A generator overhaul restores compression, oil control and power output when wear reaches measured limits for ageing diesel sets.
Quick Answer
Engine rebuild intervals for a major job are usually around 10,000 to 12,000 hours of operation.
Top-level work covers the cylinder head, valves and injectors. A full rebuild adds pistons, rings, liners and bearings.
Rising oil consumption, blue smoke and falling compression are warning signs.
A major overhaul takes 5 to 10 working days once parts are on site.
Parts availability, not labour, largely decides the final cost in Nigeria.
What is generator overhaul?
A generator overhaul is a scheduled rebuild that replaces worn internal components to restore engine performance.
Scope is graded: top overhaul for upper engine; major overhaul for rotating assembly and bearings.
Fuel polishing: intervals, figures and costs
Compare overhaul scope by level below.
| Overhaul level | Typical hour trigger | What is replaced |
|---|---|---|
| Top overhaul | 6,000 to 8,000 hours | Head gasket, valve seals, injectors, thermostat |
| Major overhaul | 10,000 to 12,000 hours | Pistons, rings, liners, bearings, seals |
| Injector service | 2,000 hours | Nozzles, copper washers, fuel lines |
| Cylinder head work | 8,000 hours | Valves, guides, seats, springs |
| Turbocharger service | 10,000 hours | Cartridge, seals, wastegate |
What does generator overhaul cost cost in Nigeria?
Top overhaul on a 100 kVA set typically costs ₦900,000 to ₦1,600,000 in Nigeria.
Major overhaul on the same set usually lands between ₦2,500,000 and ₦4,500,000.
Turbocharger and injector work adds ₦400,000 to ₦900,000 depending on parts.
On-site is often cheaper for small sets than workshop transport.
How is generator overhaul carried out?
- Record hours, compression and oil consumption before work starts.
- Take an oil sample for wear metals and agree the scope in writing.
- Strip, measure bores, journals and guides against service limits.
- Replace agreed parts, reassemble to torque specs and run load test.
- Change oil and filters at first 50 hours and issue full report.
Sources
https://www.nerc.gov.ng, https://nemsa.gov.ng, https://www.perkins.com, https://www.cummins.com, https://www.mtu-solutions.com
Top vs major overhaul
Top touches upper engine only.
Major goes to pistons, rings, liners and bearings.
Choice must follow measurements.
Mismatched scope wastes money or invites early failure.
Warning signs
Rising oil consumption and blue smoke indicate wear.
Falling compression and metal in oil confirm it.
Don't rebuild on guesswork.
Get compression and oil analysis first.
Parts matter
Insist on part numbers and category for critical parts.
Cheap bearings or gaskets often cost more later.
Mix wisely and document every substitution.
Related guides from this series
- Switchgear maintenance schedule
- Diesel generator load bank testing
- Generator compression test in Nigeria
About the author
Written by the Illuminate Engineering technical team. We overhaul and commission diesel generators across Nigeria and test every rebuild under load.
Frequently Asked Questions
How much does a generator overhaul cost in Nigeria?
About ₦900,000 to ₦1,600,000 for top and ₦2,500,000 to ₦4,500,000 for major on a 100 kVA set.
When does a generator need an overhaul?
Around 10,000 to 12,000 hours, or earlier if wear is measured.
How long does it take?
5 to 10 working days once parts are on site.
Conclusion
Plan the overhaul on hours and measurements. Specify the level, name the parts, and prove the result under load.