Giraitis and Surgailis (2002) introduced $ARCH$-type bilinear models for their specific long range dependence properties. We rather consider weak dependence properties of these models. The computation of mixing coefficients for such models does not look as an accessible objective. So, we resort to the notion of weak dependence introduced by Doukhan and Louhichi (1999), whose use seems more relevant here. The decay rate of the weak dependence coefficients sequence is established under different specifications of the model coefficients. This implies various limit theorems and asymptotics for statistical procedures. We also derive bounds for the joint densities of this model in the case of regular inputs.