Rusty piston in an old outboard.

Hi all I have recently started restoring my Granddads old seagull 102 outboard. when I take the spark plug out I can see that the top of the piston is rusty (to the point where I can scrape a small amount rust off with a flat head screwdriver) tho the engine is not seized. I was wondering is this means I am going to have to disassemble the engine to clean the bore and piston?