Editing Piston (section)

====Trunk pistons====
Trunk pistons are long relative to their diameter. They act both as a piston and cylindrical [[crosshead]]. As the connecting rod is angled for much of its rotation, there is also a side force that reacts along the side of the piston against the cylinder wall. A longer piston helps to support this.

Trunk pistons have been a common design of piston since the early days of the reciprocating internal combustion engine. They were used for both petrol and diesel engines, although high speed engines have now adopted the lighter weight [[#Slipper pistons|slipper piston]].

A characteristic of most trunk pistons, particularly for diesel engines, is that they have a groove for an oil ring below the [[gudgeon pin]], in addition to the rings between the gudgeon pin and crown.

The name 'trunk piston' derives from the '[[trunk engine]]', an early design of [[marine steam engine]]. To make these more compact, they avoided the steam engine's usual [[piston rod]] with separate crosshead and were instead the first engine design to place the gudgeon pin directly within the piston. Otherwise these trunk engine pistons bore little resemblance to the trunk piston; they were extremely large diameter and double-acting. Their 'trunk' was a narrow cylinder mounted in the centre of the piston.

{{Commons category-inline|Trunk pistons}}