A For most of the fixing or connecting bolts in construction machinery, there are requirements for tightening torque. For instance, there are bolts for fixing the fuel injector, cylinder head bolts, connecting rod bolts, and flywheel bolts. Some of them have specified tightening torque, some have stipulated tightening angle, and some have also set the tightening sequence.
 
Some maintenance personnel believe that anyone can tighten the bolts and it is of no great significance. They do not follow the prescribed torque and sequence when tightening (some do not even know that there are torque and sequence requirements for tightening), do not use torque (kg) wrenches, or randomly use extension rods, and tighten the bolts by feeling. As a result, the tightening torques vary greatly. Insufficient torque causes the bolts to loosen easily, resulting in damage to the cylinder gasket, loosening of the bearing bush, oil leakage, and air leakage; excessive torque causes the bolts to stretch and deform, or even break. Sometimes, it may also damage the threaded holes, affecting the repair quality. Therefore, when maintaining construction machinery, bolts must be tightened according to the prescribed torque and sequence to prevent mechanical failures caused by improper tightening torque, insufficient torque, or incorrect sequence.

A When repairing construction machinery, some maintenance personnel do not adopt correct maintenance methods. They believe that emergency measures are all-purpose and substitute "emergency response" for "maintenance". The phenomenon of "tackling symptoms but not the root cause" is still widespread. For instance, the common practice of "welding instead of repairing" is one such case. Some components could have been repaired, but some maintenance personnel, in an attempt to save time, often adopt the method of "welding fixation". After the connecting threads of the hydraulic cylinder ear ring and the piston rod of the hydraulic cylinder are damaged, they are directly welded. As a result, the oil seal of the hydraulic cylinder gets damaged and cannot be replaced, causing severe oil leakage. When the working device moves slowly or turns with difficulty, without checking the cause of the fault, they blindly increase the working pressure of the system, resulting in excessive system pressure and easy damage to the oil seal, pipelines, and hydraulic components. In order to make the diesel engine "powerful", they artificially increase the fuel supply of the fuel injection pump and raise the fuel injection pressure of the fuel injector.
 
These makeshift repair methods can only be used as a temporary solution but cannot be relied on for long-term use. Faults must be identified fundamentally and repaired by adopting proper methods. This should be noted by the maintenance personnel.

A During maintenance operations, some maintenance personnel often focus only on the maintenance of components such as fuel injectors, fuel 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, various instruments, etc. They believe that these "small parts" do not affect the operation of the machinery and that even if they are damaged, it is not a big deal as long as the machinery can run. However, they do not realize that it is precisely these "small parts" that lack maintenance, which leads to early wear and tear of the machinery and shortens its service life.