Eight points for attention in the repair of match

2022-08-14
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As the saying goes, a general needs to have the ability to kill six generals after five passes. In order to become a qualified and excellent repairman, we also need to have certain skills. Diesel engine repair needs to cross eight levels

first off: "three leaks" off

when repairing the diesel engine, prevent and solve the "three leaks" problem, and adopt the "five character" principle, that is, strict, clean, wipe, grind and tighten. Strict: the disassembly and installation of parts should be strictly required, and the operating procedures should be observed. It is strictly forbidden to knock randomly. For example, when screwing bolts, tighten them in sequence and several times, and do not screw them disorderly in order to prevent parts from deformation. Cleanliness: parts must be cleaned before assembly to prevent impurities. If the contact ring between the oil outlet valve and the valve seat is mixed with very small debris, it will not only leak oil, but also directly affect the work of the engine. Wipe: apply asbestos oil on the oil leakage of asbestos pad, paper pad and various plugs. When applying asbestos oil, it should be thin and uniform, not too thick, and do not apply the whole surface of the pad, just apply the oil leaking part. Grinding: grinding or milling the joint surface of parts, whose function is to restore the surface smoothness and accuracy, so that the oil pipe joint or gasket can remain sealed without oil leakage after grinding. Tightness: the tightness of the sealing device should be appropriate, and should not be too tight or too loose, such as various contact surfaces of the diesel engine and sealing nuts, which must maintain a suitable tightness

second off: cylinder pressure off

in order to ensure sufficient cylinder pressure, the matching clearance between piston and cylinder liner, the end and edge clearance of piston ring must meet the requirements, the tightness of valve and valve seat, the tightness of front end of injector, cylinder gasket and thickness must meet the requirements

third off: combustion chamber volume off

after repair, the diesel engine will often change the combustion chamber volume, change the original compression ratio, and directly affect the normal operation of the diesel engine. The factors that change the combustion chamber volume include: the piston position is installed inversely, the cylinder cushion thickness is improper, the crank connecting rod is mechanically worn or bent, the swirl chamber insert is misaligned, and the valve subsidence is too large. These conditions should be paid attention to during repair

fourth off: timing off

timing off includes oil supply timing and valve distribution timing. If the oil supply timing is not correct, S195 and X195 diesel engines can be adjusted with the help of gaskets between the fuel injection pump and the gear chamber cover. Enterprises are encouraged to use mm thick gaskets with new materials every 0.1 increase or decrease, which is equivalent to 6.3mm of flywheel arc length. If the valve distribution is insufficient, check and correct the installation error of the timing gear first, and then adjust the valve clearance. Every time the valve clearance changes by 0.1mm, the crankshaft angle changes by 3 degrees, which is equivalent to the flywheel arc length of 11.1mM. During the adjustment, it should be noted that when the piston is compressed to the top dead center, the inlet and exhaust valve clearance (cold state) should not be less than 0.2mm, so as to prevent the parts from being heated and expanded, the valve is not tightly closed, or the valve head hits the piston

fifth off: "three filters" off

poor technical status of air filter will make dust enter the valve. Accelerate the early wear of piston rings, cylinders, valves and valve seats, resulting in difficult starting and power reduction. The poor technical state of diesel and oil filters will cause impurities to enter between the relevant parts, causing early wear of the three precision coupling parts, accelerating the wear of crankshaft and bearing bush, and seriously causing early scrapping of diesel engine

sixth off: Diesel atomization off

poor technical status of plunger pair, outlet valve pair and injector needle valve pair will cause poor fuel injection atomization, making it difficult for the diesel engine to start, incomplete combustion, increased carbon deposition, resulting in decreased engine power and increased fuel consumption. Therefore, the mechanical properties of the fuel system are mainly tested for its breaking strength, elongation at break, maximum experimental force, etc, In particular, precision parts should be carefully checked

seventh close: through hole and small hole close

(1) take S195 diesel engine as an example, the five through holes of bearing and bushing should be aligned during installation

a. for main bearings, oil holes are drilled on each pair of main bearing oil grooves, which are also connected with the oil on the cylinder block and main journal respectively. During installation, as long as the flange notch of the main bearing aligns with the locating pin, the main bearing can be prevented from rotating, the oil holes can be aligned, the lubricating oil circuit can be unobstructed, and burning out can be avoided

b, rocker arm bushing. When pressing the bushing into the rocker arm, if the hole is misaligned, the rocker arm shaft and bushing will be burned due to lack of lubrication and dry friction, which will enlarge the valve clearance and produce serious knocking sound

c, connecting rod bushing. The small end of the connecting rod is drilled with an oil collecting hole, which is connected with the oil hole of the connecting rod bushing. When the copper sleeve is sleeved into the small end of the connecting rod, if the two oil holes are not aligned, the copper sleeve and the piston pin will produce a "Dangdang" knocking sound, and even bite

d. starting shaft bushing. When installing the starting shaft bushing, the oil holes of the two bushings should be connected with the corresponding oil collecting grooves on the engine body and gear cover respectively, otherwise the starting shaft and bushing will accelerate the wear, causing the change of oil supply angle and valve distribution phase, resulting in the decline of diesel engine power

(2) the small hole closure mainly includes the following four small holes

a and the vent hole of the oil tank cover. After the hole is blocked, the oil tank is no longer connected with the atmosphere, and the upper part of the oil tank will have negative pressure due to the decline of the oil level, resulting in the interruption of oil supply; The evaporation of fuel after heating will increase the pressure in the fuel tank, which will cause oil leakage at the fuel tank switch. Therefore, this hole cannot be blocked

b. Crankcase air change hole. After the air change hole is blocked, the exhaust gas in the crankcase will accumulate more and more, and the air pressure in the crankcase will rise. If there is a scratch, grind it with a fine oilstone, which will make the oil leak, and the high humidity exhaust gas will mix into the oil, which will also accelerate the deterioration of the oil and accelerate the wear of the parts. Therefore, this hole must be dredged during maintenance

c, oil drain hole of oil transfer pump. The blockage of the oil drain hole on the oil transfer pump will cause a small amount of diesel oil between the push rod and the guide pipe to leak into the fuel injection pump, dilute the lubricating oil in the housing and accelerate the wear of parts. Therefore, this hole cannot be blocked

d. If the drain hole of the water pump is blocked, the leaked water cannot be discharged out of the pump body and enter the bearing seat, which will accelerate the damage of the bearing. Therefore, this hole must be dredged during maintenance

the eighth level: running in level

(1) cold running in. Remove the fuel injector, drive the diesel engine to run with external force, check the oil pressure and the temperature of each part at the same time, and pay attention to the sound of each component. After cold running in, drain the oil and clean the oil filter and oil passage when the temperature is high

(2) thermal running in. No load thermal running in, pay attention to the working condition of the diesel engine and the noise of various parts; Heat run in according to the specified load and time, often pay attention to the sound of various parts and the blowby, smoke exhaust, oil return of fuel injector, etc., and eliminate problems in time

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