to-link pins is normal wear and cheap to fix. Play at the stick-to-boom pin is more expensive, and play at the boom foot pins is expensive and often a sign of a machine that was worked hard with a hammer. To check, have the operator curl and uncurl the bucket against light ground resistance while you watch each joint for movement, then place the bucket flat and lift the front of the machine slightly to load the boom foot. Lubrication tells a story: dry pins, missing grease zerks and sheared grease lines mean the previous owner skipped the daily routine.

Check the bucket, quick coupler and thumb separately. Coupler wedges, locking pins and hydraulic coupler hoses must work and lock positively; a coupler that does not lock is a dropped-bucket incident waiting to happen. Measure cutting edge and tooth wear, and look at the bucket’s side cutters and wear plates.

Hydraulic system

Open the pump compartment with the engine off and look for leaks, fresh paint, mismatched hoses and tool marks on pump fittings. Then start the machine and let it warm up. Work every function to full stroke and hold it against the relief: boom up, stick in, bucket curl, swing. Listen to the pumps; a healthy system whines evenly, while cavitation sounds harsh and a failing pump often screams at relief. Cycle times tell you about pump output: a Cat 320 should raise its boom, swing 180 degrees and dump within the manufacturer’s published cycle, and a machine that is visibly slow or that stalls two functions when operated together has low flow somewhere.

Do a drift test. Fill the bucket, raise the boom and curl the stick in, shut the engine off and watch for five to ten minutes. Boom drop, stick drift or bucket uncurl indicates cylinder seal leakage or a worn main control valve. Then inspect every cylinder rod for pitting, scoring and bent sections, and every rod seal for weeping. Look at the hydraulic oil in the tank sight glass: milky oil has water in it, dark oil is overdue, and metallic sheen is a reason to walk away or to demand an oil analysis.

Auxiliary circuits matter more than they used to. A thumb, a coupler, a hammer or a tiltrotator each has lines, valves and controls that must work. Check the auxiliary flow and pressure settings on the monitor against what the attachments need.

Engine and cooling

Cold-start it yourself. Watch the exhaust: a puff of blue on a cold start is normal on an older engine, but persistent blue smoke is oil consumption, white smoke that does not clear is fuel or coolant, and black smoke under load is fuelling or air restriction. Note how quickly oil pressure comes up. Pull the dipstick and check the oil for level, colour and smell; pull the coolant cap only when cold and look for oil film. Remove the oil filler cap with the engine running and feel for blow-by; a little vapour is normal, a steady plume is worn rings or liners.

Modern engines in Tier 4 Final machines, which is anything sold new in the United States since roughly 2014 in these sizes, carry diesel particulate filters and often selective catalytic reduction with diesel exhaust fluid. Ask about regeneration history, check the DEF tank and header for crystallisation, and have the fault code history read. Emissions system repairs are expensive and the components are not optional.

Check the cooling package: radiator, oil cooler and charge air cooler fins should be clean and straight, and the fan belt and tensioner in good order. Run the machine under load long enough to see the temperature stabilise. An excavator that overheats in a Florida summer is not a negotiating point; it is a machine that cannot work.

Cab, electronics and hours

Sit in the seat. Every monitor function, camera, light, wiper, air conditioner and heater should work. Scroll through the monitor’s fault code history; on Caterpillar machines the active and logged codes are a few menu levels down, and a dealer technician with a service laptop can pull a full history including engine hours recorded by the electronic control module. Compare those hours to the hour meter and to the physical evidence: pedal and joystick wear, seat condition, floor mat, door hinges. A monitor showing 4,000 hours in a cab that looks like 12,000 is a machine that has had a monitor or a meter replaced, and you should ask why.

Grade control systems, if fitted, are valuable and fragile. Check that the sensors, the display and the receivers are present and that the system powers up and shows the machine body correctly. The dealer listing for the 2023 Cat 336 in our profile, for instance, advertises grade control and a 360-degree camera system; both should be demonstrated, not described.

The working test

Finally, dig. Trench for twenty minutes in whatever material the yard has, load a pile, travel forward and back on both tracks, climb a ramp if there is one, and swing loaded. You are listening for noise, watching the temperature, and feeling for weak functions. Then park it, shut it down, and walk around it again looking for new drips. If the dealer does not have room to do this, or will not allow it, factor that into your price and your confidence. The dealer in our profile states that its lot has space for cold starts, test drives and load tests; that is the right answer, and it should be taken up.

Printable checklist

Take this to the yard. Tick each item and write a number or a word beside it; a completed checklist with photographs is also the document you will want if there is a dispute later.