tiếng anh công nghệ ô tô và chế tạo máy: phần 2

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302 you can pull it o ff the plug. The shiny thing sticking out of the e n g in e block is the term inal o f the spark plug. Figure 12-10, later in this chapter, shows you all the parts of a spark plug, including the term inal. 2. Use a nice soft rag or a sm all paint brush to clean around the area w here the spark plug enters the block - or you can blow the dirt away w ith a soda straw. D oing so keeps loose junk from falling down the hole into the cylinder w hen the plug is rem oved. 3. Find your spark plug socket (the big one with the rubber lining) and place it dow n over the spark plug; exert some pressure w hile turning it slightly to be sure that it's all the way down. Like everything else in auto repair, don’t be afraid to use som e strength. But do it in an even, controlled manner. If you bang or je rk things, you can dam age them , but you’ll never get anyw here if you tippy-toe around. 4. Pick up your ratchet handle and stick the square end into the square hole in the spark-plug socket. I f you can w ork m ore com fortably by adding a couple of extensions betw een the handle and the socket so that you can move the handle freely from side to side without hit ting anything, go ahead. You add them in the same way you added the socket to the handle. (If you have trouble with gpttinp the plug loose, see the “ D ealing with difficult plugs” section, w hich follow s, for encouragem ent.) The little knob on the back o f the ratchet handle makes the ratchet turn the socket either clockw ise or counter clockw ise) You can tell w hich way the handle will turn the plug by listening to the clicks that the handle m akes when you m ove it in one direction. If it clicks w hen you move it to the right, it will turn the socket counterclockw ise when you m ove it, silen tly, to the left. If the clicks are audible on
303 the leftward swing, it will move the socket clockwise on the rightward swing. Every screw, nut, bolt, and so on that you encounter should loosen counterclockwise and tighten clockwise. If your ratchet clicks in the wrong direction, just move that little knob to reverse the direction. Figure 12-9 shows you the proper way to use a socket wrench, and the sidebar “Breaking loose old plugs and m isconceptions” tells you how to handle difficult plugs. 5. Loosen the spark plug by turning it counterclockwise. When the ratchet turns freely, finish the job by rem oving the ratchet handle and turning the socket by hand until the plug is free from .the engine. After you’ve rem oved the spark plug from the engine, re move the plug from the socket. But don’t go on to the next plug until you’ve read the plug (see the section “Reading your spark plugs” and Table 12-1) and gapped and replaced it, follow ing the instructions later in this chapter. Dealing with difficult plugs W ith all the stuff crammed under the hoods o f vehicles, it can be hard to get at some spark plugs and, even when you can reach
304 them easily, they may be difficult to remove. This section provides tips on extracting your spark plugs with a minimum o f hassle. A lm ost every vehicle has at least one plug that’s a miser able th in g to reach. If you have one, save it for last. Then you can work on it with the satisfaction o f know ing that, when you get the darn thing finished, you will have finished the job. If you find that one or more plugs are blocked by an air conditioner or som e other part, try using various ratchet handle extensions to get around the problem . There are universal ex tensions that allow the ratchet handle to be held at odd angles; T-bar handles for better leverage; and offset handles for hard- to-reach places. (See C hapter 2 for exam ples.) On som e vehicles, you can’t get at the plugs until you re move other parts that are in the way. On som e transverse en gines, you have to rem ove the top engine m ount bolts by the radiator so that you can tilt the engine forw ard to replace the rear spark plugs. And on other engines, it m ay be easier to get to som e spark plugs from underneath or through the wheel well area. On som e sm all cars equipped with optional big engines, you have to hoist the entire engine out o f the car to reach at least one plug. I f you have one o f these beasts, I bet that when you finally get that plug out, you’ll find that it’s never been replaced during all the professional tune-ups you’ve paid for. And you’ve paid even m ore because that one funky plug probably not only increased your fuel consum ption but also added to air pollution. Both you and your car should be glad to get rid o f it! I f you absolutely cannot reach the offending plug, you can always drive to your service station and hum bly ask them to change just that one plug. T hey w on’t like it, but it is a last resort. If you get to that point, you’ll probably be glad to pay to have it done. But do try very hard first. I f you ca n ’t get to the plug in the ordinary way, go under, over, around, or through
305 gaps in the thing that’s blocking it. Or get someone to help you move w hat’s in the way (but be sure that you can get it back in place correctly). Use your imagination; it’s the only hard part of the job. And you won’t have to do it again for a long time. If you’re lucky enough to own a car without air conditioning, power steering, power brakes, and so on, chances are much greater that all your plugs will be easy to get at. Think it over next time you’re tempted to buy a vehicle with all the “extras.” Those “extras” tend to block the things you want to work on, and they often go wrong them selves. Some, like air condition ing if you live in a hot climate, are worth it. Others, like power brakes on a small car, are not. Reading your spark plugs You can actually read your spark plugs for valuable “clues” about how your engine is operating. To read your spark plugs, follow these steps: 1. When the first spark plug is out o f the engine, rem ove the plug from the spark plug socket and take a look at it. Compare the deposits on the plug to the conditions shown in Table 12-1. Figure 12-10 can help you to identify the various parts o f a plug m entioned in the table. 2. Check the plug’s shell, insulator, and gaskets for signs of cracking or chipping. 3. Look at the plug’s firing end (the end o f your plug that was inside the cylinder). The hook at the top is the side electrode (refer to Figure 12-10). The bump right under its tip is called the cen ter electrode. The spark comes up the center o f the plug and jum ps the gap between these two electrodes. This gap must be a particular distance across for your engine to run effi ciently.
Table 12-1 What Your Old Spark Plugs Tell You about Your Car Condition Clues Probable Causes Remedies N o rm a l p lu g B r o w n o r g r a y is h - ta n E v e ry th in g 's fin e . J u s t c le a n a n d re g a p th e p lu g . d e p o s it o n s id e e le c tr o d e C a rb o n -fo u le d p lu g B la c k , d ry , f lu f f y s o o t o n O v e rly r ic h f u e l/ a ir m ix tu r e ; S w it c h to " h o t t e r " p lu g s . in s u la to r tip a n d e le c tr o d e s m a lfu n c tio n in g c h o k e ; d ir t y a ir (T h e h ig h e r th e p lu g filte r ; o r ju s t to o m u c h d r iv in g a t n u m b e r, th e h o tte r th e p lu g .) lo w s p e e d s , o r s ta n d in g a n d id lin g fo r a lo n g tim e . 306 O tl-fo u le d p lu g W e t, b la c k , o ily d e p o s its O il m a y b e le a k in g in to c y lin - C le a n a n d re g a p th e p lu g o n in s u la to r tip a n d e le c tr o d e s d e r s p a s t w o r n p is to n s o r p o o r ly o r r e p la c e it, b u t fin d o u t a d ju s te d o r w o r n v a lv e s . w h e r e th e le a k is c o m in g fro m . B u r n t p lu g B lis te r s o n in s u la to r tip , E n g in e o v e r h e a tin g ; g a p to o R e p la c e th e p lu g . m e lte d e le c tr o d e s , w id e ; w r o n g o r lo o s e p lu g s ; b u r n t s tu ff o v e r ly le a n f u e l/ a ir m ix tu r e ; in c o r r e c t tim in g . W o r n p lu g S e v e re ly e r o d e d o r P lu g h a s b e e n in th e r e to o lo n g R e p la c e th e p lu g . w o r n e le c tr o d e s
307 T e rm in a l In s u la to r R e s is to r - S p r in g S h e ll - C e n te r seal G asket -T h re a d s Figure 12-10: .C e n te r The e le c tr o d e anatom y ^Gap In s u la to r of a spark - S ide tip plug. e le c tr o d e 4. Take your wire or taper feeler gauge and locate the proper wire (if your spark-plug gap specifications say .035, look for this number near one o f the wires on the gauge). Then slip that gauge wire between the two electrodes on your old plug. Figure 12-11 shows why you should never use a flat feeler gauge for this purpose. The reading will be inaccurate. Figure 12-11: W hy you can't use a fla t fe e le r gauge on an old spark plug.
308 The gauge wire probably has a lot o f room to wiggle around in. This may be because your old plug has worn down its center electrode, causing a gap that is too large. If the gauge goes in and out with a lot o f room on either side, the gap is too large. If the gauge can’t fit between the center and side electrodes, the gap is too sm all, which means that the spark plug is not burning the fuel/air mixture efficiently. 5. Look at the little center electrode bump again and use Table 12-1 to judge its condition. Is it nice and cylindrical, like the center electrodes on your new spark plugs? Has the electrod e’s flat top worn down to a rounded lump? Or has it worn down on only one side? C hances are it’s pretty w orn because it’s old. When the center electrode wears down, the gap becom es too large. W hen you do your tune-ups yourself, you’ll probably check your plugs m ore often and replace them before they get too worn to operate efficiently. 6. Clean the plug. Then either gap it or replace it with a new one, follow ing the instructions in the next two sections. To clean a plug, gently scrub the gunk and goo away with a wire brush. Keep in m ind that although you don’t need to clean new spark plugs, you do need to gap them . Some plugs are sold “ pregapped,” but I’d check them w ith a feeler gauge any way. 7. R epeat the entire process for each additional plug, work ing on only one at a time. A good w ay to keep track o f w h ich plug belongs in which cylin der is to use an egg carton as a container and put the plugs into the carton’s d epressions in numerical order as you rem ove them from the engine. E ither replace all the plugs with new ones or clean and reinstall all the old ones. Don’t m ix plugs in varying states of wear. If you do, your engine w on’t operate efficien tly. If you find
309 that a few o f your old plugs aren’t too worn and are in fairly good shape, but you need to replace the others, clean and regap the salvageable plugs and store them in your trunk com part ment tool kit for em ergencies. Som etim es you can cure a problem - such as carbon-fouled plugs - by going to a hotter- or cooler-burning plug. You can identify these by the plug number. The higher the number, the hotter the plug. Never go more than one step hotter or cooler at a time. If your plugs indicate that som ething is seriously wrong with the way your engine is running, ask a professional m e chanic for an opinion. If you’re told that it requires extensive or expensive work, get a second opinion at another service facility without telling the technicians that you went to the first place. This is a good policy to follow whenever major repair work is suggested. We wisely get second opinions when doctors tell us we need major surgery; why not give your vehicle the same thorough attention before incurring a major expense? Gapping your spark plugs As I m entioned in the preceding section, the space, or gap, between the center and side electrodes needs to be a particular distance across; otherw ise, your plugs don’t fire efficiently. A d justing the distance between the two electrodes is called g a p ping your spark plugs. Gap new as well as old spark plugs, even if the package says that the new plugs are “pre-gapped.” To avoid problem s, work on only one plug at a time, in cylinder sequence order. The follow ing steps explain how to gap your spark plugs: 1. If you're regapping a used plug, make sure that it's clean. If you’re using a new plug, it should be clean and new- looking, with the tip o f the side electrode centered over the center electrode. There should be no cracks or bubbles in the porcelain insu lator, and the threads should be unbroken.
310 2. Take your feeler gauge, select the proper wire, and run it betw een the electrodes (see Figure 12-12). If the wire doesn’t go through or if it goes through too easily, without touching the electrodes, you need to adjust the distance betw een the electrodes. 3. Adjust the gap as necessary. I f the wire didn’t go through, the gap is too narrow. Hook the part o f the feeler gauge that is used for bending elec trodes under the side electrode and tug very gen tly to widen the gap. I f the wire goes through too easily, without touching the electrodes, the gap is wide. Press the side electrode against a clean, m a r-proof surface, very gently, until it’s slightly bent down toward the cen ter electrode. 4. Run the gauge through the gap again. 5. R epeat Steps 3 and 4 until the gap is ju s t right. You want the gauge w ire to go through fairly easily, just catching the electrodes as it passes. The wire should just “hang” in the gap but go through with a little guidance. I f you keep getting the gap too narrow or too wide, don't feel bad. Everyone I know goes through the “too large-too small-too
311 large” bit a couple o f times for each plug, especially the perfec tionists. After you’re done gapping your spark plug, it’s time to in sert it in the engine. The next section has the details. Installing a spark plug To insert a spark plug into the engine, follow these steps: 1. Clean the spark plug hole in the cylinder block with a clean, lint-free cloth. Wipe away from the hole; don’t shove any dirt into it. 2. Lightly coat the threads o f the spark plug with anti-seize compound, being careful not to get any on the center or side electrodes. 3. Carefully begin threading the spark plug into the engine by hand, turning it clockwise. This is called “seating the plug.” You have to do it by hand, or you run the risk o f starting the plug crooked and ruining the threads on the plug or threads in the engine. If you have trouble holding onto the plug, you can buy a spark plug starter and fit it over the plug, or you can use an old spark plug wire boot or a piece o f vacuum hose to make your own. 4. After you engage the plug by hand, turn it at least two full turns before utilizing the spark plug socket and ratchet. 5. Slip the spark plug socket over the spark plug, attach the ratchet handle, and continue turning the plug clockwise until you m eet resistance. Don’t overtighten the plug (you can crack the porcelain); just get it in nice and tight with no wiggle. The plug should stick a little when you try to loosen it, but you should be able to loosen it again without straining yourself. Tighten and loosen the first plug once or twice to get the proper feel o f the thing.
312 I f you have a torque w rench, you can look in the manual for the proper setting and use it after you seat the plug by hand. Then try to loosen the plug by hand. T his gives you the proper feel for how tight it should be. M ost do-it- yourselfers tend to replace plugs without torque wrenches because torque w renches are difficult to w ork with in the sm all space betw een the block and the oth er parts of the vehicle. 6. Inspect the entire length o f the spark plug wire before attaching its boot to the plug. If the wire is cracked, brittle, or frayed or is saturated with oil, replace it. 7. B efore you attach the boot to the spark plug, apply some silicone lubricant to the inside o f the boot; then push the boot over the exposed term inal o f the new plug and press it firm ly into place. You’ve just cleaned, gapped, and installed your first spark plug. D on’t you feel terrific? Now you have only three, five, or seven m ore to do, depending on your engine. 8. Repeat the steps to rem ove, read, gap, and install each spark plug. It’s at tim es like these that owners o f 4 -cylin d er cars have the edge on those w ho drive those big, expensive 8-cylin- der m onsters. W hen you’re done, start your engine to prove to yourself that everything still w orks. Then wash your hands with hand cleaner. If you’ve had a hard tim e with a hard-to-reach plug, get some rest before taking on additional work. N ext tim e, the job should be a breeze. 4. Servicing your Distributor M ost cars built after 1975 have electronic ignition systems that require no regular servicing. Some have no distributors at all. All testing and servicin g o f these system s should be left to
313 trained professionals because they are easily damaged if hooked up im properly, and they employ high voltage that can also dam age you. If your car has an electronic ignition system, the only work you can do is to replace the distributor cap and rotor if they become damaged. However, even if you have a distributorless system, don’t forget to read and change your spark plugs and check that your cables and connections haven’t become corroded or detached. I’d do so at least twice a year, or w henever your vehicle stops running sm oothly or your fuel consumption sud denly increases. If you aren’t sure whether your vehicle has one o f the older non-electronic distributors that must be manually serviced, note that older distributors have one thin wire on the side, whereas the electronic ones have two wires or more. If you’re still not certain, check your ow ner’s manual or service manual, or call the service departm ent at a dealership that represents your car’s manufacturer. If you have a distributor that does need servicing, check the items in the section called “W hat You Need to Do the W ork in This C hapter,” paying special attention to the parts and tools preceded by the © symbol. Get to the scene of the action The distributor gets voltage from the ignition coil and dis tributes it to each spark plug in turn. To accom plish this, the distributor contains a set o f points, a rotor, and a condenser. Servicing your distributor involves cleaning and checking these parts and replacing them if necessary. O f course, to get to the scene o f the action, you have to remove some stuff that’s in the way. But don’t panic: The following sections take you step by step through the entire process.
314 Although you can jum p to any o f the follow in g sections to get specific inform ation, I recom m end that you read Chapter 6 before goin g any further. It will help you find your distributor and fam iliarize you with what each part looks like and does. Then return here and work your way through the rest of the sections in succession, using the ® and T sym bols to identify work that you can do on your particular system . If you go step by step, you can do everything you need to in the m ost efficien t order, thereby increasing the chances of your vehicle starting the first tim e you try it after the work is dene. R em ove y o u r d istribu tor cap The distributor cap is the first thing to go. To remove it, follow these steps: 1. Find your distributor. If you’re still not sure where to find it, C hapter 6 provides a description o f the distributor - where it is, what it does, and w hat it contains. 2. Use a long-handled screw driver to loosen the distributor cap. M ost caps are held in place by either screw s (see Figure 12-13) or clips (see Figure 12-14). 3. Now that your distributor cap is free, rem ove it without rem oving any o f the w ires that are attached to the cap. Place it to one side and take a look inside your distributor (see Figure 12-15). Does the stu ff in there look like the replacem ent parts you bought? L ook at the structure o f the rotor (and the points and con d en ser, w hen you get to them ). T hey should be sim ilar, although som e parts may be made o f plastic in stead o f m etal. If they look different, you’ve got the wrong parts. Go back to the auto parts store and start over. (You may not collect $200, but at least you w on’t go to ja il.)
315 Figure 12-13: R em oving a d is trib u to r ca p w ith s c re w clam p s. Figure 12-14: R em oving a d is trib u to r cap w ith clip s. P o in t se t h o ld -d o w n s c re w Lead w ire s P o in ts co n ta c ts . P rim a ry te rm in a l Points C o n d e nse r Figure 12-15: The a na tom y Coil w ire of a non te rm in a l e le c tro n ic d istrib u to r. V a cu um a d va n ce
316 If, w hen you look inside your distributor cap, you do not find the parts in the illustrations in the follow ing section s, you prob ably have an electronic ignition system and can consider your se lf pretty lucky. As I m entioned earlier, you don’t have to deal with adjusting or replacing traditional points and condensers. All you have to do is check and change your spark plugs now and then and check for a defective distributor cap or rotor if your en gin e starts running roughly or stops running completely. Because there are m any types o f electron ic ignition sys tem s, and adjustm ents usually require expen sive tools and spe cialized expertise com pared to conventional ignitions, I strongly advise you to rely on a good autom otive e‘ technician if neither the cap nor the rotor appears dam aged. R em o v e the rotor S ittin g on top o f everything else inside the distributor is the rotor. R otors vary in size from sm all plastic gizmos that sim ply lift o ff the distributor shaft, to big round plastic plates that have two screws to rem ove (Figure 12-16 shows different kinds o f rotors). Figure 12-16: V arious typ e s of rotors.
317 To rem ove your rotor, follow these steps: 1. Before you remove your rotor, move it on its shaft. Does it move easily? If not, you really need this tune-up badly! 2. Remove the rotor from the shaft. To remove a small rotor, just lift it straight up o ff the distributor shaft (see Figure 12-17). To remove a large ro tor, you need to unscrew the two screws and lift the rotor off the distributor shaft (see Figure 12-18). Figure 12-17: Removing a small rotor. Figure 12-18: You release this type of rotor by removing the screw s.
318 3. Take a close look at the old rotor to see how it fits onto the shaft so that you can put the new one in properly later on. A ll rotors go on in only one way: They either have a square- pin-insquare-hole/round-pin-in-round-hole arrangement, or th ey’re notched or shaped so that they fit on the shaft pointing in only one direction. Still, it’s a good habit to take a long look at anyth in g you rem ove before you remove it, because you tend to forget how it’s situated, and some tim es you have to m ake a choice. D on’t be afraid to draw pictures if you aren’t sure you’ll rem em ber how something fit together. 4. Look at the m etal contacts that conduct current to the spark plug term inals. I f the rotor contacts are corroded, broken, or cracked, you really need a new one! In any case, plan to use the new one after you’re through w orkin g on the rest o f the distributor. 5. Set the old rotor aside. U nder the rotor on som e vehicles, you may find something called the cen trifu ga l advance (see Figure 12-19). Its function is rather com plicated, it has nothing to do with this m inor tune-up, and it hardly ever breaks. Just leave it w here it is and forget it. Figure 12-19: A cen trifu ga l advance.
319 R em ove the static shield On som e vehicles, you may find a static shield, shown in Figure 12-20, which you have to remove before you can change your points and condenser. The static shield’s purpose is to prevent radio interference. Sometimes the working o f the elec trical system in your car produces strange noises on the car radio. This gizm o prevents that. The static shield isn ’t hard to rem ove, but when you finish working on your distributor, be careful to put the shield back exactly the way it was. If you can’t get it back properly, don’t worry - your car will run perfectly without it, so just put the pieces in a paper bag and drive to your friendly service station. They’ll put it back for you (although you may have to take a little kidding). Remove and replace the condenser U nder the rotor (and possibly the static shield) are the points and condenser. Before you remove the condenser, look at the two little wires, one leading to the points and the other to the
320 condenser, that jo in together - usually with som e sort o f little screw and w asher arrangem ent (refer to Figure 12-13). Take a good look at how the wires (som etim es called leads) fit together in the gadget that holds them (called the primary term inal). The m ain purpose o f the prim ary term inal is to pre vent the clips at the ends o f these wires from touching the floor o f the distributor, w hich is called the breaker plate. If they touch the breaker plate, they short out and the car doesn’t start. Now follow these steps: 1. Take a closer look at how the wires connect. Are the little clips at the ends o f the wires touching each other? Or are they separated with som ething? Does the screw that holds them in place touch them ? Or is there som ething in betw een? Figures 12-21, 12-22, 12-23, and 12-24 show how to disconnect several types o f primary term inal arrangem ents. Figure 12-21: On some distribu to rs, the w ire s m ust be loosened from the prim ary te r minal, as shown, before you can remove them.
321 Figure 12-22: On another type of dis tributor, you m ust use a special tool to remove the prim ary term inal nut and release the contact spring and lead wires. Figure 12-23: On other dis tribu to rs, the nut on the prim ary te r m inal must be loosened to release the co n ta ct spring and lead w ire s