201-L-4-E by mayank govil

4. ENGINE COMPONENTS - II In the previous unit, we had learnt about some of the major engine components like cylinder block, cylinder head, connecting rod, crankshaft, piston etc. These are the main components in an engine which are responsible for producing the required output of an engine. However, there are other components also which assist the main components in producing the desired result consistently. If these components fail, then the main components would not be able to perform consistently. In this chapter we will learn more about engine components.

4.0. Objectives i. ii.

4.1

After going through this lesson, you will be able to: List out the parts that make up an IC engine Recognize the parts and state their function, material from which they are made and the process by which they are made.

Introduction

After learning about the major components, their function and the material of manufacture in the previous lesson, we will learn about some more components which constitute the engine and are very critical in satisfactory performance of the engine. You will be introduced to valve timing mechanism, which is very critical for engine performance, oil pump and its parts which help the engine to lubricate under various conditions, oil filter, belts and pulleys, gaskets, bearings etc. It is pertinent to mention here that any problem in these minor components sometimes create a major damage in the major components studied in the earlier lesson.

4.2

Parts of an Engine

4.2.1 Valve Timing Mechanism The movement is transmitted from camshaft to the valves through a valve operating mechanism. The main parts of this mechanism are â&#x20AC;&#x201C; rocker shaft, rockers, valve springs and valve retainer. Valve timing mechanism is used to operate the inlet and exhaust valve at the correct instant of time. This mechanism transmits motion from the crankshaft to the camshaft with the help of belt, chain or gears. Gears and chain are not popular in cars now. The timing mechanism is enclosed in a timing belt cover at the front of the engine.

Fig. 5.1(a) shows the belt type timing mechanism having two grooved pulleys and a belt. The smaller pulley is mounted on the crankshaft and the bigger one on the camshaft. A groove which ensures that the pulley does Fig. 4.1: Valve timing mechanism not slip on the shaft is also (a) Belt type. (b) Chain type. visible. A grooved belt runs over the pulleys to transmit motion. Fig. 5.1(b) shows the chain type timing mechanism. It is similar to the chain of a bicycle. It has sprockets and chain instead of pulleys and belt. Small and large sprockets have teeth cut on the circumference with the chain transmitting power from the small to the large sprocket. While fitting the timing chain, it must be ensured that the timing marks on the small and large sprockets are aligned. 4.2.2 Oil Pump The oil pump supplies lubricating oil under pressure to various rubbing parts of an engine. It is attached to the cylinder block and it gets power from the crankshaft. Fig. 5.2 shows the oil pump of a Maruti 800 engine. It is a gear type pump with two gears. The rotor gets power from the crankshaft and rotates to supply oil to the engine. An oil seal is fitted to prevent leakage of oil.

Fig. 4.2: Oil pump.

4.2.3 Oil Strainer Oil strainer is a wire mesh sieve fitted on the oil pump and put inside the oil sump. Oil from the sump is sucked by the pump through this strainer and pipe so that dirt etc. does not enter the pump, preventing any possible damage to it. On one end of the pipe, an O-ring is fitted to prevent leakage of oil from the gap between pump and pipe.

Fig. 4.3: Oil strainer.

4.2.4 Oil Filter Oil from the pump goes to the engine through an oil filter which removes very small dirt and metal particles from the oil which can not be removed by the strainer. It is fitted on

Fig. 4.4: Oil filter.

one side of the engine. One side of the filter is fitted to the engine with the help of threads in the large middle hole. An O-ring is also placed to prevent leakage of oil. Oil after filtration or cleaning, goes to the engine from the large middle hole and comes to the filter from the pump through the six small holes. Oil filter is fitted onto the engine by rotating it. 4.2.5 Manifolds The purpose of manifolds is to supply fresh charge and to remove burnt gases from the engine cylinder. An engine has two manifolds â&#x20AC;&#x201C; the inlet manifold and the exhaust manifold. The inlet manifold shown in Fig. 5.5 has three pipes going in the cylinder head which shows that this manifold is for a three-cylinder engine. There are four studs for mounting the carburetor on the inlet manifold. The carburetor will be looked at in detail at a later stage. The exhaust manifold shown has a heat shield. It is required only on the exhaust manifold because it Fig. 4.5: Manifolds (a) Inlet. (b) Exhaust. becomes very hot when the engine is running.

Self-check Questions 1. 2. 3. 4. 5. 6.

Why is belt drive used now for valve timing rather than gear or chain drive? Valve clearance is kept between _____________ and _____________ In hot condition valve clearance is more. Explain. Oil pump gets its drive from the _______________ Exhaust manifold is made of ______________ Inlet manifold is made of _____________________

4.2.6 Bearings The purpose of bearings is to bear the load. They are used to support the shafts in an engine and are of different types. Ball Bearing is the most common type of bearing. It has an outer race, balls inside a ball cage and an inner race.

Fig. 4.6: Bearings.

A Sealed Type Ball Bearing has the balls and the cage sealed, and therefore, not visible. It is used to prevent dust etc. from entering the cage, preventing damage to the balls.

A Double Ball Bearing has an outer race, two cages with balls and two inner races. The outer race has grooves. The Roller Bearing has rollers instead of balls. In a taper roller bearing, rollers are fitted in a cage which has the shape of a cone. It consists of an outer race, rollers inside the cage and inner race. Needle Bearing is a type of roller bearing with very thin rollers. The needles are placed between the inner race and the outer race. 4.2.7 Belts and Pulleys Belts are used to transmit power from one shaft to another. Automobiles use V belts due to less chances of slipping as compared to a flat belt. The size of a V belt is printed on its circumference. A grooved V belt has grooves on the inside which further reduce the chances of slipping.

Fig. 4.7: (a) Grooved V-belt on pulley. (b) Timing belt.

Fig. 5.7(a) shows how a grooved V belt is mounted on a typical pulley. Fig. 5.7(b) shows the timing belt having grooves which run on a grooved pulley. This type of belt and pulley arrangement completely eliminates the chances of slipping of the belt. The timing belt and pulleys are placed inside the timing belt cover, seen in Fig. 5.8, for protection Fig. 4.8: Timing belt cover. from dust and damage. Below the timing belt cover, the lowest pulley is the crankshaft pulley which drives the water pump pulley above it for circulation of cooling water and the alternator pulley on the side with the help of a grooved V belt. 4.2.8 Gaskets Gaskets are used between two flat metallic surfaces to prevent leakage. A large number of gaskets of different types are used in an engine. Gaskets are thin sheets of soft material which are squeezed when the two parts are tightened. Once opened, they have to be replaced. Gaskets are generally made of asbestos, copperasbestos or copper-asbestos-steel, depending upon the strength required. The inlet manifold gasket is fitted between the engine and inlet manifold. It has three big holes for inlet passages and small holes for bolts which join the manifold with the engine.

Fig. 4.9: Gaskets (a) Exhaust manifold. (b) Cylinder head. (c) Oil sump.

The exhaust manifold gasket also has three big holes for exhaust gas passages and small holes for manifold mounting bolts. This gasket also has projections for accommodating spark plugs. The cylinder head gasket is used between the cylinder block and the cylinder head. It is made very strong with metallic inserts because it has to withstand high pressure and temperature. It has large circular holes for cylinder bores and small holes for cooling water and lubricating oil passages. The cylinder head cover gasket is placed between the cylinder head and the cylinder head cover. It is not required to be very strong. The oil sump gasket is used between the cylinder block and oil sump. It has holes for oil sump mounting bolts.

Self-check Questions 7. How is the timing belt prevented from slipping? 8. ______________ are placed between 2 metallic faces to prevent leakage

4.3

Assignments

4.3.1 Class Assignment 1. Discuss the importance of valve timing. 4.3.2 Home Assignment 1. Give an analogy of use of gaskets, in the kitchen. What happens when these go bad? Then what do you do?

4.4

Summing Up

In this second unit of the course we studied some engine components which make it work as required. You will become a better mechanic if you can correlate the parts of an engine to their purpose and how they are connected to the neighboring parts. You will then be able to attend to them better.

In further lessons, we will study other systems that are necessary in order to run the engine assembled from these parts.

4.5

Possible Answers to Self-check Questions

1. Belt drive is preferred over a chain / gear drive because it is less noisy than the gear / chain drive. It also has less loss in transmission of power and requires less maintenance. These days timing belts are available which are replaced at an interval of more than 100,000 kms. 2. Valve stem tip and rocker 1. aluminum cylinder head expands more than the steel valve; hence the rocker shaft moves up and clearance increases 2. crankshaft 3. cast iron 4. aluminum 5. toothed belt and pulley is used 6. gasket

4.6

Terminal Questions

1. Describe the working of the OHV operating mechanism. How is OHC better? 2. What is the significance of valve clearance? In which case is it more? Why? 1. Write a note on gaskets.

4.7

References

1. Maruti 800 Service Manual.

4.8