A modern straight six engine block for a passenger car,
integrating the crankcase and all cylinders. The cylinder head bolts to the
deck surface at top. Many ribs and bosses can be seen on the side of the
casting, as well as the passages for cooling fluid opening into the deck.
A V6 diesel engine, with both of the cylinder bank as well
as the crankcase formed en bloc. The large holes are the cylinder, while the
small ones are the mounting holes (round) and coolant or oil ducts (oval).
De Dion-Bouton engine with discrete crankcase
but with monobloc integration of the cylinder and heads, circa 1950.A discrete
crankcase with upper and lower halves (each its own casting) Can clearly be
seen, with the bottom half constituting both part of the main bearing support
and also an oil sump.
The cylinder block is an integrated structure comprising the cylinder(s) of a reciprocating engine and often some or all of their
associated surrounding structures (coolant passages, intake and exhaust passages and ports,
and crankcase). The term engine block is often used
synonymously with "cylinder block" (although technically
distinctions can be made between en bloc cylinders as a discrete unit versus engine block
designs with yet more integration that comprise the crankcase as well).
In the basic terms of machine elements, the various main parts of an engine (such as
cylinder(s), cylinder head(s), coolant passages, intake and
exhaust passages, and crankcase) are conceptually distinct, and these items can
all be made as discrete pieces that are bolted together. Such construction was very widespread in the early decades
of the commercialization of internal combustion
engines (1880s
to 1920s), and it is still sometimes used in certain applications where it
remains advantageous (especially very large engines, but also some small
engines). However, it is no longer the normal way of building most petrol engines and diesel engines, because for any given engine configuration, there are more efficient ways
of designing for
manufacture (and
also for maintenance
and repair). These
generally involve integrating multiple machine elements into one discrete part,
and doing the making (such as casting, stamping, and machining) for multiple elements in one setup with one machine coordinate system (of a machine tool or other piece of manufacturing
machinery). This
yields lower unit cost of production (and/or
maintenance and repair).
Today most
engines for cars, trucks, buses, tractors, and so on are built with fairly highly integrated design,
so the words "monobloc" and "en bloc" are
seldom used in describing them; such construction is often implicit. Thus "engine block", "cylinder block",
or simply "block" are the terms likely to be heard in the garage or
on the street.
DEVELOPMENT CONTEXT
The move from
extensive use of discrete elements (via separate castings) to extensive integration
of elements (such as in most modern engine blocks) was a gradual progression
that passed through various phases of monobloc engine development, wherein certain elements were integrated
while others remained discrete. This evolution has occurred throughout the
history of reciprocating engines, with various instances of every conceptual
variation coexisting here and there. The increase in prevalence of
ever-more-integrated designs relied on the gradual development of foundry and machining practice for mass production. For example, a practical low-cost V8 engine was not feasible until Ford developed the techniques used
to build the Ford flathead V8
engine, which
soon also disseminated to the larger society. Today the foundry and machining
processes for manufacturing engines are usually highly automated, with a few skilled workers to manage the making of
thousands of parts.
CYLINDERS INTEGRATED INTO ONE OR
SEVERAL CYLINDER BLOCK
Cylinder are cast in three pairs
Cylinder
are cast in the two block of three
DB
605 inverted aircraft engine of WW2,
with monobloc cylinder blocks and heads.
A cylinder block is a unit
comprising several cylinders (including their cylinder walls, coolant passages,
cylinder sleeves if any, and so forth). In the earliest decades of internal
combustion engine development, monobloc cylinder construction was rare;
cylinders were usually cast individually. Combining their castings into pairs
or triples was an early win of monobloc design.
Each cylinder bank of a V engine (that is, each side of the V) typically comprised one
or several cylinder blocks until the 1930s, when mass production methods were
developed that allowed the modern form factor of having both banks plus the crankcase entirely integrated.
A wet liner cylinder block features
cylinder walls that are entirely removable, which fit into the block by means
of special gaskets. They are referred to as "wet liners" because
their outer sides come in direct contact with the engine's coolant. In other
words, the liner is the entire wall, rather than being merely a sleeve. Wet
liner designs are popular with European manufacturers, most notably Renault and Peugeot, who continue to use them to the present. Dry liner designs use either the
block's material or a discrete liner inserted into the block to form the
backbone of the cylinder wall. Additional
sleeves are inserted within, which remain "dry" on their outside,
surrounded by the block's material. With either wet or dry liner designs, the
liners (or sleeves) can be replaced, potentially allowing overhaul or rebuild
without replacement of the block itself; but in reality, they are difficult to
remove and install, and for many applications (such as most late-model cars and
trucks), an engine will never undergo such a procedure in its working lifespan.
It is likelier to be scrapped, with new equipment engine or entire vehicle replacing
it. This is sometimes rightfully disparaged as a symptom of a throw-away society, but on the other hand, it is
actually sometimes more cost-efficient and even environmentally protective to
recycle machinery and build new instances with efficient manufacturing
processes (and superior machine performance and emission control) than it is to
overvalue old machinery and craft production.
CYLINDER BLOCKS AND CRANKCASE
INTEGRATED
A flathead engine with integral cylinder bank
and crankcase. The head is tipped upward to reveal the deck. The example is
typical of engine of the 1930 through 1950s.
Casting technology at the dawn of the internal combustion
engine could reliably cast either large castings, or castings with complex
internal cores to allow for water jackets, but not both simultaneously. Most
early engines, particularly those with more than four cylinders, had their
cylinders cast as pairs or triplets of cylinders, then bolted to a single
crankcase.
As casting
techniques improved, an entire cylinder block of 4, 6, or 8 cylinders could be
cast as one. This was a simpler construction, thus less expensive (unit-wise) to make. For straight engines, this meant that one engine block could now comprise all the cylinders plus the
crankcase. Monobloc straight fours, uncommon when the Ford Model T was introduced with one in 1908, became common during
the next decade, and monobloc straight sixes followed soon after. By the
mid-1920s, both were common, and the straight sixes of General Motors (along
with other features that differentiated GM's various makes and models from the
Model T) were prying market share
away from Ford.
(These were all flathead designs.) During that decade, V engines retained a separate block casting for each cylinder
bank, with both bolted onto a common crankcase (itself a separate casting). For
economy, some engines were designed to use identical castings for each bank,
left and right. The complex ducting required for intake and exhaust was too
complicated to allow the integration of the banks, except on a few rare
engines, such as the Lancia 22½° narrow-angle V12 of 1919, that did manage to use
a single block casting for both banks. The hurdles of integrating the
banks of the V for common, affordable cars were first overcome by the Ford Motor Company with its Ford flathead V-8, introduced in 1932, which was the first V-8 with a single
engine block casting, putting an affordable V-8 into an affordable car for the
first time.
The communal
water jacket of monobloc designs permitted closer spacing between cylinders.
The monobloc design also improved the mechanical stiffness of the engine
against bending and the increasingly important torsional twist, as cylinder
numbers, engine lengths, and power ratings increased.
Most engines
made today, except some unusual V or radial engines, are a monobloc of
crankcase and all cylinders. In such cases, the skirts of the cylinder banks
form a crankcase area of sorts, which is still often called a crankcase despite
no longer being a discrete part.
Engine blocks
are normally cast from either a suitable grade of iron or an aluminium alloy. The aluminium block is much
lighter in weight, and has better heat transfer to the coolant, but iron blocks
retain some advantages and continue to be used by some manufacturers. Because
of the use of cylinder liners and bearing
shells, the
relative softness of aluminium is of no consequence. Some engines have resorted
to Plasma
transferred wire arc thermal spraying to replace cylinder sleeves and reduce weight. They
can also be produced in compacted graphite
iron(CGI) such as some diesel engines
from Navistar
International.
COMBINED BLOCK, HEAD, AND CRANKCASE
Light-duty consumer-grade Honda GC-family small engines use a monobloc design where the cylinder head, block,
and half the crankcase share the same casting, termed 'uniblock' by
Honda. One reason for this, apart from cost, is to produce an overall
lower engine height. Being an air-cooled OHC design, this is possible
thanks to current aluminum casting techniques and lack of complex hollow spaces
for liquid cooling. The valves are vertical, so as to permit assembly in this
confined space. On the other hand, performing basic repairs becomes so
time-consuming that the engine can be considered disposable.
Commercial-duty Honda GX-family engines (and their many
popular knock-offs) have a more conventional design of
a single crankcase and cylinder casting, with a separate cylinder head.
Honda
produces many other head-block-crankcase monoblocs under a variety of different
names, such as the GXV-series. They may all be externally identified by a
gasket which would bisect the crankshaft on an approximately 45° angle.
Exhaust valve
failure is common and, owing to the monobloc design, so labour-intensive to repair
that the engine is normally discarded.
WORKING