What is the function of the piston pin?

• A. Link between the piston and the connecting rod
• B. Connects piston to the crankshaft
• C. Seals the piston rings
• D. Guides piston in the bore

Answer: (A)

The piston pin serves as the pivot that connects the piston to the connecting rod, allowing the rod to swing as the piston moves in the cylinder. It passes through the piston boss and the small end of the connecting rod, transmitting the forces from combustion and piston inertia into the connecting rod while permitting the rod to rotate relative to the piston. This linkage is essential for converting the piston's linear motion into the rod’s and ultimately the crankshaft’s rotational motion.

It isn’t the linkage to the crankshaft—that happens via the connecting rod’s big end to the crankpin. It doesn’t seal the combustion chamber—that’s the job of the piston rings. It also doesn’t guide the piston in the bore—that guidance comes from the cylinder walls and the piston rings.