Your Massey Ferguson 231 tractor was manufactured between 1989 and 1998. To accurately determine the year your tractor was made, you will need to reference the serial number. The serial number is a five- or six-digit number found on a plate on the side of the engine block or transmission housing. The numbers are usually engraved into the metal and can be located near the oil filter or along the frame rail. Your serial number should begin with the prefix “S1”. The number after the S1 will indicate the year and model of the tractor. For example, “S11990” indicates that your Massey Ferguson 231 was manufactured in 1990.