汽车构造英文Chapter 3 Cylinderhead and valve serviceWord文档格式.docx

1、Servicing rocker-arm assembliesServicing hydraulic lifters and lash adjustersValve refacers and refacingValve-seat reconditioningValve-seat cuttersServicing valve guides Servicing valve-seat inserts The condition of the cy1inder head, valves and associated parts will affect engine power, economy and

2、 performance.Deposits gradually accumulate in the combustion chambers, on the faces of the valves and on the heads of the pistons. The valve faces and their seats gradually deteriorate in operation as they become worn and pitted. When there is loss of compression and engine performance is affected,

3、the cylinder head needs to be serviced to restore it to its original condition.Cylinder-head serviceDuring cylinder-head service, the cylinder head is removed from the cylinder block, the valves are removed from the cylinder head and all parts are cleaned of carbon. The valves are refaced and the se

4、ats ground so that the valves seat correctly in the cylinder head.Apart from the problem of a gradual loss in engine power, the cylinder head might have to be removed because of other problems. These include a valve that has burnt, a blown cylinder-head gasket, or a coolant leak. Faulty valve seatin

5、g can cause compression in the cylinders. A blown cylinder bead gasket can also cause compression loss as well as coolant leaks. The method of checking cylinder compression is outlined in chapter 8: General engine service.The service that involves removing, reconditioning and replacing a cylinder he

6、ad is often referred to as a top overhaul. Procedures for removing and replacing cylinder heads will vary, depending on whether it is for an overhead-valve or an overhead-camshaft engine. Procedures for removing auxiliary equipment, such as air cleaners, air-intake systems, fuel systems, exhaust sys

7、tem and emission controls will also vary for different engines.When dismantling an engine while it is in the vehicle, there are two groups of parts to consider:1. Auxiliary equipment and attachments that are on.，or associated with, the engine.2.Actual mechanical parts of the engine. With most motor

8、vehicles, there are a number of parts that have to be removed before the mechanical parts of the engine are accessible. A number of these are shown in Figure 3.1.The illustration shows a cylinder head for a four cylinder, double overhead-camshaft engine with a number of dismantled components. Some o

9、f these are parts that have to be removed to gain access to the cylinder head. Others are parts that are dismantled from the cylinder head itself.Following are general points that relate to removing a cylinder head from an engine while it is in the vehicle. These are not procedures-the procedures mu

10、st be obtained from the particular vehicles service manuals. Some service manuals provide the procedures as detailed descriptions, others provide illustrations with dismantling sequences shown.Auxiliaries and attachmentsPoints relating to auxiliary parts and accessories are as follows:1. Engine cove

11、r. The cover over the top of the engine has to be removed to make other parts accessible.2. Coolant. The coolant has to be drained from the radiator and also from the engine block. Unless the block is drained, coolant that remains in the engine will find its way into the cylinders when the cylinder

12、head is removed.3. Coolant system. Coolant hoses, the thermostat and heater hoses have to be removed. 4. Air-intake system. The air cleaner or ducting is usually removed early in the procedure so that other parts are accessible. 5. Accelerator cable. The accelerator cable and electrical connections

13、at the EFI throttle body will have to be removed. 6. Emission pipes and hoses. The position and connections of emission hoses and devices should be noted. Labels should be attached before removal so that the parts can be correctly reinstalled. 7. Ignition system. The spark-plug cables and the igniti

14、on coil packs which are attached to the engine will have to be removed. If there is a distributor, it will be removed. 8. Spark plugs. These are removed so that the crankshaft is easy to rotate. 9. Electrical connections. There are various electrical connections in the engine compartment that have t

15、o be disconnected. Multipin connectors can only be connected one way, but other connections that are not obvious should be labelled.10. Drive belt. The drive belts for the alternator and other auxiliaries are removed -tensioners may have to be released.Figure3.1 Components associated with cylinder h

16、ead removal and dismantling1 intake manifold, 2 gasket, 3 throttle body, 4 fuel rail, 5 fuel damper, 6 fuel line, 7 injector, 8 valve cover, 9 gasket, 10 shim, 11 bucket tappet, 12 valve spring, 13 valve guide, 14 valve, 15 spark plug, 16 intake camshaft, 17 exhaust camshaft, 18 cylinder head, 19 ga

17、sket, 20 shield, 21 exhaust manifold, 22 cylinder-head gasket, 23 timing belt, 24 tensioner, 25 crankshaft pulley,26-28 timing belt covers, 29 gasket, 30 camshaft pulleys, 31 bearing cap, 32 gasket TOYOTA11. Fuel system parts. Many of these have to be removed so that other parts are accessible.Exter

18、nal mechanical partsThere are a number of external parts that have to be removed. These include:1. Intake manifold. This is often in two parts which can be separated for removal.2. Exhaust manifold. In-line engines have one manifold, while V-type and horizontally opposed engines have two.3.Valve cov

19、er. This is removed to gain access to the valve-operating mechanism and, on overhead camshaft engines, access to the camshaft.4. Engine timing cover. Removal of one or more timing covers gives access to the timing chain or belt and to the sprockets or pulleys.5. Engine timing. The timing marks are c

20、hecked and set with No.1 cylinder at top dead-centre （TDC）.6. Other items. Where fitted, a supercharger would have to be removed and parts of a turbocharger might have to be disconnected.Dismantling the valve mechanismThe valve operating mechanism has to be removed from the top of the cy1inder head

21、before the cy1inder head can be removed from the cy1inder block. There are a number of different arrangements and the procedures that are used will depend largely on whether it is an overhead-camshaft （OHC） engine or an overhead valve （OHV） engine.Overhead-camshaft enginesWith OHC engines, the camsh

22、aft（or camshaft） are removed from the top of the cylinder head. Variations in the dismantling procedures for different engines will depend on:l. Whether the engine has rocker arms or bucket tappets.2. Whether there are hydraulic lash adjuster.3. Whether there are one or two camshafts.4. Whether the

23、camshaft has a belt drive or a chain drive.The camshafts are carried in bearings in the cylinder head and are retained by bearing caps. With bucket-type tappets, the camshaft can be removed from the cylinder head and the tappets then removed. With rocker arms, the camshaft cannot be removed until th

24、e rocker arms or the rocker-arm assembly has been removed.Some rocker arms are mounted individually, but many are mounted on bearings or bushes on a shaft. These are removed from the cylinder head as an assembly. Rocker arms of this type are shown in Figure 3.2. The camshaft bearing caps are secured

25、 to the cylinder head with four bolts.When removing this type of assembly, the bearing cap bolts are released progressively a little at a time, and in a sequence that involves all the bolts. This isnecessary because some parts of the camshaft are under load from the compressed valve springs. Progres

26、sive loosening of the bearing cap bolts will prevent distortion of the parts. The arrangements of overhead camshafts can be seen in a number of the figures in the previous chapter.Overhead-valve enginesFigure 3.3 shows a partly dismantled V-type engine with overhead valves. Procedures for dismantlin

27、g the valve mechanism include removing the valve cover from the top of the cy1inder head and the intake manifold from between the banks of cylinders.In the illustration, the valve covers have been removed and the parts of the valve train can be seen. A single camshaft is mounted in the crankcase and

28、 this operates hydraulic valve lifters. These have rollers that bear against the cams of the camshaft; the rollers are used to reduce friction and wear.P52Figure 3.2 Valve arrangement for an in-line OHC engine FORDFigure 3.3 Partly dismantled V-8 OHV engine showing the parts of the train FORDPushrod

29、s are located between the valve lifters and the rocker arms. The rocker arms are independently mounted and they pivot about a fulcrum that is retained by a stud. The stud is threaded into the cylinder head. The camshaft and drive for this type of engine is shown in Figure 2.27 in the previous chapte

30、r.Removing and dismantling cylinder headsWith the valve gear removed from the cylinder head, the cy1inder head itself can be removed from the cylinder block. Cylinder-head bolts must be released progressively and in the correct sequence （Figure 3.4）. If the bolts are not all the same length, the loc

31、ation of the different bolts should be noted.When are the cylinder-head bolts have been removed, the head can be lifted from the block. If the head is stuck, a lever can be used between a protrusion on the head and the block. Do not lever between the mating surfaces as this will cause burrs on the surfaces and sealing on reassembly will be difficult.P53Figure 3.4 Cylinder head bolts sequence for loosening and removing TOYOTADismantling, cleaning and checkingTo remove the valves from the cylinder head, the valve springs are compresse