1, do not pay attention to the selection of bolts, the use of bolts confusion more prominent phenomenon. In the maintenance of construction machinery, the phenomenon of indiscriminate use of bolts is more prominent, bolt performance, quality does not meet the technical requirements, resulting in frequent mechanical failure after maintenance. The special bolts used in construction machinery, such as transmission shaft bolts, cylinder head Bolts, connecting rod bolts, flywheel bolts, injector fixing bolts and so on, are made of special materials after special processing, with high strength and strong shear resistance, make sure the connection and fixing are reliable. In actual maintenance work, when some maintenance personnel find these bolts damaged or missing, they can not find the standard bolts for a while, some randomly take other bolts to replace, some self-processing substitutes, these bolts because of poor material quality or processing technology is not qualified, the rear axle wheel side reducer of Type 74 type II excavators has six bolts which are connected with the planetary wheel frame and the wheel side reducer Shell to bear greater torque, and these six bolts have broken and damaged, some maintenance personnel use other bolts or self-processing substitutes, often because the bolt strength is not enough to break again; some parts need to use the "small pitch" of the "fine buckle self-tightening" bolts, copper bolts, copper-plated Bolts, instead, ordinary bolts were used, which led to the phenomenon of bolts loosening and difficulty in disassembly. For example, the fixing nut of the diesel engine exhaust manifold is usually made of copper, which prevents it from being disassembled when it is heated or used for too long, however, most of them use ordinary nuts, which is very difficult to disassemble over a long period of time. Some bolts will have defects such as stretching and deformation after being used, and some technical requirements require that new bolts must be replaced after disassembly and assembly several times, because the maintenance personnel does not understand these situations, repeatedly uses the unqualified bolt, also easy to cause the mechanical breakdown or the accident occurrence. Therefore, in the maintenance of construction machinery, when the bolt damage or loss of timely replacement of bolts to meet the requirements, do not misuse bolts. 2. The improper tightening method of bolts is more serious. Most of the fixing or connecting bolts in various parts of construction machinery have tightening torque requirements, such as fuel injector fixing bolts, cylinder head bolts, connecting rod bolts, flywheel bolts, etc. , the tightening sequence is also specified. Some maintenance staff, think that tightening bolts who will do, does not matter, not in accordance with the provisions of Torque and order tightening (some do not understand there are tightening torque and order requirements) , do not use torque (kg) spanner, or arbitrary use of afterburner, feel tightening, the resulting tightening Torque is quite different. Under Torque, Bolt easy to loose, resulting in damage to the cylinder liner, bearing Bush loose, oil leakage, gas leakage; Torque is too large, bolt easy to stretch deformation, even fracture, and sometimes damage the threaded hole, affecting the repair quality. 1 set of ZL50 loader, torque converter to throw hydraulic oil, after inspection is due to connect the pump wheel and cover wheel 24 bolts did not tighten in the prescribed order and Torque. Therefore, in the maintenance of construction machinery, must be in accordance with the provisions of Torque and order to tighten the bolts to prevent bolts tightening Torque is too large, too small or the order of mechanical failure. 3, do not pay attention to the detection of parts and components with the gap with a large number of phenomena. Diesel Engine Piston and cylinder sleeve fit clearance, Piston ring "three gaps" , Piston top clearance, valve clearance, Piston clearance, brake shoe clearance, master and slave gear mesh clearance, bearing axial and radial clearance, valve rod and valve guide fit clearance, etc. , all types of machine have strict requirements, in maintenance must be measured, do not meet the clearance requirements of parts to adjust or replace. In the actual maintenance work, there are many phenomena of assembling parts blindly without measuring the fit clearance, causes bearing early wear or erosion, diesel engine oil burning, start difficulty or deflagration, piston ring broken, machine parts impact, oil leakage, gas leakage and other failures, sometimes even due to parts with improper clearance, the occurrence of an accident resulting in serious mechanical damage. After the overhaul of a 6DB-10P diesel engine, the test engine will turn off after 30 minutes or so, then the engine will start and not catch fire, check the oil, oil circuits and so on are normal, after the engine is stopped and left for 30 minutes, the engine can start and catch fire again, but it runs for 30 minutes and then shuts itself down. Later, the fault was checked because the piston clearance of the fuel injection pump was too small, and after the temperature of the diesel engine increased, the Piston expansion and the oil outlet valve were in conflict with each other, so the fuel supply could not move back and forth normally and the engine shut off by itself. After the engine was stopped and the temperature was lowered, pLUNGER and oil valve and there is a certain gap between the normal oil supply. 4. It is not uncommon for couples or assemblies to change in pairs or sets. There are many pairs on construction machinery, such as plunger pair, outlet valve pair, injector needle valve pair of diesel fuel system, master and slave gears in main reducer of drive axle, Valve Block and valve stem in Hydraulic Control Valve; The valve core and the valve sleeve in the full hydraulic steering gear and so on, these match couplings are made by special processing in the factory, they are made by pairs of grinding, the match is very precise, they are always used in pairs during the service life, must not be interchangeable; Some of the components, such as Piston and cylinder liner, bearing and Journal, Valve and valve seat, connecting rod and big head cover and rod body, are relatively well matched after a period of running-in, do not make a string; diesel connecting Rod, Piston, Fan Belt, high-pressure oil pipe, excavator central rotary joint oil seal, bulldozer main clutch tape section, etc. , these machines use a set of accessories at the same time, in case of damage, a complete set must be replaced; otherwise, due to the great difference in the quality of the accessories, the difference in the degree of the old and the new, and the difference in length and size, it will lead to unstable operation of diesel engine, oil leakage of hydraulic system, heavy load concentration, easy early damage of replacement parts and so on. In the actual maintenance work, it is not uncommon for some people to change the above-mentioned parts in pairs or in complete sets in order to reduce expenses, some people do not understand the technical requirements, which reduces the maintenance quality and shortens the service life of construction machinery, increased the possibility of failure, should cause enough attention. 5. Parts are assembled backwards from time to time. In the maintenance of construction machinery, some parts assembly has strict direction requirements, only the correct installation, can ensure the normal work of parts. Some parts of the external features are not obvious, positive and negative can be installed, in the actual work often appear in the case of reverse loading, leading to early damage parts, machinery can not work properly, engineering machinery damage accidents. Such as engine cylinder liner, Unequal Distance Valve Spring (such as F6L912 diesel engine) , engine Piston, Piston ring, fan blades, gear oil pump side plate, skeleton oil seal, thrust gasket, thrust bearing, thrust gasket, oil stop ring, fuel injection pump plunger, clutch friction disc hub, drive shaft universal joint, etc. , these parts in the installation, if you do not know the structure and installation notes, the most easy to install the reverse, resulting in abnormal work after assembly, leading to the failure of construction machinery. If a 4120F diesel engine piston ring replacement, diesel engine blue smoke, consider may be too much oil injection or piston ring "match" caused. Check the oil is normal, remove a cylinder Piston connecting Rod group, found that the Piston ring is not "right" , but put the air ring installed, check the other Cylinder Piston rings are installed in reverse. This machine uses the inside-cut groove type twisted gas ring, when it is installed, it is required that the inside cut face up, the maintenance personnel installed exactly the opposite, because the inside-cut groove piston ring is installed backward, the Piston "pump oil" phenomenon is extremely easy to occur, the oil moves up the cut of the ring to the combustion chamber for combustion. For example, the working oil pump of ZL50 loader is equipped with 2 framework oil seals. The correct installation direction of the oil seal is: The oil seal lip on the inner side is inward, and the oil seal lip on the outer side is outward, in this way, not only can the working pump prevent the oil in the hydraulic oil tank from being pumped into the transmission through the transmission pump, it also prevents the transmission pump from driving the oil in the transmission through the working pump into the hydraulic tank (the working pump and the transmission pump are installed side by side and driven by a shaft gear) , the author has encountered two cases because of the oil pump oil seal instead of oil channeling fault. Therefore, maintenance personnel in the assembly of parts, parts must master the structure and installation direction requirements, can not be taken for granted blindly installation.
