Editing Piston (section)

====Crosshead pistons====
Large slow-speed Diesel engines may require additional support for the side forces on the piston. These engines typically use [[crosshead]] pistons. The main piston has a large [[piston rod]] extending downwards from the piston to what is effectively a second smaller-diameter piston. The main piston is responsible for gas sealing and carries the piston rings. The smaller piston is purely a mechanical guide. It runs within a small cylinder as a trunk guide and also carries the gudgeon pin.

Lubrication of the crosshead has advantages over the trunk piston as its lubricating oil is not subject to the [[heat of combustion]]: the oil is not contaminated by combustion soot particles, it does not break down owing to the heat and a thinner, less viscous oil may be used. The friction of both piston and crosshead may be only half of that for a trunk piston.{{sfnp|Ricardo|1922|page=116}}

Because of the additional weight of these pistons, they are not used for high-speed engines.

{{Commons category-inline|Crosshead pistons}}