Try doing a good solvent cleanup on the piston/wrist pin assembly. The usual piston to pin clearance is around 1/2 thousandth (.0005")and it's not uncommon for even a slight bit of rust preventive coating to make the pin so tight it can't be moved by finger pressure. When I used to fit oversize piston pins with a Sunnen hone, I would shoot for a clearance where a clean, lightly-oiled pin would slowly drop through the pin bosses of its own weight. If that doesn't happen after you do a thorough cleanup and lube, you'll need to get a machine shop to fit the pins to the pistons. If the pins are already in the pistons, they're very close to the right fit.
Jerry
