Excavators with more than 8,000 working hours are defined as high-hour equipment. After long-term high-load operation, key components such as the chassis, hydraulic system, and engine have different degrees of wear and aging, and are prone to complex failures such as walking weakness, slow movement, oil leakage, and power shortage. This professional overhaul guide aims at high-hour excavators, providing detailed diagnosis, disassembly, repair, and commissioning standards for chassis traveling devices, hydraulic systems, and engines, helping maintenance teams carry out systematic overhauls and restore equipment performance to near-new state.
The chassis traveling system is the most severely worn part of high-hour excavators, including track shoes, track chains, driving wheels, guide wheels, supporting wheels, tensioning devices, and traveling motors. After long hours of work, the track chain pin sleeve is severely worn, resulting in excessive chain pitch elongation, easy derailment, and increased walking resistance. The rolling surface of driving wheels, guide wheels, and supporting wheels is worn and grooved, resulting in poor cooperation with the track, vibration and noise during walking. The floating oil seal of supporting wheels and guide wheels is aging and invalid, resulting in oil leakage and lack of lubrication, and eventually leading to bearing burning.
The overhaul of the traveling system starts with a comprehensive inspection. Measure the elongation of the track chain. If the elongation exceeds the limit (usually more than 3% of the standard pitch), the chain must be replaced as a whole. Check the rolling circle of driving wheels and guide wheels. If the wear depth exceeds the standard, they should be replaced or repaired by surfacing welding. Check the supporting wheels one by one. If there is oil leakage, jamming, or abnormal rotation, they should be disassembled and overhauled. Replace the floating oil seal, bearing, and lubricating grease. The tensioning cylinder is prone to oil leakage and failure, resulting in loose track. The seal ring should be replaced and the performance of the tensioning spring should be checked. After the chassis components are replaced or repaired, the track tension should be adjusted to the standard sag (20-30mm) to ensure stable walking.
The traveling motor and reducer are the core power components of the chassis. High-hour traveling motors often have internal leakage, resulting in walking weakness and deviation. Test the relief valve pressure of the traveling system. If the pressure is insufficient, it indicates that the motor plunger, cylinder body, and distribution plate are worn. The traveling motor needs to be disassembled and overhauled, and worn parts such as plungers and sliding shoes should be replaced. The reducer gear pair is prone to pitting and wear, resulting in abnormal noise. Check the gear meshing clearance and bearing wear. Replace seriously worn gears and bearings, and replenish special reducer gear oil. After the overhaul, the traveling motor and reducer should be tested for no-load and load to ensure stable power output and low noise.
The hydraulic system of high-hour excavators has a high failure rate, mainly including insufficient main pump pressure, serious internal leakage of the control valve, cylinder oil leakage, and high oil temperature. The main hydraulic pump is the power source of the whole machine. After long hours of work, the plunger, cylinder body, swash plate, and distribution plate are worn, resulting in reduced volumetric efficiency and insufficient output pressure. Use a hydraulic pressure gauge to test the no-load and load pressure of the main pump. If the pressure cannot reach the standard value, the main pump must be overhauled. Disassemble the main pump, clean all parts, measure the wear size, replace the plunger, sliding shoe, distribution plate, and other wearing parts, and reassemble and debug according to the process standards. After overhaul, the main pump pressure and flow should be restored to the factory state.
The main control valve (distribution valve) is prone to spool wear and jamming, resulting in slow movement, compound action weakness, and oil leakage. Disassemble the control valve spool, check for wear, strain, and jamming. Clean the spool and valve body with professional cleaning agent. If the spool is seriously worn, it should be replaced or repaired. Check the pressure regulating spring and return spring of each spool to ensure elasticity. After assembly, test the pressure and flow of each oil circuit to ensure that the movement of boom, arm, bucket, and rotation is sensitive and coordinated.
The hydraulic cylinder includes boom cylinder, arm cylinder, bucket cylinder, and swing cylinder. High-hour cylinders often have oil leakage, slow movement, and drifting. The main reason is the wear and aging of the piston seal and guide sleeve seal. Disassemble the cylinder, replace all seal kits, dust rings, and guide sleeves. Check the surface of the piston rod for scratches and strains. Small scratches can be polished and repaired, while deep strains must be replaced, otherwise the new seal will be quickly damaged. After assembly, conduct a pressure test to ensure no internal and external leakage.
The hydraulic oil tank, radiator, and pipeline system should be thoroughly cleaned during overhaul. The hydraulic oil must be completely replaced, and all filter elements (suction filter, return filter, pilot filter) should be replaced. Check the radiator for blockage and damage, clean or replace it to ensure heat dissipation. Check all hydraulic hoses for aging, cracking, and bulging. Replace all high-hour hoses in batches to avoid sudden burst during operation.
The engine of high-hour excavators often has problems such as power attenuation, increased fuel consumption, difficult starting, overheating, and oil burning. The overhaul of the engine starts with the detection of cylinder pressure. If the cylinder pressure is insufficient, it indicates wear of piston rings, cylinder liners, and valves. Disassemble the engine, replace piston rings, cylinder liners, and valve oil seals, grind the valve and valve seat, and restore the sealing performance. Check the fuel injector and fuel pump. Clean or replace the injector, calibrate the fuel pump to ensure good atomization and correct injection time. Check the turbocharger for oil leakage and jamming, and repair or replace it if necessary. The cooling system should be thoroughly cleaned, the radiator flushed, the thermostat replaced, and the fan belt adjusted. The lubrication system should replace the oil cooler, oil filter, and engine oil to ensure smooth oil circulation. After engine overhaul, conduct idle speed, medium speed, and high-speed debugging to ensure stable operation, sufficient power, and no abnormal noise.
The electrical system of high-hour excavators is prone to aging of wiring harnesses, failure of sensors, and abnormal instrument display. Check the main wiring harness for wear and damage, replace the aging part, and fasten all connectors. Check the working status of sensors such as water temperature, oil pressure, speed, and pressure, and replace faulty sensors. Upgrade or calibrate the controller to ensure accurate signal collection and normal control logic.
After the overall overhaul of the excavator, a comprehensive test run is required. Conduct no-load test and load test for each movement, check the walking, rotation, lifting, and excavation actions, and ensure that the speed, force, and stability meet the standards. Monitor engine speed, hydraulic pressure, oil temperature, and water temperature to ensure that all parameters are within the normal range. Only after all tests are qualified can the equipment be officially put into use.
In summary, the overhaul of high-hour excavators is a systematic project involving chassis, hydraulic pressure, engine, and electrical systems. Strictly following the overhaul process and technical standards can effectively restore equipment performance, extend service life, and reduce operating costs. For engineering enterprises, scientific overhaul and maintenance of high-hour excavators are important measures to improve asset utilization and create economic benefits.
