Once defined the relationship between the Starter Motor components and their functions, it is possible to develop a mathematical model capable to predict the Starter behavior during operation. One important aspect is the engagement system behavior. The development of a mathematical tool capable of predicting it is a valuable step in order to reduce the design time, cost and engineering efforts. A mathematical model, represented by differential equations, can be developed using physics laws, evaluating force balance and energy flow through the systems degrees of freedom. Another important physical aspect to be considered in this modeling is the impact conditions (particularly on the pinion and ring-gear contact). This work is a report of those equations application on available mathematical software and the resolution of those equations by Runge-Kutta's numerical integration method, in order to build an accessible engineering tool. Copyright © 2011 SAE International. Arnold, V.I., (1989) Mathematical Methods of Classical Mechanics, , 2nd ed. Springer, 1989. New York City, United States of AmericaBartilotti, R.R., Raizer, B., Pasquini, J., Catini, A.D., Del Corsso, Jr.O., Dedini, F.G., Functional modeling of a starter motor (2008) SAE Technical Papers, , 2008-36-0312(1996) Bosch Automotive Handbook, , BOSCH, 4 th Edition, Robert Bosch GmbH(2003) Alternators and Starter Motors, , BOSCH, The Bosch Yellow Jackets, edition 2003Karnopp, D.C., Margolis, D.L., (2008) Engineering Applications of Dynamics, , John Wiley & Sons, Hoboken, United States of AmericaKreyszig, E., (1999) Advanced Engineering Mathematics, , John Wiley & Sons, Inc. 8th edition, ISBN 0-471-15496-2Norton, R.L., (1997) Projeto de Máquinas - Uma Abordagem Integrada, p. 931. , Porto Alegre, RS: Bookman, 1997, 2nd Ed. p, ISBN 0-13-897802-6