Engine Construction

The automobile engine is essentially a heat engine. The heat engines used in modern automobiles are internal combustion engines. Each of this engine has a few main working parts; the auxiliary parts are necessary to hold the working parts together or to assist the main working parts in their performance. The main parts are: (a) the engine block; (b) the cylinder; (c) cylinder head, usually holding in-let and exhaust valves; (d) the piston; € the connecting rod; (f) the crankshaft; (g) the crankshaft or main and connecting-rod bearing; and (h) the fuel pump and fuel nozzle.

The engine block forms the main framework (Fig. 4), or foun-dation, of the water-cooled engine. The block is mainly cast from gray iron or iron alloyed with other-metals such as nickel or chromium. However, some blocks have been made from aluminum. In any case, the block itself has many components cast into it or assembled onto it.

Cast into the block, for example, are the cylinders. The cylin-ders are circtjlar, tubelike openings in the block, which act as guides for the pistons as they move up and down. Engine blocks have four, six, or eight openings, or cylin-ders. In aluminum blocks, the cast-iron or steel cylinder sleeves (liners) are installed because these metals can withstand the wear caused by the moving pistons better than aluminum can.

Also cast into the block are the water jackets. The water jackets are open spaces between the inner and outer surfaces of the block and cylinders through which the coolant flows. The coolant, in turn, removes heat from the metal surfaces around such areas as the cylinder walls and valve seats and carries the heat to the radiator where it releases into the air. Cast-iron blocks usually have a number of holes along the side and in the end leading into the water jackets.Finally, the block has cast-in bores for both camshaft and crankshaft. The crankshaft bore has a machined finish, which accommodates a bushing that actually supports the revolving shaft in the block. However, only haft the crankshaft bore is cast into the block. The other half is ma-chined into a bearing cap. The block bearing saddles (the halt bores) and the caps also have a machined finish, which accommodates the main bearings, which in turn support the crankshaft.

Many parts also attach by fastening devices to the average engine block. These items include the water pump, oil pan, timing gear or chain cover, the flywheel or clutch housing, the ignition distributor, Oil and fuel pump, and the cylinder head. The water pump is a component of the cooling system. The crankshaft usually rotates this unit by means of a belt. When revolving, the water pump circulates coolant between the engine water jackets and the radiator.

The oil pan and the lower portion of the block together are known as the crankcase; they enclose or encase the crankshaft. The oil pan is usually formed of pressed steel. The pan itself is also a reservoir, which usually holds 4 to 9 quarts of lubricating oil, depending on the design of the engine.

When the engine is operating, the oil pump of the lubri-cating system draws oil from the pan and pumps it to all the moving parts of the engine. Alter the oil lubricates these parts, it drains off and runs back down into the pan. Consequently, there is a constant circulation of oil between the pan and the moving parts of the engine.

The timing gear or chain cover, as its name implies en-closes and protects the timing gears or timing chain and sprockets from foreign materials. This cover, like the oil pan, can be formed from pressed steel. However, in some cases. The cover will be formed from cast iron or aluminum because these particular covers have not only the fuel pump but also the water pump attached directly to it and have coolant flowing through special passages formed into the cover.

In addition, the cover has a machined area that accommodates the timing-cover seal. The seal prevents leak-age of lubricating oil from around the area where the crankshaft protrudes through the cover to the outside of the engine. The seal itself is a lip type bonded to a steel backing that presses into the machined bore in the cover.

The detachable flywheel or clutch cover encloses and protects the flywheel and the clutch assembly. This cast-iron or aluminum component also supports a portion of the clutch linkage and provides the mating-surface area to which the transmission attaches.

The ignition distributor usually attaches to the block via a c shaped clamp and a cap screw and serves two basic functions. First.it closes and opens the electrioai circuit between the battery and the ignition coil. When the points close and completes this circuit battery current flows into the coil and permits the coil to build up a strong magnetic field. As the points open. The circuit opens and the magnetic field in the coil collapses, which causes the coil to produce a high-voltage source of current. The second task of the distributor is then to direct each high voltage surge to the correct spark plug at the correct instant in the engine cycle by the distributor rotor cap, and secondary wiring.

The oil pump usually mounts to the upper crankcase area of the block. The camshaft usually drives both the oil pump and distributor by a spiral gear. As mentioned the task of the oil pump is to draw lubricating oil from the pan and force it to all the moving parts of the engine.

The camshaft also activates the timing cover or block mounted mechanical-tye fuel pump. This pump is actually part of the fuel system. Its function is to transfer fuel from the fuel tank to the carburetor.