ENGINE CLASSIFICATION

Introduction. The major similarities among engines are a requirement for fuel and a method for igniting the fuel/air mixture. The major differences among engines are the number and arrangement of the cylinders, the valve arrangement, the method of operation, the type of fuel used, and the cooling system.To properly maintain and repair an engine, you must first know how it is constructed and designed. At the completion of this study unit, you will have a thorough knowledge of the types of engine designs and the components that make up the engine's design. 

ENGINE BLOCK 

Engines are classified in three ways--by the arrangement of the cylinders in the engine block, the fuel used (diesel, gasoline, etc.) and by the method used to cool the engine (air or water). The three most common types of engine blocks by cylinder arrangement are the in-line, the "V," and the horizontally opposed. 

1. In-Line Engine Block

The cylinders are positioned vertically, directly above the crankshaft (fig. 2-1A) or with the cylinders cast at a 300 angle to the vertical plane (fig. 2-1B). As you can see, the engine in figure 2-1B presents a much lower silhouette. The cylinders in the in-line engine are numbered from front to rear and there are usually four, six, or eight of them. 

Partial cutaway front view of the in-line six-cylinder engine. 

2. V-Type Engine Block

The V-type engine consists of two or more cylinders which, when viewed from the front, form the letter "V" (fig. 2-2). The V-type engine block has the cylinders located on each side of the engine at approximately a 450 angle to a vertical plane. 

Partial cutaway front view of the V-type engine. 

The cylinder banks (each line of cylinders) are cast at approximately a 900 angle in relation to one another. The casting of the cylinder block in the V-type engine reduces the engine's vibrations because the engine is shorter and more rigid than the in-line engine. Another engine that you may have heard of is the "Y" block. The Y-block is merely a V-type engine with a deeper crankcase.

The cylinder casting angle of the V-type engine. 

3. Horizontally Opposed Engine Block

Horizontally opposed engines consist of two or more cylinders lying on a horizontal plane in two banks with a crankshaft between them. The cylinders and the crankcase are cast as separate components of the engine and the cylinders may be removed from the crankcase individually. 

Partial cutaway view of the horizontally opposed engine. 

4. Water-Cooled Engines

Water-cooled engines are cooled by the circulation of engine coolant (water and antifreeze) through the engine block. The engine block is cast as one solid piece. In some engines, the cylinders are cut into the cylinder block and are surrounded by the water jacket while others have been designed to use insert-type cylinders. The engine coolant circulates through the water jacket removing the heat from the cylinder walls. The heated water then moves out to the radiator where it is cooled by fan-assisted air flow. Once cooled, the engine coolant returns to the engine block. 

Engine with cylinder liners. 

Those water-cooled engines designed to use insert-type cylinders will have a longer life span because the cylinder liners are replaceable. There are two types of cylinder liners, wet and dry. The dry liner receives full length support from the block while the wet liner receives support only at the top and bottom portions of the liner. Due to the lack of support normally provided by the engine block, the wet liner is much thicker then the dry type. 

Types of cylinder block liners. 

5. Air-Cooled Engines

There are various types of air-cooled engines. Some air-cooled engines are similar to water-cooled engines with cylinders in the block. The difference between the two is that the air-cooled engine's cylinder head contains external cooling fins, while other air-cooled engines have no cylinder block, only the crankcase and the cylinders themselves. Each cylinder is cast separately as a cylinder barrel and has cooling fins cast around the outside. The cylinders in this type of engine are replaceable. If one cylinder becomes scored, only the scored cylinder needs to be removed and replaced with a new cylinder. The cylinder head is of the I-head design. The crankcase is cast as a two-piece unit and bolted together. 

AIR COOLED ENGINE