Production for a four-station manual assembly line, notionally balanced with respect to station service time means and unpaced in the mechanical sense is simulated in order to determine the effects of station service time variance on operating characteristics of the line. A deeper insight into this problem than has been reported in previous research is presented for small assembly line operation. Details of operating characteristics, including production rate, idle time and buildup of inter-process stock, are measured against station service time variance over a wide spectrum of levels and varying conditions.