1. Judgment and Implementation of Engine Overhaul

After an engine has been in service for a certain number of years, three typical 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 of these three signals appear, a generator engine overhaul needs to be scheduled. An overhaul is not simply replacing parts; it is a complete process. After the engine is removed from the generator set, it is completely disassembled, and all components go through a cleaning process to remove carbon deposits and sludge. The cylinder block is measured on an inspection stand for bore roundness and cylindricity. If wear exceeds limits, a cylinder boring machine is used to restore roundness, and oversized pistons are fitted. The crankshaft is measured for journal wear and straightness, reground on a crankshaft grinding machine to restore precision, and fitted with undersized bearings. Wear-prone parts such as piston rings, connecting rod bearings, main bearings, front and rear oil seals, cylinder head gaskets, intake and exhaust valves, and valve stem seals are all replaced with new ones. After assembly, the engine must undergo load testing on a dynamometer, and only when power output, fuel consumption, exhaust temperature, and smoke opacity all meet specifications can it be released. Under Hainan's bonded maintenance policy, the imported piston rings, bearings, and seals needed for generator engine overhaul can enter duty-free, and the procurement cycle is compressed from two to three months to one to two weeks.

2. Tiered Standards for Daily Repair Services

The core of diesel engine repair services is tiered maintenance based on operating hours. At 250 operating hours, change the oil, oil filter, and fuel filter, clean the air filter with low-pressure air from the inside out, and check fan belt tension. At 500 hours, in addition to first-tier maintenance, check valve clearance (standard: intake valves 0.25–0.30 mm, exhaust valves 0.30–0.35 mm); check fuel injector atomization quality—clean or replace if poor; check turbocharger impeller clearance—rotate the impeller by hand to feel for binding. At 1,000 hours, in addition to second-tier maintenance, measure cylinder compression pressure with a compression gauge (normal range: 2.5–3.0 MPa, pressure difference between cylinders not exceeding 8%); check crankshaft end play (standard: 0.10–0.30 mm); and check connecting rod bearing clearance. The essence of tiered diesel engine repair services is using small, distributed investments to avoid large, concentrated expenditures. Under Hainan's bonded maintenance policy, the imported filters and sensors needed for daily maintenance can be procured duty-free.

3. Classification and Troubleshooting of Common Faults

Diesel generator common faults mainly include five types: difficult starting, insufficient power output, unstable voltage, frequency fluctuation, and automatic shutdown. The troubleshooting sequence for difficult starting is: first, check battery voltage—12V system not below 10V, 24V system not below 20V; second, check fuel level and air ingress in fuel lines; third, check whether the preheating device is working; finally, check cylinder compression pressure. The troubleshooting sequence for insufficient power output is: first, check whether the air filter is clogged; second, check the fuel filter and fuel injectors; third, check the turbocharger; finally, check cylinder compression. The troubleshooting sequence for unstable voltage is: first, check carbon brushes and slip rings; second, test rectifier diodes; third, check the automatic voltage regulator; finally, check the stator windings. The troubleshooting sequence for frequency fluctuation points to the engine—check the governor and fuel system. The troubleshooting sequence for automatic shutdown is: check the triggering causes of protection devices, including low oil pressure, high coolant temperature, overspeed, etc. The logic of the troubleshooting sequence is from simple to complex, from high probability to low probability. Proper identification of diesel generator common faults allows for faster diagnosis and repair. Under Hainan's bonded maintenance policy, the imported rectifier diodes, AVRs, and sensors identified as needing replacement can be quickly sourced.

4. Specific Steps for Generator Troubleshooting

The most common fault in generator troubleshooting is the generator running normally but not producing voltage. The correct troubleshooting sequence is as follows. 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 without needing to disassemble the windings. Under Hainan's bonded maintenance policy, the imported carbon brushes, rectifier diodes, and AVRs identified as needing replacement can arrive quickly.

5. Data Interpretation of Performance Testing

Generator performance testing focuses on three key indicators. The first is 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. If this value is continuously decreasing, the windings are absorbing moisture or aging, and maintenance should be scheduled. The second is three-phase DC resistance. Use a bridge meter to measure the DC resistance of the three-phase windings. The deviation among the three values should not exceed 2%. An increasing deviation may indicate inter-turn short circuits or poor connections in the windings. The third is 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 automatic voltage regulator. A single test data point only indicates the current condition. Comparing multiple test data points reveals trends. Store each set of generator performance testing data and plot trend lines. If insulation resistance has been declining for three consecutive months, maintenance should be scheduled. If voltage regulation suddenly increases, the excitation system should be inspected. Under Hainan's bonded maintenance policy, the imported rectifier diodes and AVR modules identified during testing can be replaced through bonded channels.

6. Generator Refurbishment Process

Generator refurbishment is different from engine overhaul. It focuses on the comprehensive restoration of the generator's electrical parts. Refurbishment is applicable to generators where the equipment has overall aged but the base components have no structural damage. The refurbishment process includes: complete disassembly, cleaning of the stator and rotor, winding insulation testing, drying or re-impregnation of moisture-affected or aged windings, bearing replacement, excitation system repair including rectifier diode testing and AVR calibration, slip ring turning and polishing, and external surface treatment of the complete unit. After refurbishment is completed, the generator must undergo no-load and load testing on a dynamometer to confirm that voltage, frequency, insulation, and other indicators meet specifications. The cost of refurbishment is about 30–40% of a new unit, with performance restored to 80–90%. Under Hainan's bonded maintenance policy, the imported bearings, seals, rectifier diodes, and other components needed for refurbishment can enter duty-free.

7. The Bonded Maintenance Policy in the Hainan Free Trade Port

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 eliminated. 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 can now be released for other uses. 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 the traditional two to three months to one to two weeks. These three policy provisions combined result in lower maintenance costs, shorter lead times, and higher capital efficiency. Hainan Longpan Oilfield Technology Co., Ltd. is Hainan Province's first pilot enterprise for bonded maintenance outside the free trade port area and possesses this qualification.

From the judgment criteria for overhauls to the tiered execution of daily repairs, from the troubleshooting sequence for common faults to the specific steps for failure to energize, from the data interpretation of performance testing to generator refurbishment, and to the specific application of the bonded maintenance policy—each stage has its technical specifications and operating requirements. 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.

If you are seeking a more reliable solution for your diesel generator maintenance—from fault diagnosis to performance testing, from daily servicing to deep refurbishment—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.