Crankcase
Encyclopedia
In an internal combustion engine
of the reciprocating type
, the crankcase is the housing for the crankshaft
. The enclosure forms the largest cavity in the engine and is located below the cylinder(s)
, which in a multicylinder engine are usually integrated into one or several cylinder block
s. Crankcases have often been discrete parts, but more often they are integral with the cylinder bank(s), forming an engine block
. Nevertheless, the area around the crankshaft is still usually called the crankcase. Crankcases and other basic engine structural components (e.g., cylinders, cylinder blocks, cylinder head
s, and integrated combinations thereof) are typically made of cast iron
or cast aluminium
via sand casting
. Today the foundry
processes are usually highly automated
, with a few skilled workers to manage the casting of thousands of parts.
A crankcase often has an opening in the bottom to which an oil pan
is attached with a gasket
ed bolted joint. Some crankcase designs fully surround the crank's main bearing
journals, whereas many others form only one half, with a bearing cap forming the other. Some crankcase areas require no structural strength from the oil pan itself (in which case the oil pan is typically stamped
from sheet steel
), whereas other crankcase designs do (in which case the oil pan is a casting in its own right). Both the crankcase and any rigid cast oil pan often have reinforcing ribs cast into them, as well as bosses
which are drill
ed and tapped to receive mounting screws/bolts for various other engine parts.
Besides protecting the crankshaft and connecting rod
s from foreign objects, the crankcase serves other functions, depending on engine type. These include keeping the motor oil
contained, usually hermetically
or nearly hermetically (and in the hermetic variety, allowing the oil to be pressurized); providing the rigid structure with which to join the engine to the transmission
; and in some cases, even constituting part of the frame of the vehicle (such as in many farm tractor
s).
In two-stroke
gasoline
engines, the crankcase is sealed and is used as a pressurization chamber for the fuel/air mixture. As the piston rises, it pushes out exhaust gases and produces a partial vacuum
in the crankcase which aspirates fuel and air. As the piston travels downward, the fuel/air charge is pushed from the crankcase and into the cylinder.
Unlike four-stroke gasoline engines, the crankcase does not contain engine oil because it handles the fuel/air mixture. Instead, oil
is mixed in with the fuel, and the mixture provides lubrication for the cylinder walls, crankshaft and connecting rod
bearings
.
A majority of ship
s today use two stroke diesel engine
s, where the crankcase is completely separated from the cylinders. Unlike smaller engines, they usually have a separate tank below the crankcase as an oil holding tank (sump tank).
engine, the crankcase is filled mainly with air and oil, and is largely sealed off from the fuel/air mixture by the pistons.
, and is pumped through the oil filter to remove grit. The oil is then squirted into the crankshaft and connecting rod bearings and onto the cylinder walls, and eventually drips off into the bottom of the crankcase. In a wet sump
system, oil remains in a reservoir at the bottom of the crankcase, referred to as the oil pan. In a dry sump
system, oil is instead pumped to an external reservoir.
Even in a wet sump system, the crankshaft has minimal contact with the sump oil. Otherwise, the high-speed rotation of the crankshaft would cause the oil to froth, making it difficult for the oil pump to move the oil, which can starve the engine of lubrication. Small amounts of oil may splash onto the crankshaft during rough driving, referred to as windage
.
In a wet sump system, the main dipstick
and oil filler cap connect to the crankcase.
s and enter the crankcase, referred to as "blow-by". If these gases had no controlled escape mechanism, the gasketed joints would leak (as they "found their own way out"); also, if the gases remained in the crankcase and condensed, the oil would become diluted and chemically degraded over time, decreasing its ability to lubricate. Condensed water would also cause parts of the engine to rust. To counter this, a crankcase ventilation system exists. In all modern vehicles, this consists of a channel to expel the gases out of the crankcase, through an oil-separating baffle, to the PCV valve
, into the intake manifold. In a non-turbo engine, the intake manifold is at a lower pressure
than the crankcase, providing the suction to keep the ventilation system going. A turbo
engine usually has a check valve
somewhere in the tubing to avoid pressurizing the crankcase when the turbo produces boost.
If an engine is damaged or enters old age, gaps can form between the cylinder walls and pistons, resulting in larger amounts of blow-by than the crankcase ventilation system can handle. The gaps cause power loss, and ultimately mean that the engine needs to be rebuilt or replaced. Symptoms of excessive blow-by include oil being pushed up into the air filter, out the dipstick, or out the PCV valve. In rare cases of serious piston or ring damage, the oil filter housing's sheet metal can even burst at its seam.
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
of the reciprocating type
Reciprocating engine
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...
, the crankcase is the housing for the crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
. The enclosure forms the largest cavity in the engine and is located below the cylinder(s)
Cylinder (engine)
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...
, which in a multicylinder engine are usually integrated into one or several cylinder block
Cylinder block
A cylinder block is an integrated structure comprising the cylinder of a reciprocating engine and often some or all of their associated surrounding structures...
s. Crankcases have often been discrete parts, but more often they are integral with the cylinder bank(s), forming an engine block
Monobloc engine
A monobloc or en bloc engine is an internal-combustion piston engine where some of the major components: cylinder head, cylinder block, or crankcase are formed, usually by casting, as a single integral unit, rather than being assembled later...
. Nevertheless, the area around the crankshaft is still usually called the crankcase. Crankcases and other basic engine structural components (e.g., cylinders, cylinder blocks, cylinder head
Cylinder head
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...
s, and integrated combinations thereof) are typically made of cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...
or cast aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
via sand casting
Sand casting
Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material.It is relatively cheap and sufficiently refractory even for steel foundry use. A suitable bonding agent is mixed or occurs with the sand...
. Today the foundry
Foundry
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron...
processes are usually highly automated
Automation
Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization...
, with a few skilled workers to manage the casting of thousands of parts.
A crankcase often has an opening in the bottom to which an oil pan
Sump
A sump is a low space that collects any often-undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers....
is attached with a gasket
Gasket
thumb|sright|250px|Some seals and gaskets1. [[o-ring]]2. fiber [[Washer |washer]]3. paper gaskets4. [[cylinder head]] [[head gasket|gasket]]...
ed bolted joint. Some crankcase designs fully surround the crank's main bearing
Main bearing
In a piston engine, the main bearings are the bearings on which the crankshaft rotates, usually plain or journal bearings.All engines have a minimum of two main bearings, one at each end of the crankshaft, and they may have as many as one more than the number of crank pins...
journals, whereas many others form only one half, with a bearing cap forming the other. Some crankcase areas require no structural strength from the oil pan itself (in which case the oil pan is typically stamped
Die (manufacturing)
A die is a specialized tool used in manufacturing industries to cut or shape material using a press. Like molds, dies are generally customized to the item they are used to create...
from sheet steel
Sheet metal
Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material...
), whereas other crankcase designs do (in which case the oil pan is a casting in its own right). Both the crankcase and any rigid cast oil pan often have reinforcing ribs cast into them, as well as bosses
Boss (engineering)
In engineering, a boss is a protruding feature on a workpiece.A common use for a boss is to locate one object within a pocket or hole of another object...
which are drill
Drill
A drill or drill motor is a tool fitted with a cutting tool attachment or driving tool attachment, usually a drill bit or driver bit, used for drilling holes in various materials or fastening various materials together with the use of fasteners. The attachment is gripped by a chuck at one end of...
ed and tapped to receive mounting screws/bolts for various other engine parts.
Besides protecting the crankshaft and connecting rod
Connecting rod
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....
s from foreign objects, the crankcase serves other functions, depending on engine type. These include keeping the motor oil
Motor oil
Motor oil or engine oil is an oil used for lubrication of various internal combustion engines. The main function is to lubricate moving parts; it also cleans, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts.Motor oils are derived from...
contained, usually hermetically
Hermetic seal
A hermetic seal is the quality of being airtight. In common usage, the term often implies being impervious to air or gas. When used technically, it is stated in conjunction with a specific test method and conditions of usage.-Etymology :...
or nearly hermetically (and in the hermetic variety, allowing the oil to be pressurized); providing the rigid structure with which to join the engine to the transmission
Transmission (mechanics)
A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...
; and in some cases, even constituting part of the frame of the vehicle (such as in many farm tractor
Tractor
A tractor is a vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or construction...
s).
Two-stroke engines
Two-stroke cycle
A two-stroke engine is an internal combustion engine that completes the process cycle in one revolution of the crankshaft...
gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
engines, the crankcase is sealed and is used as a pressurization chamber for the fuel/air mixture. As the piston rises, it pushes out exhaust gases and produces a partial vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
in the crankcase which aspirates fuel and air. As the piston travels downward, the fuel/air charge is pushed from the crankcase and into the cylinder.
Unlike four-stroke gasoline engines, the crankcase does not contain engine oil because it handles the fuel/air mixture. Instead, oil
Oil
An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....
is mixed in with the fuel, and the mixture provides lubrication for the cylinder walls, crankshaft and connecting rod
Connecting rod
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....
bearings
Plain bearing
A plain bearing, also known as a plane bearing or a friction bearing is the simplest type of bearing, comprising just a bearing surface and no rolling elements. Therefore the journal slides over the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole...
.
A majority of ship
Ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...
s today use two stroke diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
s, where the crankcase is completely separated from the cylinders. Unlike smaller engines, they usually have a separate tank below the crankcase as an oil holding tank (sump tank).
Four-stroke engines
In a four-strokeFour-stroke cycle
A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine's crankshaft, and one single thermodynamic cycle.There are two...
engine, the crankcase is filled mainly with air and oil, and is largely sealed off from the fuel/air mixture by the pistons.
Oil circulation
Oil circulation is kept separate from the fuel/air mixture, thereby preserving oil rather than burning it as happens in two-stroke engines. Oil moves from its reservoir, is pressurized by an oil pumpOil pump (internal combustion engine)
The oil pump in an internal combustion engine circulates engine oil under pressure to the rotating bearings, the sliding pistons and the camshaft of the engine...
, and is pumped through the oil filter to remove grit. The oil is then squirted into the crankshaft and connecting rod bearings and onto the cylinder walls, and eventually drips off into the bottom of the crankcase. In a wet sump
Wet sump
A wet sump is a lubricating oil management design for four-stroke piston internal combustion engines which uses a built-in reservoir for oil, as opposed to an external or secondary reservoir used in a dry sump design....
system, oil remains in a reservoir at the bottom of the crankcase, referred to as the oil pan. In a dry sump
Dry sump
A dry sump is a lubricating motor oil management method for four-stroke and large two-stroke piston internal combustion engines that uses external pumps and a secondary external reservoir for oil, as compared to a conventional wet sump system....
system, oil is instead pumped to an external reservoir.
Even in a wet sump system, the crankshaft has minimal contact with the sump oil. Otherwise, the high-speed rotation of the crankshaft would cause the oil to froth, making it difficult for the oil pump to move the oil, which can starve the engine of lubrication. Small amounts of oil may splash onto the crankshaft during rough driving, referred to as windage
Windage
Windage is a force created on an object by friction when there is relative movement between air and the object.There are two causes of windage:# the object is moving and being slowed by resistance from the air...
.
In a wet sump system, the main dipstick
Dipstick
A dipstick is one of several measurement devices.Some dipsticks are dipped into a liquid to perform a chemical test or to provide a measure of quantity of the liquid....
and oil filler cap connect to the crankcase.
Air ventilation
During normal operation, a small amount of unburned fuel and exhaust gases escape around the piston ringPiston ring
A piston ring is a split ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine.The three main functions of piston rings in reciprocating engines are:...
s and enter the crankcase, referred to as "blow-by". If these gases had no controlled escape mechanism, the gasketed joints would leak (as they "found their own way out"); also, if the gases remained in the crankcase and condensed, the oil would become diluted and chemically degraded over time, decreasing its ability to lubricate. Condensed water would also cause parts of the engine to rust. To counter this, a crankcase ventilation system exists. In all modern vehicles, this consists of a channel to expel the gases out of the crankcase, through an oil-separating baffle, to the PCV valve
PCV valve
A crankcase ventilation system is a way for gases to escape in a controlled manner from the crankcase of an internal combustion engine. A common type of such system is a positive crankcase ventilation system, the heart of which is a PCV valve—a variable-restriction valve that can react to changing...
, into the intake manifold. In a non-turbo engine, the intake manifold is at a lower pressure
Manifold vacuum
Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere....
than the crankcase, providing the suction to keep the ventilation system going. A turbo
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
engine usually has a check valve
Check valve
A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....
somewhere in the tubing to avoid pressurizing the crankcase when the turbo produces boost.
If an engine is damaged or enters old age, gaps can form between the cylinder walls and pistons, resulting in larger amounts of blow-by than the crankcase ventilation system can handle. The gaps cause power loss, and ultimately mean that the engine needs to be rebuilt or replaced. Symptoms of excessive blow-by include oil being pushed up into the air filter, out the dipstick, or out the PCV valve. In rare cases of serious piston or ring damage, the oil filter housing's sheet metal can even burst at its seam.