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1、Engine Servive and Maintenance (I)This section and the following two describe various engine services and explain how various troubles in the engine are corrected. Later sections discuss servicing of the fuel, lubricating, cooling, and ignition systems. You will notice, in the discussions of various
2、 engine-servicing jobs, that the time to do the job is often given. These figures are included to give you some idea of the size of the job and must not be considered accurate enough for cost-estimating jobs. The procedures discussed in the three engine-sections are aimed at correction specific trou
3、bles.The major enemy of good work is dirt. A trace of dirt left on a bearing or cylinder wall would ruin an otherwise good job. Thus, you must be absolutely sure that you do not leave dirt or abrasive in the engine or on engine parts when you finish a job. Before any major job, the block should be c
4、leaned. Electrical units should be removed or covered if the engine is steam-cleaned so that moisture does not get into them. Connecting rods and rod bearings serviceOn many engines, the connection-rod and main bearings (crankshaft bearings) can be checked for wear with an oil-leak detector before t
5、he engine is torn down. To use the detector, the oil pan is removed, and the detector hose is connected to the pressure side of the engine lubricating system (at the oil filter, for example). Then, with the detector filled with oil, an air pressure of 175 kPa is applied to the detector tank. This pr
6、essure forces oil through the engine lubricating system. If bearings are worn, considerable oil will leak from them. Worn bearings greatly increase engine oil consumption because they pass more oil. The detector manufacturer states that a normal bearing will leak between 20 and 150 drops of oil a mi
7、nute. If it leaks more, the bearing is worn. If it leaks less than 20 drops per minute, then either the bearing clearance is too small or else the oil line to the bearing is stopped up.Connecting rods and pistons are removed as assembly from the engine. Removing, servicing, and replacing connecting
8、rod requires about 5 to 8 hours, according to the type of engine. About 3 additional hours are required to install new piston rings. Additional time is needed for such services as piston-pin or bushing replacement.Pistons and rings serviceAfter the piston-and-connecting-rod assemblies have been remo
9、ved from the engine and the pistons and rods separated, the rings should be removed from the piston. A special ring tool is required for ring removal. The tool has two small claws that catch under the ends of the ring. Then, when pressure is applied to the tool handles, the ring is sprung enough tha
10、t it can be lifted out of the ring groove and off the piston.(1) Piston cleaning. Remove carbon and varnish from piston surfaces. Do not use a caustic cleaning solution or a wire brush! These could damage the piston-skirt finish. Use solvent to remove deposits. Clean out ring grooves with a clean-ou
11、t tool. Oil ring slots, or holes, must be clean; a drill of the proper size is handy for this job. Be sure that you do not remove metal when cleaning ring grooves or oil slots.(2) Piston inspection. Examine the pistons carefully for worn, scuffed, or scored skirts and for cracks at the ring lands, s
12、kirts, ring bosses, and heads. Check the piston with a micrometer. Compare the sizing-point reading with the measurement of the cylinder diameter taken with an inside micrometer, an outside micrometer and a dial indicator, or a telescope gauge and a micrometer. If the cylinder wall is excessively wo
13、rn, it will require refinishing. Cylinder wall refinishing means that an oversize piston will be required.(3) New pistons. New pistons are supplied either finished or semifinished. The finished type, ready for installation, is available in a number of sizes. When these are used, the cylinders must b
14、e finished to fit the pistons, as a rule, engine manufacturers supply oversize pistons of the same weight as the standard pistons. Thus, it is not necessary to replace all pistons when only part of the cylinders require service. There is no problem of balance if all pistons are of the same weight, e
15、ven if some are oversize. Semifinished pistons are oversize and must be finished down to size to fit the cylinders.If an engine is torn down for overhaul after considerable mileage, the chances are that the rings will require replacement. Sometimes, all that is required is to free up the rings in th
16、e ring grooves by cleaning out carbon. In examining rings to determine whether or not they should bereused, several conditions may be found. Conditions requiring ring replacement include loss of tension, irregular lightand dark areas (showing uneven wear caused by warped or worn rings), and scores o
17、r scratches.Engine Service and Maintenance ()This section describes the servicing of crankshafts, main bearings, and engine blocks and cylinders.Crankshaft and main bearings serviceMost modern automotive engines have precision-insert-type main bearings which can be replaced without removing the cran
18、kshaft. Many bearing difficulties can be taken care of by this method of bearing replacement. However, if the bearing problem has been caused by such conditions as a warped engine block, stopped-up oil passages, a worn crankshaft journal, or a bent crankshaft, then simply replacing the bearings will
19、 not correct the condition. Such conditions as these will cause uneven bearing wear, with some bearings wearing faster (and more unevenly) than others.If the bearings seem to have worn fairly uniformly, then the chances are that only crankshaft-journal checks and bearing replacement will be required
20、. Use of the bearing oil-leak detector will determine whether or not bearing wear has been uneven.If bearing wear is uneven, then the safest procedure is to remove the crankshaft from the engine block and check both separately for alignment and for clogged oil passages.Replacing precision-insert mai
21、n bearings without removing the crankshaft requires about 5 hours. Removing and replacing the crankshaft requires several additional hours.Semifinished main bearings require finishing and fitting after installation, so that the crankshaft must be taken out. To perform the complete replacement job on
22、 semifinished main bearings requires about 19 to 22 hours.Cylinder and cylinder blocks service and maintenanceBefore any service operations are performed, the cylinder block should be cleaned and inspected. There are several methods of cleaning. One method uses steam directed by a nozzle onto the bl
23、ock to wash away oil, sludge and dirt. A good solvent applied with a brush will also clean the block. After the block is cleaned, inspect it for cracks, especially in the cylinder walls, top, water jackets, and main-bearing webs.The piston and ring movement, the high temperatures and pressures of co
24、mbustion, the washing action of gasoline entering the cylinder - all these tend to cause cylinder-wall wear.There are certain limits to which cylinders may wear tapered or out of round before they require refinishing. Special drastic replacement rings will control compression and oil in cylinders wi
25、th some taper and out-of-round wear. But when wear goes beyond a certain point, even the severest rings cannot hold compression and control oil; loss of compression, high oil consumption, poor performance, and heavy carbon accumulations in the cylinders will result. In such a case, the only way to g
26、et the engine back into good operation condition is to refinish the cylinders and fit new pistons and new rings to them.If wear, taper, or eccentricity is not too great, only honing will be required. In operation, the hone revolves in the cylinder, and the abrasive stones in the hone remove material
27、 from the cylinder wall. If wear is too great to be taken care of by honing alone, cylinders must be bored first and them boned. Cylinders must be cleaned thoroughly after the honing or boring operation. Even slight traces of grit or dust left on the cylinder walls may cause rapid ring and wall wear
28、 and early engine failure.Refinishing cylinders requires 12 to 20 hours (according to the type of engine). This includes fitting and installing new pistons, rings, piston pins, and connection rods. When new bearings are fitted, about 10 additional hours is required. Grinding valves would require sev
29、eral more hours. These various times are mentioned because an engine that requires cylinder refinishing is usually in need of a general overhaul and these other services will also be required. Engine Service and Maintenance (III)Valves and valve mechanisms serviceValves must be properly timed. They
30、must seat tightly and operate without lag. Valve-tappet clearance, as well as the clearance between the valve stems and guides, must be correct. Failure to meet any of these requirements means valve and engine trouble.Types of valve troubles include sticking, burning, breakage, wear, and deposits.Va
31、lve sticking. Gum or carbon deposits on the valve stem will cause valve sticking. Excessive valve-stem clearance speeds up valve deposits. Another cause of valve sticking is warped stems. This could result from overheating, an eccentric seat (which throws side pressure on the valve), or from a cocke
32、d spring or retainer (which tends to bend the stem). Insufficient oil would also cause valve sticking. Sometimes valves will stick when cold but will work free as the engine warms up. Valve burning. This is usually an exhaust-valve problem. Any condition that prevents normal exhaust-valve seating ma
33、y lead to valve burning.Valve breakage. Any condition that causes the valve to overheat or to be subjected to heavy pounding (as from excessive tappet clearance or from detonation) may cause valves to break.Valve-face wear. In addition to the conditions discussed above, excessive tappet clearance or
34、 dirt on the valve face or seat could cause valve-face wear. Dirt may cause valve-face wear if the engine operates in dusty conditions or if the car-burettor air cleaner is not functioning properly. The dust enters the engine with the air-fuel mixture, and some of it settles on the valve seat. The d
35、ust will also cause bearing, cylinder-wall, and piston and ring wear.Valve deposits. If the fuel has excessive amounts of gum in it, some of this gum may be deposited on the intake valve as the air-fuel mixture passes the valve on the way to the engine cylinder. Carbon deposits may form because of a
36、n excessively rich mixture or because of oil passing a worn valve guide (in the intake valve). Improper combustion, due to a rich mixture, defective ignition system, loss of compression in the engine, a cold engine, and so forth, will result in carbon deposits on the exhaust valves. Dirty or imprope
37、r oil will cause deposits to form on the valves.Valve Service and Maintenance includes adjusting valve-tappet clearances (also called adjusting valve lash), grinding valves and valve seats, installing new seat inserts, cleaning or replacing valve guides, servicing the camshaft and camshaft bearings,
38、 and timing the valves. A complete valve Service and Maintenance job, including grinding valves and seats, checking springs, cleaning guides, and tuning the engine, requires from about five hours (for an overhead-valve six-cylinder engine) to about eight hours (for an eight-cylinder L-head engine).
39、Replacing the camshaft requires about eight hours; four additional hours are required for replacing camshaft bearings.译文：发动机维修(I)本节和下面两节的内容是介绍各种发动机的维修，并讨论如何正确处理发动机的各种故障。再后的几节讨论燃料供给系、润滑系、冷却系和点火系的维修。你会注意到在讲述发动机的各种维修工作时，都提供了完成各项工作所需的时间。这些数据会使你了解维修工作的规模，但并非精确到可以作为维修价格的参考。这三节有关发动机维修工作的内容，其目的在于介绍排除发动机具体故障
40、的方法。高质量维修工作的最主要问题是油污。残留在轴承或是气缸壁上的油污会影响维修工作的质量。当维修工作完成时，必须保证不能把油污或磨料残留在发动机内部或发动机机件上。在进行重要维修工作之前，气缸体应加以清洗。如果发动机进行高压清洗，电气部件必须拆卸或遮盖。这样，水分才不会渗入。连杆和连杆轴承的维修许多发动机在拆卸之前，可以用漏油检测装置检查连杆和主轴承(曲轴轴承)的磨损情况。使用这种装置时，拆掉油底壳，并把该装置的油管连接到发动机润滑系统加压的一侧(如滤清器上)。这时，检查器充满油，提供给检查器油槽l 75千帕的压力，这一压力使油流过发动机的润滑系统。如果轴承磨损，从轴承中漏出的油会较多。磨损
41、的轴承大量增加了发动机油的消耗，因为更多的油是漏掉的。这种装置的制造厂商指出，标准轴承每分钟应漏油201 50滴。如果油漏的过多，轴承即以磨损；如果每分钟漏油少于20滴，那么或是轴承的配合间隙太小，或是油道堵塞。把连杆和活塞做为整体组件从发动机上拆卸下来。不同类型的发动机，拆卸、维修和更换连杆的时间从5小时到8小时不等，安装新活塞环需要另外增加3小时；像更换活塞销或衬套之类的维修项目，也需要另外增加时间。活塞和活塞环的维修先将活塞及连杆组件从发动机上拆下再把活塞与连杆分开之后，即可将活塞环从活塞上取下。活塞环的拆卸要求使用专用工具进行。这种工具有两个小爪，可以伸到活塞环下端将其卡住。然后用力压
42、住工具手柄，使活塞环足以弹起，即可使之从环槽中脱出，而将其从活塞上取下。(1)清洁活塞环：绝不能使用苛性溶液或金属刷清除活塞表面的积碳和漆膜。因为这样会损坏活塞裙部的粗糙度。可使用溶剂清除积垢；使用清除工具清洁活塞环槽；油环开缝或孔隙必须清理干净，用适当尺寸的钻机进行这项工作较为便利。清洁活塞环槽或油环开缝，绝对不能损伤金属部分。(2)活塞探伤：仔细检查活塞，找出裙部的磨损，划伤或划痕，以及环槽岸、裙部、轴套和顶部的裂痕。可使用千分尺检查活塞，用内径千分尺、外径千分尺和千分表或用内径规和干分尺测量出气缸直径，并与原尺寸标准进行对照。如果气缸壁磨损过大，就需要修整表面，这意味着需要更换较大尺寸的
43、活塞。(3)更换新活塞：新活塞或者是精加工的；或者是半精加工的。可直接装配的精加工的活塞有若干种尺寸可供选择。更换时，气缸必须与活塞具有装配精度。通常情况下，发动机制造厂商提供具有相同重量的，与标准活塞相比尺寸较大的活塞。这样，当气缸仅需要部分维修时，就不必更换全部活塞。所有的活塞，包括加大尺寸的活塞，重量都相同，也就不存在平衡问题了。半精加工的活塞是加大尺寸的，必须进行修整以便与气缸相配合。在行驶了一定的里程后，发动机被拆下检修，这正是维修更换活塞环的机会。有时，所要做的仅仅是清除积碳，使活塞环在活塞环槽中活动自如。检查活塞环，判断是否还可以继续使用。张力下降，有的部位凹凸不平(由翘曲或磨损
44、的活塞环所引起的不平整)，有裂痕或划痕的活塞环需要更换。发动机维修(II)本节介绍曲轴、主轴承、发动机机体和气缸的维修。曲轴和主轴承的维修大多数现代汽车发动机的主轴承是精密嵌入型，不必拆下曲轴即可更换。许多轴承故障能够通过更换主轴承或轴承来解决。如果轴承问题是由缸体翘曲、油道堵塞、曲轴轴颈磨损或是曲轴弯曲变形所引起，那么仅更换轴承就不能解决问题。类似这样的情况会造成轴承不均匀磨损，而且一些轴承会比另一些磨损得更快。如果轴承看上去似乎已磨损的相当均匀，那么只需要检查曲轴轴颈并更换轴承。使用漏油检测装置即可判定轴承磨损是否均匀。如果轴承磨损不均匀，那么较为保险的作法是从发动机机体上卸下曲轴，然后分
45、别进行调校，并检查油道是否堵塞。不拆曲轴更换精密嵌入型主轴承，大约需要5小时，拆卸和更换轴承要额外增加几小时。半精加工的主轴承安装后需要修整和调配，这样曲轴就必须拆下。完成更换半精加工主轴承的工作需要1 920小时。气缸和气缸体的维修在进行任何维修工作之前，应对气缸体进行清洁处理和探伤检查。有几种清洁方式可供选择。一种是直接用喷管喷出的蒸汽冲洗气缸体，从中清洗出油、金属碎屑和污垢。当然，也可使用刷子和优质清洁剂清洗气缸体。气缸体清洁之后，检查有无裂痕，尤其是气缸壁、顶部、冷却水套和主轴承腹板。活塞和活塞环的运动，燃烧产生的高温、高压，以及汽油进入气缸时的冲刷作用，均是造成气缸壁磨损的原因。气缸
46、磨损形成锥度或不圆，在达到一定的限度前，不必整修表面。在这种情况下，特别精选的油环有助于控制气缸的压力和油耗。但是，一旦磨损超过某一限度，即使是严格挑选的活塞环也无法保持压力和控制油耗，而且产生压力不足、油耗高、效率低、积炭严重等情况。在这样的情况下，要使发动机保持良好的工作状态，只有整修气缸表面，并配装新的活塞和活塞环。如果磨损造成锥度或偏心度不是很严重，仅需要进行衍磨即可解决问题。操作时，衍磨头在气缸中旋转，衍磨头上的磨石从气缸壁上磨去余量。如果磨损严重，仅靠衍磨不能解决问题，那么气缸必须先进行镗削，然后再衍磨。镗削和衍磨加工之后，气缸必须彻底清洁。残留在气缸壁上的砂砾或尘埃所造成的划痕，
47、均能引起活塞环和气缸壁的迅速磨损以及发动机的早期损坏。整修气缸需要1 220小时(时间长短取决于发动机的类型)，这包括调配和安装新活塞、活塞环、活塞销和连杆。新轴承的配装大约需增加1 O小时。磨削气门则需要更多的时间。这里之所以提供几种不同的时间，是因为需要整修气缸的发动机通常必须进行大修，那么这些维修工作也就必不可少。发动机维修(III)气门和气门机构的维修气门必须严格定时，落座严密并且开启无滞怠。不仅气门杆与气门导管之间的间隙，气门推杆间隙也必须适当。不能满足这些要求意味着气门和发动机发生了故障。气门故障包括沾着、烧伤、破裂、磨损和积炭。气门沾着：气门杆上的胶质或积炭是造成沾着的原因。气门
48、杆间隙过大会加速气门的积炭。气门沾着的另一个原因是气门杆变形，产生的原因是过热、气门落座不正常(使气门受到侧压)以及气门弹簧或锁销上翘(使气门杆弯曲)。润滑不良也是沾着的原因。有时，发动机冷态时，气门也会粘住；发动机预热后，气门工作就正常了。气门烧伤：这种情况通常发生在排气门。任何妨碍排气门密封面贴合的情况都会导致气门烧伤。气门破裂：气门过热或遭受重载(气门杆间隙过大或爆裂)均可造成气门破裂。气门表面磨损：除上述介绍的情况外，气门间隙过大或气门表面与气门座的污垢均会使气门表面磨损。如果发动机在高尘条件下工作，或者化油器净化空气的效果较差，灰尘会造成气门表面磨损。灰尘会随混合油气进入发动机，其中
49、一些会沉积在气门表面。灰尘同样也会导致轴承、气缸壁、活塞和活塞环的磨损。气门积垢：如果燃油中含有过量的胶粘剂，当混合油气通过气门进入气缸时，就会沉积在进气门上。混合气过浓或润滑油流到磨损的气门导管中(进气门)，都可形成积炭。因混合气过浓、点火系统有故障、发动机内压力损失、冷机等导致的不正常燃烧都会形成气门积炭。含有灰尘或不合格的油也会在气门上形成积炭。气门维修包括调校气门间隙(也称气门余隙)，研磨气门和气门座，镶配气门座，清洁或更换气门导管，保养凸轮轴和凸轮轴轴承，气门的正时调整。全部气门维修工作，包括研磨气门和气门座，检查气门弹簧，清洁气门导管，调整发动机，大约需要5小时(顶置气门六缸发动机)到8小时(侧置气门八缸发动机)。更换凸轮轴需要8小时左右；更换凸轮轴轴承需要额外增加4小时。
