This is the sequence our engineers actually work through before we put money on a second-hand set. It is written down here in full because a buyer who runs these checks is a better customer than one who does not — the deals that sour in this market are the ones where nobody looked past the paint.
TL;DR
- Start with the papers, not the machine. Nameplate year and consent status can end the conversation before you spend a day on site
- The hour meter is a claim, not a fact, until it reconciles with a service log
- Buy the alternator as carefully as the engine — a rewind is a large bill and it does not announce itself
- Never buy without an on-load test. A set that starts beautifully and cannot hold rated load is a common and expensive trap
- Bring this list. If the seller resists any of it, that is information too
Before you travel: three things that can end it on the phone
1. Year of engine manufacture, from the nameplate. Ask for a legible photograph of the engine nameplate, not the canopy sticker and not the invoice. If the engine was made and installed before 1 July 2004, stop — those engines are to be scrapped rather than resold, and the reasoning is set out in can you legally buy and install a used DG set.
2. Where it is going to run. Maharashtra, Karnataka and Delhi-NCR each attach obligations to an in-use set that most of India does not. A set that is a bargain in one state is a retrofit bill in another.
3. Whether the paperwork exists at all. Original invoice, current consent to operate, RECD certificate if one is fitted, and the service history. A seller who has none of these is not necessarily hiding anything — but you are buying an unknown machine, and the price should say so.
On site: the engine
4. Reconcile the hour meter against the log book. The reading alone means little. Compare it with service records, and with the wear you can see — a set claiming 3,000 hours with a polished-smooth throttle linkage and a heavily worn seat is telling you two different stories. Meters do get replaced legitimately; when that has happened, the seller should be able to say when and at what reading.
5. Cold-start it yourself. Insist on a genuine cold start rather than arriving to find the set warm. How it starts from cold tells you about compression, battery, fuel system and glow arrangement in one event — and a set that has been “warmed up for you” has had a problem hidden.
6. Compression across cylinders. What matters is less the absolute figure than the spread between cylinders: an even set of readings on a tired engine is a better buy than an uneven set on a low-hours one. A large outlier points at rings, a valve, or worse.
7. Blow-by at the breather. With the engine at temperature and on load, look at the crankcase breather. Heavy, pulsing blow-by is worn rings or bores, and that is a top-overhaul conversation at minimum. This is the single check most casual buyers skip.
8. Oil and coolant, looked at properly. Oil that is milky means water. Coolant with an oil sheen means the same problem from the other side. Both are head-gasket or liner territory. If the seller changed the oil the morning you arrived, note that and weight everything else accordingly.
9. Exhaust colour under load, not at idle. Idle tells you very little. Under load, persistent blue is oil, persistent black is fuelling or air starvation, and white after warm-up is unburnt fuel or water.
10. A borescope through the injector ports, if the deal is large enough. On a 500 kVA-plus purchase this is cheap insurance: it shows bore glaze and scoring directly rather than by inference. We do this before we buy anything at the top of the range.
On site: the alternator
11. Make, frame and serial — recorded, not glanced at. The alternator is a third or more of what you are buying and it is the part buyers under-inspect.
12. Insulation resistance, by megger. This is the number that predicts an expensive future. A low reading on a set that has stood in a damp yard may recover with drying out; a low reading on a set in regular use is a different and worse signal. What the readings mean, and what a rewind actually involves, is set out in alternator and stator rewinding.
13. AVR behaviour. Watch voltage as load is applied and removed. Slow recovery, hunting, or a voltage that will not hold is an AVR or excitation problem — sometimes cheap, sometimes not.
14. Bearing noise and end-float. Listen at speed and check for play. Bearings are a routine replacement; a bearing that has already run rough may have taken the rotor with it.
On site: everything around the engine
15. Control panel and its readouts. Confirm the controller model, that the display is intact, and that AMF and any sync function actually work rather than merely being fitted. Panel faults are common on stored sets and are worth real money to correct.
16. Radiator and cooling pack. Look for blocked fins, past leak repairs and fan condition. Overheating is what turns a used-set bargain into a rebuild.
17. Canopy, base frame and fuel tank. Rust at the base frame and around the tank is the structural version of the same story. On an acoustic set, check the internal foam has not degraded into dust — that is both an acoustic and a fire consideration.
18. Fuel system. Water in the tank, contaminated filters, and the condition of the lift pump and injectors. Injector work is a known and bounded cost, and it is far better to price it now than discover it later.
The test that decides it
19. Run it on load, at rated kVA, for long enough to matter. Not a five-minute idle. A load bank, or a genuine site load, held long enough for temperatures to stabilise — watching voltage, frequency, temperature and exhaust throughout. Plenty of sets start well and cannot hold rated load; there is no substitute for this check and no honest seller should refuse it.
We do not sell a used set until it has passed an on-load test at our own workshop, and the report goes with the machine.
The India-specific items, which no imported checklist covers
20. The emission stage the engine was certified to at manufacture — a fact about the engine, not a claim about the paperwork.
21. Whether an RECD is fitted, as a separate question. A retrofit device is not a CPCB IV+ certification and must never be described as one.
22. Whether the destination site can actually get consent — stack height for the new building, acoustic conditions, and the Electrical Inspectorate approval. Consents do not transfer with the machine.
If you would rather not do this yourself
We inspect used sets for buyers as a paid job, and we run the same list whether we are buying the machine ourselves or checking one you found elsewhere. The report tells you what we found, including when the finding is that you should walk away — ask us to inspect one. If you are on the other side of the deal, the same checks are what set the number when we value a set you want to sell.