1. About Refurbishment: Value Recovery of Aging Equipment
A diesel generator set that has been operating for over ten years experiences power loss, increased fuel consumption, and an aged appearance. Should it be scrapped and replaced with a new one, or should ways be found to keep it running? Generator refurbishment offers a middle path. Refurbishment is not simply external cleaning and painting; it is a comprehensive restoration of the equipment. Engine part: complete disassembly, cleaning and inspection, cylinder boring to restore roundness, crankshaft grinding to restore precision, replacement of piston rings, bearings, and gaskets. Generator part: stator and rotor cleaning, varnishing and drying, bearing replacement, excitation system repair. After complete reassembly, the unit undergoes dynamometer testing. Refurbishment costs about 30–40% of a new unit, restores performance to 80–90%, and can last for several more years. Under Hainan's bonded maintenance policy, the imported piston rings, bearings, seals, and other components needed for refurbishment can enter duty-free, and the procurement cycle is compressed from two to three months to one to two weeks.
2. About Overhaul: Timing and Methods for Deep Engine Restoration
When equipment has been in service for a certain number of years, three signals appear: oil consumption exceeding 1% of fuel consumption, significant power loss under load, and cylinder compression pressure falling below 20% of the standard value. When two appear, a generator engine overhaul should be scheduled. Overhaul is different from refurbishment—refurbishment focuses on comprehensive restoration of appearance and function, while overhaul focuses on deep restoration of engine mechanical performance. The overhaul process: the engine is removed from the set, completely disassembled, and all components go through a cleaning machine to remove carbon deposits and sludge. The cylinder block is measured for bore roundness and cylindricity; if out of tolerance, it is machined on a cylinder boring machine. The crankshaft is measured for journal wear and straightness; if out of tolerance, it is reground on a grinding machine. Piston rings, connecting rod bearings, main bearings, and all engine gaskets are replaced with new ones. After assembly, the engine undergoes load testing on a dynamometer, and only when power, fuel consumption, and exhaust temperature are acceptable can it be released. The cost of a generator engine overhaul is about 40% of a new unit, and after overhaul, it can last another five to six years.
3. About Daily Maintenance: Execution Standards for Tiered Maintenance
The core of diesel engine repair services is tiered maintenance based on operating hours. At 250 hours, change the oil, oil filter, and fuel filter, clean the air filter with low-pressure air from the inside out, and check belt tension. At 500 hours, in addition to first-tier maintenance, check valve clearance (intake valves 0.25–0.30 mm, exhaust valves 0.30–0.35 mm), check fuel injector atomization quality, and check turbocharger impeller clearance. At 1,000 hours, in addition to second-tier maintenance, measure cylinder compression pressure with a compression gauge (normal 2.5–3.0 MPa, difference between cylinders not exceeding 8%), check crankshaft end play (0.10–0.30 mm), and check connecting rod bearing clearance. The essence of tiered diesel engine repair services is using small investments to avoid large expenditures.
4. About Fault Diagnosis: Sequence for Locating Common Problems
Diesel generator common faults include difficult starting, insufficient power output, unstable voltage, frequency fluctuation, and automatic shutdown. Diagnosis must follow a fixed sequence. Difficult starting: first check battery voltage (12V system not below 10V, 24V system not below 20V), then check fuel level and air ingress in fuel lines, then check the preheating device, finally check cylinder compression. Insufficient power: first check whether the air filter is clogged, then check the fuel filter and injectors, then check the turbocharger, finally check cylinder compression. Unstable voltage: first check carbon brushes and slip rings, then test rectifier diodes, then check the AVR, finally check the windings. The logic of this sequence is from simple to complex, from high probability to low probability—most problems are found within the first few steps. Proper identification of diesel generator common faults allows for faster diagnosis and repair.
5. Detailed Fault Diagnosis: How to Check When the Generator Does Not Produce Power
The most common issue in generator troubleshooting is "it runs but does not produce power." The diagnosis sequence: Step one: open the protective cover and check the carbon brushes. Any brush shorter than 10 mm must be replaced. Also check the slip ring surface—if there is an oxide film or burn marks, polish it with fine sandpaper. These two steps resolve about 30% of faults. Step two: check residual magnetism. Self-excited generators rely on residual magnetism to establish initial voltage. After long-term shutdown, residual magnetism may disappear. Use a 12-volt battery to briefly energize the excitation winding for two to three seconds to remagnetize it. Step three: use a multimeter in diode test mode to test the rotating rectifier diodes. A normal diode conducts in one direction and blocks in the reverse. If faulty diodes are found, replace them in complete sets. Step four: check the automatic voltage regulator—check whether the fuse is blown, whether the indicator light is on, and whether the potentiometer is oxidized. Step five: only then consider the stator windings. Following this generator troubleshooting sequence, most failure-to-energize issues are resolved within the first few steps.
6. About Performance Testing: How to Interpret the Data
Generator performance testing focuses on three key indicators. Insulation resistance: use a 500-volt megohmmeter to measure stator winding-to-ground resistance. In cold condition, it should be greater than 5 MΩ; in hot condition, greater than 1 MΩ. A continuous decrease indicates winding aging. Three-phase DC resistance: use a bridge meter to measure the DC resistance of the three-phase windings. The difference among the three values should not exceed 2%. An increasing difference may indicate inter-turn short circuits or poor connections. Voltage regulation: from no load to full load applied incrementally, voltage variation should be less than ±2.5%. Exceeding this range indicates problems with the excitation system or AVR. A single test data point indicates the current condition; comparing multiple test data points reveals trends. Store each set of generator performance testing data. If insulation resistance has been declining for three consecutive months, schedule maintenance.
7. About the Policy: What Bonded Maintenance Has Brought
The core of understanding the bonded maintenance policy in the Hainan Free Trade Port consists of three provisions. First, imported maintenance components are exempt from tariffs. Previously, importing parts such as piston rings, bearings, rectifier diodes, and AVRs required tariff payments—ranging from thousands to tens of thousands—and this expense is now saved. Second, overseas equipment shipped in for repair is exempt from tariff deposits. Previously, equipment shipped in for repair required a deposit equivalent to a certain percentage of the equipment's value—tens of thousands tied up for months—and this capital is now freed up. Third, the policy is supported by an intelligent customs clearance system, with enterprise ERP systems linked to customs, automatic customs declaration for imported parts, and the procurement cycle compressed from two to three months to one to two weeks. These three changes result in lower maintenance costs, shorter lead times, and more liquid capital.
From refurbishment to overhaul, from daily maintenance to fault diagnosis, from performance testing to policy application, each stage has its technical points and operating standards. The bonded maintenance policy in China's Hainan Free Trade Port makes the imported components involved in these stages arrive faster and at lower cost. Hainan Longpan Oilfield Technology Co., Ltd. is Hainan Province's first pilot enterprise for bonded maintenance outside the free trade port area, with a technical team of over 300 members and specialized equipment including cylinder boring machines, crankshaft grinding machines, injector test stands, and load bank test systems. Its business scope covers generator refurbishment, generator engine overhaul, diesel engine repair services, generator troubleshooting, generator performance testing, and analysis of diesel generator common faults.
If you are seeking a more reliable solution for your diesel generator maintenance—from refurbishment and rebuilding to deep overhaul, from fault diagnosis to performance testing, from daily servicing to policy application—professional technical support can help you leverage the bonded maintenance policy to reduce maintenance costs, shorten equipment downtime, and ensure the long-term reliability of your equipment.