Crankpin

Crankpin
  Crankpins highlighted in blue
A crank pin of a ship steam engine with the lubricating system visible

In a reciprocating engine, the crankpins, also known as crank journals are the journals of the big end bearings, at the ends of the connecting rods opposite to the pistons.

If the engine has a crankshaft, then the crank pins are the journals of the off-centre bearings of the crankshaft. In a beam engine the single crank pin is mounted on the flywheel; In a steam locomotive the crank pins are often mounted directly on the driving wheels.

Big end bearings are commonly bushings or plane bearings, but less commonly may be roller bearings, see crankshaft.

In a multi-cylinder engine, a crankpin can serve one or many cylinders, for example:

  • In a straight (parallel) or flat (boxer) engine each crankpin normally serves just one cylinder.
  • In a V engine each crankpin usually serves two cylinders, one in each cylinder bank.
  • In a radial engine each crankpin serves an entire row of cylinders.

Big end design

There are three common configurations of big end bearing:

  • If a crankpin serves only one cylinder, then the big end is a relatively simple design, accommodating only one connecting rod. This design is the cheapest to produce, and is used in:
  • If a crankpin serves more than one cylinder, then the corresponding cylinders may have an offset, to simplify the design of the big end bearing. This design is used in:
  • If more than one cylinder is served by a single crankpin but there is no offset, then some or all of the connecting rods must be forked at the big end. This design provides better engine balance than designs with an offset, but requires extra complexity and cost in both design and manufacture, and more weight or closer manufacturing tolerances to achieve the same strength and reliability. Any extra weight added to the big end itself also carries a penalty of adding vibration and reducing balance. As the number of cylinders grows, the effect of the offset on balance becomes less important, and forked connecting rods become less common. They are mainly used in:
    • Single-row radial engines.
    • Some V-twin engines, notably including motorcycle engines.

See also


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Look at other dictionaries:

  • crankpin — [kraŋk′pin΄] n. the offset part, often a cylindrical bar or pin, of a crank or crankshaft to which a connecting rod is attached: also crank pin …   English World dictionary

  • crankpin — noun Date: 1839 the cylindrical piece which forms the handle of a crank or to which a connecting rod is attached …   New Collegiate Dictionary

  • crankpin — /krangk pin /, n. Mach. a short cylindrical pin at the outer end of a crank, held by and moving with a connecting rod or link. Also, crank pin. Cf. web (def. 11). [1830 40; CRANK1 + PIN] * * * …   Universalium

  • crankpin — noun The pin that attaches a connecting rod to a crank …   Wiktionary

  • crankpin — That portion of the crankshaft to which the connecting rod is attached. See crankshaft …   Aviation dictionary

  • crankpin — noun a pin by which a connecting rod is attached to a crank …   English new terms dictionary

  • crankpin — crank′pin or crank′ pin n. mac a short cylindrical pin at the outer end of a crank, held by and moving with a connecting rod or link Compare web 11) Etymology: 1830–40 …   From formal English to slang

  • crankpin — /ˈkræŋkpɪn/ (say krangkpin) noun a pin or cylinder at the outer end or part of a crank, as for holding a connecting rod …  

  • crankpin — The bearing surface on a crank of the crankshaft to which the connecting rod is attached. Also called the journal or crank throw. Also see splayed crankpins …   Dictionary of automotive terms

  • crankpin — n. a pin by which a connecting rod is attached to a crank …   Useful english dictionary

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