1985 Mercury Outboard V-300 V-3.4L Shop Service Manual, Page 125Get this manual
POWERHEAD REASSEMBLY Coat cylinder hore with light oilMatch pislon assembl with cylinder it was removed from and position pislon as described below, the push pislon into cylinder
IMPORTANT: Piston Positioning Plslon mUll be correctly Installed and positioned 81 shown
Pi stons wilh th let teI' musl be in the pori side of ngine and the leit er1''' facing up towa rd top of engi nePi stons with the leiter "s" must be installed in the sta rboard side of engine nd th le iter "5" fac ing toward top of engine