语音型汽车多功能报警器设计-英文资料

Chapter 18 Lubrication System ServiceCHAPTER PREVIEWIf the lubrication system becomes contaminated with dirt or if it stops operating properly,the engine may be damaged in a very short time .A mechanic must be able to troubleshoot a malfunction in the system and perform preventive maintaince to prevent a failure in the system. The troubleshooting and preventive maintenance operations are presented in this chapter along with the major service procedures for each of the components in the lubrication system.18.1 TROBLESHOOTINGThe first sign of a lubrication system problem is usually that the oil pressure warning light comes on,indicating low oil pressure in the engine.18.2 Checking the oil and the GaugeThe first thing the mechanic should do is make sure that the engine has the proper amount o f oil. If oil level is too low,there is not enough oil flow for proper lubration.When there is enough oil in the engine and the warning light continues to burn,find out whether the problem is really low oil pressure or just a malfunction in the electrical warning circuit.The quickest way to do this is to install a test pressure gauge,operate the engine,and accurately measure the oil pressure.Oil pressure test gauges are available that will read pressures of 0 to 100 psi(0 to 690 kpa or so).Remove the sending unit for the oil pressure warning light and install a hose for the oil pressure test gauge in its place.Connect the oil pressure gauge to the hose and start the engine.If the gauge shows no oil pressure,stop the engine to prevent further damage.If the gauge shows there is oil pressure ,operate the engine at several different speeds and note the oil pressure.Compare these readings with specifications in the manufactures service manual.18.3 Using a PrelubricatorLow oil pressre may be caused by wear or damage to interal engine components.It may be due to a problem in the lubrication system.If oil pressure is low,the next step is to locate the cause.One useful tool for this is an prelubricator(Fig.18-1).It is an oil reservoir or tank attached to an air supply line that supplies a certain amount of oil at a specific pressure to the engine oil system when the engine is not operating.The prelubricator has three purpose.First,it can indicate how badly the bearings are worn.To find the amount of engine bearing wear,remove the pan from the worm engine and hook up the engine prelubricator.If all the bearings are worn,oil will spray from every bearing,possibly in a stream.Oil leakage may indicate extreme wear in any one of the bearings.The second use of the engine prelubricator is to check a job after new bearings have been installed.In many cases,the mechanic is not sure that the right undersized bearings were used or that enough oil clearance was allowed.The engine prelubricator checks this and shows any points of the excessive leakage.It also checks points of no leakage where a badly installed bearing may cover up an oil supply hole,or where the oilways are still pluged with rags used in boring to keep out dirt.Even threaded oil plugs have been known to be left out in the assembly of the reconditioned engine.Such a problem would be seen immediately with the use of the engine prelubricator.The third use of the engine prilubricator is to completely charge the reconditioned enging with oil before being turned over under its own power.A good deal of engine wear may be caused when a newly rebuilt engine is first started because there is a small time lag while the oil pump fills the lubrication system.Prelubricating the engine before starting it eliminates this problem.18.4 oil AnalysisAnother troubleshooting procedure now used in some automotive and truck fleet operations is oil analysis.A sample of oil may be removed from the oil pan and sent to an analysis company.Here chemists exmine the oil to determine its condition and the level of contamination by dirt,water,or acid.They can also tell whether the engine is wearing normally by measuring the amount of engine metal in the oil.The more oil and steel present in the oil,the more wear is occuring in the engine.Regular oil analysis allows a fleet operator to adjust maintance procedures to engine needs.It may also be used to predict when an engine is likely to fail.18.5Checking After engine failureLubrication system troubleshooting can also be used after the engine has failed to determine the cause of failure.This is done by a close examination of the engines bearings.In some cases,worn bearings are sent to a laboratory for expert analysis under a microscope.Usually, however ,the mechanic will examine the bearings visually for two common causes of failure,dirt and not enough lubration.Normal engine oil and filter changes usually remove the fine dirt produced by normal engine wear.If these very fine articles,however,are permitted to build up,more and possibly larger particles are produced.The wear is no longer normal.Fine dirt particles,if they are not too normous,will imbed into the bearing lining.Large particles,however,can bottom against the steel bearing backing and damage both the bearing and the shaft(Fig.18-2).Insufficient lubrication system means too little oil gets through the engine bearings to lubricate them.It may affect all of the bearings or only one,possibly only the mains or only the connecting rod bearings.The appearance of bearings damaged by insufficient lubracation may be seen in Figure 18-3.Insufficient lubrication may be due to a dry start,too little oil clearance,low oil supply,low oil pump delivery, a malfunction in the relief valve,and oil dilution.A dry start is a condition in which the lubrication system has not been primed with oil before starting the engine for the first time after an overhaul.A lag occurs between the the engine is started and the time oil is actually delivered under pressure to the bearings.Bearingdamage and seizure can also result from too small an oil clearance space between shaft and bearing.This is often shown by wear on one or two bearings in the set with little or no wear on the others.Bearings can be affected by lack of oil or by an extremely low oil supply.This can result from extreme oil leakage at the crankshaft front or rear oil seal,around new piston rings,or at gaskets.The oil pump is an important part of an engine that is often overlooked.It may be responsible for too low oil pressure,particularly at low engine speeds.The oil pump shlould be servicec when the engine is overhauled.A worn oil pressure relief valve can prevent the flow of oil .If the plunger and hole become enlarged,the plunger may cock slightly or stick open .With the pluger open,oil is by passed to the crankcase at lower engine speeds.This lowers oil pressure to the bearings and reduces their lubrication. Too much leakage or blow-by around the pistons and a rich combustion mixture of raw fuel can cause oil dilution in a worn engine.Oil dilution reduces the lubracating value of the oil,for the oil thickness goes down when the oil becomes lower in viscosity.Another cause of bearing troubles is leakage of the coolant down into the crankcase,particularly if the coolant contains an antifreeze such as ethlene glycol.This substance forms a gaummy material which coats the bearings and shaft ,reducing oil clearance and in many stopping the oil flow.18.6 PREVENTIVE MAINTENANCEThe lubrication system requires some periodic preventive maintenance in order to operate propeyly.The oil level must be checked regularly.The oil and oil filter must be changed regularly.18.7Checking Oil LevelThe first step in checking oil level is to locate the dipstick,which is usually mounted on the side of the engine.Turn the engine off. Pull the dipstick out.Wipe it clean with a rag.Look at the marks on it.There is no standardized marking system.Some dipsticks have two lines,one marked full and another add.Many just have lines with no markings.Find out what the marks mean by looking in the owners manual.push the dipstick firmly back into its hole,pull it out again,and read the oil level from the marks.firmly seated so no water or dirt can enter the engine.18.8Changing oilChanging the engine oil regularly i s the most important thing that can be done for long engine life.The more frequently oil is changed,the longer the engine can go before it needs an overhaul.Most manufactures oil change recommendations are based upon a time/mileage interval.For example,the interval may be 3,000 miles or three months,whichever comes first.It makes more sense to change oil on the basis of operatings conditions.During cold or wet weather,it should be changed more freruently,because water tends to collect in the oil and cause sludge.Short trip and stop-and-start driving are harder on oil than long trips and highway driving.Oil should be changed more frequently if the automobile is driven in areas where there is a lot of dirt and dust in the air.Most experts recommend that oil be changed more frequently than the owners manual suggests.Oil changes are done incorrectly at many service stations and garages.The customer drops off his car,and it is parked until the attendant gets into to change the oil .This allows the oil to cool and gives particles of dirt and water time to stick to parts of the engine.When the oil is drained,the dirt and water stay in the engine.Oil is best changed while hot,after a long drive.Check the operators manual to find out how many quarts of oil are required.An additional quart will be needed if the oil filter is to be changed.Set the emergency brake,put the transmission in park,and lift the automobile on a hoist,if available.Use an oil drain pan that will hold five or six quarts.Look for the engine drain plug.Do not confuse it with the drain plug for transmission.When the plug is located,place the correct size open-end rench snugly on the drain plug.Have the pan ready .Turn the drain plug counterclockwise to loosen.Pull it out quickly,allowing the oil to drain into the pan.Be careful.The oil is hot!Allow the oil time to drain.Replace the drain plug,turning it clockwise by hand.Tighten it with the wrench.If torque specifications are available,use a torque wrench to tighten the drain plug.Remove the oil filter cap.Push the oil spout into an oil can and pour oil into the engine until the recommended amount has been added.Check the oil level with the dipstick.Replace the filler cap.Check the drain plug for leaks.18.9 Changing the Oil FilterThe oil in the engine is pumped through a filter to remove particles and acids.When the filter is full,it clogs and the bypass valve is activated.The filter should be changed at least every other oil change,and preferably every oil change.While the oil is draining,locate the filter.Most automobiles now use a throwaway cartridge.Put a pan or drain under it to catch the oil which will come out.Put the oil filter tool around the filter cartridge (Fig.18-4).Turn it counterclockwise with the tool until it can be turned by hand.Set the filter in the pan to drain and then throw it away.With a rag,wipe the mounting surface on the engine where the filter fits.Put a light coat of grease or oil on the rubber gasket of the new filter.Screw the filter on by turning it clockwise.Tighten it snugly by hand.Do not use the tool to tighten it.An additional quart of oil will be required if the filter is changed.After the oil change is completed and the required amount of oil is added,start up the engine.If the filter leaks,shut the engine off.Either the filter is not tight enough or the filter gasket is defecter.Take it off,clean up the gasket area,and try again.Another filter may be used if necessary.18.10 LUBRCATION SYSTEM SERVICEWhen an engine has a major overhaul,each part in the lubrication system must be serviced.In this section we will present the typical service procedures necessary to ensure proper lubrication system operation.18.11 Oil Pan ServiceDuring an engine overhaul,the oil pan is removed.The pan is thoroughly cleaned,usually with a steam cleaner or in a hot tank.Inspect the threads in the oil drain plug for signs of damage.Inspect the baffles inside the pan to make sure theyre tightly fastened.The oil pan-to-crankcase surface sealed with two side gaskets and a front and rear seal mounted to the underside of the candcase(Fig.18-5).Remove the old gaskets from the oil pan.After gasket surfaces are cleaned, install new gaskets and before putting it back on the engine.18.12 Servicing the Oil Pump and Relief Valve AssemblyThe oil pump and relief valve assembly is disassembled and washed in solvent.Inspect each of the parts for wear.The mating face of the oil pump cover should be smooth.If it is excessively scratched or grooved,it should be replaced.Test cover-to-rotor wear by laying a straightedge across the cover surface.Use a feeler gauge(Fig.18-6)to determine cover flatness.No feeler gauge thicker than the service manuals specification should be able to slide under the straight edge.Measure the diameter and thickness of the outer rotor with an outside micrometer(Fig.18-7).If the dimensions are less than spicified in the service manual,replace the outer rotor.Measure the inner rotor thickness with an inside micrometer(Fig.18-8).If the dimensions are less than specifications,relplace the inner rotor.The outer rotor is assembled into the pump body.Measure the clearance between the outer rotor and the body with a feeler gauge(Fig.18-9).If the measurement is larger than the specifications call for,replace the pumpbody.The inner rotor is assembled into the pump.Measure the clearance between the outer and inner rotor with a fleeler gauge(Fig.18-10).If the clearance is beyond specifications,replace the inner and outer rotors. place a straightedge across the pump housing over the assembled rotors and measure the clearance over the rotors with a feeler gauge(Fig.18-11).A measurement beyond specifications means that the pump body should be replaced.Inspect the relief ball or plunger and bore bore for scratches and scoring.If there is any evidence of damage,replace the plunger or ball.Measure the length of the relief valve spring and compare against specifications.Reassemble compents that pass these tests.Check the relief valve for three operation in its bore.If it moves freely,the retainer that holds the relief valve assembly in its bore may be replaced.18.13 Oil passagesuring engine cleaning,give careful attention to the oil passages in all the components.Drilled holes in