Car Parts and Accessories

The cylinder block, the main shell of the engine, is usually combined with the crankcase in one casting.

Most blocks are made of cast iron because it is fairly strong, cheap and easy to machine for mass-production. The block’s strength can be improved by alloying cast iron with other metals.

Some cylinder blocks are made of light alloys, which makes them lighter and better for conducting heat; but they are more costly.

They are also too soft to provide a working surface for the cylinder bores, and separate cast-iron liners or sleeves must be inserted into the bores.

The water jacket—passages through which water circulates to cool the cylinders —is usually cast as an integral part of the cylinder block. It is linked with the corresponding water jacket of the cylinder head through openings at the top.

A block can be cracked by water expanding as it freezes in the jacket. Sometimes the expansion will dislodge the core plugs which seal holes required in the process of casting the cylinder block ; but core plugs cannot be relied on to act as ’safety valves‘ in this way.

Cylinders can be arranged in one row (in-line), in two rows set at an angle (V engine) or set sideways in two rows, on either side of the crankshaft (flat or horizontally opposed). Most 4 and 6- cylinder engines are in-line.

The greater the number of cylinders in an engine, the smoother will be the running, particularly at low engine speeds. In some larger cars, with six or eight cylinders, the V-6 or V-8 layout is used.

Horizontally opposed cylinders are used in only a few engine designs, usually those with engines at the rear, where space is limited. However, one air-cooled range is produced in very large numbers.

Cylinder Head and Valves

Cast iron and aluminium are the materials most commonly used for the construction of cylinder heads.

Aluminium is also used for the construction of the engine block on a number of high-performance engines, particularly in sports cars, because it weighs less and is a better conductor of heat. An aluminium cylinder head, however, needs inserts to strengthen the valve seats and guides, and may present difficulties in making an effective joint with a cast-iron cylinder block, as the two metals expand at different rates.

The lower face of the cylinder head is machined flat to mate with the upper face of the cylinder block. A gasket usually seals the two surfaces, but a few designs rely on a perfect face-to-face gas seal, with rubber seals to prevent any seepage of water from the cooling system.

Any distortion of the faces of the head and block can lead to gasket failure which will result in gas or water leakage. Distortion can be caused by running an engine with insufficient water in the cooling system

Because of the high temperatures they can reach, the combustion chambers and exhaust ports must be adequately cooled.

While the inlet manifold can be of aluminium, the exhaust manifold must be of a highly heat-resistant material such as cast iron or steel.

Cooling the valves

Inlet valves are usually larger than exhaust valves, as the gas flow into the cylinder is slower than the flow of exhaust gas which escapes under pressure.

The exhaust valve may become red hot when the engine is driven hard, so it has to be made of heat-resistant metal. It gets rid of excess heat through its seating when it is closed, and through the guide in which its stem slides.

Possibly related posts: (automatically generated)
Cylinder Block and Car Engine Valves

• Mechanics of the Car
• Engine where the fuel burns
• How heat becomes driving power in Car Engine?
• Automobile Transmission Axles Care
• Auto Pistons and Connecting Rods of Car Engine
• Camshafts and Valves, how the valves open and close
• Auto kits or tools for the Car and the Garage
• Mechanic guide, Car Engine and Cooling System
• Petrol injection, Auto Fuel System and Auto Part Repair Guide
• Inlet Manifold and Automobile Carburettors