The internal combustion (IC) engine is an important source of vibration in many vehicles, and understanding its dynamic response to demands from both the vehicle operator and the terrain is essential to proper engine and mount design and optimization. Development of an engineering tool for understanding this dynamic response and the resulting forces transmitted from the engine block to the supporting structure is a priority in both commercial and military engine applications. Ideally, engine dynamics and vibration would be directly simulated through effective and efficient analytical and computational models of both the internal engine component dynamics as well as engine block vibrations.The present analytical study was undertaken to produce a comprehensive and efficient rigid-body engine dynamics and vibration model which predicts engine block motion, engine mount load transmission, as well as instantaneous engine crankshaft rotational speed. This study's unique contribution is the introduction of a fully-coupled low degree of freedom rigid-body model capable of simultaneously simulating both internal engine component dynamics and engine block vibrations. Here, this model is applied to both a single-cylinder and an in-line six-cylinder engine.The results from this new fully-coupled modeling method show that rigid-body engine vibration predictions can be enhanced beyond the capability of an uncoupled model. Here, this enhanced capability is shown through a single-cylinder engine simulation. However, in some cases an uncoupled model provides an acceptable prediction of rigid-body vibration as shown in an in-line six-cylinder heavy-duty Diesel engine. Engine mount force predictions from both models are also compared with experimental measurements. While the models developed here are applicable to in-line engines, they can easily be extended to piston engines of any configuration.