5. ENGINE DISASSEMBLY – I In last lesson we learnt how to disassemble various accessories attached to an engine. We also learnt the use of some special tools, which are helpful in disassembling these accessories. In this lesson, we will introduce you to dismantling the various parts of an engine. Dismantling, though not as skilled a job as assembly of an engine, but proper inspection and arrangement of parts during assembly helps a person in fast and quality job of assembling the engine back.
5.0
Objectives
After going through this lesson, you will be able to: i. Understand the step by step process of dismantling of the following engine parts: a. Cylinder head cover. b. Rocker arm shaft assembly. c. Camshaft. d. Cylinder head.
5.1
Introduction
We will continue from where we left in the previous lesson. In the first part on engine disassembly, we saw the removal of all accessories and sub-assemblies from the engine. We are now left with just the engine along with its internal components which we will learn to remove in this and the subsequent lesson. We will begin with the cylinder head cover that will expose the cylinder head. The head contains the rocker arm shaft assemblies and the camshaft which will be removed. Finally the head will be removed from the block.
5.2
Fig. 5.1: Cylinder head cover.
Cylinder Head Cover
The cylinder head cover is seen at the top of the engine. The cover is bolted to the cylinder head by four bolts. We loosen and
Fig. 5.2: Cylinder head cover gasket.
remove these four bolts using a number 10 ring spanner. Once all the four bolts have been removed, the cylinder head cover can be lifted off. The cap on the top of the cover is used for filling or topping up of engine oil. Adjacent to the cap, there is a small pipe where the breather hose is fixed. This hose collects and passes the crankcase gases into the intake manifold and thereafter to the cylinders for re-combustion. On the inner side of the cover, there is a gasket which is made of cork material and is used to seal any oil leakage from between the cylinder head cover and cylinder head.
5.3
Rocker Arm Shaft Assembly
In order to remove the rocker arm and the rocker arm shaft, we first loosen the valve adjusting screw check-nuts with a number 12 open end spanner and then use a screw driver to loosen the adjusting screws but leave these screws in place. Next, we remove the eight rocker shaft securing screws with Philips or 'plus' tip screw driver. These set screws are provided with counter sunk head.
Fig. 5.3: Valve adjusting screws.
After all the eight rocker shaft securing screws have been Fig. 5.4: (a) Rocker arm shaft. (b) Assembly. removed, we push the two rocker arm shafts, one by one, with the help of screw driver, simultaneously removing the rocker arms and rocker arm springs as they come. The four threaded holes in the rocker shaft are for locking it in position by the set screws. The shaft also has holes provided for feeding lubricating oil to the rocker arm. This is necessary since the rocker arm continuously moves on the rocker shaft during engine operation. Even though both the rocker arm shafts and all the rocker arms and rocker arm springs are identical and of the same size, we must tag them and keep separately so that at the time of assembly these are put in their original position.
Self-check Questions 1. 2. 3. 4.
The cap on the top of the cylinder head cover is removed for _______________. _________________ is fixed in the small pipe in the cylinder head cover. What is the function of breather hose? Rocker arm shaft has holes for feeding lubricating oil to the rocker arm. State whether True/False.
5.4
Camshaft
To remove the camshaft, we first remove the camshaft thrust plate by unscrewing the two set screws with the help of a Philips or plus type screw driver. This thrust plate holds the camshaft in position and takes axial load or thrust. Next, we Fig. 5.5: Camshaft (a) Thrust plate. (b) Components. draw the camshaft out toward the side of distributor gear case. The camshaft has four bearing journals and six cam lobes. At one end of the camshaft, the drive gear for distributor is located and next to it is the eccentric which is provided to operate the fuel pump lever. The camshaft timing belt pulley is mounted on the other end of the camshaft.
Self-check Questions 5. 6. 7. 8.
Camshaft can be removed only after the ____________ is removed. The __________ holds the camshaft in position and takes axial thrust. The camshaft is drawn out toward the side of __________________. What parts are driven by the camshaft?
5.5
Cylinder Head
The cylinder head is fixed on the top of cylinder block with the help of eight bolts. These bolts are opened by using a number 14 socket spanner with tommy bar. The cylinder head is an important part of the engine. It contains seats for valves, valve guides, combustion chamber, mountings for rocker shaft and bearings for camshaft beside openings for inlet and exhaust manifolds and oil and water passages. The cylinder head is an aluminum alloy casting.
Fig. 5.6: Cylinder head.
After all the eight bolts have been removed, we lift off the cylinder head from the block. Utmost care has to be taken to avoid Fig. 5.7: Cylinder head bolt. any damage to the faces of the cylinder head and the cylinder block while the head is being removed. The bolts used for fixing the cylinder head are not full-threaded. The unthreaded portion of the bolts works as locating pins due to less clearance between the holes in cylinder head and the bolts.
The head gasket which is placed between the cylinder head and block is of preformed asbestos and copper sheet with steel rings and makes a leak proof joint not only between the cylinder head and cylinder block but also prevents the possibilities of inter-cylinder short circuiting or leakage.
Fig. 5.8: Cylinder head components.
Fig. 5.9: Cylinder head gasket.
Self-check Questions 9. List the parts of cylinder head. 10. Cylinder head is a casting of _________________. 11. What is the function of cylinder head gasket?
5.6
Class Assignment
1. In earlier engines the camshaft was provided in the cylinder block. In this engine the camshaft has been provided in the cylinder head. This is called overhead camshaft (OHC). Discuss the advantages of this method.
5.7
Summing Up
In this lesson, we learnt how to disassemble some parts from the engine. These included the rocker arm shaft assemblies. After removal, you must tag the rocker arm shafts and all the rocker arms and rocker arm springs and keep them separately so that at the time of assembly these are put in their original position. This is important because old parts make their seat and proper clearances in places where they have been running which should not be disturbed for smooth running of the engine. Now in the next lesson we will remove the internal components of the engine.
5.8
Possible Answers to Self-check Questions
1. Filling or topping up of engine oil. 2. Breather hose 3. The breather hose collects and passes the crankcase gases into the intake manifold and thereafter to the cylinders for re-combustion. 4. True 5. Thrust plate 6. Thrust plate 7. Distributor gear case 8. Distributor, fuel pump, intake and exhaust valves 9. seats for valves, valve guides, combustion chamber, mountings for rocker shaft and bearings for camshaft beside openings for inlet and exhaust manifolds and oil and water passages. 10. aluminum alloy 11. makes a leak proof joint between the cylinder head and cylinder block and also prevents the possibilities of inter-cylinder short circuiting or leakage
5.9
Terminal Questions
1. Describe the procedure of removing the rocker arm shaft assembly.
5.10 References 1. Maruti 800 Service Manual.
5.11 Suggested Further Reading 1. Lewis, G., 1986. Engine Service, 2nd Edition. Prentice-Hall, New Jersey. 2. Chhikara, A., 1999. Automobile Engineering, Vol 3: Automotive Marketing & Workshop Techniques. Satya Prakashan, New Delhi.
5.12 Glossary Breather
Outlet to remove the blow by gases from the crankcase.
Combustion chamber
The space left within the cylinder when the piston is at the top of its stroke.
Cork
Soft material made out of bark of a tree
Counter sunk bore / head
Tapered end of bore so that the head does not project out
Gasket
A seal or ring of soft material pressed between two surfaces to prevent leakage
Hose
A flexible tube conveying water
Manifold
A casting of passages or set of pipes which connect the cylinders to an inlet or outlet source.
Philips head
‘ ’ tip head
Rocker arm
A lever which rotates around a shaft pushing down (opening) the valve with an end when the other end is pushed up by the pushrod. Spring pressure will later close the valve
Rocker arm shaft
A shaft on which rocker arms rotate
Topping up
Filling up to specified level