On Evinrude and Elto there is a 3/4 inch diameter round brass plug on the crankcase or cylinder that has the model and serial number. Johnson motors serial numbers are usually on the rope plate or on the crankcase. Most motors from 1950 to 1960 have a serial number plate on the transom clamp bracket. For PRE-1959 MOTORS ONLY, if you Contact us with the model (or horsepower) & serial number we’ll be glad to look up the year for you.