A motorcycle engine includes a crankcase housing a crankshaft, and a transmission unit therein, a cylinder block disposed above the crankcase, a cylinder head disposed above the cylinder block, and an intake system arranged behind the cylinder head, and a knock sensor arranged on an upper surface of the crankcase. The knock sensor is arranged behind the cylinder head, and disposed between the intake system and the cylinder block, such that the knock sensor does not restrict arrangement of additional functional parts of the engine on an upper surface of the crankcase. The knock sensor is substantially surrounded and protected by the intake system, the cylinder head, the cylinder block and the crankcase.