Maintenance of Used Construction Machinery
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After a period of service, machinery such as excavators and loaders often suffers from problems including reduced sensitivity of control mechanisms and slow operation of working mechanisms.
1. Problems
(1) The engine shows abnormal exhaust emissions, operation and noise, with difficult starting and slow acceleration.
(2) The hydraulic oil is contaminated; there is serious internal and external leakage in hydraulic components, pipelines and joints; hydraulic cylinders fail to hold position and retract automatically.
(3) The transmission linkages of various control levers become loose, causing resistance and heavy operation.
2. Causes
(1) Mainly long-term overloading and operation in unsuitable environments.
(2) Inadequate routine maintenance, and failure to meet standards in overhaul, medium repair and minor repair.
3. Measures
(1) Strictly manage and continuously improve the technical competence of operators to ensure proper use of construction machinery.
(2) Strengthen daily maintenance and inspection to improve equipment availability.
(3) Improve the technical level and sense of responsibility of maintenance personnel to ensure the quality of major, medium and minor repairs. Appropriately increase special maintenance equipment, tools, instruments and technical data.
(4) Adjust and repair the machinery as needed.
4. Adjustment and Repair Methods
(1) Engine Throttle Adjustment
For example, diesel engines installed on truck cranes may show slow acceleration, failure to reach maximum speed or rated power when operating the on-board throttle after long-term use. In such cases, inspect and adjust the entire transmission linkage of the on-board foot throttle. This work requires two people: one operating the throttle pedal in the upper cab, and the other observing the movement of the speed control lever at the fuel injection pump.
On older cranes, even when the operator fully depresses the throttle pedal, the speed control lever of the diesel fuel injection pump may still not reach its limit position. This is often due to excessive accumulated backlash in the throttle transmission dimensional chain, or loose fasteners such as set screws. The transmission chain should be checked step by step to ensure that when the throttle is fully depressed, the speed control lever also reaches its limit. The free travel in the throttle linkage must be adjusted and secured according to equipment specifications.
(2) Gear Pump Repair
Wear mainly occurs on the inner surface of the pump housing, gear tips and gear thickness.
Repair methods:
- Brush-plate a layer of metal coating on the worn inner surface of the pump housing to restore original dimensions.
- Electroplate the gear tips and thickness to recover their dimensions.
- Bushings are generally replaced rather than repaired; ensure correct axial length with no end clearance.
Measure multiple used pumps of the same model, reassemble less-worn gears and housings, and test on a test bench.
(3) Piston Pump Repair
Wear mainly occurs on piston surfaces and rotor bores matching the pistons.
Manufacture new pistons according to the measured worn bore dimensions, complying with material, heat treatment, outer diameter and surface roughness requirements. Lap new pistons into the bores before assembly. Alternatively, match less-worn pistons and rotors from used pumps of the same model.
Normally, the clearance between used pistons and bores should not exceed 35μm; scrap when wear reaches 45μm.
(4) Control Valve Repair
Manufacture new valve stems according to the worn stem bore dimensions, meeting requirements for material, heat treatment, dimensions and surface roughness. Lap new stems into the valve body bores before assembly. Check the elasticity of positioning springs and return springs in pressure adjustment devices to ensure compliance.
Valves can be matched and swapped among multiple used units of the same type based on wear severity. After repair, test on a test bench, or perform a leakage test by filling the valve with kerosene and timing the leakage rate to evaluate sealing performance.
(5) Hydraulic Cylinder Repair
Internal and external leakage is caused by:
- Severe wear or scoring on piston rod surfaces: repairable via electroplating or brush plating.
- Worn inner surfaces of guide sleeves: usually replaced due to low cost.
- Severe wear, scoring or cavitation on cylinder bores: repairable by brush plating.
- Worn piston seals: replace directly.
Leakage causes automatic retraction. Three inspection methods for vehicle-mounted cylinders:
- Use a dial indicator mounted on the piston rod to measure retraction within 15 minutes after engine shutdown.
- Attach a paper strip to the rod with grease and measure distance changes.
- Clamp a rubber plate on the rod and measure similarly.
These methods help determine internal leakage severity. Short service life indicates seal damage from improper assembly, helping to correct assembly practices.
(6) Clean Hydraulic System and Filter Oil
Hydraulic oil contamination causes about 80% of construction machinery failures. Regularly inspect oil and filter it through a 120-mesh screen if conditions are limited. Clean the oil tank and full hydraulic system periodically, or change the oil at scheduled intervals.
(7) Adjust and Repair Operating and Control Devices
Inspect and tighten loose levers, adjust or replace severely worn parts, and repair or replace electrical switches and buttons to ensure proper contact and function.
CN Used Machinery buyer update
After a period of service, machinery such as excavators and loaders often suffers from problems including reduced sensitivity of control mechanisms and slow operation of working mechanisms. 1. Problems (1) The engine shows abnormal exhaust emissions, operation and noise, with difficult starting and slow acceleration. (2) The hydraulic oil is contaminated; there is serious internal and external leakage in hydraulic components, pipelines and joints; hydraulic cylinders fail to hold position and.
This update adds practical context for overseas buyers who use industry news to compare excavators, loaders, road machines, trucks, and other construction equipment before purchase.
Key Takeaways
- Use this topic to compare machine demand, brand positioning, and likely resale interest before choosing equipment.
- When a model or market trend looks attractive, confirm real stock condition, photos, working video, service access, and export documents.
- Do not rely only on a model name. Check configuration, year, hours, engine, hydraulics, tires or undercarriage, and destination shipping cost.
How Buyers Can Use This Information
For procurement decisions, connect this article with actual equipment inspection. A market trend can help narrow the brand or machine type, but the final decision should be based on verified machine condition, application fit, spare parts availability, and total landed cost.
Inspection Questions
- Which model, serial number, configuration, and condition photos are available?
- Can the supplier provide a working video and loading photos before shipment?
- Are export documents, shipping route, and destination port requirements confirmed?
- Does the machine match the buyer's actual project: road work, earthmoving, quarry, logistics, or rental use?
FAQ
Does this article replace machine inspection?
No. It should support research, but buyers should still confirm the exact machine condition before payment.
Can CN Used Machinery help verify equipment?
Yes. Buyers can request photos, working video, condition details, and export support for specific machinery listings.