Joe, that Holden red motor had the pin restrained by a tight fit in the rod, not in the piston. The workshop manual says you need to heat the little-end of the rod to install the pin. The heating is done either by immersion in hot oil, or putting the set of rods in an ordinary oven. Don't overheat them, obviously - I no longer recall the correct temperature, but it wasn't very high.
Dario, fitting piston pins always requires care, lubrication and cleanliness. Essentially you get pin and piston bore surgically clean, lubricate both with light oil (sewing machine oil, also known as DTE Light, is good), line the pin up with the hole very carefully, and when it has just started under thumb pressure and you have verified that it is exactly straight, you smack the far end of the pin with the side of your hand, not terribly hard, to get it in half an inch or so. After that it is legitimate to push harder if necessary. I have several times watched this being done on a production line, packing service replacement pistons (which are conventionally sold with pins fitted). All of the people doing it were women, and they were by no means strong. If it won't go in that way, you have started it crooked.
