STATIONARY PARTS OF AN ENGINE

The stationary parts of an engine include the cylinder block and cylinders, the cylinder head or heads, and the exhaust and intake manifolds. These parts furnish the framework of the engine. All movable parts are attached to or fitted into this framework.

Engine Cylinder Block
 The cylinder block is the basic frame of a liquid-cooled engine whether it be in-line, horizontally opposed, or V-type. The cylinder block (fig. 3-1) is a solid casting made of cast iron or aluminum that contains the crankcase, the cylinders, the coolant passages, the lubricating passages, and, in the case of flathead engines, the valves seats. the ports, and the guides.

The cylinder block is a one-piece casting usually made of an iron alloy that contains nickel and molybdenum. This is the best overall material for cylinder blocks. It provides excellent wearing qualities, low material and production cost, and it only changes dimensions minimally when heated. Another material that is used for cylinder blocks, although not extensively, is aluminum. Aluminum is used whenever weight is a consideration. It is not practical to use for the following reasons:

• Aluminum is more expensive than cast iron.
• Aluminum is not as strong as cast iron.
• Because of its softness, it cannot be used on any surface of the block that is subject to wear. This necessitates the pressing, or casting, of steel sleeves into the cylinder bores. Threaded holes must be deeper. This introduces extra design considerations and increases production costs.
• Aluminum has a much higher expansion rate than iron when heated. This creates problems with maintaining tolerances.

The cylinders are bored right into the block. A good cylinder must be round, not varying in diameter by more than approximately 0.0005 inch (0.012 mm) (fig.3-2). The diameter of the cylinder must be uniform throughout its entire length. During normal engine operation, cylinder walls wear out-of-round, or they may become cracked and scored if not lubricated or cooled properly. The cylinders on an air-cooled engine (fig. 3-3) are separate from the crankcase. They are made of forged steel. This material is most suitable for cylinders because of its excellent wearing qualities and its ability to withstand high temperatures that air-cooled cylinders obtain. The cylinders have rows of deep fins cast into them to dissipate engine heat. The cylinders are commonly mounted by securing the cylinder head to the crankcase with long studs and sandwiching the cylinders between the two. Another way of mounting the cylinders is to bolt them to the crankcase, and then secure the heads to the cylinders.

In liquid-cooled engines cylinder sleeves or liners (fig. 3-4) are used to provide a wearing surface, other than the cylinder block, for the pistons to ride against. This is important for the following reasons:

• Alloys of steel can be used that wears longer than the surfaces of the cylinder block. This increases engine life while keeping production costs down.
• Because the cylinders wear more than any other area of the block, the life of the block can be greatly extended by using sleeves. When overhaul time comes, the block can be renewed by just replacing the sleeves.
• Using a sleeve allows an engine to be made of other materials, such as aluminum, by providing the wearing qualities necessary for cylinders that aluminum cannot.

There are two types of cylinder sleeves: the dry-type and the wet-type. A dry-type sleeve does not contact the coolant. The dry-type sleeve is pressed into a full cylinder that completely covers the water jacket. Because the sleeve has the block to support it, it can be very thin. The wet-type sleeve comes in direct contact with the coolant. It is also press-fitted into the cylinder. The difference is that the water jacket is open in the block and is completed by the sleeve. Because it gets no central support from the block, it is made thicker than a dry sleeve. Also because the sleeve completes the water jacket, it must fit so it seals in the coolant. This is accomplished by using a metallic sealing ring at the top and a rubber sealing ring at the bottom. There are three basic ways of securing the sleeves in the cylinder block as follows:

• Press in a sleeve that is tight enough to be held by friction.
• Provide a flange at the top of the block that locks the sleeve into place when the cylinder head is bolted into place. This is more desirable than a friction fit, because it locks the sleeve tightly.
• Cast the sleeve into the cylinder wall. This is a popular means of securing a sleeve in an aluminum block.

Whatever method is used to secure the sleeves, it is very important for the sleeve to fit tightly. This is so the sleeve can transfer heat effectively to the water jackets.

Most cylinder sleeve casualties are directly related to a lack of maintenance or improper operating procedures. Figure 3-5 shows two common types of cylinder sleeve casualties: cracks and scoring. Both types of casualties require replacement of the sleeve.

The cylinder block also provides the foundation for the cooling and lubricating systems. The cylinders of a liquid-cooled engine are surrounded by interconnecting passages cast in the block. Collectively, these passages form the water jacket that allows the circulation of coolant through the cylinder block and the cylinder head to carry off excessive heat created by combustion.

The water jacket is accessible through holes machined in the head and block to allow removal of the material used for casting of the cylinder block. These holes are called core holes and are sealed by core hole plugs (freeze plugs). These plugs are of two types: cup and disk. Figure 3-6 shows a typical installation of these plugs.

The crankcase (fig. 3-7) is that part of the cylinder block below the cylinders. It supports and encloses the crankshaft and provides a reservoir for lubricating oil. The lower part of the crankcase is the oil pan, which is bolted at the bottom. The oil pan is made of cast aluminum or pressed steel and holds the lubricating oil for the engine. Since the oil pan is the lowest part of the engine, it must be strong enough to withstand blows from flying stones and obstructions sticking up from the road surface.

The crankcase also has mounting brackets to support the entire engine on the vehicle frame. These brackets are either an integral part of the crankcase or are bolted to it in such a way that they support the engine at three or four points. These points are cushioned by rubber mounts that insulate the frame and body of the vehicle from engine vibration. This prevents damage to engine supports and the transmission.

The crankcase (fig. 3-8) is the basic foundation of all air-cooled engines. It is made as a one- or two-piece casting that supports the crankshaft, provides the mounting surface for the cylinders and the oil pump, and has the lubrication passages cast into it. It is made of aluminum since it needs the ability to dissipate large amounts' of heat. On air-cooled engines, the oil pan usually is made of cast aluminum, and it is covered with cooling fins. The oil pan on an air-cooled engine plays a key role in the removal of waste heat from the engine through its lubricating oil.

Figure 3-1.—Cylinder block and components.

Figure 3-2.—Requirements of a cylinder.

Figure 3-3.—Air-cooled cylinder.

Figure 3-4.—Cylinder sleeves.

Figure 3-5.—Cylinder sleeve casualties.

Figure 3-6.—Core hole plugs installed in cylinder block.

Figure 3-7.—Engine crankcase.

Figure 3-8.—Aircooled crankcase.