In this paper, a simultaneous design and development work for a diesel engine valvetrain system is presented. The rocker arm is one of the most important components of the valvetrain system which is transmitting the energy between the valves and the camshaft. Valvetrain system becomes even more complicated, when the extreme high speed of the system and nonlinear character of combustion is combined with the unpredictable behavior of the hydraulic lost motion mechanism during engine brake. As the complexity increases, it gets harder to predict valvetrain stress values especially while engine brake is in action. By taking all of these effects into account, that is reducing reliability of virtual analysis, requirement to conduct a strain measurement on valvetrain became inevitable. Therefore the challenge to make instrumentation on a complete fast moving, lubricated system which operates around 140°C and to select a proper location that can reflect the right stress values is solved by instrumenting one of the six rocker arms on the system. The engine is tested with a specific cycle, covering all critical operating regions including engine braking. As a result, during engine brake switch on and off maneuvers some unpredictable extreme stresses which can lead to mechanical failure are revealed. Upon completion of root cause identification of these extreme loadings, turbocharger control is manipulated at those critical switching regions in order to smoothen the transient response of the system, especially when engine brake is turned off. With all these optimization studies and verification processes, the risk of a possible catastrophic failure of the valvetrain system and relevant engine components is ruled out.