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1、Passage 1Valve drive mechanism The valve drive mechanism commands the inlet and exhaust valves at the required timing. The valve drive mechanism consists of an inlet and exhaust cam follower (8) each suspended in a plunger of the tappet assembly (7), two tubular push rods (4) with ball joints, two n
2、odular cast iron rocker arms (2) suspended in a rocker arm bearing bracket, two yokes (5) and a yoke guide pins. See Fig. 4-1. The tappet rollers follow the cam profiles and transfer the movements through push rods to the rocker arms. The rocker arms operate the inlet and exhaust valves through yoke
3、s (5). Lubrication for the rocker arms comes from the engines secondary oil supply manifold throughdrillings in the cylinder head and rocker arm bracket. The tappet assembly receives lubricating oil via channels in the engine block from the main supply manifold. For the roller and shaft, the oil is
4、supplied through the guiding plunger. To compensate for heat expansion a clearance must exist between the rocker arm and yoke. All adjustments have to be done on a cold engine only.1. According to the passage, the best time to adjust the valve clearance is _.A. before the engine is startedB. when th
5、e engine is running C. after the engine has just been stopped D. when something has gone wrong with the engine 2. The roller and the tappet assembly are lubricated by means of_. A. the main lube system B. the secondary oil system C. the special pumping system D. the turbine oil system 3. According t
6、o the passage, the valve drive mechanism does not include_. A. tappet milers B. push rods C. nodular cast iron D. yokes and guide pins 4. To close valves tightly, which clearance should be inspected according to the maintenance schedule? A. The one between the cam and the tappet roller. B. The one b
7、etween the push rods and the ban joints. C. The one between the rocker arms and the yoke D. The one between two tubular push rods. 5. Which statement about the passage is not true? A. All adjustments have to be made on a hot engine only. B. For the miler and shaft, the oil is supplied through the gu
8、iding plunger. C. The valve drive mechanism commands the inlet and exhaust valves at the required timing. D. The rocker arms operate the inlet and exhaust valves through yokes.Passage 2Compressor cleaning during engine operation The compressor may be cleaned by water injection during the engine oper
9、ation. The cleaning process will have good results as long as the deposit formation has not gone too far. In ease a very thick hardened crest of dirt the compressor has to be dismantled for cleaning. In this method of cleaning the water is not acting as a solvent but instead removes the deposits mec
10、hanically by the impact of the water droplets. It is therefore recommended to use clean water without additives. The water should not contain any additives which might remain on the compressor blades. Periodically cleaning of the compressor (Fig. 4-2) prevents or delays excessive build-up of dirt bu
11、t in no way replaces the usual overhauls where the turbocharger is completely dismantled. The turbocharger is provided with a water container (1). During the cleaning procedure the container is pressurized with the charge air (2) and from where the water is forced to the compressor inlet (3). 1. Whi
12、ch of the following statements can be used to clean the compressor with the engine running? A. Water droplets B. Water with additives C. Charge air D. Hard crust 2. What principal is used in this method of cleaning? A. The cleanser solves the deposits. B. The cleanser melts the deposits. C. The clea
13、nser beats the deposits mechanically. D. The high pressure of the cleanser removes the deposits. 3. Which of the following statements is not correct? A. The compressor needs regular cleaning. B. Periodical cleaning of the compressor contributes to reducing build-up of dirt. C. Its not necessary to d
14、ismantle the turbocharger if periodical cleaning of the compressor is performed. D. Additives should better be avoided during the cleaning process. 4. The cleaning water should not contain any additives, because_. A. they may delay build-up of dirt B. they might remain on the blades of the compresso
15、r C. they may be forced to the compressor inlet D. they are not good solvents 5. The cleaning process will have good results if_. A. there is a very thick crust of dirt on the compressor B. the compressor is not dismantled C. the deposit formation is not very serious D. the water droplets are small
16、enoughPassage 3Charge air cooler The engine is equipped with a charge air cooler. The insert type charge air cooler is mounted in a welded casing (air trunk). The trunk is bolted to the engine block. Standard is a two-stage cooler mounted. The first stage, through which the charge air flows, iscoole
17、d with water from the HT cooling system and cooks the charge air till approx. 90 100oC. The second stage is supplied with water coming from the LT water system and cooks the charge air further till therequired temperature of approx. 50oC. By controlling the water flow through the LT cooler the charg
18、e air temperature can be kept constant at the required temperature. The circulating coolant water should always be under positive pressure and should be as clean as possible. The operating air temperature should be maintained by controlling the coolant inlet temperature. Whilst the engine is running
19、 the air and coolant temperatures and pressures at inlet and outlet should be checked and logged periodically. Variations from normal indicate faults developing such as fouling of the film plates or obstruction of the water tubes. Check daily, during operation of the engine, the working of the tellt
20、ale hole at the free end of the charge air receiver. The function of this hole is to inform the operator the presence of water in the charge air receiver. Under normal condition only compressed air should escape from this hole. 1. According to the passage, the expression HT probably means_.A. HIGH T
21、ANK B. HIGH TEMPERATUREC. HEAT TRANSMISSION D. HEAT TRANSFER 2. In order to maintain the change air temperature we should control_. A. the coolant inlet temperature coming from the first stage cooler B. the coolant flow coming from the second stage cooler C. the coolant outlet temperature coming fro
22、m the second stage cooler D. the coolant flow coming from the flint stage cooler 3. The charge air temperature departing from normal may indicate that_. A. condensate can be formed B. only compressed air should escape from the telltale C. the film plates are becoming dirty or the water tubes are blo
23、cked by scale D. cooling water may have been carried into the cylinders 4. The function of the telltale hole is to_. A. detect whether compressed air has escaped from the hole B. control the coolant inlet temperature C. determine whether the coolant water is under positive pressure D. inform the ope
24、rator the presence of water in the charge air receiver 5. Which of the following statements is not true? A. The engine is equipped with a charge air cooler. B. A two-stage cooler mounted is standard. C. The first stage is cooled with water from the LH water system. D. The second stage cools the char
25、ge air further till about 50oC.Passage 4 The vibration damper serves to reduce the torsional vibration generated by the crankshaft. The damper consists of a housing and a free rotating inertia ring supported by an axial bearing. It forms a totally enclosed unit. The free space between inertia ring a
26、nd damper housing is filled with a high viscous fluid. When the crankshaft rotates at constant speed, the inertia ring will follow this movement. The combustion pressure exerted on each piston generates vibration in the crankshaft, and each variation generated by such a vibration will affect the mov
27、ement of the inertia ring. The resulting shift of the ring to the damper housing is opposed by the viscous fluid and the vibration will be reduced. The energy, absorbed during the process, is converted into heat and then radiated to the surrounding air. Hence, proper ventilation of the damper is ess
28、ential. The viscous damper fluid is during engine operation subjected to ageing and the fluid becomes more viscous. In sending fluid samples on a regular base to the damper manufacturer the rate in reduction of the viscosity can be determined. As sampling interval time is 6000 hours advised. Dampers
29、 with a too high fluid viscosity may cause crankshaft breakdown. The damper cover has two filling holes located 180o opposite each other and closed by screw-in filler plugs. If one of these plugs is accessible, a fluid sample container can be screwed in and a sample taken with the damper in place. O
30、n a spare damper, sampling must be effected with the damper in the vertical position. For liquid sampling, a special kit can be ordered from Stork-Wartsila Diesel. 1. The general description of the vibration damper tells us that_. A. the free space between inertia ring and damper housing is filled w
31、ith a low viscous fluid B. when the inertia ring moves at constant speed , the crankshaft follows this movement C. the damper is made up of a housing and a free rotating inertia ring D. no ventilation of the damper is necessary as the vibration reduction process absorbs little energy 2. Which of the
32、 following statements is not true about maintenance of the viscous damper? A. Sampling interval time for determining the quality of the fluid is 6000 hours. B. For liquid sampling, a special kit can be used. C. On a spare damper, sampling must be effected with the damper in place. D. The viscous flu
33、id in a damper becomes more viscous as time goes by. 3. During the engine operation, the vibration damper can_. A. transfer the energy of the engine B. absorb the combustion heat C. oppose the crankshaft rotating D. reduce the vibration of the crankshaft 4. According to the passage, we learn that tw
34、o filling holes in the damper cover are used _. A. to recharge the fluid B. to ventilate the damper C. to fit the container D. to take the sample 5. If the damper fluid becomes highly viscous, _. A. the torsional vibration of the crankshaft may be reduced B. the damper may absorb more heat C. the in
35、ertia ring may rotate faster D. the crankshaft may break downPassage 5 The vibration damper employs a high viscous fluid to oppose the shift of the inertia ring to thedamper housing. It is necessary to get samples to determine the rate in reduction of the viscosity. The steps to draw off the sample
36、are as follows(Refer to the Fig. 4-3): 1. Turn the engine until the drain plugs are easy accessible. Do not unscrew the drain plug until the damper is luke warm (approx. 40oC ). 2. Carefully tap the locking of the upper drain plug backwards, using a punch, and unscrew the threaded plug. Do not yet r
37、emove the plug! 3. Unscrew one cap nut from the (plastic) liquid container. 4. Remove the drain plug and screw the liquid container instead. 5. Remove the outer cap nut from the liquid container. Make sure that no machine oil or dirt can enter the liquid container! 6. Screw the outer cap nut again,
38、once the liquid has reached the open end of the liquid container. The filling-up period of the liquid container may take from a few seconds up to more than an hour, depending on the liquid condition. 7. Unscrew the liquid container from the damper and fit the drain plug using a new joint ring (suppl
39、ied with the mounting kit). 8. Fit the second cap on the liquid container. If no sample can be taken in this way, you can proceed as follows: - If still no liquid appears after a while, remove the second drain plug, too. - Supply nitrogen of 3.5 bar maximum pressure through the open filling hole. If
40、 no nitrogen is available, air may be used, provided this air is properly filtered and dry. - Once the liquid has reached the open end of the liquid container, cut off the supply of nitrogen and screw the cap on the liquid container. - After the nitrogen supply has cut off, unscrew the liquid contai
41、ner, screw the second cap and fit both drain plugs. If a liquid sample cannot be obtained this way either, it can be assumed that the damper liquid has thickened to an inadmissible value, necessitating the replacement of the damper. 1. According to the passage, we can learn that_. A. before using th
42、e container to draw off the sample, both ends of it are closed B. the liquid container must be washed with machine oil before sampling C. liquid sampling must take more than one hour D. two liquid samples should be taken every time 2. If the liquid sample cannot be taken any way, it means_. A. nitro
43、gen pressure is too low B. the quantity of the damper fluid is insufficient C. the viscous fluid in damper becomes too thick D. the method of liquid sampling is incorrect 3. Which statement is tree about the sampling process? A. The drain plug can be unscrewed regardless of the damper temperature. B
44、. The drain plug should not be removed until one cap nut from the liquid container is unscrewed. C. The outer cap nut must be screwed before the liquid reaches the open end of the liquid container. D. The drain plug can be fit by using the old joint ring. 4. If no sample can be taken by removing the
45、 first drain plug, then which of the following is done? A. The second drain plug should be removed too. B. A pressure of 5.3 bar should be applied. C. Clean and damp air is used instead of nitrogen if the latter is not available. D. The nitrogen supply continues when the liquid has reached the outer end of the liquid container. 5. During the sampling process, if no nitrogen is available, _ may be used.
