Fourteen Common Problems in Construction Machinery Maintenance

It is common to see people failing to accurately diagnose and analyze faults and blindly disassembling them

Some maintenance personnel, due to their lack of understanding of the structure and principles of construction machinery, do not carefully analyze the causes of faults and cannot accurately determine the faulty parts. Relying on the idea of "roughly or almost", they blindly disassemble the machinery. As a result, not only are the original faults not eliminated, but also new problems arise due to their poor maintenance skills and techniques. Therefore, when a mechanical device malfunctions, it should be inspected through detection equipment. If there is no such equipment, traditional fault diagnosis methods and means such as "asking, observing, checking, and testing" can be used, combined with the structure and working principle of the construction machinery, to determine the most likely faulty part. When diagnosing faults in construction machinery, the "elimination method" and the "comparison method" are generally used. The process should be carried out in the order from simple to complex, from the exterior to the interior, and from the assembly to the component. It is essential to avoid "disassembling blindly without considering the facts".

The phenomenon of blindly replacing parts and components and simply "replacing parts for repair" exists to varying degrees

The diagnosis and elimination of faults in construction machinery are relatively more difficult. Some maintenance personnel have always adopted the method of replacing parts for testing. Regardless of whether it is a large or small part, as long as they think the parts might be causing the fault, they replace them one by one for testing. As a result, not only are the faults not eliminated, but also the parts that should not be replaced are replaced at will, increasing the expenses of consumers. Some faulty components can be fully restored to their technical performance through repair without the need for complex repair processes. However, maintenance personnel insist that users replace them with new parts, blindly adopting the method of "replacing parts for repair", which leads to serious waste. The above-mentioned blind replacement tests and the practice of blindly replacing repairable parts still exist to varying degrees in some repair units. When conducting maintenance, one should carefully analyze and determine the cause and location of the fault based on the fault phenomenon. For components that can be repaired, repair methods should be adopted to restore their technical performance, and the practice of blindly replacing components should be strictly avoided.

3. It is quite common for faults to occur after assembly without checking the quality of new parts

Before replacing the parts, some maintenance personnel do not conduct technical checks on the new parts and directly install them on the construction machinery. This practice is not scientific. At present, the quality of spare parts sold on the market varies greatly, and some counterfeit and shoddy parts are mixed in. Some accessories, due to being in stock for too long, have changed in performance. If not inspected, they often cause malfunctions after assembly. Before replacing new parts, it is essential to conduct necessary inspection and testing. The inspection includes appearance and performance tests to ensure that the new parts are free of faults and avoid unnecessary troubles caused by them.

4. The phenomenon of not paying attention to the model of accessories, substituting or misusing accessories is quite common

When repairing construction machinery, the phenomenon of substituting or misusing parts is still quite common. Some parts can be used as emergency substitutes, but long-term use is harmful rather than beneficial, affecting the safety and technical performance of the machinery. Some maintenance personnel have little knowledge of mechanical structure and principles, and many spare parts do not match the model. However, they think that as long as they can be installed, it is fine, without considering whether the technical performance of the machinery can be brought into play. Therefore, when repairing construction machinery, it is advisable to use the original model parts as much as possible. Do not substitute parts of other models, let alone use them wrongly.

5. The selection of bolts is not given due attention, and the phenomenon of chaotic use of bolts is quite prominent

When repairing construction machinery, the phenomenon of using bolts randomly is still quite prominent. Due to the performance and quality of the bolts not meeting the technical requirements, mechanical failures occur frequently after repair. Special bolts used in construction machinery, such as drive shaft bolts, cylinder head bolts, connecting rod bolts, flywheel bolts, and fuel injector fixing bolts, are made of special materials through special processing. They have high strength and strong shear resistance, ensuring reliable connection and fixation. In actual maintenance operations, when some maintenance personnel find that these bolts are damaged or missing and cannot find standard bolts for the time being, some randomly take other bolts as substitutes, and some process and use them by themselves. Due to poor material quality or unqualified processing techniques, these bolts leave potential faults for the later use of construction machinery. In some parts, "small-pitch" "fine-thread self-tightening" bolts, copper bolts, and copper-plated bolts are needed, but ordinary bolts are used instead, resulting in phenomena such as self-loosening of the bolts and difficulty in disassembly. Some bolts may develop defects such as stretching and deformation after use. Some technical requirements stipulate that new bolts must be replaced after several disassemblies and assemblies. Due to the maintenance personnel's lack of understanding of these situations, repeatedly using substandard bolts can also easily lead to mechanical failures or accidents. Therefore, when repairing construction machinery, if bolts are damaged or lost, they should be replaced in a timely manner with bolts that meet the requirements. It is strictly forbidden to use bolts randomly.

6. The situation where the bolts are tightened improperly is rather serious

Most of the fixing or connecting bolts of various parts of construction machinery have requirements for tightening torque, such as the fixing bolts of fuel injectors, cylinder head bolts, connecting rod bolts, flywheel bolts, etc. Some specify the tightening torque, some specify the tightening Angle, and also specify the tightening sequence. Some maintenance personnel believe that tightening bolts is something that anyone can do and is unimportant. They do not tighten them according to the specified torque and sequence (some have no idea about the requirements for tightening torque and sequence at all), do not use torque (in kilograms) wrenches, or use extension rods at will and tighten them by feeling, resulting in a significant difference in tightening torque. Insufficient torque can easily cause bolts to loosen, leading to damage to the cylinder gasket, loosening of the bearing bush, oil leakage and air leakage. Excessive torque can easily cause the bolt to stretch and deform, or even break. Sometimes, it can also damage the threaded holes, affecting the repair quality. Therefore, when maintaining construction machinery, it is essential to tighten the bolts in accordance with the specified torque and sequence to prevent mechanical malfunctions caused by excessive, insufficient tightening torque or improper sequence of the bolts.

There are quite a few cases where the fit clearance of components is not properly inspected

The fit clearance between the diesel engine piston and cylinder liner, the "three clearances" of the piston ring, the top clearance of the piston, the valve clearance, the residual clearance of the plunger, the clearance of the brake shoe, the meshing clearance of the driving and driven gears, the axial and radial clearance of the bearing, the fit clearance between the valve stem and the valve guide, etc., all types of models have strict requirements and must be measured during maintenance Components that do not meet the clearance requirements should be adjusted or replaced. In actual maintenance work, there are quite a few cases where components are blindly assembled without measuring the fit clearance, which leads to early wear or burning of bearings, oil burning of diesel engines, difficult starting or explosion, piston ring breakage, component impact, oil leakage, air leakage and other faults. Sometimes, even due to improper fit clearance of components, serious mechanical damage accidents may occur.

8. It is also not uncommon for pairs or assemblies to be replaced in sets

There are many pairs on construction machinery, such as the plunger pair, fuel outlet valve pair and fuel injector needle valve pair pairs in the diesel engine fuel system. The driving and driven gears in the main reducer of the drive axle; The valve block and valve stem in the hydraulic control valve; The valve core, valve sleeve and other mating parts in the fully hydraulic steering gear are specially processed and ground in pairs during factory manufacturing. They fit very precisely and should always be used in pairs throughout their service life and must not be interchanged. Some mutually cooperating components, such as the piston and cylinder liner, bearing bush and journal, valve and valve seat, connecting rod big end bearing cover and rod body, etc., after a period of running-in use, have relatively good fit. During maintenance, it is also necessary to pay attention to assembling them in pairs and avoid stringing them together. Diesel engine connecting rods, pistons, fan belts, high-pressure oil pipes, oil seals of the central rotary joint of excavators, rubber joints of the main clutch of bulldozers, etc., these parts that are used in a single set for one machine must be replaced as a complete set when they are damaged. Otherwise, due to the significant differences in quality, newness, and length and size of the parts, It will lead to unstable operation of the diesel engine, oil leakage in the hydraulic system, severe load concentration, and premature damage of replaced parts, etc. In actual maintenance work, it is not uncommon for some people to replace the above-mentioned parts in pairs or sets in order to cut costs or due to a lack of understanding of the technical requirements. This not only reduces the maintenance quality of construction machinery, shortens the service life of the components, but also increases the possibility of faults. Sufficient attention should be paid to this.

9. It is not uncommon for components to be installed in reverse during assembly

When repairing construction machinery, there are strict directional requirements for the assembly of some components. Only by installing them correctly can the normal operation of the components be guaranteed. Some components have no obvious external features and can be installed in either direction. However, in actual work, they are often installed in reverse, leading to premature damage of parts, abnormal operation of machinery, and damage accidents of construction machinery, etc.

Such as engine cylinder gaskets, unequal distance valve springs (such as F6L912 diesel engines), engine pistons, piston rings, fan blades, side plates of gear oil pumps, skeleton oil seals, thrust washers, thrust bearings, thrust gaskets, fuel retaining rings, fuel injection pump plungers, clutch friction plate hubs, universal joints of drive shafts, etc., when installing these components, If one is not familiar with the structure and installation precautions, it is most likely to be installed in reverse, resulting in abnormal operation after assembly and causing faults in construction machinery. Therefore, when maintenance personnel assemble components, they must be familiar with the structure and installation direction requirements of the components and must not install them blindly based on assumptions.

10. The maintenance methods are not standardized. "Treating the symptoms rather than the root cause" is still a common tactic used by some maintenance units

When maintaining construction machinery, some maintenance personnel do not adopt the correct maintenance methods. They believe that emergency measures are omnipotent and use "emergency" instead of "maintenance", which only treats the symptoms but not the root cause. There are still many such phenomena. For instance, the frequently encountered "welding instead of repair" is a case in point. Some components could have been repaired, but some maintenance personnel, for the sake of convenience, often resort to the method of "welding them all together". After the connecting thread between the hydraulic cylinder earring and the cylinder piston rod was damaged, the direct welding method was used, which led to the damage of the cylinder oil seal and made it impossible to replace, resulting in severe oil leakage. When it is found that the working device moves slowly or has difficulty turning, without checking the cause of the fault, blindly increasing the working pressure of the system can lead to excessive system pressure, which is prone to damage oil seals, pipelines, hydraulic components, etc. To make the diesel engine "powerful", the fuel supply volume of the fuel injection pump is manually increased and the fuel injection pressure of the fuel injector is raised. These irregular maintenance methods can only be used as an emergency measure and should not be employed for a long time. It is necessary to identify the root cause of the fault and adopt regular maintenance methods to eliminate it, which should draw the attention of maintenance personnel.

11. The phenomenon of non-standard and random use of gaskets still exists

There are many types of gaskets used between the mating surfaces of construction machinery parts. Commonly used ones include asbestos gaskets, rubber gaskets, cardboard gaskets, cork gaskets, felt gaskets, non-ferrous metal gaskets (copper gaskets, aluminum gaskets), copper (steel) asbestos gaskets, insulating gaskets, spring gaskets, flat gaskets, etc. Some are used to prevent oil, water, gas and electricity leakage between the mating surfaces of components, and some serve to tighten and prevent loosening. The timing and occasions for the use of each type of gasket have different regulations and requirements. During the maintenance of construction machinery, the phenomenon of non-standard or even random use of gaskets is still quite serious, resulting in frequent leakage between mating surfaces, and the self-loosening and detachment of bolts and nuts, which affects the normal use of construction machinery. If the cylinder gasket of the engine is too thick, it will cause the compression ratio to decrease and make it difficult for the engine to start. Copper gaskets are used between the mating surfaces of the fuel injector and the cylinder head. If asbestos gaskets are used instead, it is easy to cause poor heat dissipation of the fuel injector and lead to burning. The gasket between the fuel transfer pump and the fuel injection pump of the diesel engine is too thick, resulting in insufficient fuel delivery volume and pressure, and a decrease in the power of the diesel engine. If the spring gasket, locking gasket or sealing gasket is not installed properly, resulting in a loose connection, it is easy to cause loosening or oil leakage and other phenomena. The phenomenon of engine bearing seizure and shaft seizing, as well as the radiator boiling over, often occurs because there are holes in the middle of the gasket but the holes are forgotten to be drilled. Here we would like to remind all maintenance personnel that when repairing construction machinery, they must remember that "although gaskets are small, they are of great use."

12. Not paying attention to the quality of "small parts" leads to an increase in malfunctions due to the "small" losing the "big"

When performing maintenance work, some maintenance personnel often only focus on the maintenance of components such as fuel injection pumps, fuel transfer pumps, pistons, cylinder liners, piston rings, hydraulic oil pumps, control valves, braking systems, and steering systems, but neglect the maintenance of "small parts" like filters, relief valves, and various instruments. They believe that these "small parts" do not affect the operation of the machinery, and even if they are damaged, it is not a big deal. As long as the machinery can move, they just make do with it. Little do they know that it is precisely the lack of maintenance of these "small parts" that leads to early wear and tear of the machinery and shortens its service life. Such as diesel filters, oil filters, air filters, hydraulic oil filters, water temperature gauges, oil temperature gauges, oil pressure gauges, induction plugs, sensors, alarms, preheating plugs, oil filter screens, radiator covers, oil tank covers, oil filling port covers, grease nozzles, air storage tank drain switches, battery boxes, fuel injector return oil connectors, cotter pins, fan deflector covers, and drive shaft bolts used in construction machinery Lock plates and other such "small parts" are indispensable for the normal operation and maintenance of construction machinery, and are crucial for extending the service life of the machinery. During maintenance operations, if maintenance and care are not paid attention to, it often leads to "losing the big picture for the small details", resulting in the occurrence of construction machinery failures.

13. After forgetting the maintenance taboos, hidden faults occur frequently

When maintaining construction machinery, some maintenance personnel are not aware of some issues that should be noted during the maintenance process, which leads to frequent "habitual" mistakes during disassembly and assembly, affecting the maintenance quality of the machinery. If the engine cylinder head is disassembled and assembled while the vehicle is hot, it is easy to cause deformation and cracking of the cylinder head. When installing the piston pin, if the piston pin is directly driven into the pin hole without heating it, the deformation of the piston will increase and the ellipticity will rise. Copper or paper gaskets are added to the back of the crankshaft bearing bush or connecting rod bearing bush, which can easily clog the oil passage and cause bearing bush burning and shaft seizing accidents. When maintaining a diesel engine, excessive scraping of the bearing bush caused the anti-friction alloy layer on the surface of the bearing bush to be removed, resulting in direct friction between the steel back of the bearing bush and the crankshaft, leading to premature wear. When disassembling interference fit components such as bearings and pulleys, do not use tensioners. Hard hammering can easily cause deformation or damage to the components. When opening new pistons, cylinder liners, fuel injector pairs, plunger pairs and other parts, burning the oil or wax sealed on the surface of the parts can cause changes in the performance of the parts, which is not conducive to their use.

14. Incomplete decontamination and cleaning of parts often lead to premature wear and corrosion

When repairing construction machinery, correctly removing oil stains and impurities from the surface of components is of great significance for improving the repair quality and prolonging the service life of the machinery. Due to the lack of attention to strengthening the cleaning of parts, the unreasonable selection of cleaning agents, and improper cleaning methods, the phenomenon of early wear and corrosive damage of components still occurs from time to time in some repair units. If the carbon deposits in the cylinder liner steps and piston ring grooves, debris in the bolt holes, and sand particles in the hydraulic components are not thoroughly removed, it will lead to insufficient bolt torque, easy breakage of the piston rings, erosion of the cylinder gasket, and premature wear of the hydraulic components.

During major overhauls of construction machinery, if the accumulated oil stains or impurities on diesel filters, oil filters, hydraulic oil filters, diesel engine water jackets, radiator surfaces, and lubricating oil channels are not properly removed, the maintenance work will be incomplete and the fault-free operation time of the construction machinery will be reduced. When repair personnel are cleaning components, they must first correctly select the cleaning agent. For the cleaning of various components, different cleaning agents should be correctly selected based on their different requirements for cleanliness. Second, it is necessary to prevent the corrosion and rusting of components. To ensure the quality of components, it is necessary to prevent their corrosion and rusting, especially for precision components, which are not allowed to have any degree of corrosion or rusting. Therefore, when cleaning, do not use alkaline cleaning agents (especially strong alkaline cleaning agents) to clean aluminum alloy parts (such as aluminum alloy cylinder heads, etc.), and even less should strong acid cleaning agents be used to clean copper parts (such as the main valve of the thermostat), in order to minimize the corrosion of the machine parts to the greatest extent. Third, different components should be cleaned separately. Aluminum alloy and copper parts should not be cleaned together with alkaline or acidic cleaning agents. Rubber parts should not be cleaned together with other steel parts in gasoline, diesel or acidic or alkaline cleaning agents.