Thursday, May 19, 2011

Cylinder-Head and valve service

Cylinder-Head and valve service

The condition of the cylinder-head, valves and associated parts will affect the engine power, economy and performance.
Deposits gradually accumulate in the combustion chambers, on the faces of the valves and on the heads of the positions. 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, the cylinder head needs to be serviced to restore it to its original condition.

Cylinder Head Service

During cylinder-head service, the cylinder-head is removed from the block, the valves are removed from the cylinder-head and all the parts are cleaned of carbon.  The valves are refaced and the seats ground so that the valves seat correctly in the cylinder-head.
Apart from the problem of a gradual lost an engine power, the cylinder-head might have to be removed the cause of other problems.  These include a valve that has burnt, a blown cylinder-head gasket, or a coolant leak.  Faulty valve seating can cause loss of compression in the cylinders. A blown Cylinder-Head gasket can also cause compression loss as well as coolant leaks.
The service that involves removing, reconditioning and replacing a cylinder-head is all fun referred to as
top overhauls.  Procedures for removing and replacing cylinder-head 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 systems and emission controls will also vary for different engines.
When dismantling an engine when it is in the vehicle, there are two groups of parts to consider:

1.          Auxiliary equipment and attachments that car on, or associated with the engine.

2.          Actual mechanical parts of the engine.

With most motor the vehicles; there are a number of parts that have to be removed before the mechanical parts of engine are accessible.  The numbers of these are shown in figure 3.1.

Illustration shows a cylinder-head for a four cylinder, double overhead camshaft engine with the number off dismantled components.  Some of these are parts that have to be removed to gain access to the cylinder-head.  Others are the parts that are dismantled from the cylinder-head itself.

Following are the general points that relate to removing the cylinder-head from an engine while it is in the vehicle.  These are not procedures –the procedures must be obtained from the particular vehicle’s service manuals.  Some service manuals provided the procedures as detailed descriptions, other provide illustrations with dismantling sequences shown.

The components of fig.3.1 are labeled below:
1. 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. Gasket, 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 

Auxiliaries and attachments
Points relating to auxiliary parts and accessories are as follows:

1.   Engine cover:  Cover over 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-head is removed.

3.   Coolant system: coolant hoses, 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 at the EFI throttle body will have to be removed.

6.  Emission pipe 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 ignition coil packs which are attached to the engine will have to be removed.  If there is a distributor, it’ll be removed.

8.   Spark plugs: these are removed so that the crankshaft is easy to rotate.

9.  Electrical connections: there are various electrical connections than the engine compartment that have to be disconnected.  Multi pin connectors can only be connected one way, but other connections that are not obvious should be labeled.

10. Drive belts: the drive belts for the alternator and other auxiliaries are removed-tensioners may have to be released.

11. Fuel system parts: many of these have to be removed so that other parts are accessible.

External Mechanical Parts
There are number of external parts that have to be removed. These include:

Intake manifold: This is often in two parts which can be separated for removal.

Exhaust manifold: In-line engines have one manifold, while V-type and horizontally opposed engines have two.

Valve cover: This is removed to gain access to the valve-operating mechanism and, on overhead camshaft engines, access to the camshaft.

Engine timing cover: Removal of one or more timing covers gives access to the timing chain or belt and to the sprocket or pulleys.

Engine timing: The timing marks are checked and set with No.1 cylinder at top dead centre (TDC).

Other items: Where fitted, a supercharger would have to be removed and parts of a turbocharger might have to be disconnected.

See Valve dismantling mechanism

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