Motorcycles with a separate transmission unit that can be unbolted from the engine are relatively uncommon, as most motorcycles have an integrated engine and transmission design. However, there are a few notable exceptions where the transmission can be separated from the engine:
Some BMW Motorrad models: Certain BMW motorcycles, such as the BMW R1200GS and BMW R1250GS, feature a separate transmission housing that can be unbolted from the engine. This design allows for easier maintenance and repairs, as well as the ability to replace the transmission unit independently if necessary.
Moto Guzzi motorcycles: Moto Guzzi, an Italian motorcycle manufacturer, is known for their longitudinal V-twin engine configuration. In some Moto Guzzi models, the transmission unit is mounted as a separate unit directly behind the engine and can be unbolted from it.
Older British motorcycles: In the past, some British motorcycle manufacturers, such as Triumph and BSA, employed a separate gearbox design where the transmission could be disconnected from the engine. This design allowed for easier maintenance and repairs on the transmission unit.
It's worth noting that the majority of modern motorcycles have integrated engine and transmission units, where the transmission is an integral part of the engine casing. This design simplifies the overall construction and reduces the number of separate components, making the engine and transmission unit more compact and efficient.