The present disclosure relates to an engine assembly for a vehicle. The engine assembly comprises an engine including an extended crankshaft with additional main bearings, an alternator or a generator, a drive chain assembly, and a starter motor assembly. The engine may be used in different models of the vehicle having different characteristics, which enables to interchange or replace an internal generator with an external alternator, and vice versa in addition enable to use a common starter motor assembly, crankshaft, crankcase, and drive chain assembly for both engine configuration without modifying a basic design of the engine. Further, placement of the starter motor assembly provides a compact arrangement. In addition, the extended crankshaft with the additional main bearings enables low noise level operation, avoids additional shafts and roller bearings to be attached, and cost effective. Similarly, the drive chain assembly produces less vibration and noise.