A crosshead is a mechanism used as part of the slider-crank linkages of long reciprocating engines

and reciprocating compressors to eliminate sideways pressure on the piston. Also, the crosshead enables the connecting rod to freely move outside the cylinder.

Why is there no cross head in a 4 stroke engine?

In four stroke or trunk piston engines the skirt has arrangement for gudgeon pin, which transmits power from the piston to the gudgeon pin or top end bearing. As there are no cross head guides in four stroke engines, these skirts help in transferring the side thrust produced from the connecting rod to the liner walls.

Why crosshead pin is biggest pin?

To accommodate higher downward load and aid in effective lubrication, the crosshead pin has a large diameter. 8 This increases the relative sliding speed between crosshead pin and the bearing, as well as reduces the load on per unit area of the bearing.