This paper describes the effectiveness of an Oldham- coupling- type balancer in reducing the first- and second-harmonic rotating unbalance couples of a90ﮠV6 even-firing engine. It is shown that the prototype balancer can be configured to eliminate the residual, first-harmonic rocking couple usually remaining in a conventionally balances 90ﮠV6 engine. Further, the Oldham- coupling- type balancer can be used to reduce the elliptical second-harmonic rotating couple to a horizontal rocking couple. The power consumption of the balancer was measured to be approximately 0.35 kW at 2000 r/min and 1.5 kW at 4500 r/min.