In an internal combustion engine, the '''crankcase''' is the housing for the [[crankshaft]].  It
also refers to the largest cavity in the engine that it encloses, which is separated from the
[[cylinder (engine)|cylinder]] by the reciprocating [[piston]].

Besides providing room for the crankshaft and [[connecting rod]] to freely rotate, the crankcase
serves other functions, depending on engine type.

[[Image:Two-Stroke Engine.gif|right]]
In a two-stroke engine, [[




M-W: houses the crankshaft

The crankcase contains oil which helps lubricate the pistons and piston bearings.  The oil doesn't
actually touch the crankshaft, because if the quickly moving parts contact the oil, oil froth is
formed, which is difficult for the oil pump to move.  If too much oil foam is formed, the engine
can be starved of oil. [http://www.cartalk.com/content/columns/Archive/1996/October/08.html]

The oil dipstick measures the amount of oil sitting in the crankcase.  

In a [[wet sump]] system, the oil is stored in the crankcase.  In a [[dry sump]] system, a
scavenging pump moves the oil from the crankcase to an external oil reservoir.

In carbeurated engines, there are some situations where too much gas will be added to the cylinders,
and this extra gas can leak around the piston rings into the crankcase, and dilute the engine oil.
[http://www.cartalk.com/content/columns/Archive/2004/April/01.html]

== Ventilation system ==
In a normally functioning engine, a small amount of exhaust gases
[http://cartalk.com/content/columns/Archive/2002/August/07.html] and water
[http://www.cartalk.com/content/columns/Archive/1994/May/09.html] invariably leak around the piston
rings and enter the crankcase.  The crankcase is designed to remove these by continually refreshing
the air inside the crankcase.  Postive air pressure comes in from the air filter, and is exhausted
through the [[PCV valve]].

If the piston rings begin leaking an abnormal amount of gas, a situation called [[blow-by]] occurs.
This can cause contamination and dillution of the engine oil, and ultimately requires an engine
rebuild to fix. [http://www.cartalk.com/content/columns/Archive/2004/October/02.html]



Related:
* [[PCV valve]]
* [[Blow-by]]
* [[Piston rings]]
* [[Dipstick]]

Use these images:
* [[Image:Two-Stroke Engine.gif]]
* [[Image:4-Stroke-Engine.gif]]


References
* http://wright.nasa.gov/airplane/crankcase.html

    The crankcase is the "body" that holds all of the other engine parts together. It's the largest
    part of the engine

    Also: use the bottom IMAGE from this.

* http://www.cartalk.com/content/columns/Archive/1999/September/08.html
    
    Crankcase ventilation system, milky fluid, ...  If it gets really bad, replacement of the 

    "'Blowby' is combustion gases that have 'blown' past the rings and into the crankcase, where
    they don't belong."


* http://www.cartalk.com/content/columns/Archive/2004/May/08.html
    
    There's an air hose that comes from the [[air filter]].  When blow-by gets really bad, it can
    start 

* http://en.wikipedia.org/wiki/Motor_oil
  http://www.tpub.com/content/construction/14264/css/14264_242.htm

    In the crankcase of a vehicle engine, motor oil lubricates rotating or sliding surfaces between
    the crankshaft journals, bearings, and rods connecting the pistons to the crankshaft. The oil
    collects in an oil pan at the bottom of the crankcase. In some small engines such as lawn mower
    engines , dippers on the bottoms of connecting rods dip into the oil at the bottom and splash it
    around the crankcase as needed to lubricate parts inside. In modern vehicle engines, the oil
    pump takes oil from the oil pan and sends it through the oil filter into oil galleries from
    which the oil lubricates the main bearings holding the crankshaft up at the main journals and
    camshaft bearings operating the valves. In typical modern vehicles, oil pressure-fed from the
    oil galleries to the main bearings enters holes in the main journals of the crankshaft. From
    these holes in the main journals, the oil moves through passageways inside the crankshaft to
    exit holes in the rod journals to lubricate the rod bearings and connecting rods. Some simpler
    designs relied on these rapidly moving parts to splash and lubricate the contacting surfaces
    between the piston rings and interior surfaces of the cylinders. However, in modern designs,
    there are also passageways through the rods which carry oil from the rod bearings to the
    rod-piston connections and lubricate the contacting surfaces between the piston rings and
    interior surfaces of the cylinders. This oil film also serves as a seal between the piston rings
    and cylinder walls to separate the combustion chamber in the cylinder head from the crankcase.
    The oil then drips back down into the oil pan. To see these details on a crankshaft, see "How
    Car Engines Work" at HowStuffWorks or "Types of Lubricating Systems" at Integrated Publishing.

* http://auto.howstuffworks.com/engine1.htm

    Piston rings keep oil in the sump from leaking into the combustion area, where it would be
    burned and lost.

    The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom
    of the sump (the oil pan).

* http://auto.howstuffworks.com/engine2.htm

    In most cars, oil is sucked out of the oil pan by the oil pump, run through the oil filter to
    remove any grit, and then squirted under high pressure onto bearings and the cylinder walls.
    The oil then trickles down into the sump, where it is collected again and the cycle repeats.

http://auto.howstuffworks.com/engine3.htm

    In a two-stroke engine, the oil is mixed with the gas, becuase the holes in the cylinder wall
    prevent the use of rings to seal the combustion chamber. 

http://auto.howstuffworks.com/question331.htm
    
    In a wet sump, turning, braking and acceleration can cause the oil to pool on one side of the
    engine. This sloshing can dip the crankshaft into the oil as it turns or uncover the pump's
    pick-up tube.

http://science.howstuffworks.com/two-stroke5.htm

    On the other side of the piston is the crankcase, where the piston is creating a vacuum to suck
    in air/fuel from the carburetor through the reed valve and then pressurizing the crankcase so
    that air/fuel is forced into the combustion chamber.

    In a two-stroke engine, the crankcase is serving as a pressurization chamber to force air/fuel
    into the cylinder, so it can't hold a thick oil.


Things that attach/stick out of the crankcase:

    - crankcase ventilation system
        - piston rings
        - air hose coming from air filter
        - PCV valve

    - oil circulation
        - oil pump

    - crankshaft

    - passageway to the dipstick
    - passageway to the oil fillup spout [http://www.cartalk.com/content/columns/Archive/2005/June/05.html]



Questions:

    - what does the crankcase do in a 2-cycle engine?  Is there a positive ventilation system?  Or
      is it just a simple cavity (since there's no piston rings?)?

    - what does the crankcase do in a diesel engine?


Post-creation:
    - redirect [[oil pan]] to [[crankcase]] {{R with possibilities}}
    - redirect [[blow-by]] to [[crankcase]]?
    - link crankcase from:


Things to be sure to note:
    - A wet-sump four-stroke requires the engine to be oriented properly to keep the oil in the
      bottom fo the sump.  Neither the dry-sump four-stroke or the two-stroke engine require a
      specific orientation