Sears had outboard motors built for sale under its name from 1914 -- three years after Ole Evinrude first patented his outboard design -- until 1996. The motors were built by 10 different manufacturers under a variety of brands, sometimes with more than one manufacturer using the same model numbers, but different model names. Sometimes when model names were the same, the model number prefixes were different. As long as you have the model name and the model number, you can generally figure out when your motor was built.
Search for the prefix "M" on the model number of outboards labeled "Motorgo" or "Sears Motorgo." The model number is found on a tag attached to the right side of the powerhead. It may also be stamped below the Motorgo name on the front of the motor. If the Motorgo outboard has no model number, it was built by Lockwood-Ash from 1914 to 1927. If it has the "M" prefix before the model number, it was built between 1928 and 1932 by Motorgo or Caille.
Remove the top cover of "Waterwitch" motors and locate the tag on the right side of the power head. If the model number on the tag begins with "550," it was built by Johnson Outboard Motors between 1932 and 1940.
Lift the top cowling of the motor. Look inside the cowling for a plate with the model number. The manufacturer's name will be included on the plate. Model numbers that begin with a 571 prefix were built by Muncie Gear Works date from between 1932 and 1936. If the manufacturer is Kissel Industries, the motor dates from between 1936 and 1945.
Look at the motor's product name: if the motor is an "Elgin," it was built between 1946 and 1960 by West Bend. If the motor is identified as an "Eldin," "Sears" or "Ted Williams," it's model number prefix is 574, and it was built by McCulloch between 1959 and 1968. If the model number of a Sears or Ted Williams outboard begins with 217, it was built by Eska Outboards -- which purchased Tecumseh's designs before Tecumseh built any motors -- between 1968 and 1986. Eska also built the Sears "Gamefisher," also with the 217 model number prefix, during the same period. Gamefisher motors with a model number prefix of 225 were built by Force Outboards -- the Force logo is found on the powerhead -- from 1987 to 1996.