Figure 4- 1 connecting rod tester
(a) Bending test (b) Torsion test
1. Small angle iron fixing screw 2. Vertical plate 3. Small angle iron 4. Connecting rod 5. Centering block 6. Transverse shaft adjusting bolt
(1) Install the bearing cover at the big end of the connecting rod (without bearing), tighten the connecting rod bolt and nut according to the specified torque, and install the piston pin into the hinged connecting rod bushing.
(2) Install the big end of the connecting rod on the horizontal shaft of the testing machine, tighten the adjusting bolt on the horizontal shaft to make the centering block expand outward, and fix the connecting rod on the testing machine.
(3) Move the small angle iron downward to make its lower plane lean against the piston pin, tighten the fixing screw of the small angle iron, observe the contact between the lower plane of the small angle iron and the piston pin, and check the bending direction and degree of the connecting rod, as shown in Figure 4- 1(a).
(4) On the basis of checking the bending, move the small angle iron downward to make its side contact with the piston pin, as shown in Figure 4- 1(b), observe the contact situation, and check the direction and degree of torsion of the connecting rod.
In practical work, it is usually after the connecting rod bearing and bushing are repaired, the newly assembled bearing and piston pin are installed to check and correct the bending and deformation of the connecting rod, which can eliminate the influence of the repair deviation of the connecting rod bearing and bushing on the parallelism of the upper and lower holes of the connecting rod.
274. How to correct the bending and distortion of the connecting rod?
After inspection, if the connecting rod is bent or twisted beyond the specified value, the bending and twisting directions should be remembered and corrected. The correction of bending and twisting of connecting rod is generally carried out on connecting rod straightener, and it can also be corrected by other methods. As shown in fig. 4-2(a), the method of correcting the bending of the connecting rod with a connecting rod corrector can also be corrected with a press. As shown in Figure 4-2(b), the method of correcting the torsion of connecting rod with connecting rod corrector can also be corrected with long-handled wrench or pipe wrench.
Figure 4-2 Correction of Connecting Rod Bending
275. How to match the piston?
When the engine is overhauled, the piston should be selected and the repair size of the cylinder should be determined according to the wear condition of the cylinder. The following points should be paid attention to when replacing the piston:
(1) On the same engine, pistons of the same brand, grade and group should be selected, so that the material, performance, quality and size are consistent.
(2) The diameter difference of the same group of pistons should not exceed 0.025mm, and the quality difference is generally not more than 8g. Otherwise, match again.
(3) The tolerance of diameter difference between piston head and skirt, roundness and cylindricity of skirt shall meet the technical requirements.
276. How is the carbon deposit on the top of the piston formed? What are the disadvantages?
(1) Formation of carbon deposit
First of all, the fuel used in the engine will undergo oxidation reaction during storage and transportation, resulting in colloidal substances. These colloidal substances can be divided into soluble colloid and insoluble colloid according to the solubility of gasoline. Insoluble colloid, also known as deposit, sticks to the fuel filter when it is added to the fuel tank with fuel, blocking the filter medium, reducing the fuel supply, causing poor fuel atomization, diluting the combustible mixture, and reducing the power and economy of the engine. However, after the soluble rubber enters the combustion chamber and burns with gasoline, many hard carbon deposits are formed in the intake valve, piston crown, piston ring groove, combustion chamber, spark plug and other parts, resulting in a series of faults such as poor valve closure, poor engine working environment, poor acceleration, unstable idle speed, serious jitter and even knocking. Secondly, when the engine is working, neither fuel nor engine oil can be completely burned. Under the catalysis of high temperature and oxygen, some unburned fuel oil forms hydrochloric acid and resinous colloid, which adheres to the surface of parts, and then further concentrates into a complex mixture of asphaltene and oil coke under the action of high temperature, which is called carbon deposition.
(2) Hazards of carbon deposition
Carbon deposition on the top of the piston will form a lot of heat, which will lead to premature combustion and deflagration and shorten the service life of the engine.
277. How to remove carbon deposits?
(1) mechanical method
Mechanical method is a method to remove carbon deposits with wire brush, scraper, bamboo chips or emery cloth. Special brushes and scrapers can be made according to the shape of the parts to be cleaned: for example, fine copper wire brushes can be used to clean the carbon deposits around the nozzle holes of the fuel injector; The carbon deposit in the pressure chamber can be scraped off by inserting a special through needle made of copper wire; The carbon deposit on the valve guide and valve seat can be removed with a cylindrical metal brush. Mechanical methods to remove carbon deposits have low efficiency and poor quality, and some parts are difficult to scrape clean, leaving many tiny scratches, which become the increase points of new carbon deposits and increase the roughness of parts. Therefore, this method is generally not suitable for parts with high precision.
(2) Nuclear spray method
Core-spraying method is a method that uses high-speed airflow to spray the crushed particles of walnut endocarp, peach pit and apricot pit on the surface of parts to remove carbon deposits. This method is efficient and clean in removing carbon deposits, but it needs special equipment to form high-speed airflow, which is expensive and not suitable for wide use.
(3) Chemical methods
Chemical method is a method to soften the carbon deposit on the surface of parts with chemical solvent-carbon remover, so that it loses its ability to combine with metals, and then remove the softened carbon deposit. This method has high carbon removal efficiency and good effect, and it is not easy to damage the surface of the ring. Decarburization agent is generally composed of four components: carbon deposition solvent, diluent, slow-release agent and active agent. There are many kinds of decarburization agents, which can be divided into steel decarburization agents and aluminum decarburization agents according to the different materials of metal parts. These decarburization agents contain components (such as caustic soda) that have chemical corrosive effects on aluminum products, so they are only suitable for decarburization of steel parts.
When using inorganic decarbonization agent, the solution should be heated to 80 ~ 90℃, and the parts should be soaked in the solution for 2 hours, and then taken out after the carbon deposits are softened; Then, remove the softened carbon deposit with a brush, and then clean it with hot water containing 0. 1% ~ 0.3% potassium dichromate; Finally, dry it with a soft cloth to avoid corrosion.
(4) fuel system cleaning protective agent
After the fuel system cleaning protective agent is added to the fuel supply system, the hard carbon and colloid can be automatically removed when the engine works normally, and the engine performance can be restored to normal.
278. How to eliminate the unstable working speed of diesel engine?
When the tractor works normally, no matter how the load changes, the engine speed remains relatively stable. This is because the diesel engine is equipped with a governor, which can automatically adjust the oil supply according to the load change. The stable working speed of diesel engine must meet two conditions: one is that the governor works well, and the other is that the oil supply system works normally. The reasons for the instability of diesel engine speed should be found from these two aspects.
The instability of diesel engine speed is characterized by high and low speed, and sometimes it fluctuates regularly, which affects the power of diesel engine. Causes of unstable speed of diesel engine;
(1) governor failure
① The gap between the fuel quantity adjusting arm of the fuel injection pump and the fork groove of the speed regulating pull rod is too large, resulting in serious wear.
② The elasticity of the speed regulating tension spring is weakened.
③ There is friction between the speed-regulating pull rod and the shell of the high-pressure oil pump, and the gap between the gear room and the speed-regulating pull rod is too small, resulting in jamming.
④ The contact parts between the two forks of the short arm of the speed-regulating pull rod and the one-way thrust bearing of the speed-regulating slide plate are seriously worn, and the gap is too large.
⑤ The uneven end faces of the two forks of the short arm of the speed regulating pull rod cause the one-way thrust bearing to be stuck.
⑥ The speed regulating gear shaft is not perpendicular to the cylinder, and it is skewed, which makes the axial movement of the speed regulating slide plate inflexible.
⑦ The connecting parts of the governor are loose and the fit clearance is too large.
In view of the above situation, repair or replace parts.
(2) Fuel system failure
(1) There is air, moisture or oil blockage in the fuel system, which makes the oil supply intermittent.
② The plunger does not rotate flexibly in the plunger sleeve. When replacing the plunger, the lower spring seat is installed backwards, which will also make the plunger rotate inflexibly.
(3) The oil injector is dripping.
④ The positioning screw of the plunger sleeve of the fuel injection pump is loose or the sealing washer is not tightly sealed.
⑤ The oil outlet valve is badly worn and the seal is not tight; The gasket of the oil outlet valve is cracked or the seal is not tight.
If this happens, please repair or replace the parts in time.
279. How to solve the main bearing cover oil leakage?
The oil leakage of the main bearing cover of S 195 diesel engine can be divided into two situations: one is the oil leakage of the newly assembled main bearing cover of the machine after overhaul; The other is that the main bearing cover leaks oil after being used for a period of time. There are two places where the main bearing cover leaks oil: one is the joint surface between the main bearing cover and the engine body, and the engine oil flows down from the engine body wall; Second, the crankshaft oil seal leaks oil, which is thrown out through the flywheel rim.
(1) Causes of oil leakage of main bearing cover after overhaul
(1) Oil leakage is caused by the material of machine parts, such as cracks, sand holes, multiple pinholes and slag inclusion.
(2) The hole on the machine body and the large excircle of the main bearing cover are transitional fit, which increases the error and makes the actual assembly into clearance fit, and the engine oil will ooze from this clearance fit. Therefore, the machining accuracy should be controlled in the machining process.
(3) Before assembly, scratches and abrasions formed on the workpiece were not effectively handled, resulting in undue deviation and clearance, which made oil leakage possible. Therefore, attention should be paid to the machining quality of the workpiece surface before assembly.
(4) When assembling, the paper pad is uneven, and the bolt tightening torque is not equal. Failure to tighten the bolts according to the requirements will cause the diesel engine to leak air and oil. Therefore, the paper pad should be flat when assembling, and the tightening sequence and torque of bolts must meet the requirements.
(2) The reason of oil leakage at the joint surface between the main bearing cover and the engine body in use.
① The bearing cover gasket is damaged.
② The oil pressure of the oil pump is too high.
(3) The main bearing cover is loosely fitted with the machine body.
④ The crankcase breather is blocked, and the air pressure in the crankcase is too high.
⑤ The main bearing cap bolt is not tightened or loosened due to vibration.
(3) Causes of oil leakage of crankshaft oil seal in use
① After the crankshaft oil seal is used for a long time, the sealing lip is worn or cracked, or the rubber ages and hardens, thus losing its sealing function.
② Accidentally installed the crankshaft oil seal, which caused the sealing lip of the oil seal to break.
(3) Due to wear, grooves appear at the joint of crankshaft and oil seal.
④ The oil seal spring falls off and the oil seal loses its self-tightening function.
⑤ The crankshaft main bearing is seriously worn, or after the main bearing is replaced, the main bearing hole and the center of the oil seal are different axes, which makes the crankshaft loose while it is running, and the loose side will leak oil.
⑥ The oil pressure of the oil pump is too high.
⑦ The oil is packaged backwards.
⑧ The crankcase respirator is not smooth, and the air pressure in the crankcase is too high.
Pet-name ruby oil seal itself is of poor quality.
(4) Check and eliminate the oil leakage of the main bearing cover.
① If the fit clearance between crankshaft and main bearing is too large, it will greatly affect the working performance of oil seal. Check the fit clearance between the crankshaft journal and the main bearing, and lift the flywheel by hand. If it feels like shaking up and down, it means that the fit gap is too large. If the clearance exceeds 0.25mm, replace the main bearing.
② If the fit clearance between the main bearing and the crankshaft journal is not large, remove the main bearing cover and check whether the oil seal is seriously worn, whether the sealing lip is broken and whether the rubber is aged and hardened. In this case, replace the oil seal. When replacing the oil seal, the new oil seal should be immersed in engine oil to avoid dry friction damage to the lip of the oil seal when it is started for the first time after replacement. At the same time, when installing, pay attention to the fact that the oil seal lip cannot be scratched by the keyway on the crankshaft, nor can the oil seal lip turn over or the spring fall off, and the side equipped with the self-tightening spring should face the main bearing. Check whether the crankshaft is grooved.
③ If the washer of the main bearing cover is damaged, it should be replaced. The axial clearance of the crankshaft should be controlled at 0.15 ~ 0.25mm. If the fastening bolt is loose and causes oil leakage, tighten the bolt.
④ Check whether the crankcase breather is blocked. If there is any blockage, remove and clean it, and pay attention to check whether the breathing valve is closed tightly.
⑤ If the fault cannot be eliminated after the above inspection, check whether the oil pressure is too high. If it is too high, a paper pad with appropriate thickness can be added to the joint surface of the oil pump cover and the oil pump body. The paper pad should not be too thick, otherwise the volumetric efficiency of the oil pump will be reduced too much, the oil pump will be weak and the oil supply will be insufficient, resulting in the burning of the bearing bush.
280. How to treat crankcase oil leakage?
Crankcase oil leakage can be removed from the crankcase cover and gasket for inspection. If it is intact, clean it and coat it with lead oil, dry it and install it. If it is damaged, replace it with a new gasket. Before installation, the new gasket should be soaked in diesel oil for 20 minutes, coated with lead oil and dried before installation. The screws should be symmetrical and tightened evenly from the middle to all sides.
28 1. How to treat oil leakage at crankshaft oil seal?
Cylinder liner, piston, piston ring, crankshaft journal and bearing bush of single-cylinder diesel engine should be in good technical condition, and parts that do not meet technical requirements or are damaged should be repaired or replaced in time.
When replacing the oil seal, apply a little lubricating oil to the oil seal lip, and then rotate and install it. Never smash it to death to prevent the oil seal from warping or breaking the spring. The vent holes on the diesel engine and gearbox cover should be dredged frequently; When replacing the main bearing cover, check the oil drain hole.
282. How to repair the bearing of the outer ring?
After the bearing seat hole is seriously worn, the bearing outer ring will move relative to the seat hole, which will affect the power transmission. This kind of fault is commonly known as bearing outer ring. Repair method:
(1) napping method
If the bearing seat hole is not worn much, the surface of the bearing outer ring can be roughened. The method is to put the bearing on the grounding wire of the electric welding machine, clamp a scrap saw blade on the pliers of the electric welding machine, and use the contact between the saw blade and the bearing bush to pull a layer of hair (pit) on the outer ring surface of the bearing. Pay attention to the fineness and uniformity of the pits during cauterization, and the temperature should not be too high, preferably not more than 100℃.
(2) Insertion method
If the bearing seat is seriously worn, use a reamer to ream the worn bearing hole to a certain repair size, and match the corresponding bushing according to the reamed hole of the machine body. When turning the bushing, we should consider the fit tightness between the outer diameter and the hole of the machine body, and the shrinkage of the inner hole of the bushing after the bushing is inserted into the machine body.
283. How to judge the diesel engine bearing clearance is too large?
If the following symptoms appear in the operation of diesel engine, it can be considered that the bearing bush fit clearance is too large.
(1) The oil contains more alloy chips.
Because the thickness of lubricating oil film between bearing bush and journal decreases, semi-dry friction occurs, which promotes a large number of alloy powder peeling off of bearing bush. When working under heavy load, the alloy powder falls off more seriously. If you dip your finger in some engine oil and twist it, you can feel or see more alloy chips, so you can judge that the fit clearance between the bearing bush and the journal is too large.
(2) the oil pressure is reduced
Normal diesel engine pressure is lower than the normal pressure at rated speed. If the pressure can't be reflected from the oil pressure gauge, the oil pressure value still doesn't increase after replacing the new oil, which indicates that the fit clearance between the main bearing bush, connecting rod bush and journal of the engine is too large, and it is difficult to form the rated oil pressure.
(3) Abnormal sound
Use a listening stick to auscultate on both sides of the cylinder. If you hear a short, pure, solid and rhythmic "click, click" sound, the sound will be clearer when you suddenly accelerate and increase the load, indicating that the fit clearance between the connecting rod bushing and the journal is too large. Then auscultate with a stick near each main bearing tile, or open the fuel filler cap for auscultation. If you hear a low and heavy "empty" sound, the noise will be small when working at low temperature; When the temperature is high, the noise is high; When working at full load and suddenly increasing the speed, the noise is loud and clear, indicating that the fit clearance between the main bearing bush and the journal is too large.
284. How to scrape the connecting rod bearing?
(1) scraping process
Put the connecting rod of the assembled bearing on the journal, tighten the nut until there is resistance to pulling the connecting rod, pull the connecting rod back and forth several times to make the bearing rub against the journal, then remove the connecting rod and check the contact between the bearing and the journal to see if there are any scratches. The method is: hold the connecting rod or cover with the left hand, make the scraper form an angle of 30 ~ 40 with the bearing surface with the right hand, and exert force with the wrist. When scraping, pay attention to big scraping, heavy scraping and light scraping. The knife should be stable and sharp. At the beginning, the contact surface of the bearing is generally at both ends. After several scratches, the contact surface gradually expanded to the middle. The bearing must be scraped repeatedly until the tightness and contact surface are suitable.
(2) Quality inspection after scraping
Ying Xing points of contact marks are everywhere, with the same weight, and the contact area exceeds 75%. Tightness is mainly checked by empirical methods. Apply a layer of engine oil to the bearing surface, put it on the journal, and tighten the connecting rod bolts and nuts according to the specified torque. The torque is shown in Table 4- 1. It is advisable to shake the connecting rod by hand. The connecting rod can rotate around the crankshaft 1 ~ 1.5 times. Pull the connecting rod along the axial direction of the crankshaft. If there is no gap, feel the tightness is appropriate, as shown in Figure 4-3.
Table 4- 1 Torque of crankshaft bearing bolt (internal thread) (n m)
Figure 4-3 Inspection of Bearing Looseness
285. Scraping crankshaft spindle bearing need to pay attention to?
(1) In order to prevent the bearing cover from breaking, the bolts must be tightened gradually when fastening the bearing cover, and the bearing cover with four studs should also be tightened gradually. (2) When scraping the main bearing, the bearing cover should not be screwed too tightly. The crowbar used to pry the crankshaft should not exceed 600 mm in length, otherwise it will distort the crankshaft or crush the alloy, which will make the alloy and the bottom plate not firmly combined, and it will easily fall off due to fatigue, resulting in serious consequences such as burning tiles. (3) Due to the different alloy compositions of bearings, the requirements for sealing performance of bearings should be different. Due to the large expansion coefficient of high-tin aluminum alloy bearings, the radial clearance of bearings should be the upper limit of the standard or about 0.0 1 mm greater than the upper limit.