CYLINDER BLOCK
5-2. The part of the engine frame which supports the engine’s cylinder liners and head or heads is generally
referred to as the cylinder block. The blocks for most large engines are of welded steel construction. In this
type construction, the block is of welded steel with plates located at the places where loads occur. Deck plates
are generally fashioned to house and hold the cylinder liners. The uprights and other members are welded with
the deck plates into one rigid unit. Blocks of small, high-speed
engines may be of the en-bloc construction, in
which the block is one piece of cast iron. A cylinder block may contain passages to allow circulation of cooling
water around the liners. If the liner is constructed with integral cooling passages, the cylinder block generally
does not have cooling passages. Most 2-stroke cycle engines have air passages in the block. In other words, a
passage which is an integral part of an engine block may serve as a part of the engine’s cooling system,
lubricating system, or air system. One cylinder block is generally thought of in connection with all cylinders of
an engine. However, some engines have one cylinder block for each cylinder or for each pair of cylinders.
Engines that have V-type cylinder arrangements may have a separate block for each bank of cylinders. The
Chapter 5
5-2 TC 55-509 4 June 2009
cylinder block shown in Figure 5-1 is somewhat larger than the one just described. It is constructed of welded
steel forgings and steel plate. This type of block is secured to a separate engine base. When the two parts are
bolted together, they form the frame for the main bearings which carry the crankshaft. Note that the camshaft
bearing supports, consisting of forged transverse members, are an integral part of the block. Pads are welded to
the block and are machined to carry engine parts and accessories. The block shown has no water passages
because each cylinder liner and cylinder head has its own water jacket. The block discussed so far is from an
engine with in-line cylinder arrangement. The block illustrated in Figure 5-2 represents blocks constructed for
some engines with the V-type cylinder arrangement. Blocks of this type are usually constructed of forgings and
steel plates welded together. In the V-type construction, the upper and lower deck plates of each side of the V
are bored to the cylinder liners. The space between the decks and the space between the two banks form the
scavenging air chamber or air box. In some V-type blocks, the liner bore in the lower deck plate is made with a
groove that serves as a cooling water inlet for the liner. Some V-type blocks are constructed with the mounting
pads for the main bearing seats as integral parts of the forged transverse members at the bottom of the block. In
some blocks, the lower bearing seats for the camshaft are located in a pocket which is an integral part of the
block. Note the camshaft pocket in Figure 5-2.