Used Drilling Rig Inspection Checklist: 40 Checks Before You Pay

In February a drilling contractor in Kitale asked me to look at a used rig he had already paid a deposit on. Eleven hundred hours on the meter. Paint still glossy. The seller had even steam-cleaned the engine bay.

It took forty minutes to find the problem. The mast had been welded. Not at the base, where you would look, but along the side rail, halfway up. Somebody had repaired a stress crack and then sanded and repainted it. Under load that mast was going to flex where it was never designed to flex.

He got his deposit back. Most people do not.

I sell new drilling rigs for a living, so read the next few thousand words with that in mind. But I also get called in to inspect machines that customers bought somewhere else, and I have watched the same six failures repeat across water well, DTH and core rigs on three continents. This checklist is what I actually do in a seller’s yard — the order, the tools, and the numbers that make me walk away.

One note before we start. A used rig is not a used excavator. An excavator fails where you can see it: a burst hose, a cracked boom, a leaking cylinder. A drilling rig fails inside tolerances — thread profiles worn past spec, a hydraulic pump that holds pressure at idle and loses it under thrust, a rotary head gearbox with backlash you can only feel with the spindle turning. None of that shows up in a photograph, and very little of it shows up in a ten-minute walk-around.

Why Used Rigs Hide Their Wear

Three reasons, and they all matter when you are negotiating.

Hours are not work. A rig that idled at 40% of its life did more damage per running hour than the meter suggests. An engine hour counter cannot tell you whether those hours were spent turning a 4-inch bit in soft clay or hammering a 6-inch button bit through granite. Only the maintenance file, the oil analysis and the ECM data can tell you that.

Wear parts are priced like capital items. A full rod string, a rotary head gearbox, or a set of track chains can each cost a meaningful fraction of what you are paying for the machine. Sellers replace the cheap part to make the expensive part look healthy — new track on a hooked sprocket, fresh paint over a weld, a new hour meter on an old engine.

Nobody documents anything. In markets where rigs change hands between contractors, the maintenance log is often a notebook, or a WhatsApp history, or nothing. Absence of paperwork is information in itself, not a neutral gap.

Before You Book the Flight

Ask for these six items before you commit to travel. What the seller cannot or will not send tells you as much as what arrives.

Document	What you are looking for	Why it matters
Maintenance log	Filter and fluid intervals, parts replaced, dates	Handwritten is fine if it is consistent. Inconsistency means someone reconstructed it
Hour meter photo + ECM / telematics export	Actual operating hours vs indicated hours, fault history, idle ratio	Most engines built after 2013 store this. A rig that “cannot export it” is telling you something
Oil analysis report	Iron, copper, silicon, water content trend	Bearing wear and dust ingress show up here months before they show up as noise
Hydraulic pressure test sheet	Thrust, rotation and auxiliary circuits against the model’s published spec	If it does not exist, budget for two hours of dealer shop time before you buy
Title, lien and export status	Ownership, outstanding finance, customs documents	A rig with a lien is a rig you may lose after you have paid for it
Prior application, in writing	Water wells, quarry blasting, exploration, anchor work	Abusive duty cycles leave marks that a clean exterior does not reveal

If the machine is in another country, add one more: a short video of a cold start, taken before the seller knows you are serious. Cold start tells you more about an engine than a warm idle ever will.

What to Bring Into the Yard

You need less than people think, but you need it in your pocket, not in the seller’s workshop.

• Dial calipers, for rod outside diameter and pin dimensions
• A thread profile gauge matched to the thread form on the rig (API REG, IF, metric trapezoidal, or the rope thread used on wireline rods)
• A strong flashlight, ideally with a side emitter
• A small magnet, for finding body filler over welds
• A camera phone with storage space, and the discipline to photograph every defect with the hour meter visible in at least one frame
• A notebook, because you will forget the third defect by the time you reach the sixth

Two hours of inspection, done in a fixed order, beats a whole day of poking around at random. The forty checks below run from the structure outward, because a bent mast makes every downstream measurement meaningless.

Structure, Mast and Frame

Start at the back of the machine and sight down the full length of the mast. It should look straight as a rifle barrel, from both front and rear. Any bow, twist or kink means the rig took an overload event, and a mast that is out of line will eat the wear pads, the slide rails and the rotary head carriage for the rest of its life.

Then walk every weld you can reach. Pay particular attention to the mast root, the outrigger or jackleg mounts, the crown block area, and the joint where the mast attaches to the chassis. Stress cracks radiate outward from the weld toe, so look at the parent metal next to the weld, not just the bead itself. A grinder mark that runs across a weld, followed by fresh paint, is a repair someone hoped you would not notice.

Run the magnet over suspect panels. Body filler over a welded rail is common, and filler will not hold a magnet the way steel does.

Pins, bushes and slides

Grab the mast and try to rock it with the machine off. You are looking for play at the pivot pins. A little is normal on a machine with real hours; a visible clunk means the bushings are gone and the pin holes may already be oval. Oval pin holes are a machining job, not a part swap, and they are one of the quiet reasons a “cheap” rig becomes expensive.

Check the wear pads or slide blocks on the rotary head carriage. If the pads are down to the backing plate, the carriage has been running metal on metal and the rail itself may be scored.

Rotary Head, Top Drive and Gearbox

The rotary head is where a used rig’s price is decided. Rebuild costs here are in the same order of magnitude as a set of tracks, and the failure is usually invisible from outside.

With the engine off, grab the spindle or the chuck and try to move it radially. Any perceptible movement is bearing wear. Then check the chuck or the rod clamp jaws: worn jaws slip, and a slipping chuck rounds off rod shoulders and chews through the wrench flats.

Ask to run the head at low speed and listen. A whine that rises with speed, a knock once per revolution, or a vibration that comes and goes with load all point at gear or bearing damage. Look under the head for oil staining — a gearbox that has been “topped up regularly” is a gearbox with a seal problem.

On a wireline or core rig, add the wireline swivel and the head’s hollow spindle. Check that the wire passes freely, that the swivel seals, and that the water swivel does not leak at pressure. A leaking water swivel looks trivial until you are losing flush pressure at 300 m.

Hydraulics: Where the Surprise Costs Live

Hydraulic faults are the most expensive category on a used rig, and the hardest to see. A pump that holds pressure at idle can cavitate or fall off under sustained thrust. You will not find that in a walk-around — you find it in a load test, or you find it three weeks after you have paid.

Start with the fluid. Pull the dipstick or sight glass. Amber and clear is healthy. Dark or black means oxidation and heat. Milky means water, and water means contaminated bearings somewhere downstream. Look at the bottom of the tank if there is a drain — a white emulsion layer there never fully cleans out.

Check	Accept	Walk away or renegotiate
Fluid colour and smell	Amber, no burnt smell	Black, varnish smell, or milky emulsion
Hose condition	Supple, no cracking, factory crimps	Brittle, bulging, or field-repaired with clamps — hoses have a service life of roughly five to seven years regardless of hours
Filter bypass indicator	Not tripped	Tripped: the system has been running unfiltered fluid through every component
Pressure under sustained load	Holds within a few percent of spec for a full minute of thrust	Falls away after 20–30 seconds, or recovers only when you release the lever
Pump noise under load	Steady, no whine change	Rising whine or cavitation rattle as load increases
Cylinder rods	Clean chrome, no pitting	Scored or pitted chrome: seals will keep failing

If the seller has no pressure test results, pay a dealer to run them. Two hours of shop rate is a rounding error against a pump and motor rebuild, and an independent number changes the negotiation more than any argument you can make on the spot.

Engine and Power Pack

Insist on a cold start. Arrive early, before the seller has had a chance to warm the machine. Listen for the first thirty seconds with the throttle at idle: knock, rattle, or persistent blue smoke at cold start is disqualifying on its own, no further inspection needed.

Then work through the boring items. Coolant should be clean, not rust-brown. The air filter restriction indicator should not be red. Check the date written on the fuel and air filters — undated filters, or filters older than the service interval, tell you about the maintenance culture better than any conversation. Look at the oil on the dipstick: grey or milky means coolant is getting in.

With the engine warm and under load, watch the exhaust. Blue is burning oil. Black is over-fuelling or overload. White that persists after warm-up is coolant. None of those are acceptable on a machine you are about to buy.

On a Tier 4 or Stage V machine, verify that the aftertreatment system is intact and functional, and that the DEF system has not been disabled. Emissions tampering is a regulatory liability that transfers to you, and it is usually a sign the engine was run hard by someone who did not want to pay for upkeep.

Wireline Winch, Rope and Brakes

On a core rig the winch is a safety item, not a convenience. Inspect the rope along its full length: broken outer wires clustered in one lay, kinks, bird-caging, or flat spots from sheave wear. A rope with more than a handful of broken wires in a single lay, or any sign of core protrusion, is scrap — and a seller who lets a rope get to that state has probably let other things slide.

Check the sheave grooves. A worn groove pinches the rope and accelerates both rope and sheave wear. Then test the brake: with the rope unloaded, raise and hold a load, then release the control and confirm the brake holds without creep. A winch brake that creeps is the kind of defect that hurts people, not budgets.

Rod String and Threads

Rods are a wear item priced like a capital item. A full string for a mid-size rig is a five-figure replacement in most markets, and worn threads fail underground where the recovery cost is measured in days.

Measure the outside diameter with calipers at several points along each rod, and compare against the manufacturer’s spec for that rod size — our drill rod sizes and thread types guide lists the common diameters and thread forms if you need a reference. Then check the pin threads with a profile gauge, holding it against the thread and looking for light between gauge and thread. Light means worn. Sharp or rounded thread crests both mean replacement, and thread crests rounded over are the failure mode that quietly destroys a whole string.

Roll each rod on a flat surface. A slight wobble is a bend; a pronounced wobble is a reject. Then look at the couplings and subs. Coupling sleeves wear on the thread flanks, seize from galling, or erode internally from abrasive flush — all three are common on a rig that drilled in sand. Count the rods and get the count written into the bill of sale, because “a full rack” means different things to different sellers.

If the rig comes with a hammer and bits, inspect the hammer’s wear limits rather than its paint: piston and cylinder bore scoring, bit shank spline wear, and the condition of the check valve. Our DTH rig maintenance checklist covers the wear points in the order they fail. A hammer that needs a piston and cylinder is a four-figure repair before it drills a metre.

Mud Pump and Air Package

If the rig comes with a mud pump, run it against a known volume. Fill a marked tank and time it. Flow below the published figure for that liner size means worn pistons, worn liners, or leaking valves — and everything inside the pump except the crank is a wear part. Pop the valve covers if the seller will let you: valve seats with grooves cut into them will never hold pressure properly again.

On a DTH package, the compressor deserves its own inspection. Check for oil carry-over in the discharge — an oily film on the separator outlet means the separator element is past its life and the downstream hammer has been running on dirty air. Run the machine up to working pressure and confirm it holds. A screw compressor that will not reach rated pressure is usually a separator, a control valve, or an airend problem, and only one of those three is cheap.

If you are buying a rig and a compressor together, read the compressor’s rating the way a driller reads it — working pressure and free air delivery at that pressure, not the headline CFM on the badge. Our guide to portable air compressors for drilling rigs explains why those two numbers diverge in the field.

Undercarriage and Travel

Tracks and tyres tell you how the machine was treated. On a crawler, measure cleat or bar height against a new one, check rollers and idlers for seal leaks, and look at the drive sprocket teeth. Hook-shaped or pointed teeth mean the sprocket is finished. If the seller has fitted new track on a worn sprocket, the new track will be chewed to match within a season.

Check track tension. If the adjuster is already fully extended, the chain has stretched to the end of its life and replacement is due regardless of how the pads look. On a truck-mounted rig, inspect the chassis mounting, the subframe welds, and the condition of the outrigger beams — a rig that has travelled thousands of kilometres on bad roads shows it at the mounting points long before it shows it in the hydraulics.

The Thirty-Minute Live Test

A walk-around finds maybe half the problems. The rest come out when the machine works. Run this sequence in order, and do not let the seller shorten it.

1. Cold start and idle. Ten minutes at idle. Listen, watch the exhaust, check for leaks appearing as the oil warms.
2. Mast raise and lower. Full cycle twice. Watch for hesitation, listen for the relief valve, check that the mast locks mechanically as well as hydraulically.
3. Outriggers or jacks. Set them on firm ground and hold the machine’s weight. Any creep in a cylinder shows up here.
4. Rotation, no load. Low, then high. Listen for the knock or whine that only appears at speed.
5. Rotation under load. If the seller has a test piece or a length of pipe, put torque through the head and watch the pressure gauge. This is the single most informative two minutes of the inspection.
6. Feed and retract under load. Hold thrust for a full minute and watch whether pressure holds. A pump that fades here is a pump you will replace.
7. Winch. Raise and hold, then check brake creep with the load suspended.
8. Mud pump or compressor. Run at working pressure for five minutes and check for leaks, oil carry-over, and pressure stability.
9. Travel. Drive forward and back, turn both directions, and listen to the final drives. A rig that pulls to one side has a track or final drive problem.
10. Shutdown. Switch off and watch for twenty minutes. Hot leaks that only appear after shutdown are the ones nobody demonstrates.

Photograph the hour meter at the start and at the end of the test. It is a small thing, but it closes the door on “the test was short because the machine was already warm”.

Red Flags That End the Inspection

Some defects are negotiable. These are not, at least not without a professional rebuild quote in hand before you pay.

• A repaired mast or boom. A cracked structural member that has been welded in the field is a fatigue question you cannot answer from the outside.
• Missing or disabled ECM data on a modern engine. No history means no way to verify hours, faults or duty cycle.
• Emissions system deleted. Regulatory liability, and a reliable indicator of maintenance culture.
• Milky hydraulic fluid. Water has already travelled through the pumps, motors and valves. Flushing does not undo the wear.
• A pump that holds pressure at idle and loses it under load. The most common expensive surprise on a used rig.
• No title, no lien release, or a seller who is not the registered owner. Everything else is secondary to actually owning the machine.
• A seller who will not allow an independent inspection. There is no benign explanation for this one.

What a Defect Is Actually Worth

Do not negotiate on feelings. Convert each defect into a number, then subtract it.

A hydraulic pump or motor rebuild typically lands around half the price of a new unit, and on a mid-size rig that is already a serious figure. A rotary head gearbox rebuild is in the same bracket. Track chains, a full rod string, or a hammer piston and cylinder set are each priced like a component, not a consumable. Write the quotes down, add a contingency for the things you will only find after the first fifty hours, and make the offer against that total rather than against the asking price.

One practical rule I use: if the estimated repair bill plus the purchase price exceeds roughly two thirds of what a comparable new rig would cost landed in your country, the used machine is not the cheaper option. It is just a smaller payment now.

New or Used: The Honest Math

Used makes sense when the machine is simple, the duty is light, and you can inspect it properly. If you are pricing a replacement, a crawler water well rig like the WD-W260 and a full hydraulic DTH rig such as the ZJ516 are the two classes most often compared against second-hand machines in this size bracket. It makes less sense when the rig is your only production unit and a gearbox failure stops a contract.

If you are weighing the two, our truck-mounted water well rig buying guide covers the new-versus-used decision alongside the chassis and depth questions, and the core drilling rig for sale guide sets out what actually drives price in the exploration segment. For a straight read on what a new machine costs at each tier, the DTH drilling rig price breakdown separates split, integrated and crawler configurations — and explains why the compressor and tooling often decide the total more than the rig itself.

What new buys you is not paint. It is a documented test sheet, a warranty with a named party behind it, and a spare parts channel that answers within a day. The same logic applies to the tooling: a drilling tools and consumables supplier who can ship a hammer, a set of bits and a rod string together is worth more than a rig priced a few thousand dollars lower. If none of those three matter to your operation, a well-inspected used rig can be the better commercial decision. If all three matter, they are what you are paying for.

Questions I Get Asked in the Yard

How many hours is too many on a used drilling rig?

There is no single number, and anyone who gives you one is guessing. A 6,000-hour rig maintained on schedule with clean oil analysis is a better buy than a 2,000-hour rig that ran dry once. Judge by the maintenance record, the oil analysis trend, and the load test — in that order. Hours are a tiebreaker, not a verdict.

Should I pay for a third-party inspection?

Yes, if you cannot run the load test yourself and the machine costs more than a few months of your revenue. A dealer inspection with pressure readings against spec is worth more than any amount of haggling, because it converts opinion into numbers both sides can argue about.

Is a used rig from China worth considering?

The country of origin matters less than the documentation and the parts channel. What matters is whether you can get a test sheet, a real warranty, and consumables — bits, rods, seals, filters — without waiting three months. Our guide to buying a drilling rig from China covers the mistakes that actually cost money, most of which are contractual rather than mechanical.

What should I check first if I only have an hour?

Mast straightness and welds, hydraulic fluid condition, and one minute of thrust under load. Those three checks catch the majority of the expensive failures. Everything else can wait for the second visit.

Does a repainted rig mean anything?

Only that somebody cared about the sale. Judge paint as a mask, not as evidence: a magnet over the mast rails and a flashlight along the weld toes will tell you whether the repaint is hiding a repair. Fresh paint on a machine with an untouched undercarriage is usually cosmetic. Fresh paint on one rail, and only one, is not.

If you want a second opinion on a specific machine, send me the photographs — mast root, rotary head, hydraulic tank, hour meter and the rod pins — and I will tell you what I would check next. That costs nothing and has saved a few deposits.