STATIONARY PARTS OF AN ENGINE
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.
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.
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:
is more expensive than cast iron.
is not as strong as cast iron.
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
has a much higher expansion rate than iron when heated. This creates problems with
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.
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
of steel can be used that wears longer than the surfaces of the cylinder block. This
increases engine life while keeping production costs down.
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.
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:
in a sleeve that is tight enough to be held by friction.
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
the sleeve into the cylinder wall. This is a popular means of securing a sleeve in an
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.
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.
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.
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.
(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.
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.
(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.
3-1.Cylinder block and components.
3-2.Requirements of a cylinder.
Figure 3-3.Air-cooled cylinder.
3-5.Cylinder sleeve casualties.
3-6.Core hole plugs installed in cylinder block.