A camshaft is simply a shaft on which cams are mounted. The camshaft is mounted in bearings in the lower part of the cylinder block in most inline engine. In few engines, it is located on the cylinder head. A cam is a device that changes rotary motion of the camshaft into linear motion of the follower or lifter. The cam has high spot or love the follower riding on the cams will move away from or toward the camshaft as the cam rotates. A camshaft is responsible for opening the valves. A camshaft has a number of cams along the length, two cams for each cylinder, one to operate the inlet valve and the other the exhaust valve. The camshaft is driven by the crankshaft either by a pair of meshing gears or by means of a pair of timing sprockets connected by a chain. The camshaft turns at half the speed of the crankshaft. The gear and sprocket maintain a definite time relationship between the camshaft and the crankshaft to ensure opening the valves exactly at the correct time in relation to piston position.

Valve is a device to close and open a passage in motor vehicle engines. Two valves are used for each cylinder - An inlet or intake valve and an exhaust valve. Fuel is admitted to the cylinder by the inlet valve, and the burnt gases escape from the exhaust valve. When closed, the valve must seal the combustion space tightly. The valves are usually made of Austenitic stainless steel which is a corrosion and heat resisting material. Exhaust valve is usually made of silchrome steel which is an alloy of silicon and chromium with unusual resistance to heat. Inlet valve being subjected to less heat is usually made of nickel chromium alloy steel. The valves used in modern passenger car engines are termed as poppet or mushroom valves.

Valve mechanism:

Flywheel is a heavy steel wheel attached to the rear end of the crankshaft. The size of the flywheel depends upon the number of cylinders and the general construction of the engine. 

The flow of power from the engine cylinder is not smooth although the power impulses in a multi-cylinder engine overlap or follow each other to provide a fairly even flow of power, however additional leveling off of power impulse is required. This is done by a flywheel. To understand the function of a flywheel in a better way, take the example of a four stroke, single cylinder engine. There are times when more power is being delivered than at other times. This tends to make the crankshaft speed up and then slow down. The engine delivers power during one stroke only - the power stroke and it absorbs power during the other three strokes - to push out the exhaust gases, to intake fresh charge in the cylinder and to compress this charge. Thus during power stroke, the engine tends to speed up and during the other three strokes, it tends to slow down. The inertia of the flywheel tends to keep it running at constant speed. When the engine tends to speed up, the flywheel resits it. When the engine tends to slow down, the flywheel resists it. Thus the flywheel absorbs energy as the engine tries to speed up and gives back energy when the engine tries to slow down, keeping the engine speed almost constant.

Flywheel is also used as a part of clutch mechanism and fluid drive unit. The flywheel also has a teeth on its outer edge to mesh with the electric cranking motor driven pinion when the engine is being cranked to start it.

Crankshaft is the first part in the power transmission system onto which the reciprocating motion of the piston is converted into rotating motion with the help of connecting rod. A crankshaft consists of crank pin, crank arm, balancing weight and main journals. Big end of the connecting rod is connected to the crank pin of the crankshaft. Center to center distance between the crank pin and crankshaft is half of the piston displacement during a stroke. Thus one complete revolution of the crankshaft makes two stroke of the piston. The parts of the crankshaft inside the main bearings are called the main journals. The crankshaft is supported by the main bearings on the main journals. Balancing weights are provided on the opposite side of the crank arms for balancing. 

The connecting rod is the connection between the piston and the crankshaft. It joins the piston pin with the crank pin. Small end of the connecting rod is connected to the piston pin and larger end to the crank pin. The function of the connecting rod is to convert linear motion of the piston into rotatory motion of the crankshaft. The connecting rod usually has I-beam cross-section and made of forged steel. Aluminium alloy is also used for connecting rods. They are carefully matched in sets of uniform weight in order to maintain engine balance. The connecting rod carries the power thrust from piston to the crank pin and hence it must be very strong, rigid and also as light as possible.

Piston pin or wrist pin or gudgeon pin connects the piston and small end of the connecting rod. Piston pin is generally hollow and made from case hardened steel heat treated to produce a hard, wear resisting surface. Piston pin may be selectively fitted and, if supplied with the piston, are not interchangeable. The external bearing surface is finished to a very high degree of accuracy to ensure correct fit in the piston and connecting rod. Piston pin should be inspected for wear, cracking or pitting. Circlips should always be renewed and where soft end pads are fitted, check that they are not loose or cracked. Circlips are types of rings which prevent pin to come in contact with cylinder wall.

Piston rings are usually made of fine grained alloy cast iron. This material possesses excellent heat and wear resisting qualities inherent in its graphitic structure. The elasticity of this material is also sufficient to impart radial expansion and compression which is necessary for assembly and removal of the ring, and particularly to enable it to exercise flexible pressure on the cylinder valves.

1. Compression rings
2. Oil control rings

Piston (Image credit: btechgurus.blogspot.com)

Piston is one of the most important part in a reciprocating engine in which it helps to convert the chemical energy obtained by combustion of fuel into useful mechanical power. The purpose of the engine is to provide a means of conveying the expansion of the gases to the crankshaft via the connecting rod, without loss of gas from above or oil from below. Piston is essentially a cylindrical plug that moves up and down in the cylinder. It is equipped with piston rings to provide a good seal between the cylinder wall and piston. The efficiency and economy of the engine primarily depends on the working of piston. It must operate in the cylinder with minimum friction and should be able to withstand a high explosive force developed in the cylinder and also the very high temperature ranging from 2000 C to over 2800 C during operation. The piston should be as strong as possible, however its weight should be minimized as far as possible in order to reduce the inertia due to its reciprocating mass. The top of the piston is called head. Ring grooves are cut on the circumference of the upper portion of the piston. The parts below the ring grooves is called skirt. The portion of the piston that separates the grooves are called the lands. Some pistons have a groove in the top land called a heat dam which reduces heat transfer to the rings. The piston bosses are the reinforced sections of the piston designed to hold the piston pin or wrist pin.

There is problem of cylinder wear in I.C. engine and this is solved by use of cylinder liners. Cylinder liners are in the form of barrels made of special alloy iron containing silicon, manganese, nickel and chromium. They are cast centrifugally. It is now customary to fit cylinder liners on engines of cars and commercial vehicles. These liners are of the oil hardening type and offer considerably longer life for the engine. 

The cylinder liners are of two types:

1. Dry liners - Dry liner is made in the shape of barrel having a flange at the top which keeps it into position in the cylinder block. The entire outer surface of the dry liner bears against the cylinder block casting and hence has to be machined very accurately from the outside also. Thus it is not in direct contact with the cooling water and hence is known as dry liner. Its thickness ranges from 1.5mm to 3mm. It is used mostly for reconditioning warm cylinders.

2. Wet liners - A Wet liner forms a complete cylinder barrel. It is provided with a flange at the top which fits into the groove in the cylinder block. At the bottom either the block or the liner is provided with grooves, generally three in numbers, in which the packing rings made of rubber are inserted. The liner is in direct contact with the cooling water and hence is known as wet liner. The outer surface of the liner does not require accurate machining. Wet liners are thicker than dry liners, ranging from 1.5mm to 6mm.

Crankcase is attached to the bottom face of the cylinder block in I.C.engine. It acts as the base of the engine. It supports the crankshaft an camshaft in suitable bearings and provides the arms for supporting the engine on the frame. The oil pan and the lower part of the cylinder block together are called the crankcase.

In an Internal Combustion Engine, the top of the cylinder is covered by a separate cast piece known as the cylinder head. The cylinder head is bolted to the top of the cylinder block. It contains combustion chamber. Spark plug and sometimes valves are mounted in it. It incorporates passages for the flow of cooling water.

Cylinder head (Image credit: dodgeram.info)

The cylinder head is usually made of gray iron or aluminium alloy. Aluminium has the advantages of lightness in weight and high heat conductivity. It is cast separately from the cylinder block so that it may be removed for cleaning carbon and grinding valves. To retain compression in the cylinder, a flat piece of gasket is placed between the cylinder head and the cylinder block. In certain cases such as a racing car engine, a separate head is not used. But a single piece of cylinder block and a head is difficult and costlier to make, and the internal parts of the engine are not as accessible.

Cylinder block, cylinder head and crankcase are the main stationary bodies of the automobile engine. They serve as support and enclosure for moving parts. Nowadays the cylinder block and crankcase form a single casting which gives a rigid structure. Ribs are cast in the crankcase to give it extra strength and to support the main and camshaft bearings.

Cylinder Block (Image Credit:the-nerd.org)

A cylinder block consists of three parts:

Internal Combustion Engine (I.C. Engine) is basically heat engine and converts heat energy into mechanical energy. I.C. engines are used mainly in the field of transportation but in many industries, farms; simplicity and low cost of operation are the determining factors in the adoption of I.C. engine. Internal Combustion Engine is that type of engine in which combustion takes place inside the cylinder itself. Air fuel mixture in case of petrol engine is compressed inside the cylinder and only air is compressed inside the cylinder in case of diesel engine and diesel is injected through injector and combustion takes place.