An assembly of an engine and a transmission is disclosed. An output shaft of the engine and an input shaft of the transmission extends in parallel to protrude from the assembly. The assembly typically comprises a first fitting portion that is formed in a crankcase of the engine and is configured to surround the output shaft, a second fitting portion that is formed in a housing of the transmission and is configured to surround the input shaft, and a coupling element having a first opening fitted to the first fitting portion and a second opening fitted to the second fitting portion. A center distance between the output shaft and the input shaft is fixed with the coupling element fitted to the first and second fitting portions.