Today, fuel consumption and weight reduction issues in automotive industry leads to downsizing with the development of 3-cylinder engines. These powertrains present high level of idle vibrations due to the excitation of engine rigid body modes. Inertia properties thus need to be well known to be reintroduced into finite element analysis.

Pendulum method and modal method are well-known methods to estimate the inertia tensor of a solid, but reveals quite difficult and time consuming to be applied in situ on a complete vehicle. This paper proposes an original method to estimate the inertia properties (c.o.g. position, mass and inertia tensor) of a powertrain using operational vibrations. Both numerical and test results are presented showing the efficiency of the method. Previously to this method, a quick analysis of first engine order vibrations is conducted in order to estimate real unbalance so that the inertia properties should be more accurately evaluated.