3. ENGINE COMPONENTS - I Now that we have an idea of an engine as a power producing device in an automobile, let us see what all parts are required to construct an engine. We looked at the four major parts of the engine viz. cylinder, piston, connecting rod, and the crankshaft. But an engine is built up of many parts, some of which are of metal, both ferrous and non-ferrous, and some of other materials. Some major parts are common to 2-stroke and 4-stroke engines; but the 4-stroke engine has many parts which are not found in 2-stroke engines. Hence the 4-stroke engine is bigger and bulkier than a 2-stroke engine.
3.0. Objectives i. ii. iii.
3.1
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
In the previous lesson, an engine was defined as a device that converts heat energy into mechanical energy. We also understood the working of an IC engine in detail. We had occasion to study some parts of an IC engine there. However, those are not the only parts that an IC engine is built up of. In this lesson, we will study all the parts of an engine, their respective locations, materials from which each of these is manufactured, processes of manufacturing and the purpose of each part in an engine. It is noteworthy that each part costs money to produce and increases the cost of a vehicle. Hence, no part is redundant. This should specially be kept in mind when assembling an engine – even the most humble nut or washer is important, so do not leave it out. You never know when the absence of even a tiny part may make the whole engine break down, leaving you stranded.
3.2
Parts of an Engine Fig. 3.1 shows the various components of an engine. These are: A. B. C. D. E.
Valve Cylinder head cover Inlet passage Cylinder head Cooling water passage F. Crankcase G. Oil sump H. Lubricating oil
I. J. K. L. M. N. O. P.
Camshaft Rocker Spark plug Exhaust passage Piston Connecting rod Big end bearing Crankshaft main bearing
Fig. 3.1: Parts of an engine.
Self-check Questions 1. List out the various parts of an engine.
3.2.1 Cylinder Block and Crankcase The cylinder block and crankcase is the largest part of the engine and is made of cast iron or aluminum alloy. All the main components that are responsible for conversion of energy obtained by the burning fuel to mechanical energy are housed in this block. Fig. 3.2 shows the cylinder block of a Maruti 800 car with all the three bores visible. The bores have a very smooth mirror like surface. There are holes for cooling water passage between cylinder block and cylinder head. The outer holes are for lubricating oil Fig. 3.2: Cylinder block. passage and the circular holes are for joining the block and head with the help of bolts. There is a pipe which has a metallic strip called dipstick. The dipstick has two marks showing the maximum and minimum permissible levels of lubricating oil in the engine. On the bottom side of the cylinder block or the crankcase, the crankshaft is mounted on the crankshaft main bearings, which are provided with holes for flow of lubricating oil from cylinder block to Fig. 3.3: Crankshaft bearings.
crankshaft. The crankshaft is mounted on bearings that are in two halves. After putting the crankshaft in place, caps are placed over it and it is secured with the help of bolts. 3.2.2 Cylinder Head The cylinder head is a casting made of aluminum alloy. It is attached at the top of the cylinder block with the help of bolts. The entire valve operating mechanism is inside the cylinder head. It has holes for oil passage, for placement of bolts that are used for joining it with the cylinder block and for water passage. It also has bearings to support the camshaft and the rocker shaft. The cylinder head of Maruti 800 engine can be seen in Fig. 3.4. There are three passages for exhaust gases for the three cylinders. Exhaust manifold is fitted at the side above the three spark plugs. In the top view, valves Fig. 3.4: can be seen. Valves have Cylinder head (a) Side view. (b) Top view. been removed from one of the cylinder so that one may see clearly. Valves will be discussed a little later. There are valve guides to guide the valve movement. There is a big through hole (see Fig. 3.5 (a)) for fitting the camshaft and two smaller holes on the top for fitting the rocker shaft. On the bottom side of the cylinder head (see Fig. 3.5 (b)), there are inlet and exhaust valves and a combustion chamber with spark plugs corresponding to each cylinder. The cylinder head has many holes for cooling water and lubricating oil passage and there are the two dowel pins for locating the cylinder head on the cylinder block correctly. There are also some more holes near the edge of the cylinder head for fixing the cylinder head over the Fig. 3.5: Cylinder head cylinder block with the help of (a) Camshaft hole. (b) Bottom view. bolts. 3.2.3 Cylinder Head Cover The cylinder head cover is to protect the cylinder head and its components from dust and damage. It has an oil filler cap from which the lubricating oil is filled when the level of oil in the engine goes down. A breather pipe is provided for the removal of gases from the cylinder head to the air intake
Fig. 3.6: Cylinder head cover.
passage and a gasket is used between the cylinder head and cylinder head cover to prevent leakage. There is a plate to prevent surge of oil. Gases from cylinder head flow through the holes provided to the breather pipe.
Self-check Questions 2. 3. 4. 5. 6.
Which is the largest part of an IC engine? What is the function of dipstick? Why are crankshaft main bearings in two halves? Lubricating oil is filled in the engine through the _____________________ A breather pipe is provided in the cylinder head cover for the removal of gases from the cylinder head to the air intake passage. Where do these gases come from?
3.2.4 Piston Piston is a cylindrical plug that reciprocates inside an engine cylinder. The top of the piston, known as the head or crown, has depressions to accommodate the valves when the piston is at the top dead centre and valves are open. Near the head of the piston, there are three grooves for rings. The top two grooves are for compression Fig. 3.7: Piston. rings and the bottom one is for oil control ring. The piston also has a hole for the gudgeon pin and a groove for a circlip to lock the gudgeon pin inside the piston so that it does not come out of the piston boss. The boss is the reinforced section of the piston to withstand force, especially during the power stroke. There also holes for lubrication. The lower side of the piston is also known as the piston skirt. 3.2.5 Piston Rings Piston rings are fitted in the piston ring grooves so that when the air-fuel mixture is compressed, it may not leak from top of the piston to the bottom of the piston. Also, during power stroke and exhaust stroke, gases should not leak from top to bottom of the piston. The top two compression rings are used to seal the compression within the Fig. 3.8: Piston rings. cylinder and the bottom oil control ring is used to scrape the lubricating oil from the cylinder surface to the oil sump. The rings have spring action. The oil control ring is in three parts – the topmost part is known as the upper rail, the middle part is known as the spacer and the lower part is known as the lower rail.
3.2.6 Gudgeon Pin The gudgeon pin, Fig. 3.9, used to join the piston and the connecting rod, is a hollow cylindrical pipe-shaped component. It has a very smooth mirror like surface with its ends chamfered. The gudgeon pin is held in its place with the help of two circlips, one on each side and is fitted inside the piston. Fig. 3.9: Gudgeon pin.
3.2.7 Connecting Rod The connecting rod, Fig. 3.10, connects the piston to the crankshaft. It is made of alloy steel and manufactured by forging to enable it to withstand the loads that are exerted on it by the piston during power stroke. It consists of a small end, a shank and a big end. The big end is in two pieces that Fig. 3.10: Connecting rod. are joined by nuts and bolts. It has a hole for lubrication. The small end also has three holes for lubrication. Inside the big end, there are two half bearing shells made of white metal from inside and steel from outside. The lubricating holes of big the end cap and shell must match while fitting. Fig. 3.11 shows the piston, gudgeon pin and connecting rod after assembly. The connecting rod also has a sideways play. 3.2.8 Crankshaft
Fig. 3.11: Piston, gudgeon pin and connecting rod.
The linear motion of the piston in an engine is converted to rotary motion of the crankshaft. The crankshaft is also made by forging process and the big end of connecting rod is connected to it. A pulley is mounted at the front end of the crankshaft to drive the water pump and alternator. The crankshaft is supported in the crankcase on the main bearings and the big end of connecting rod is connected at the crank pins. It also has webs and balancing Fig. 3.12: Crankshaft. weights to balance the crankshaft. The balancing weights have holes which are drilled to balance the crankshaft accurately to avoid vibrations. The flywheel is attached to the back side of the crankshaft with the help of bolts through the holes. There are through holes that run from main bearing to big end bearings to allow the flow of lubricating oil.
Self-check Questions 7. Movement of piston in the cylinder is __________ 8. _ Nos. of compression ring and _ oil control ring is used in the _______ 9. Why two compression rings are provided? 10. Piston pin is held in place by ________ 11. Why is the gudgeon pin required to be held in place by circlips? 12. Small end of connecting rod has ___________ for lubrication of piston pin 13. Big end of connecting rod is split. State whether True/False 14. Bearing shells are made of _______________ 15. Rotary motion is available at the __________
3.2.9 Flywheel A flywheel, Fig. 3.13, is used for smooth transmission of power from the engine. It is attached to the back side of the crankshaft with the help of six bolts through the holes provided. There is a ring gear on the circumference of the flywheel which meshes with a small gear (starter pinion) of the starter motor to start the engine. A hole is provided for dowel pins for correct location. In case the flywheel is not accurately balanced, holes may be drilled to balance it. The top dead centre of the first cylinder is marked on the flywheel. The T and 10 seen written on the flywheel in Fig. 3.14 indicate the TDC and 10째 before TDC. There is a timing mark which shows 7째 before TDC which is for correct timing of ignition.
Fig. 3.13: Flywheel.
Fig. 3.14: Flywheel markings.
3.2.10 Camshaft The camshaft has a number of cams integral to it and is placed generally in the cylinder head. There may be one camshaft operating the inlet valve as well as the exhaust valve with the help of rockers or there may be separate camshafts for inlet and exhaust valves. Fig. 3.15 shows a camshaft with two cams for each cylinder, one for inlet and the other for exhaust valve. The camshaft is supported on bearings. On the rear side, there is a gear which drives the distributor and if a mechanical fuel pump is used, it gets its drive from the rear end of the camshaft. A
Fig. 3.15: Camshaft.
timing pulley is mounted on the front side with the help of a key. 3.2.11 Valves Every cylinder has at least one inlet and one exhaust valve. Some car engines may have more than two valves in each cylinder. Fig. 3.16 shows the two valves of a Maruti 800 engine. The inlet valve is larger than the exhaust valve. This is because suction takes place at a pressure difference of less than 1 kg/cm2 whereas after the Fig. 3.16: Valves. power stroke, pressure inside the cylinder is so high that exhaust gases start flowing out of the cylinder by themselves and further the piston pushes them out during the exhaust stroke. Components of the valve assembly are shown in Fig. 3.17. The valves are fitted in the cylinder head from the bottom side and the valve seal, spring and retainer are fitted from the top side. Two locks are fitted at the top of the spring so that the spring does not come out. The rocker shaft has holes for mounting and for lubrication of Fig. 3.17: Components of valve assembly. rockers. Rockers and rocker shaft springs are fitted on this shaft. The cam rider is in contact with the cam. On the other side is the tappet which pushes the valve down and a lock nut which is used to adjust the clearance between valve and tappet. 3.2.12 Oil Sump Oil sump, Fig. 3.18, is a container of lubricating oil that is fitted at the bottom of the cylinder block. A gasket is placed between the oil sump and the cylinder block. There are holes for fixing it under the cylinder block with the help of bolts. There is also a baffle plate to prevent the surge of oil when the vehicle is suddenly started or stopped. The oil strainer is placed in the oil sump. At the bottom of the oil sump, there is a drain plug which is opened to remove the oil when it has to be changed.
Self-check Questions 16. Flywheel is attached to the _____________ with bolts
Fig. 3.18: Oil sump.
17. Camshaft is mounted in the _______________ 18. Fuel pump is driven by the _____________ 19. __________ valve is larger in diameter
3.3
Activity
1. Check the level of oil in the engine in the workshop. 2. How would you check the level of oil in a 2-stroke engine?
3.4
Home Assignment
1. Write down the names of various components in the following figure.
2. Study the data of at least 5 different engines and tabulate the number of valves per cylinder, number of cylinders, oil sump capacity.
3.5
Summing Up
In this lesson we have had an overview of the various components inside the engine. You should now be able to recognize the parts and state their location and function. You should also be able to state the material from which they are made and the process by which they are made. This knowledge will make engine overhauling easy to understand and interesting. Some more parts will be studied in the next lesson.
3.6
Possible Answers to Self-check Questions
1. 2. 3. 4.
See list. cylinder block and crankcase to check the level of oil in the sump the crankshaft is in one piece and the throws extend in the Y-plane hence it cannot be inserted from one end, rather it is placed from below and the cap bolted over it 5. filler hole in the cylinder head cover 6. these are blow-by gases which leak past the piston into the crankcase and are removed from there so that crankcase pressure does not increase other wise oil will leak past the seal 7. linear 8. 2, 1 9. compression rings have open ends and gases can leak past the open end, hence 2 rings are provided and their open ends staggered so that gases do not leak past the rings 10. circlip 11. so that the pin does not come out of the piston otherwise it will scratch the cylinder bore 12. 3 holes 13. True 14. white metal 15. crankshaft 16. crankshaft 17. cylinder head 18. camshaft 19. inlet
3.7
Terminal Questions
1. List the various parts of an IC engine and give the function of each in brief. 2. Write notes oni. cylinder block, head, and cover ii. piston assembly iii. valve assembly
3.8
References
1. Maruti 800 Service Manual.
3.9
Suggested Further Reading
1. Gupta, K. M., 2002. Automobile Engineering, Vol. 1. Umesh Publications, Delhi. 2. Nakra, C. P., 2007. Basic Automobile Engineering (English). Reprint. Dhanpat Rai Publishing Co., New Delhi. 3. Chhikara, A., 1999. Automobile Engineering, Vol 1: Engine Systems. Satya Prakashan, New Delhi.
3.9
Glossary
Breather pipe
Pipe through which blow-by gases from the crankcase are collected and sent to the air cleaner for accompanying the fresh charge into the cylinder for re-combustion.
Casting
Process of manufacturing by pouring molten metal into moulds.
Circlip
Ring of steel which holds the piston pin in place; circlip is fixed in a groove in the piston boss.
Dipstick
Flat strip which measures the level of oil in the sump.
Distributor
That which distributes high voltage to the spark plugs in proper firing order; it gets drive from the camshaft.
Ferrous
Metal containing iron.
Forging
Process of manufacturing in which metal is heated and hammered.
Gudgeon pin
Piston pin, which holds the piston to the connecting rod.
Linear motion
Move in a straight line.
Non-ferrous
Metal not containing iron.
Oil strainer
Oil in sump is cleaned before being sent to the main filter by strainer which is of steel wire-mesh.
Reciprocate
Move up and down (or to and fro).
Timing of ignition
Correct instant at which ignition should occur to get maximum power and fuel economy from the engine.