Piston assembly and wrist pin therefor providing a method of controlling rotation of the wrist pin within corresponding piston pin bores and connecting rod wrist pin bore

A piston assembly, comprising:

• a piston crown with pin bosses depending therefrom, said pin bosses having axially aligned pin bores;
• connecting rod having a small end with a bore;
• and
• a wrist pin having a cylindrical body with a through bore, said through bore having a first diameter arranged for receipt in one of said connecting rod bore or said pin bores and a second diameter arranged for receipt in the other of said connecting rod bore or said pin bores, said first diameter being less than said second diameter, said first diameter transitioning to said second diameter generally between the small end of the connecting rod and the pin bores of the piston, wherein said first diameter is substantially different from said second diameter.

A method of controlling the rotation of a wrist pin within pin bores of a piston and a wrist pin bore of a small end of a connecting rod by providing controlled expansion of the wrist pin in use, comprising:

• providing a cylindrical body having opposite end portions spaced axially from one another by a central portion;
• forming a through bore in said body having a first diameter defined in one of said central portion or said opposite end portions and a second diameter defined in the other of said central portion or said opposite end portions, with said first diameter being about 30-60 percent less than said second diameter;
• and
• forming a pair of transitions between said first diameter and said second diameter so that the transitions are located generally between the small end of the connecting rod and the pin bores of the piston.