A piston design where the skirt is long enough to act as a cylindrical guide within the cylinder bore, absorbing the side thrust from the connecting rod. It eliminates the need for a separate crosshead and piston rod. This design is standard in most high-speed internal combustion engines because it reduces engine height and moving mass.
Heard on the job
We need to check the skirt clearance on that trunk piston before installing the new rings.
Do not mix it up with
- Crosshead: A trunk piston takes the side loads directly against the cylinder wall, whereas a crosshead engine uses a separate sliding block to take those lateral forces.
Related terms
Piston
A sliding cylinder that moves back and forth inside a hollow tube to compress fluid or transmit force.
Crosshead
A sliding block that connects a piston rod to a connecting rod, absorbing lateral forces.
Two-stroke
Describing an engine that completes a power cycle in just one upward and one downward piston movement.